CHAPTER 4




HIGHER LEVEL CONSUMER INTERACTIONS









            H. A. Brooks




           J. V. Merriner




            C. E. Meyers




             J. E. Olney




           G. W. Boehlert




           J. V. Lascara




            A. D. Estes




            T. A. Munroe

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                         6OOR81105
            CHAPTER 4




HIGHER LEVEL CONSUMER INTERACTIONS








           H. A. Brooks




          J. V. Merriner




           C. E. Meyers




            J. E. Olney




          G. W. Boehlert




          J. V. Lascara




           A. D. Estes




           T. A. Munroe

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                   Higher Level Consumer Interactions

                                CONTENTS
                                                                  Page

I.   Introduction	  1

II.  Materials and Methods

     A.  Field sampling program	  4

     B.  Laboratory procedures	 15

III. Results

     A.  Field program	22

         1.  Migratory predators	 22

         2.  Resident fishes	 36

         3.  Zooplankton	 60

         4.  Ichthyoplankton	 70

     B.  Laboratory analysis

         1,  Food habits of SAV fishes ,	130

         2 .  Feeding periodicity and daily ration studies	164

         3.  Predator-prey experiments*.	171

         4.  Routine respiration of Bairdiella chrysoura	178

IV.  Discussion	,	181

V.   .Summary	189

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             Higher Level Consumer Interactions
                        Introduction



          The basic objectives within this subtask of the



grant were to analyze the structural and functional ecology



of fish communities in submerged aquatic vegetation (SAV)



and to assess the importance of SAV to the production and



maintenance of important commercial fish populations.   Areas



that were addressed include the relative benefit of SAV



from trophic and refuge standpoints, the effects of large



migratory predators (megapredators) which may frequent the



SAV areas, biomass estimates of the components of the fish



community, sources of production consumed by the fish



populations, the importance of SAV to early life history



stages of fishes, and the determination of time of immigration



and residence for dominant fishes of SAV areas.



          The structural and functional ecology of resident



fish communities in eelgrass (Zostrea marina) beds has been



studied in the Beaufort, North Carolina area  (Adams, 1976



a, b, c).  Species composition as well as feeding habits



of the benthic fish community in the study site have been



qualitatively described (Orth and Heck, 1980).  The



dominant resident species in the lower Chesapeake Bay eelgrass



bed was spot (Leiostomus xanthurus), contrasting with the

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 North Carolina eelgrass fish community,  where pinfish (Lagodon



 rhomboides)  and pigfish (Orthopristes chrysoptera)  were the



 dominant species (Adams,  1976a).   Mid- and late-summer gill



 netting also revealed certain of  the migratory predators



 (Orth and Heck, in press),  including the sandbar shark



(Carcharhinus milberti = Carcharhinus plumbeus) and bluefish



 (Pomatomus saltatrix).   Preliminary feeding' analysis by Orth



 and Heck suggested that these predators were feeding in the



 eelgrass area.  In other parts of the lower Chesapeake Bay,



 the cownose ray (Rhinoptera bonasus) has been shown to feed



 and have dramatic effects in eelgrass beds (Orth, 1975).



      Previous characterizations of Chesapeake Bay ichthyo-



 plankton assemblages (Pearson, 1941; Dovel, 1971; Olney, 1971)



 have concentrated on midchannel portions of the estuary and



 have concentrated on midchannel portions of the estuary and



 have neglected the generally inaccessible nearshore, shallow



 environments.  As a result, the extent to which Chesapeake Bay



 fish stocks utilize these nearshore zones as spawning and/or



 nursery sites in unknown.  This lack of data takes on added



 significance as a result of the recent emphasis on the importance



 of shallow seagrass beds as refuge and feeding grounds for



 many species of marine and estuarine fishes (Reid, 1954;



 Adams, 1976 a, c).



           Our approach to the structural and functional



 ecology of fish communities in SAV has been to combine a



 program of field  sampling with laboratory study.  Field

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sampling for one and a half years with six different types



of fishing gear has defined the structure of the fish com-



munity's three main components:  i) fish eggs, larvae,



postlarvae, and pelagic juveniles; ii) resident fishes; and,



iii) megapredators.  The laboratory effort involved predator/



prey experiments as well as determination of several physio-



logical parameters for two dominant fishes in the eelgrass



study area.

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                    MATERIALS AND METHODS





Field Sampling



          The field sampling was conducted at the Vaucluse



Shores study site, north of the channel of Hungar's Creek



(Figure 1).  Sampling of relatively large areas was required



for adequate estimations of fish densities; for this reason



our sampling areas were not distinctly defined with respect



to vegetation type.  Sampling was divided to three areas,



designated as representative of Zostera marina, Ruppia



maritima, and an  adjacent unvegetated area.  The nominal



Zostera area was  located between the sandbar and land, along



transect A.  The  nominal Ruppia area was located on and north-



east of transect  C.  The unvegetated sampling area was on



the sandbar west  of transect markers B and A in depths



appropriate for the particular sampling gear.  As was



apparent  in vegetation maps of the bed, the nominal sampling



areas for Ruppia  and Zostera contained mixed stands as well



as pure stands of the respective vegetation types  (Figure  1).



Differences noted between the two sampling areas may have



therefore represented faunal changes due to isolation from



deeper water rather than differences attributable to vegetation



type.



          Sampling gears generally broke down to those for



1) ichthypplankton and  zooplankton, 2) resident fishes, and



3) migratory predators.  A variety of gears were tested for

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R=RUPPIA
Z=ZOSTฃRA
S=SAND
/ = MIXED
ft-ซ^
  = TRANSECTS
CHESAPEAKE   -.'.••# /R /V
    BAY   _  :.Y# /..-..:.:••   R
     M
                     Figure 1

                       5

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sampling these components of the fauna during the project.


The field sampling schedule is presented in Table 1.


Ichthyoplankton and zooplankton were a initially sampled with


towed, bridled nets; these were abandoned due to excessive


disturbance ahead of the net from the outboard motor which


resulted in avoidance by fishes and samples with excessive


silt, detritus, and dislodged vegetation.  Resulting samples


were often impossible to preserve and sort (especially zoo-


plankton samples with large amounts of sand).  Routine sampling


for ichthyo- and zooplankton consisted of two replicate collections


in each habitat (Zostera, Ruppia, and sand) utilizing a pushnet


(Figure 2) constructed of %" diameter galvanized pipe and


deployed over  the bow of a 19 foot outboard craft.  The


frame was equipped with a 1 meter ichthyoplankton net (500 um


mesh) and two  18.5 cm zooplankton (202 um mesh); the ichthyo-


plankton net and one zooplankton net were fitted with calibrated


General Oceanics flowmeters to assess the volumes of water


filtered.  Nets were fished at high tide for 2-3 minutes


depending on abundance of plankton.  The sampling duration


and boat speed allowed the ichthyoplankton net to cover 74-

      2                                        3
175 m of sea  surface and filter from 68-117 m  of water.


Routine monthly sampling was conducted at night; daylight


samples  were  taken at high tide in selected months.

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Table 1 .  Field Sampling Program
     Gear
1978
M  0
                                                          1979
                                            1980
MAMJJASOND
J  F  M  A  M  J  J
Gillnet

  7" mesh
  5" mesh
  3%" mesh

Haul Seine

Trawl

Zooplankton

Ichthyoplankton

Pushnet

Food Analysis

Residents

Migratory predators

Periodicity
X  X
              XXXXXXXXX
              XXXXXXXXX
              XXXXXXXXX

                                XXX

              xxxxxxxxxx

              xxxxx.xxxxx
              XXXXXXXXX- X

                    X     '   X       X
                                           X  X  X  X  X

                                          DISCONTINUED

                                           X  X  X  X  X

                                    X  X   X  X

                                    X  X

                                           X  X  X  X  X
                                          X  X  X  X  X

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5
3
>
•••





202u
NET
" 70cm—>
505pm
METER
NET

23cm



202 p
NET

B
                          Figure 2

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     Each time the pushnet was deployed, one ichthyoplankton


and two zooplankton samples resulted.  One zooplankton sample


was preserved in the 10% formalin: for later taxonomic analysis


and estimation of abundance; the other was washed with distilled


water, frozen in the field on dry ice, lyophilized, weighed,


and ashed in a muffle furnace (6 hours at 500ฐC) to determine


organic biomass per unit volume.  Ichthyoplankton samples


were preserved in 5-10% buffered formalin.  In the laboratory


they were whole sorted for fish eggs, larvae, postlarvae,


juvenile, and adult stages.  Specimens were later identified


to the lowest taxon possible, measured, and curated.


     For sampling resident fishes, a portable dropnet similar


to those described in Moseley and Copeland (1969) and Adams

                                              2
(1976a) was built; it covered an area of 9.3 m  .  Our initial


experiences with this gear proved it to be unsatisfactory


due to the small area covered, long deployment times, and


instability in rough weather.  We therefore abandoned the


dropnet in favor of a 40 m long, 2.4 m deep seine (Figure 3)


fished in the manner described for long haul seines by Kjelson


and Johnson (1974).  Briefly, the seine was deployed bag end


first from the bow of an outboard craft travelling in reverse.


The net was set in a circle and the long wing pulled past the


bag end to decrease the circumference of the circle to


approximately 7.3 m, after

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Figure 3
  10

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which the bottom of the net was closed off by tightening



a purse line.  The catch remained in the pursed section of



net and was brought on board the boat for processing.  When



set in an ideal circle, this gear encompassed an area of



127 m2.  Duplicate or triplicate samples were taken monthly



(from March through December, 1979) in each of the three



habitats.  Daylight samples were also taken in selected



months for diel comparisons.  Large specimens were identified,



measured, and noted on the field sheets; the remainder of



the catch was preserved in 10% buffered formalin for later



identification in the laboratory.



          In August 1979, a comparison of haul seine catch



to Orth and Heck's otter trawl collections  (in press)



indicated that certain members of the benthic fish community



were not being adequately sampled by the haul seine.  There-



fore an otter trawl was employed to supplement the routine



haul seine sampling.  Samples were collected with a 4.9 m



otter trawl  (1.9 cm mesh wings, .6 cm mesh  liner, 15.2 m



bridles) pulled behind the 19 foot outboard craft operated



at 2000 RPM for two minutes.  Area swept per trawl was



calculated as the product of the distance across the opening



of the trawl mouth and the average distance travelled during



a trawl.  The trawl opening was determined  from measured



horizontal net openings while the net was dragged over a



shallow sand bottom.  Distance travelled by the trawl was



determined by suspending a calibrated General Oceanics flowmeter
                               11

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from the side of the boat during each trawl.  Triplicate day


and night samples were taken monthly from August through November


1979 and from March through July 1980.


          From March to July 1980 resident fishes were


sampled with a pushnet described by Kriete and Loesch


(1980) and illustrated in Figure 4.  This pushnet was


constructed and operated in the same manner as the zooplankton


pushnet.  One flowraeter monitored volume strained by the


modified 1.2 by 1.8 m Cobb Trawl net mounted on the pushnet


frame. .The body of the net was constructed of 1.9 cm stretch


mesh while the cod end was made of 1.27 cm stretch mesh.
                                                             i

Triplicate day and night samples were collected in each


habitat.


          Migratory predators were sampled in 1979 by


deploying 30.5 meters each of .12.7 and 17.8 cm stretched



mesh gill net perpendicular from shore in each of the three


sampling habitats.  These nets were fished every four hours


over a 24 hour period.  At each sampling time, the catch


was removed, identified, measured, weighed, and the net was


reset.  Observations were made on  relative fullness of


stomach contents and selected stomachs were removed and


preserved for analysis of contents.   In November of 1979


a  comparison of  the catch of the 12.7 and 17.8 cm stretch
                              12

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Figure 4

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mesh gill nets indicated that the 12.7 cm mesh gill nets



caught a larger diversity as well as a greater number of



megapredators than the 17.8 cm mesh gill nets.  Therefore,



in 1980 the 12.7 stretch mesh gill nets were retained as



megapredator sampling gear while the 17.8 cm stretch mesh



gill nets were replaced by 8.8 cm stretch mesh gill nets.



The sampling procedure remained the same for both years.



As with other collection included date, time, habitat, tide



stage, depth, water temperature, salinity, dissolved oxygen,



and comments on weather.



     To define residence time for Carcharhinus milberti in the



study area, 10 sandbar sharks in June of 1980 and 50 sharks



in August of 1980 were marked with Peterson disk tags



supplied by NMFS (Narragansett Laboratory, RI).  Sharks



were examined for tags during routine sampling in July.



Two weeks after the August shark tagging, gill nets were  set



overnight in each habitat to recapture marked sharks.
                               14

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Laboratory Procedures



          To determine the feeding behavior of the fishes



and their impact upon the resident secondary producers,



stomach contents and feeding periodicity studies were con-



ducted.  The resident fishes were collected by trawl during



the times of day when feeding was actively occurring; stomach



contents were removed for taxonomic analysis.  For determination



of feeding periodicity, trawling was conducted over 24 hour



periods in May and August 1979.  Stomachs from the larger,



migratory predators were sampled during the monthly gill



net collections.



          The method of stomach collection depended upon



the size of the fish.  For resident fishes larger than 150



mm and for all migratory predators, stomachs were removed



in the field and preserved in 10% buffered formalin immediately



after capture.  Tags were placed with the stomach describing



fish length,  species, and collection number to associate



the stomach with further information available on the field



data sheets.   For resident fishes smaller than 150 mm,



specimens were preserved whole in 20% buffered formalin; the



body cavity was slit to facilitate penetration of the formalin.



Contents were transferred to 40% isopropyl alcohol prior to



analysis.



          Analysis of stomach contents of piscivorous fishes



was conducted by the Higher Level Consumer Interactions group;



identification of stomach contents of fishes feeding on inverte-
                                15

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brate secondary consumers was conducted by the Resident



Consumer Interactions group.  After contents were identified



to the lowest toxon possible, individual food items were



dried to constant weight at 56ฐC and weighed.  An average



individual weight for small prey items such as nematodes



and harpacticoid copepods was obtained by .pooling like food



items from several fish stomachs, obtaining a pooled dry



weight, and then dividing this weight by the number of



individual prey that were weighed together.



          Feeding periodicity was determined for spot



CLeiostomus xanthurus), pipefish  (Syngnathus fuscus), and



silver perch  CBairdiella chrysoura).  Collections were made



by otter trawl over a 24 hour period.  From each sampling



period, total gut contents  of up  to six specimens were



removed.  The contents and  the fish were then dried and



weighed separately; the ratio of  dry gut content weight to



dry body weight yielded a measure of feeding periodicity and



when combined with estimates of evacuation rate at  the



temperature of collection,  allowed  analysis of daily



ration  CPeters and Kjelson,  1975) .



          In July 19.80, a series  of storms disrupted the first



attempt at routine sampling of migratory predators.  All



sandbar shark stomachs  (.full as well as empty) were processed



from the resulting one and  a half sets of  gillnet collections.
                              16

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July feeding periodicity and daily ration for C. milberti



were then calculated using a model developed by Lane et al.



U979).



     Length to dry weight relationships for Leiostomus xanthurus,



Brevoortia tyrannus, Bairdiella chrysoura, Syngnathus fuscusy



Membras martinica, Menidia menidia, and Anchoa mitchilli



were determined from fresh as well as preserved specimens



which were measured and then dried (at 56ฐC) to a constant



weight.




          Laboratory experiments were conducted to  examine



the effect of artificial  Zostera marina on  predator-prey



relationships of migratory predators and  resident fishes.



The experimental setup  (Figure 5)  consisted of  two  circular



wading pools,  (3.66 m in  diameter, 0.9 meters deep) with



a volume of approximately 9500 liters each.  A  closed,



recirculating system with a biological filter was utilized.



The filter was comprised  of a 0.24 m3 of  coarse sand, oyster



shell, and gravel; circulation was provided by  two  38 liter



per minute pumps.  Experimental fish, both  predator and



prey, were caught by a  variety of  methods,  including  (1)



hook and line;  (2) 16'  otter trawl; and,  (3) 50' beach



seine.  Predators were  maintained  as residents  in the tanks;



holding tanks provided  a  supply of both predator and prey



fishes.  Artificial eelgrass  (3/16" wide  green  polypropylene



ribbons, 0.6 density) mats   were    woven  to observed



field densities  (dense  -  1750 blades/m2;  average -  875 blades/



m2).  Mats were placed  in the center of the tank to mimic
                               17

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Figure 5
   18

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an eelgrass habitat; prey were released into the center of



the tanks in both eelgrass densities and in base sand bottom



controls.



          Predator species; Paralichthys dentatus, and



Cynoscion regalis were acclimated to experimental conditions



for a minimum of 30 days.  During this period predators



were fed a variety of live prey fish.  Prey species,



Leiostomus xanthurus and Menidia menidia were acclimated



for a minimum period of 14 days.  Prey were fed Purinaฎ



trout chow.




           Preliminary  experiments were  conducted  to establish



the  sizes  and numbers  of  both predators and prey.   Predators



were  selected such  that  the confines of the model ecosystem



did  not  severely inhibit  their ability  to  pursue  and capture



prey.  Prey were of a  size small enough to be  captured and



consumed yet not so small as  to be  unattractive.   Four



predators  and 12 prey  of  each species were used in each



experimental replicate.



          .Each  predator-prey  combination was tested in



triplicate against  five  substrate variations:



              (1)  'N1 - no artificial vegetation,  bare



                  sand  substrate;



              (2)  'A1 - average density  artificial grass,



                  1m2, 7% area covered;



              (3)  'H1 - high density artificial grass,



                  1m2, 7% area covered;
                               19

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             (.4)  'IA1  - increased area, 3 m2,  1450 blades/
                 m2,  22% area covered;
             (5)  '1C1  - increased complexity,  3-1 m2 evenly
                 spaced, 1450 blades/m2, 22% area covered.
          One hour observations were made at morning, midday
and evening.  Surviving prey were enumerated and behavioral
characteristics of both predator and prey were noted at
these times.  All remaining prey were removed at the conclusion
of each experiment.  Predators were starved for a 24 hour
period prior to initiating the next experiment.
          Predator versus M. menjdia were conducted for
12 hours from first to last daylight.  Predator versus
L. xanthurus experiments started at dawn and were conducted
for a 24 hour period.
          Temperature acclimation tanks were set up in the
laboratory with optional flow-through or closed system
capabilities.  Typical acclimation temperatures were 12ฐ,
17ฐ, 22ฐ, and 27ฐC.  This allowed temperature related
analysis of respiration rates of Bairdiella chrysoura, the
silver perch, and analysis: of evacuation rate for the pipefish
Syngnathus fuscus.  Respiration chambers  (Figure 6) were
constructed with flow-through characteristics to allow
analysis of metabolic rate at different temperatures.
                              20

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Figure 6
  21

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                           Results



Field Program



 Migratory predators



          Migratory predators sampled with gill nets were



represented by 889 specimens of nineteen species in eleven



families.  Table 2 summarizes monthly gill net catch by year



and mesh size.  Catches represent the aggregate number of fish



caught over a 24 hour period with gill nets fished every



four hours.  Menhaden (Brevoortia tyrannus) comprised 86% of



the small catch in March over both years.  In April and May,



the total catch increased with movement of teleosts Pomatomus



saltatrix, Cynoscion regalis, C. nebulosus, Paralichthys



dentatus and the elasmobranchs Rhinoptera bonasus and Dasyatis



sayi into the bay.  In June  the sandbar shark, Carcharhinus



milberti dominated the catch and continued as the dominant



species through September.   Summer flounder (Paralichthys



dentatus), spotted seatrout  (Cynoscion nebulosus), and bluefish



(Pomatomus saltatrix) inhabited the study area throughout



the summer.  By November, only menhaden, bluefish, and spotted



seatrout were caught by the  gill nets.



          A comparison of April through July catch in 12.7 cm



mesh gill net for 1979 and 1980 indicates that the major



difference between the two years was  the absence  of bluefish



in April 1979.  The variability in the catch of bluefish is



typical of patterns observed for most of migratory predators.



One net fished overnight in  the sand  area 3 days  prior to



the April 1979 sampling caught 45 bluefish.  Continuation



of this sampling series was  aborted   by weather'.  Therefore,




                                22

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1979 and 1980 migratory predator catches appear quite similar.



          Table 2 also compares gill net catch by size of



netting (8.8, 12.7, 17.8 cm stretch mesh).  With the exception



of Rhinoptera bonasus and Dasyatis sayi. in 1979 the 12.7 cm



mesh gill nets was more effective than the 17.8 cm mesh nets



for most species.  The larger mesh nets were initially selected



to catch sandbar shark; however, only 14% of the 1979 catch



of this species was made in the 17.8 cm mesh nets.  Therefore



in 1980, the 17.8 mesh gill nets were replaced by 8.8 cm stretch



mesh gill nets.  In 1980, ฃ. milberti, Dasyatis sayi,  -



Pomatomus saltatrix and Rhinoptera bonasus were caught in greater



numbers by 12.7 cm mesh nets than 8.8 cm mesh nets.  The



greatest differences in catch between these two net mesh



sizes were seen in the catch of weakfish (ฃ. regalis) and



menhaden (B. t'y'r ahnus) ; 100% of the weakfish and 96% of the



menhaden were caught by 8.8 cm mesh gill nets.





          Tables 3 and 4 describe the migratory predator catch



by year, habitat,  and day or night.  In 1979,  more migratory



predators were caught in the Zbstera area (44%) than the sand



(34%) or Ruppia area (27%).   This tendency was not duplicated in



1980 where the greatest catch of migratory predators occurred



in the sand area (37%) followed by the Ruppia (35%) and Zbstera



areas (28%).
                                23

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Table2..  Comparison of migratory predator catch summarized by gear, month and year.
Month
March
April
May
June
17.8 cm
stretched mesh
Number Size Range
Species (SL in mm)
Brevoortia tyrannus 2 253-254
Morone saxatllis
Morone americana
Pomatomus saltatrix
Paralichthys dentatus
Morone saxatllis
Alosa sapidissima
Brevoortia tyrannus
Cyno scion regalis
Alosa mediocris
Opisthonema oglinum
Cynoscion nebulosus
Pomatomus saltatrix 5 340-465
Rhinoptera bonasus 13 890-980*
Cynoscion regal is
Dasyatis sayi 5 490-600*
Sciaenops ocellata
Tylosurus acus
Brevoortia ty_rannus
Paralichthys dentatus
Alosa pseudoharengus
Carcharhinus milberti 1 600
Pomatomus salta'fr'fx 4 295-590
Rhinoptera bonasus 4 850-860*
Dasyatis sayl 3 420-470*
Cynoscion regalis
Cynoscion nebulosus
Paralichthys dentatus
Brevoortia tyrannus 1 167
Tylosurus acus
12.7 cm
stretched mesh
Number Size Range
(SL in mm)
1
6-
9
5
10
1
1
1
33
11
2
2
6
1
1
247
410-540
210-740
850-910*
260-600
600*
765
1250
500-820
305-870
800-930*
540-660*
330-482
400
220
1979
Catch
3
6
14
18
10
6
1
1
34
15
6
5
6
1
1
1
12.7 cm
stretched mesh
Number Size Range
(SL in mm)
17
1
1
1
1
1
11
4
1
39
1
2
1
498-732
255
381
457
239
526
275-532
920-940*
167
501-716
519
480-710*
292
8.8 cm
stretched mesh
Number Size Range
(SL in mm)
21
2
2
5
1
139
16
1
1
16
2
4
2
1
2
5
2
17
1
1
4
5
213-265
286-307
204-205
310-710
290
250-352
326-479
251
325
296-535
878-950
321-475
260-268
185
230-285
515-680
272-289
320-524
411
119-291
848-1000
1980
Catch
21
2
2
22
1
2
1
140
16
1
1
1
27
6
4
3
1
2
44
3
2
17
1
2
4
5
Total
Catch
26
2
2
22
1
2
1
140
16
1
1
7
41
24
14
6
1
1
3
1
2
78
18
6
7
23
2
3
5
5

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      Table  2.   (Continued).
K>
Ln
Month
July
August
September
October
November
17.8 cm
stretched mesh
Number Size Range
Species (SL 1m mm).
Carcharhlnus mllbertl
Cynoscion nebulosus
Rhinoptera bonasus
Cynoscion regalis
Paralichthys dentatus
Micropogonias undulatus
Pomatomus saltatrix
Brevoortia tyrannus
Dasyatls sayi
Carcharhinus milberti
Pomatomus saltatrix
Rachycentron canadum
Rhinoptera bonasus
Paralichthys dentatus
Cynoscion regalis
Cynoscion nebulosus
Carcharhinus milberti
Pomatomus saltatrix
Cynoscion nebulosus
Cynoscion regalis
Paralichthys dentatus
Sphoeroides maculatus
Sciaenops ocellata
Rhinoptera bonasus
Paralichthys dentatus
Cynoscion nebulosus
Pomatomus saltatrix
Pomatomus saltatrix
Cynoscion nebulosus
Brevoortia tyrannus

9
1
1
5
6
1
1
3
1
9
5
4
1
1
2.
4
13
1
570-780
885*
385
600-730
380-450
755*
280
370-430
448
530-765
303-514
318-425
400
946* .
304-308
333-390
333-460
165
12.7 cm
stretched mesh
Number Size Range
(SL in mm)
49
2
2
44
8
1
1
5
1-
28
6
5
3
6
1
1
4
5
7
8
1
14
500-990
414-475
452-990*
420-880
410-590
490
938*
260-290
300
480-667
254-502
489-533
267-540
279-324
165
384
252-294
403-560
320-504 .
340-412
485
152-222
12.7 cm 8.8 cm
stretched mesh stretched mesh
1979 Number Size Range Number Size Range
Catch (SL in mm) (SL in mm)
58 63 486-644 61 440-710 .
2 1 565 3 325-485
3
1 2 339-425
1 430 4 165-257
2 336-370 6 305-325
5 295-376 5 280-415
5 193-205 1 260
1 700*
49
14 End of 1980 Sampling
1
2
6
4
1
37
11
5
7
7
1
1
1
6
5
11
21
1
15
1980 Total
Catch Catch
124 182
4 6
3
2 3
5 5
8 8
10 .10
6 6
1 1
49
14
1
2
6
4
1
37
11
5
7
7
1
1
1
6
5
ii
21-
1
15
       * Disc Width

-------
Table 2'-   (Continued).
17.8 cm
stretched mesh
Number Size Range
Month Species (SL in mm)
TOTALS Pomatomus saltatrix
Carcharhinus milberti
Cynoscion nebulosus
Cynoscion regalis
Paralichthys dentatus
Rhinoptera bonasus
Dasyatis sayl
Sphoeroides maculatus
Rachycentron canadum
Sciaenops ocellata
Brevoortia tyrannus
Alosa sapidissima
Tylosurus acus
Morone saxatilis
Mo rone americana
Alosa mediocris
Opisthonema oglinum
Alosa pseudoharengus
Micropogonias undulatus
37 295-590
24 530-780
1 448
8 318-430
4 304-400
20 755-980*
8 420-600*
4 165-254
106
12.7 cm
stretched mesh
Number Size Range
(SL in mm)
49
154
20
20
16
10
3
1
1
2
15
1
292
210-870
430-990
370-560
260-600
220-324
452-990*
5407-660*
165
490
384-765
152-247
1250
1979
Catch
86
178
21
28
20
30
11
1
1
2
19
1
398
12.7 cm
stretched mesh
Number Size Range
(SL in mm)
34
102
1
3
4
3
7
1
1
2
158
275-732
430-716
455-565
255-430
920-940*
480-710*
167-239
457
381
336-370
8.8 cm
stretched mesh
Number Size Range
(SL in mm)
28
66
5
39
6
.2
167
3
2
1
1
2
6
333
272-710
440-710
325-485
320-524
165-257
878-950*
225-325
848-1030
286-307
204-205
251
325
230-325
305-325
1980.
Catch
62
168
6
39
9
6
3
174
1
5
4
2
1
1
2
8
491
Total
Catch
148
346
2.7
67
29
36
14
1
1
2
193
1
6
4
2
1
1
2
8
889
* Disc Width

-------
                                              Table 3




Monthly Catch of Migratory Predator Species by Gillnets Within Habitat Types in Day and Night Sets.

Carcharhinus milberti
Pomatorous saltatrix
Cynoscion regalis
Paralichthys dentatus
Cynoscion nebulosus
Tylosurus acus
Dasyatis sayi
Rhinoptera bonasus
Sciaenops ocellata
Rachycentron can ad urn
Brevoortia tyrannus
Sphoeroides maculatus
Totals

D
N
D
N
D
N
D
N
D
N
D
N
D
N
D
N
D
N
D
N
D
N
D
N
March April May
ZRS ZRS ZRS
2 3
234
3
421
3 1
2
1
1 2
1 2
1 11
2 4
1
3
3 19 11 26
1979
Z
10
6
3
5
1
2
1
2
1
4
1
36
Migratory
June
R S
4 8
5 1
2 3
1 1
3
1
1 1
2
17 16
Predators
July August
Z .R S ZRS
21 2 1 762
23 8 3 12 15 7
10
2 2
1 31
3
3
11 1
1 11
1 1
1
45 14 5 30 24 23
September October November
ZRS ZRS ZRS
5
5
1
1
3
1
2
1
19
11 11
1 4
7 1
3 19 21
2
1
22 11
2 31
111 1
2 21
1
1 • ,
15
33 18 8 4 10 1 36
Totals
88
90
31
55
7
21
9
11
10
11
1
7
4
21
9
2
1
19
	 1
398

-------
                                                                    Table 4


                      Monthly Catch of Migratory Predator Species by Gillnefs Within Habitat Types in Day and Night Sets.
to
oo

Carcharhinus milberti
Pomatomus saltatrix
Cynoscion regalis
Paralichthys dentatus
Cynoscion nebulosus
Tylosurus acus
Dasyatis sayi
Rhinoptera bonasus
Morone saxatilis
Micropogonias undulatus
Brevoortia tyrannus
Morone americana
Alosa mediocris
Alosa sappadissima
Opisthonema oglinum
Alosa pseudoharengus
Totals
March
Z R S
D
N
D
N
D
N
D
N
D
N
D
N
D
N
D
N
D 2
N
D
N
D 162
N 336
D . 1
N 1
D
N
D
N
D
N
D
N
4 11 10
1980 Migratory Predators
April May
Z R S Z R S
1 18 263
21 853
7
621 121
1 1
1
3
1 2
2
18 3 79
11 1 28 3
1
1
1
1 1
39 7 138 17 19 8
June . July
Z R S Z R S
2 22 17 13 7
18 2 16 59 12
1 3.1
2 33
4 12 1 11
3 1
11 1
2
1 11
1 4
1
2
1
2 4. 1
31 6
30 44 4 46 93 21
Totals
61
107
35
27
7
32
4
5
3
3
5
1
2
3
3
4
1
7
109
65
1
1
1
1
1
2
491

-------
 Figure 7 relates gill net catch of the seven dominant migratory
 species to habitat and year.  Weakfish (ฃ. regalis) spotted
 seatrout (ฃ. nebulosus),  sandbar shark (C_. milberti) and
 summer flounder (P. dentatus) were more abundant in the
 vegetated areas while bluefish (P. saltatrix), cownose ray
 (R. bonasus) and menhaden (B. tyrannus) were more numerous
 in the sand area.
         Nine species were captured more frequently at night
 than during the daylight period.  For most species there
 were insufficient captures to provide an adequate estimate
 of diel temporal abundance patterns.  Diel patterns of catch
 for three of the most abundant/'migratory predators are
 presented in Figure 8A and 8B.  The sandbar shark, bluefish,
 and weakfish enter the study area after 10 a.m.  The number
 of bluefis'h captured in the study area decreased around
 twilight while the sandbar shark and weakfish increased
 in number until midnight.  These patterns may be related
 to feeding activity and will be discussed later under feeding
 analysis.  Figure 9A and 9B indicate that C. regalis, P.
 saltatrix,  and C_. mi Iberti were caught at a higher frequency
 during, -flooding ti;de stagey than ebbing ti.de stages.
          The sandbar shark tagging exercise produced two returns
A shark tagged in June was recaptured during July.routine
sampling.  No tagged sharks were recaptured in the September
gill net sets in the study area.  A shark tagged in August was
recaptured 38 days after release at the mouth of Onancock Creek,
Va.  (20 miles north of the study site).  The low number of
                               29

-------
 ABUNDANCE OF DOMINANT  MIGRATORY  PREDATORS OF SAV  STUDY AREA
                                  BLCfrt CHRP.! OF SUMS
r . OtMTRTuS   C . P.EDRLIS  r. SRITRTRIX   B- •TKRNNuS
                                                 BS55SS5 82
                             TOTAL ABUNDANCC GIVEN WITHIN EACH BLOCK
               HISTOGRAM OF C MILBERTI AND B. TYRANNUS WERE SCALED TO ONE HALE ACTUAL ABUNDANCE
                                 Figure  7

                                         30

-------
CATCH PER  UNIT EFFORT OF C.  REGALIS AND P. SALTATRIX VERSUS TIME
CfiTCH
 0.39-1
 0.36-
 0.33-
 0.30-
 0.2-7-
 0.24-
 0.21-
 0.18-
 0.15H
 0.12-J
 0.09-
 0.06-
 0.03-
 0.00-
         LEOEND: SPECIES
8    10    12    14    16    18    20    22
      TIME
     C. RECflLIS      ซ-•ป-ป P .  SflLTRTRIX
                       Figure 8A

                             31

-------
CATCH  PER UNIT EFFORT OF CARCHARHINUS MILBERTI VERSUS TIDE STAGE
 CflTCH
  1 .6 H
  1 .5 -


  I .4 -


  1 .3 -


  1 .2 -


  1 .1 -


  1 .0 -


  0.9 -


  0.8 -


  0-7 -


  0-6 -


  0.5 -


  0.4 -


  0.3 -


  0.2 -
              E
              fl
              R
              L
              Y

              F
              L
              0
              0
              D
M
R
X
F
L
0
0
D
L
R
T
E

F
L
0
0
D
S
L
R
C
K
E
fl
R
L
Y

E
B
B
M
R
X
              E
              B
              B
L
R
T
E

E
B
B
S
L
R
C
K
                                  TIDE
                   LEGEND:  SPECIES
                      C. MILBERTI
                             Figure  8B
                                32

-------
CATCH PER  UNIT EFFORT OF CARCHARHINUS MILBERTI VERSUS  TIME
CflTCH
 1 -2 H
 1.1 -
 1 .0 -
 0.9 -
 0-8 -J
 0.7 -
 0.6 -i
 0.5 -\
 0.4 H
 0.3 -
 0-2 -
 0-1 -
 0.0 -
                     6     8   10    12    14    16    18    20   22
                                TIME
                  LEGEND: SPECIES    •*-*-* C. MILBERTJ
                         Figure 9A
                              33

-------
CATCH  PER UNIT EFFORT OF C.  REGALIS AND P. SALTATRIX VERSUS TIDE STAGE

 CflTCH
  0-7 H
  0.6 -
  0.5 -
  0.4 -
  0.3 -
  0.2 -
  0-1 -
  0.0 -
              E
              R
              R
              L
              Y

              F
              L
              0
              0
              D
n
R
X
F
L
0
0
D
L
R
T
E

F
L
0
0
0
S
L
R
C
K
E
R
R
L
Y

E
B
B
M
R
X
               E
               B
               B
L
R
T
E

E
B
B
S
L
R
C
K
         LEGEND:  SPECIES
             TIDE

           C- RECRLIS
                    *-ซ*-•ป P. SRLTflTRIX
                           Figure 9B
                                34

-------
recaptures (2 out of 60) in the study area indicates that the



sandbar shark is a highly mobile species and



individual sharks may have a short residence time in the



study area.



          The two rays  (R. bonasus and D. sayi) and summer



flounder  (P. dentatus) were probably sampled poorly by gill



nets since most captures occurred through entanglement



rather than via "gilling" due to body shape.  The needlefish,



Tylosurus acus, were, bbiserved to b,e very-;,abundant :at night



but due to its long slender body was seldom caught in



the gill nets.
                               35

-------
Resident Fishes
        Resident fishes were sampled with the haul seine from
March through December, 1979.  Haul seine collections include
178 night and 40 day sets.  Eighty-seven hauls were made
in Zostera habitat; 72 in Ruppia and 56 over sand bottom.
Thirty-seven species from 23 families, representing 6,259
individuals were collected (Table 5).
        Densities of resident species taken in the monthly
night collections were presented in Table 6.  Generally,
numbers and diversity of species were greatest in the
Zostera area followed by Ruppia and sand areas.  The number
of species captured and total fish density increased with
temperature through October.  Species diversity and population
densities both declined rapidly with decreasing water temp-
eratures in November and December.
        Most species captured in the haul seine were
taken sporadically; only Anchoa mitchilli was taken during
every month (Table 6).  This species was the numerical
dominant in the sand area in March and May and in all
habitats during June through November.  The lowest densities
       2
(0.26/m ) for this species were noted in December.
Membras' martihica was present in collections from
April through November.  However, this species was never
abundant (densities ranged from 0.30-12.82/m2) in the
collections.  Pipefish  (Syngnathus fuscus) were collected
                              36

-------
Table 5.  List of Resident Species captured by Haul Seine,  16' Otter Trawl
          and Pushnet
Anguilla rostrata
Alosa aestivalis
A. sapidissima
Brevoortia tyrannus
Anchoa mitchilli
Opsanus tau
Gobiesox strumosus
Urophycis regius
Hemiramphus brasilienis
Tylosurus.acus
Strongylura marina
Hyporhamphus unificiatus
Lucania parva
Membras martinica
Menidia menidia
Apeltes quadracus
Gasterosteus aculeatus
Hippocampus erectus
Syngnathus floridae
S. fuscus
S. louisianae
Centropristis striata
Orthopristis chrysoptera
Bairdiella chrysoura
Cynoscion nebulosus
jC. regalis
Leiostomus xanthurus
Menticirrhus saxatilis
Menticirrhus americanus
Micropogbnius undulatus
Sciaenops ocellata
Tautoga onitis
Astroscopus guttatus
Chasmodes bosquianus
Hypsoblennius hentzi
Gobiosoma bosci
(J. ginsburgi
Peprilus alepidotus
Prionotus evolans
Paralichthys dentatus
Scophthalmus aquosus
Pseudopleuronectes americanus
Trinectes maculatus
Symphurus plagiusa
.Sphoeroides maculatus
Chilomycterus schoepfi
Haul Seine

   X
   X
   X
   X
   X
   X
   X
   X
   X
   X
   X
   X
   X
   X
   X
   X
   A.
   X
   X
   X
   X
   X
   X
   X

   X
   X
   X
   X
Otter Trawl

    X
    X

    X
    X
    X
    X
    X
                                                                       Pushnet
    X
    X
    X
    X

    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
    X

    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
    X
X
X
                                       X
                                       X
X
X
                                        37

-------
                                                                  Table 6
                                             Resident Fishes Collected by Haul  Seine  at Night  in  Zostera  (Z),  Ruppia (R)  and Sand (S) habitats
                                                                  It/100 m*
Species
Anguilla rostrata
Alosa aestivalis
A. sapidissima
Brevoortia tyrannus
Anchoa mitchilli
Opsanus tau
Gobiesox strumosus
Rissola marginata
Hemiramphus brasiliensis
Strongylura marina
Lucania parva
Membras martinica
Menidia men id i a
Gasterosteus aculeatus
Syngnathus fuscus
Centropristis striata
Orthopristis chrysoptera
Bairdiella chrysoura
Cynoscion nebulosus
C. regal is
Leiostomus xanthurus
Menticirrhiis americanus
Sciaenops ocellata
Chasmodes bosquianus
Hypsoblennius hentzi
Gobiosoma bosci
G. ginsburgi
Paralichthys dentatus
Scophthalmus aquosus
Pseudopleuronectes americanus
Trlnectes maculatus
March April
Z R S Z R S Z
1.97
3.15 0.30 1.79
0.31
1.21 2.86 69.68
0.49 0.94 1.30 44.49 25.46 27.50 27.16
0.79 1.21 1.58
0.78
8.66
1.18 0.91 3.21 1.97
9.31 9.40 0.44 1.97 0.30 1.07
0.49
3.15
259.8 148.8 71.07 37.40
0.39 0.39
0.49
May June
R S Z R S
71.43 31.03 1.00 9.40
33.99 49.26 95.36 57.86 47.58
0.49
0.49
0.49 1.00
1.48 2.96 5.51 1.50 ,0.30
1.97 1.74 0.75
0.49
5.42 10.84 5.80 8.48 3.03
0.29 0.25 0.30
0.49
0.29
July
Z R S
0.58
0.29 0.26
31.21 21.78 42.86
0.26 0.28
4.62 1.58 2.52
3.47 4.20 1.12
0.28
1.73 4.48
Sphoeroides maculatus

-------
                                                      Table 6.  (Continued).
      Species
                                       August
                                    Z     R
                          September
                       Z     R     S
                                   October
                                Z     R     S
                        November
                        Z   R    S
            December
          Z     R    S
Angullla rostrata
Alpsa aestlvalls
^. sapidissima
Brevoortia tyrannus
Anchoa mltchilli
Opsanus tau
Gobiesox strumosus
Rissola marginata
Hemlramphus brasillensls
Strongylura marina
Lucanla parva
Membras martinica
Menidia men id la
Gasterosteus aculeatus
Syngnathus fuscus
Centroprlstls striata

Orthopristls chrysoptera
Bairdlella chrysoura
Cynoscion nebulosus
C._ regalls
Lelostomus xanthurus
Sciaenops ocellata
Chasmodes bosqulanus
Hypsoblennius hentzl
Gobiosoma bosci
ฃ. Ginsburgl
Parallchthy3 dentatus
Scophthalmus aquosus
Pseudopleuronectes americanus
Trinectes maculatus
Sphoeroldes maculatus
       0.16
 0.23  0.49
51.04 36.36 14.47
 3.22  1.46
       0.16

 3.45  1.95  0.22
 1.84  0.97  0.22
 1.38        1.20
 1.14  0.49
 2.07        0.66
         8.38  3.62 14.64
         0.31
         0.31  0.99
               0.33
         1.55  1.64
         1.24  1.64  4.05
         5.59 12.17  0.31
         3.73  1.97
         0.62

         0.62  0.33
         0.93  1.32
               1.64  0.31
81.09 38.30 22.05
 0.32  0.29
 0.32  1.46
       0.29
 8.01  0.88
12.82  3.22  5.74
 0.32

 6.73  5.56  0.60
 0.64
                                            1.28  0.29
                                            0.32  0.58
                                            4.17
                                                                         11.53
0.50
         0.26
      1.58

0.29 18.90 0.83

0.26
                                                                                         1.58
                                                                          0.25
 0.23
0.22

-------
from May through October, and once in December.  Most pipefish



were collected in the vegetated areas (see Table 5).  Much



lower densities were present over sand areas, particularly



during July and August.  Spot, Leiostomus xanthurus,



recruited to Chesapeake Bay in April and at this time were



clearly the numerically dominant species of fish in all



habitats.  Atlantic menhaden, Brevoortia tyrannus, was



present from April through August and was the dominant



species in vegetated areas during May (Table 6).



     Length - dry weight relationships were determined for



seven dominant species collected by haul seine  (Table 7).



These equations were used to determine biomass of field



collected individuals of these species.  Seasonal biomass



(dry weight) measurements of seven dominant species are



presented in Table 8.  The dominant species in terms of



biomass differed from the numerical dominant in certain months;



with few exceptions, however, Anchoa mitchilli remained the.  •<,..



dominant species.  In March and December, M. menidia was



dominant in all habitats; L. xanthurus was the dominant



species only in May in the Zostera sampling area.  Although spot



was clearly the numerical dominant in April  (Table 6), all



specimens were newly recruited postlarvae  (mean length 18.1



mm) which individually contribute little to the fish biomass.



Other species collected  in the haul seine and contributing



significantly to the fish biomass at particular times were



Atlantic menhaden in May and June, rough silverside in June



and July; and silver perch in September.  Menhaden and silver
                               40

-------
Table 7  .  Length - dry weight relationships  for dominant  fishes.  Dry weight  (w)  is



            in  g and length  (1) is  standard length  in mm.
Species
Leiostomus xanthurus
Leiostomus xanthurus
Brevoortia tyrannus
Bairdiella chrysoura
Syngnathus fuscus
Membras martinica
Menidia menidia
Anchoa mitchilli

LOG
LOG
LOG
LOG
LOG
LOG
LOG
LOG

(w)
(w)
(w)
(w)
(w)
(w)
(w)
(w)

— "3
— ' •
= 3.
= 3.
= 3.
= 3.
= 2.
= 2.
= 3.

1858
2726
902
304
7906
9569
9582
5281

LOG
LOG
LOG
LOG
LOG
LOG
LOG
LOG

(1)
(1)
(1)
(1)
(1)
(1)
(1)
(1)

- 5.
- 5.
- 6.
- 5.
- 8.
- 5.
- 5.
- 6.

8013
8751
8819
869
6256
5342
5615
6570
n
17
32
21
31
29
8
39
16
Size
Range
(mm)
14- 23
>32
25- 60
35-140
90-200
26-100
25-100
38- 75
r2
0.87
0.99
0.95
0.99
0.92
0.98
0.97
0.96

-------
                                                                TABLE 8
                                                Resident Fishes Collected by Haul Seine
                                                         Biomass (mg dry wt/m2)
*Brevoortia tyrannus
      Zostera
      Ruppia
      Sand

*Anchoa mitchilll
      Zostera
      Ruppia
      Sand

 Membras martinica
      Zostera
      Ruppia
      Sand

 Menldia Menidia
      Zostera
      Ruppia
      Sand

 Syngnathus fuscus
      Zostera
      Ruppia
      Sand

 Bairdiella chrysoura
      Zostera
      Ruppia
    .  Sand

 Lelostomus xanthurus
      Zostera
      Ruppia
      Sand
March

0.79
3.92 '
2.63

104.98
73.14
8.46
April
0.49
1.11
178.16
87.44
113.26
16.14
12.13
46.25
22.56
1.30
17.51
May
92.71
91.65
53.82
46.74
50.60
73.18
26.63
15.47
40.44

June
7.62
79.62
180.93
100.27
80.73
68.89
13.82
3.48

July
10.11
6.09
80.32
48.08
95.47
43.86
19.21
18.03

August
9.29
38.16
133.86
95.72
41.59
37.56
15.11
1.33
Sept.

2.99
4.60
38.30
6.49
9.82
31.06

Oct.

180.48
76.75
41.46
28.65
6.56
14.48
4.81
Nov. Dec.

0.15
18.93
1.86
2.74
24.75
10.82
41.36
25.49
11.70
           11.62
            6.46
             8.19
             0.60
            4.71
            6.69
            1.81
93.85
12.16
24.98
37.95
31.61
10.46
18.97

33.85
             3.09
             4.47
             2.19
                                               1.90
                                               0.70
                                               2.19
21.27

24.35
             4.84
            11.25
             3.11
                                              127.07
                                               24.67
8.48
              78
              47
              37
                                                4.81
            2.92
                                                                                             0.08

-------
perch are schooling species which undergo seasonal migrations.

Therefore catches of these species were quite variable

depending upon the presence of schools in the sampling area.

Rough silversides were present in the study area for most of

the year at relatively low densities and biomass.

         Comparative day-night collections were made with

the haul seine in June, September and December.  Results

are presented in Table 9.  There were no clear trends in

the data.  Day collections in June yielded more species and

individuals  than were taken  during night  collections.

Additionally biomass of those fishes collected during the day

was greater than for night collections.  In September both

the number and biomass of species collected at night were

greater than corresponding daytime collections.  In December,

night-time collections resulted in a greater catch in terms

of all three parameters than daytime hauls.

         Biomass of the dominant species for day and night

collections from June, September and December  is presented
                                                        i
in Table 10.  In June, Brevoortia tyrannus wasdominant in the

Zostera area during the day;  all specimens, however, were

taken in a single collection and none were taken in the

two other sets made in daylight in Zostera.  By comparison this

species was common at night only in the sand area, where

it was taken in all three collections.  It is possible that

these juveniles school in daylight and disperse at night.
                               43

-------
                                    TABLE 10
                   Day-Night  Comparison of  Resident Fishes
              Biomass (mg dry wt/m^) from haul seine collections
Brevoortia tyrannus
Anchoa mitchilli
Membras martinica
Menidia menldia
Syngnathus fuscus
Leiostomus xanthurus
Brevoortia tyrannus
Anchoa mitchilli
Membras martinica
Menidia menidia
.Syngnathus fuscus
Leiostomus xanthurus
Brevoortia tyrannus
Anchoa mttchilli
Membras martinica
Menidia menidia
Syngnathus fus cus
Leiostomus xanthurus
JUNE
Zostera
D
511.80
3.42
6.55
41.60
16.39
5.02
N
0
180.93
68.89
0
8.19
37.95
Ruppia
D
0
12.08
5.82
8.86
0.99
10.92
N
7.62
100.27
13.82
0
0.60
31.61
D
0
0
18.
4.
0
0.
Sand
N
79.62
88.47
61 3.48
06 0
0
43 10.46
SEPTEMBER
Zostera
D
0
41.26
0
-i -ii.
i . / 1
9.74
3.42
N
0
2.99
6.49
0
4.84
8.48
Ruppia
D
0
0.12
0.85
0
0.45
0
N
0
4.60
9.82
r\
\J
11.25
0
D
0
0
4.
0
0
0
Sand
N
0
38.30
56 31.06
0
0.11
0
DECEMBER
Zostera
D
0
0
0
0
0
0
N
0
0.15
0
2.74
0.08
0
Ruppia
D
0
0
0
0
0
0
N
0
0
0
24.75
0
0
Sand
D N
0
0.
0
18.
0
0
0
65 0
0
28 12.82
0
0
                                        45

-------
With the exception of the September Zostera collections,
Anchoa mitchilli was more abundant at night than during the
day.  Membras martinica exhibited the same trend in day-night
abundance as did A. mitchilli  (except for the night time sand
collections).
     For these two species it  is unlikely that the. day-
night difference is an effect  of enhanced avoidance during
the daylight samples, since Menidia menidia is captured
during the  day.  The increased abundance of Synghathus  fuscus
during the  day is probably due to increased activity during
daylight hours and greater availability to the sampling
gear.  Lower daytime catches of Leiostomus xanthurus in
vegetated areas, probably represents increased avoidance of
the sampling gear.  The ratios of night to day catch of spot
are much greater in sand, however, suggesting that some
movement from the vegetated areas may occur at night.
                                46

-------
     In September 1979, a comparison of the haul seine data from this study




to trawl data of Orth and Heck (1980) indicated that benthic species, especially




spot, were not adequately sampled by the haul seine.  Therefore, sampling




with a 16 foot otter trawl supplemented the routine haul seine collections.




September day and October night samples in 1979 were representative of the




relative gear selectivity of the haul seine and otter trawl for various




species (Table 11).  Planktivorous fishes such as Anchoa mitchilli. Menidia




menidia and Membras martinica were more effectively captured with the haul




seine than the otter trawl.  Pipefish (S_. fuscus) were also captured in




greater numbers by the haul seine than the trawl.  Density estimates




for silver perch by both gears were the same in September but differed in




October, which was probably due to increased haul seine avoidance as silver




perch grew larger.  Spot was avoiding the haul seine as demonstrated by




the small haul seine catch and trawl density estimates in September and




October.  Similar trends were evident in comparisons of trawl and haul




seine biomass estimates (Table 12).




     Anchoa mitchilli. Leiostomus xanthurus, and Syngnathus fuscus were




regularly captured by the otter trawl (Tables 13 and 14).  A. mitchilli




was taken during every month.  This species was the numerical dominant in




the sand area in March and April of 1980 and in the Zostera area in November




1979 and March 1980.  Pipefish (ฃ. fuscus) were collected from September




1979 through July 1980.  Low densities of pipefish were seen over sand




areas during October, March, June and July.  As seen in the haul seine




and trawl collections, spot recruited to the study area in April.




Spot was the numerical dominant in all habitats from September to




November 1979 and May through July 1980.  Spot was more abundant in the




Zostera and Ruppia  areas than the sand area.
                                     47

-------
                Table 11
    Comparison of 1979 September Day and
October Night Haul Seine and Otter Trawl Catch
             Density (#/100 m2)
September Day
Zostera
Species
Anguilla rostrata
Anchoa mitchilli
Opsanus tau
Gobiesox strumosus
Urophycis regius
Rissola marginata
Lucania parva
Membras martinica
Menidia menidia
Syngnathus louisianae
Syngnathus fuscus
Centropristis striata
Orthoprlstis chrysoptera
Bairdiella chrysoura
Cyno scion nebulosus
C. regalis
Leiostomus xanthurus
Tautoga onitis
Chasmodes bosquianus
Hypsoblennius hentzi
GoBiosoma bosci
Peprilus alepidotus
Paralichthys dentatus
Trinectes maculatus
Sphoeroides maculatus
Chllomycterus schoepfi
Haul
Seine
96.87
3.13
.85
15.33
8.83
.28-
1.99
.28
15.38
Trawl
1.17
.05
.05
.53
9.78
.05
10.21
.05
.11
1.28
.11
.11
.05
.05
Ruppia
Haul
Seine Trawl
.31 ..16
.08
.31
. 31 .J38
.31 .64
.08
3.03
3.11
.08
.32
.08
.08
.16
Zostera
Haul
Seine
81 .p9
.32'
.32
8.01
12.82
.32
6.73
.64
1.28
.32
4.17
Trawl
.12
.12
.36
.12
6.22
.12
.12
4.31
.12
39.12
.72
4.66
.12
.36
October
Night
Ruppia
Haul
Seine Trawl
38.30
.29
1.46
.29
.88
3.22
5.56
.29
.29
.58
.24
.12
.36
.60
.36
.12
1.80
.72
2.51
94.02
.84
2.51
.12

Sand
Haul
Seine Trawl
22.05 I
S
A
M
5.74 f
it
E
.60 S
T
A
K
E
N

-------
                                                       Table 12
                                 Comparison of 1979 Haul Seine and Trawl Collections
                                                   (mg dry wt/m2)
September-Day
Species
Anchoa mitchilli
Membras martinicia
Menidia menidia
Syngnathus fuscus
Bairdiella chrysoura
Leiostomus xanthurus


41
7
9
3
Haul Seine
Z R S
.26 .12
.85 4.56
.74
.74 .45
.42
Trawl
Z
3.56
.50
111.50
160.85
R
.41
1.04
1.02
33158
53.92
S
N
0
S
A
M
P
L
E
October-Night
Haul Seine
Z
180.48
28.65
4.81
4.78
4.81
R S
76.75 41
. 6.56 14
7.47 1
2

.5
.48
.37
.92
Z
.2
11.3
39.9
658.16
Trawl
R
•32
.46
3-57
20.62
1607. 6

S
N
0
S
A
M
P
L
E
vo

-------
             Table  13
Resident Fishes Caught by Trawl 1979 by Month, Time of Day, a'nd Habitat
           Density/100 m
September
Zoster a Ruppia Sand
Species
Anguilla rostrata
Anchoa mitchilli
Opsanus tau-
Gobiesox strumosus
Rissola marginata
Lucania parva
Membras martinicia
Menldia menidia
Syngnathus louislanae
S. fuscuB
Centropristis striata
Orthopristis chrysoptera
Bairdiella chrysoura
Cyno scion nebulosus
ฃ. regalis
Leiostomus xanthurus
Sciaenops ocellata
Tautoga onitis
Chasmodes bosquianus
Hypsoblennius hentzi
Goblosoma bosci
Peprilus alepidotus
Paralichthys dentatus
Trinectes maculatus
Sphoeroides maculatus
Chllomycterus schoepfi
D
1.17
.05
.05
.53
.11
9.78
.05
10.21
.05
.11
1.28
.11
.11
.05
.05
N
N
0
S
A
M
P
L
E
T
A
K
E
N
D
.16
.08
.08
.64
.08
3.03
3.11
.08
.32
.08
.08
.16
N
N
0
S
A
M
P
L
E
T
A
K
E
N
D N
N
0
S
A
M
P
L
E
T
A
K
E
N
Zoster a
D
0.6
5.38
,12
.06"
2.33
.06
.12
1.20
10.53
.06
.84
.30
.06
N
.12
.12
.36
.12
6.22
.12
.12
4.31
.12
39.12
.72
4.66
.12
.36
October
Ruppia
D . ft
.24
1.02 .12
.36
.60
.36
.06
.12
2.33 1.80
.72
1.62 2.51
4.31 94.02
.60 .84
.42 2.51
.06 .12
November
Sand Zostera Ruppia Sand
DN DN D N' DN
N N
.90 0 2.03 0
S C
A A
M T
P C
L H
E
.06 .36 .96 .72
T
A
K .96 .36
E
N
1.08 2.03
.12
.06
.12

-------

Species
Anguilla rostrata
Alosa aestivalis
Brevoortia tyrannus
Anchoa mitchilli
Opsanus tau
Gobiescrx strumosus
Urophycis regius
Rissola marginata
Menidia menidia
Apeltes quadracua
Hippocampus erectus
Syngnathus floridae
S. fuscus
Centropristis strlata
Orthopristis chrysoptera
Lagodon rhoraboides
Bairdiella chrysoura
Leiostomus xanthurus
Menticirrhus saxatilis
Mlcropogonius undulatus
Tautoga onitis
Aatroacopus guttatus
Hypsoblennius hentzi
Gobiosoma bosci
G. ginsburgi
Peprilus alepldotus
Prionotus evolans
Paralichthys dentatus
Scophthalmus aquosus
Pseudopleuronectes americanus
Trinectes maculatus
Table
Resident Fishes
Density/ 100
1980
March
Zostera Ruppia Sand Zostera
DNDNDN- D N
.12
.12
1.04 .12
.24 .08 .32 4.78 .16 .22 27.63
.11 .12
.08 .16 .11 .24
.48
.11
.16 .11
.16 .08 .44 2.39
6.59. .12
.08
.24
.08
.32 .12
14
Caught by Trawl by Month,
ID
April
R uppia Sand
D N D N
.09 .48
4.48 .48
.09 ,..1.68 1.70 20.21
.08
.08
.08
.08 .24
.09 .18
.54 .64
.09
.54 10.21
.08
8,16 1.12 .09 .24
.09
.12
.16
.08
.48
Time of Day,
and
Habitat

May
Zostera Ruppia Sand
D N D
.26 .
3.34 .91
.39
.23-
.23 .26
.13
1.16
1.71 3.50 5
8.61 35.61 34
.39 .26
.13
.23 2.20

55
.82
.36
.27
.09
.46
.09
:50
.09
.09
.09
.27
N D N
.37
2.94 2.55 ..3
.13
.24
.49
.24
6.38
19.74 4.78 18
.37
.12
.12 .16
.49
1 i

.59
.06
.90
.66
.06
.18

-------
                                                                Table 14 continued
                                                       Resident Fishes  Caught by Trawl 1980 by Month, Time of-Day, and Habitat
                                                            Density/100 nT

                                                                1980
      Species
                                                             June
                                                   Zostera	Ruppla  .  Sand
                                                      N
                                                                   N
                                                                July
                                                       Zostera	Ruppla    Sand
                                                                                                        N
                                                                                                                              N
Anguilla rostrata
Anchoa mitchllll
Opsanus tau
Gobiesox strumosus
Rieaoia marglnata
Menldla menidia
Apeltes quadracus
Syngnathus" floridae
j>. fuscus
Centropristls striata
Orthoprlstls chrysoptera
Lagodon rhomboldes
Bairdiella chrysoura
Lelostomus xanthurus
Astroscopus guttatus
Hypsoblennlus hentzl
Prionotus evolans
Parallchthys dentatus
Pseudopleuronectes amerlcanus
Trlnectes maculatus
Symphurus plaglusa
Sphoeroides maculatus
  .08    .49   .32   .72
         .24   .08  4.54       .96
         .49   .16   .24

        2.21
  .08          .16
  .24   1.47  1.12   .96

 5.54  19.97  3.59 13.64       .24
                     .48

               .08

40.34 146.55 56.70 91.9.9 5.98 8.49
  .16   1.96         .48
        1.59
  .41   5.02  1.52  2.63
  .41   7.35   .32  4.31
         .24     .    .24
        4.78
.12
.24
                    .24
        .12         .16      .48
        .12   .24   .40
        .12         .16
        .12                  .36

 ..16   .36   .08   .40
                    .40
 4.94 15.43  2.39  9.01 .08  .24
        .12         .48
                    .08
        .24   .32   .08
              .08   .08
11.96  8.97 14.35 11.72     7.42
        .12
  .32   .96
                             .12
  .96   .72   .72  1.75 .08  .72
  .56  2.03   .32  1.12 .08
        .12

        .12

-------
TABLE 15.  Resident Fishes Collected by Trawl in 1979 Biomass  (mg dry wt/m2)
September
Zoster a Ruppia
D N D 'N
Anchoa mitchilli 3.56

Membras membras

Menidia menidia

Syngnathus fuscus .51

Bairdiella
chrysoura 111.50
Lelostomus
xanthurus 160.85

N .41
0
S
1.04
A
• 1.Q2
M

P 33.58
L
53,92
E
N
0
S
A
M

P
L
E
Sand
D N
N
0
S
A
M

P
L
E
N
0
S
A
M

P
L
E
October
Zostera Ruppia Sand
D N D N D N
15.158 .21 1.90 .32 .62 N
0
.46
S
.84
A.
3,:>6 11.32" 3.57 .05
M

15.77 39.92 20.62 . P
L
194.87 658.16 59. ซ6 1607.59 45.26
E
November
Zostera Ruppia
D N D N D
6.94 N
0
C
A
.29 1.09 .84
T

9.42 3.41 C
H
48.54

Sand
N
N
0
C
A
T

C
H

-------
                                                                      Table 16
                                                       Resident Fishes Collected by Trawl In 1980
                                                                (Biomass gm/100 m^)
March
Zoster a Ruppia Sand
D N D N D N
Snchoa mitchllll .20 .09 .94 9.6 .34
Brevoortla tyrannus .40
Menidia menidia
Syngnathus fuscus .21 .09
Bairdiella chrysoura
m Leiostomus xanthurus
I- "" 	
April May
Zostera Ruppia Sand Zostera Ruppia Sand
D N D N D N DNDNDN
.97 71.05 .49 5.20 6.03 47.89 5.82 1.38 1.70 7.35 5.0 11.18
10.8 2.60 15.18
2.07 2.76 3.56
1.08 10.4 1.59 27.77 10.44 16.71 20.21 23.45
5.29 .02 7.19 .15 .07 .04 15.26 25.60 31.18 30.84 5.74 54.43
                                          •  June

                               Zostera	Ruppia  •    S and
                                                               July

                                                   Zostera	Ruppia
Sand
                                  N
                                                N
                                                              N
                                                                              N      D..     N
Anchoa mltchilll

Brevoortla tyrannus

Menidia menidia

Syngnathus fuscus

Bairdiella chrysoura

Leiostomus xanthurus
        .75    .24    10.72         1.92            .24           .40            1.16



 2.51          3.67

 32.05 110.65  24.87  87.83         1.60     15.41  43.96   43.96  5.84    29.27   2.03  '

                                                                  .212    .12

265.67 684.15  254.76 359.36 21.05  44.42   145.92  117.29  146.73  195.85         70.41

-------
     Seasonal biomass (dry weight) measurements of seven dominant species




are presented in Table 15 and 16.  In terms of biomass, spot was the




dominant species in all habitats.  During September through November,




the biomass of silver perch was larger than that of pipefish.  April




through July 1980, pipefish were the second most dominant species.




     Comparative day-night otter trawl collections (Table 13 and 14),




indicated that density estimates of silver perch and pipefish were




typically higher at night than during the day.  Except for April and July,




spot was more abundant at night than during the day.  Anchoa mitchilli




was typically more abundant at night than during the day.  As with the




haul seine, the observed day/night differences in trawl catch may be due




to gear avoidance.  The large day densities of spot in April may -be due




to minimal gear avoidance by 15-25 mm spot.




     From March to July 1980, resident pelagic species were sampled with




a nekton push net instead of a haul seine.  This gear has effectively




sampled juvenile alosines (Kriete and Loesch, 1980) and was less labor




intensive than the haul seine.  The push net captured 1139 specimens




representing seven species in six families of fishes (Tables 17 and 18).




Catches were more diverse and numerically greater at night than during




the day.  Anchoa mitchilli was the only species captured every month.




The push net caught more A. mitchilli at night than did the trawl (Table 19).




Spot was poorly sampled by the push net.  Although no direct gear comparison




was made between the haul seine and the nekton push net; the haul seine




was more consistent in capturing pelagic fishes in the SAV area than was




the push net.  Table 5 lists the species captured by the haul seine, trawl,




and push net.
                                     55

-------
                                                Table 17
                                        Resident Fishes Collected by Nekton Push  Net in 1980
                                               (#/100 m2)
Daytime
Species
Brevoortia tyrannus
Anchoa mitchilli
Leiostomus xanthurus
Membras martinicia

March April
Z R S ZRS Z
6.0 3.2 4.0
.7 1.6 4.2 .1
.1
May June July
R S Z RS ZRS
1.2 .3 1. no catch
1.6 3.5
1.8
.1
Nighttime
Species
Brevoortia tyrannus
Anchoa mitchilli
Menidia menidia
Membras martinica
Leiostomus xanthurus
Hyporhamphus unifaciatus
March April
Z R S Z R S Z
.2 No samples 7.0
taken
.6 .7 .4
May June July
RS ZRS Z R S
10.4 .7 .2 .4
2Q.6 11.2 12.2 36.9 .4 4.6 9.4
.5
.8 .8 1.7 .4 4.1 3.4
1.9 .2
.1 .3 .2 .2
Tylosaurus acus
.1

-------
                                                           Table  18
                                            Resident Fishes Collected by Nekton Push  Net in 1980
                                                    flng dry wt/m? )
Ln
Daytime
Species
Brevoortia tyrannus
Anchoa mitchilli
Leiostomus xanthurus
Membras martinicia

March April
Z R S Z R S Z
2.3 2.4 5.5
2.4 3.1 7.8 .04
.2
May . June July
RS ZRS ZR S
1.0 .3 no catch
3.3 5.0
6.0
.4
Nighttime
Species
Brevoortia tyrannus
Anchoa mitchilli
Menidia menidia
Membras martinica
Leiostomus xanthurus
Hyporhamphus unifaciatus
March April
Z R S Z R S Z
.4 No samples 10.0
taken
7.9 5.6 2.4
May June July
RS ZRS ZR S
11.5 2.2 1.0 1.5
31.4 16.5 30.1 175.4 .7 12.7 25.3
8.4
.9 8.4 14.3 4.9 3.7 33.5
1.5 1.2
N/A N/A N/A N/A
      Tylosaurus acus
N/A

-------
Table 19.  Comparison of resident fishes captured by Nekton Push Net and Otter Trawl (#/100m2)
                                 DAY COLLECTIONS
Brevoortia tyrannus
Anchoa mitchilli
Menidta menidia
Membraa martinica
Leloatomus xanthurus
Hyprohamphus unifaclatus
Ln
00 Tylosurus acus

SPECIES
Brevoortia tyrannua
Anchoa mitchilli
Menidia menidia
Membras martinica
Leiostomus xanthurus
Hyporhamphus unifaciatus
Tylosurus acus
MARCH APRIL
Push Net Trawl Push Net Trawl
ZRS ZRS ZRS ZRS
6.0 . 1.4 3.2 .. . 4.48
.7 . . . .24 .32 4.78 1.6 4.2 . . .22 .09 1.70
.... ... 6.59 8.96 .09
NIGHT COLLECTIONS
MARCH APRIL
Push Net . " Trawl Push Net Trawl
ZRS ZRS ZRS ZRS
'..'.. ... No samples taken ,12 . . ,48
.2 .08 . .16 No samples taken 27.63 1.68 20.21
•6 .7 .4 . . . NO samples taken
No- samples taken
No samples taken .12 1.12 .24
No samples taken
No samples taken
MAY
Push Net Trawl
ZRS Z R Z
4.00 1.20 .30
.10 1.60 3.50 3.34 .82 2.55
.10 . ...
.10 . . 8.61 34.50 4.78
MAY
Push Net Trawl
ZRS ZRS
. 10,4 ,7 , . .
7.0 20.6 11.2 .91 2.94 3.6
.8 . ...
1.9 . 35.6 19.7 18.7
.1 .

-------
                                                             Table 19 (Cont'd)
                                                              DAY COLLECTIONS
Species
Brevoortia tyratmus
Anchoa mitchilli
Menidia menidla
Membras martinica
Leiostomus xanthurus
\B 	
Hyporhamphus unifaclatus
Tylosurus acus

Species
Brevoortia tyrannus
Anchoa mlt chilli
Menidla menldia
Membras martinica
Leiostomus xanthurus
Hyporhamphus unifaciatus
JUNE JULY
Push Net Trawl Push Net
ZRS ZRS .ZRS
. ^ . . • No catch
.08 . No catch
.08 .16 No catch
No catch
1.8 40.3 56.70 5.98 No catch
No catch
No catch
NIGHT COLLECTIONS
JUNE JULY
Push Net Trawl Push Net
ZRS ZRS ZRS
.2 .4 ... ...
12.4 36.9 .4 .24 4.54 .96 4.6 9.4
.5 . ... ...
.8 1.7 .4 ... 4.1 3.4
.2 . . 146.6 !)2.0 8.5
. .3 .2 ... .2

Trawl
ZRS
.12 .16 .48
• • •
11.96 14.35 11.72

Trawl
ZRS
.12 .16 .48
8.97 11.72 7.42
Tylosurus acus

-------
Zooplankton




     Abundance, diversity, and diel availability of zooplankton components




within the shallow water seagrass ecosystem and adjacent deep water unvegetated




areas were analyzed and compared.  A total of 118 species were identified




from all habitats combined through the thirteen month study period (Table 20).




The zooplankton assemblage consisted of obligate planktonic forms (holo-




plankton and meroplankton) and facultative planktonic forms (demersal




plankton).  Holoplankton was the numerically dominant component and included




species of copepods (calanoids and cyclopoids), cladocerans, chaetognaths,




rotifers, jellyfish and hydromdus.ae.  The meroplankton component was made up




of fish eggs and larvae, decapod larvae and larvae of gastropod, pelecypod,




polychaete and barnacle species.  Demersal plankters have been defined as




organisms which are resident members of the bottom substrate community but




emerge periodically to move into the water column, swimming freely (Hobson




and Chess, 1976; Robertson and Howard, 1978).  Amphipods, isopods, cumaceans,




tanaids, leeches, adult polychaetes and mysids constituted the demersal




component sampled in this study.




     Temporal and spatial variations in zooplankton community structure




were documented during the thirteen month program.  Two distinct seasonal




zooplankton communities were identified: a winter-spring assemblage peaking




in March and a summer-fall assemblage peaking in July.  In both cases




holoplankters dominated the assemblage numerically, specifically calanoid




copepods (Figure 10). During periods of peak abundance, calanoids accounted




for 95% of the total zooplankton standing stock.  Only during the transition




periods (May-June; November-December) were copepods not the dominant taxon.




At this time meroplanktonic forms such as larvae of polychaetes and barnacles




constituted up to 45% of the total zooplankton community numerically.  Temporal




variations in abundance and distribution over a diel cycle were exhibited






                                       60

-------
TABLE 20.  Number of species identified within individual taxa of the three
          zooplankton components.
                           ZOOPLANKTON COMPONENTS
              Obligate
                                                       Facultative
Holoplankton
   Meroplankton
Demersal Plankton
Copepods n = 12

Cladoceran n = 12

Chaetognath n = 4

Jellyfish n = 3

Hydromedusae n = 1

Rotifer n = 1
            23
Decapod larvae n = 23

Fish eggs and larvae n = 20

Pelecypod larvae n = 1

Gastropod larvae n = 1

Polychaete larvae n = 1

Barnacle larvae n = 1
                    47
Total number of species 118
Amphipods n = 21

Cumaceans n .= 6

Isopods n = 4

Mysid n = 3

Polychaete, adult n

Tanaid n = 1

Leech n = 1
= 12
                                                                  48
                                        61

-------
     FIGURE 10. Dominant  zooplankton taxa.  Percent of total community.
r~     LH —
O
OL
LJ
CX
                                                           SPECIES    SYMBOL
D

-------
for holoplankters and demersal plankters.  In addition, interhabitat




differences in abundance and distribution were observed for specific species




of obligate and facultative zooplankters.






Holoplankton




     Calanoid copepods were represented by the greatest number of species




of all holoplankters and dominated this group numerically.  The copepod




population exhibited a seasonal succession pattern (Table 21). . The winter-



spring assemblage consisted of Acartia clausi, Acartia copepodites, Centropages




hamatus, Eurytemora affinis, Oithona sp., Pseudocalanus minutus, Paracalanus




crassirostris and Acartia tonsa.  In 1979 Acartia clausi had replaced




Acartia tonsa by March, a phenomenon well documented for Middle Atlantic




estuaries (Jeffries, 1962; Jacobs 1978).  Acartia clausi adults and Acartia




copepodites constituted greater than 85% of the March 1979 copepod total.




Acartia tonsa was present in low numbers, 4% or less of the total.  In




March 1980 a numerical pulse in copepod numbers was observed as expected,




however the community structure differed considerably from that of 1979.




Acartia clausi was not the dominant species nor had A. tonsa numbers




decreased markedly to the levels observed in 1979.  Acartia clausi represented




less than 30% of the total and A. tonsa between 15-35%.  In addition,




Centropages hamatus and Pseudocalanus minutus increased in numbers well




beyond the 1979 levels reaching 30% and 18% of the numerical total, respectively.



     Species diversity was greater for the winter-spring community than




the summer-fall copepod community.  Acartia tonsa dominated the latter




assemblage, accounting for 60-90% of the total, May through January 1980




reaching a peak abundance of 33,000/m  in July.  Acartia copepodites,




Pseudodiaptomus coronatus, and Labidocera aestiva were also present within




this seasonal assemblage in relatively low numbers.  The annual maximum
                                      63

-------
Table 21. Average density per cubic meter of dominant  copepod species,  all
          habitats combined.

1970
March
April
May
June
July
August
September
October
November
December
January
February
March
Acartia
tons a

532
124
275
551
27600
8813
6272
15108
84
194
1103
809
3809
Acartia
clausi

7998
2059
0
0
0
10
0
0
0
5
8
380
3065
Centropages
hamatus

362
141
0
0
0
0
0
0
1
0
6
1961
3203
Pseudodiaptomus
coronatus

0
0
6
23
50
1342
1025
8
0
0
66
107
105
Pseudc
minut

227
143
0
0
0
10
0
0
0
0
88
1918
946
                                        64

-------
density of copepods was observed in July coinciding with the Acartia tonsa



peak.



     Spatial variability in terms of abundance was evident for specific



calanoid species between the three habitats.  Eurytemora affinis, a winter



species present in low density, occurred more often and in much higher


                                 3                                     3
relative numbers .in Ruppia (585/m ) compared to the sand habitat (158/m ).



In contrast Labidocera aestiva, a large summer-fall calanoid, was sampled


                                                    o

more often and in greater numbers in the sand (328/m ).  Very low numbers


                                   o
were noted in the Ruppia area (20/m ).   Total copepod density was also much



higher overall in the sand habitat from July to November.



     Diel availability of calanoid copepods varied markedly between the



three habitats.  Similar abundance values of total copepods were observed



at night in all three habitats for the May and August die! samples.  In the



sand, day and night densities were also similar.  However daytime copepod



abundances within areas of submerged aquatic vegetation were substantially



lower (more than an order of magnitude) than night time densities or the



sand day density.  This held true in both diel comparisons and was consistent



with trends in diel availability observed by Robertson and Howard (1978)



in Australian eelgrass beds.



     Of the other holoplanktonic taxa,  cladocerans were second in numerical


                                                                          2
abundance.  Their peak was of very short duration, numbers reaching 1850/m



during July, approximately 5% of the total zooplankton density.  Podon



polyphemoides accounted for 95% of the total cladocerans; Evadue tergestira



was observed sporadically in low numbers.



     Jellyfish abundance and species composition also exhibited a trend



typical of the Chesapeake Bay (Jacobs,  1978).  Chrysaora quinq.uecirrha



dominated during the summer months while Cyanea capillata was present
                                       65

-------
in low numbers during the winter season.  Only one species of hydromedusae

Nemopsis buchei was observed during the sampling period.  This species was

present in low numbers May through April, peaking in
                       33                              3
September, Ruppia (41/m ) and Zostera (61/m ).  Numbers never exceeded 3/m

in the sand area.

     Chaetognaths were the second most diverse holoplankton group sampled,

abundance and species structure varied seasonally.  The summer fall population

was comprised of Sagitta tenuis (95%), Sagitta enflata, and low numbers of
                                           3
j^. hispida.  Maximum densities reached 22/m  in September for shallow water
                        3 '
vegetated areas and 36/m  in October for the sand.  A winter species,
                                                                       3
Sagitta elegans, was present February and March reaching a peak of 15/m .

Mefdplankton

     Decapod larvae were the most diverse group of all zooplankton taxa

sampled.  The number of species present in one sample was highest in the

summer  reaching a maximum during August.

     The winter-spring decapod population (December through April) consisted

almost entirely of larval Crangon septemspinosa.  During March 1979 and 1980,

this species was present in densities greater than 100/m  , resulting in the

annual peak for total decapod larvae.  Total larval decapod densities

declined from June to August, however the number of species increased 5

fold by May and continued to increased to the August maximum.  Very low
                       3
abundance values ( 10/m ) were observed September through January.

     Spatial differences among habitats were noted for abundances of specific
                                                                         3
decapods.  Paleomonetes larvae increased in numbers markedly by May (28/m )

accounting for greater than 85% of the total within the Ruppia habitat.
                                                3
However the numbers in sand were much lower (2/m ), 6% of the total decapod

density.  This trend continued resulting in higher total decapod abundances
                                        66

-------
in Ruppia through August.   Many other larval decapod species exhibited inter-


habitat differences in distribution.  In general, higher numbers of Paleomonetes


spp., Neopanope texani sayi, and Pinnixa chaetopterana were observed in Ruppia.


Likewise Crangon septemspinosa, Uca spp., Pagurus longicarpus and Callianassa


spp. were observed in higher densities in the sand.


     Fish eggs and larvae were the second most diverse group within the


meroplankton compartment.   Abundance values however were the lowest of the


meroplankters.  Community structure and distribution is described elsewhere


in this report utilizing data from the 505 u mesh pushnet.


     The remaining meroplankters were evaluated as broad taxonomic groups.


Molluscan larvae, both gastropod and pelecypod, reached relatively high

               o
numbers (1000/m ) sporadically during the summer fall period.  However at


no time did either group account for more than 10% of the total zooplankton


community.  Barnacle larvae, both naupliar and cypris stages, were important


constituents of the zooplankton community April through June, reaching up


to 35% of the total within SAV areas and 45% in the sand.  During the day


(May) barnacle larvae accounted for up to 65% of the numerical community


total in SAV areas.  This was an artifact of very low copepod abundances


during the day; the absolute density of barnacle larvae did not exhibit a


diel pattern.


     Polychaete larvae also contributed in high numbers to the winter-


spring assemblage.  This group accounted for 20-35% of the total zooplankton


density consistently in all three habitats, April through June.  Maximum

                             3
densities greater than 1500/m  were observed in April.



Demersal Plankton


     Of the major plankton components, demersal plankters (facultative)


exhibited the most variation between habitats with respect to species


richness and abundance.  Generally, greater diversity and higher densities


                                       67

-------
were observed within the Ruppia habitat compared to the sand.  Diel availability


also varied greatly, in that very few demersal plankters were captured during the day


The observed trends were consistent with those of other studies (Alldredge


and Kins, 1977; Robertson and Howard, 1978; Hobson and Chass, 1979).


     Mysids were the numerically dominant taxa of the demersal component.


Neomysis americana dominated the population throughout the study.  .This


species exhibited patchy distribution between the three" habitats and between

                                  2
replicates.  High densities (500/m ) were noted in August and September in


sand but only in September for the SAV areas.  Adult mysids far outnumbered


juveniles at this time.  A greater percentage of males were captured in


the sand, also higher numbers of females with broods were observed in the


sand habitat at this time.  Neomysis americana remained in all three habitats


in moderate numbers  from October through January, peaking in February.  However


juveniles outnumbered adult during this season.


     Within the Ruppia habitat, amphipods and cumaceans constituted a


maximum of 5% of the total zooplankton standing stock numerically.  This


was observed during the transition between the seasonal winter-spring and


summer-fall communities when holoplankton numbers were low.  At no time


did a  demersal category other than mysids reach 5% of the total in the


Zostera and sand areas.  Cumaceans exhibited seasonal shifts in community


structure.  Cyclaspis varicaus and Oryurostylis smithi dominated this group


July-September, succeeded by j). smithi and Pseudoleptocuma minor during

                                                                  3
November through February.  The summer peak in August reached 10/m  while

                                         o
the winter peak in December exceeded 19/m  .


     Amphipods were the most diverse group of demersal plankters sampled


in this study.  Monoculodes edwardsi, Gammarus mucronatus and Microprotdpus


raneyi were the most frequently occurring species year round and dominated


March-June.  Species number increased in May and remained at a high level
                                      68

-------
through October.  At times Ampelisca sp., Cymadusa compta and Cbfophium sp.

                                          o
were present in densities greater than 2/m .


     Adult polychaetes were observed in low numbers throughout the study.


Nereis succinea, Eteone heteropoda. JE. lactea, and Scblbplos sp. were the


most commonly occurring species.  Erichsonella attenuata and Idotea triloba

                                                                 3
dominated the isopod population reaching a peak in Ruppia of 12/m .(August).


     Demersal plankton greatly influence the food availability and feeding


strategies of pelagic feeding fishes (Hammer and Zimmerman, 1979).  Possible


explanations for the diel vertical migration are reviewed in Robertson and


Howard (1978) and Alldredge and King (1980).


     A more comprehensive and comparative analysis of trends in abundance,


composition and diel availability of all 3 zooplankton components will be


presented in a thesis entitled "Structural and Functional Aspects of


Zooplankton within Areas of Submerged Aquatic Vegetation in lower Chesapeake


Bay" by Cathy Meyer.  The thesis will be completed later this year and a


copy will be submitted to EPA for their information and review at that


time.


     A zooplankton  flux study was undertaken to determine the movement of


zooplankton  into and out of the bed relative to tidal cycles to analyze


the input of zooplankton energy to the eelgrass ecosystem.  Samples were


collected and archived in April and August of  1980.  Analysis was not


conducted due to insufficient funding.
                                        69

-------
Ichthyoplankton Data and Hydrography




         Pushnet sampling for ichthyoplankton and pelagic juvenile




fishes resulted in 88 total collections  (sand n=28; I*, maritima n=29;




Z. marina n=31) during the period 26 March 1979 - 7 March 1980 (Table




22 ).  Sampling was conducted monthly through January 1980, however




inclement weather in February 1980 delayed completion of the 12-month




survey until early March 1980.  Day-night comparison pushnet sampling




was conducted on successive high tides during May and August 1979.




         Volumetric and areal estimates  of pushnet sampling effort




(Table 22 ) revealed moderate monthly variability and almost equal




effort between habitats.  Statistics calculated for total effort per




habitat per month are presented in Table 23 .




         Hydrographic measurements taken concurrently with pushnet




collections revealed temporal variability typical of shallow, nearshore




environments which are rapidly affected  by short-term climatic changes




(Table ^2_).  Observed ranges of salinity, temperature and dissolved




oxygen  (14.1-21.5 ฐ/oo; 1.5-28.0ฐC; 6.6-12.6 mg/1, respectively) were




similar to those recorded by Briggs and  O1Conner  (1971) and Orth and




Heck (1980).       Occasionally, temperature and salinity varied widely




between successive sampling periods as evidenced by measurements




recorded between 27 September and 1 November 1979  (Table 22_).  October
                                70

-------
Table 22.  Ichthyoplankton pushnet collection data summary, March 1979-1980.
           Abbreviations used are:  S - sand, R - Ruppia maritima, Z -
           Zostera marina, N - number of collections, VF - water volume
           filtered, AC - surface area covered, DO - dissolved oxygen, T -
           surface temperature, SAL - surface salinity.
Date
26 Mar 79


26 Apr 79


1 May 79
31 May 79





26 Jun 79


23-24 Jul 79


23 Aug 79





27 Sept 79


25 Oct 79

1 Nov 79


Time
(hrs)
1935
2045
2130
2230
2110
2153
0105
0240
0038
0155
1520
1400
1440
2135
2235
2347
0020
2230
2320
2013
2058
2154
1115
0935
1035
0145
0050
2335
0100
0200
2125
2010
2210
Habitat
S
R
Z
S
R
Z
Z
S
R
Z
S
R
Z
S
R
Z
S
R
Z
S
R
Z
S
R
Z
S
R
Z
R
Z
S
R
Z
N
3
2
2
2
2
2
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
2
2
2
2
2
2
2
VF
(m3)
272.2
180.7
194.4
271.6
246.7
269.1
136.0
180.7
219.6
152.9
217.4
212.9
258.8
258.6
221.5
275.1
164.0
192.8
206.2
270.1
221.9
245.7
251.1
175.3
193.8
61.3
114.3
210.7
236.4
232.2
249.3
229.0
260.1
AC
(m3)
277.9
194.6
198.5
277.3
265.7
274.8
138.9
194.6
274.0
164.7
234.2
293.6
278.8
278.2
328.4
296.4
176.7
240.6
257.3
283.2
232.6
279.9
286.1
241.8
241.9
64.3
130.2
220.9
294.9
264.7
254.6
261.0
280.2
DO
(mg/1)
11.8
12.3
12.6
__
—
. ' —
—
9.1
7.8
8.7
10.2
8.3
9.9
7.1
6.6
8.3
__
9.4
9.4
_
10.8
10.8
—
10.8
10.8
8.0
7.8
8.7
8.2
8.7
__
8.5
8.4
T
8.0
8.0
8.0
15.0
15.0
15.0
18.6
21.5
21.5
21.5
21.5
21.5
21.5
20.8
20.6
20.7
28.0
27.0
27.0
—
28.0
28.0
24.4
23.4
24.1
21.0
21.0
21.0
13.1
13.1
15.5
15.0
15.5
SAL
17.4
17.2
17.7
18.5
18.5
18.5
17.5
17.6
16.9
17.0
17.6
16.6
17.2
19.0
20.0
20.0
15.2
15.8
15.3
—
—
—
—
—
—
21.5
20.9
20.8
14.3
14.1
20.5
19.3
19.2
                                     71

-------
Table 22 (continued)
Date
19 Nov 79


18 Dec 79


17 Jan 80


6 Mar 80


Totals


Time
(hrs)
2210
2130
2030
2108
2017
1934
2143
2056
1956
2355
0105
0145



Habitat
S
R
Z
S
R
Z
S
R
Z
S
R
Z
S
R
Z
N
2
1
2
2
2
2
1
2
2
2
2
2
28
29
31
YF
(nป3)
262.4
97.6
260.7
314.9
245.7
293.9
77.5
140.7
243.9
295.7
159.4
327.7
3230.0
2894.5
3761.2
AC
(m3)
267.9
111.2
277.1
321.5
338.8
316.6
164.1
151.4
249.1
302.0
220.0
353.0
3282.6
3578.8
4092.8
DO
(mg/D
11.1
12.0
11.1
__
—
—
__
—
—
11.8
11.4
11.7



T
12.0
12.5
12.0
4.0
4.0
4.5
5.5
5.5
5.5
1.5
2.0
2.0



SAL
16.8
16.4
16.9
—
—
—
__
—
—
19.0
18.7
19.0



                                      72

-------
Table 23ซ  Statistics describing monthly total volumetric and
           areal estimates of sampling effort, March 1979 -
           March 1980.  Abbreviations are:  N - number of
           observations, M - mean estimate, S - standard
           deviation around mean estimate, M - meters.
Habitat
Sand m
Ruppia m^
Zostera m^
m^
N
14
14
15
15
16
16
Range
61.3
64.3
97.6
111.2
136.0
138.9
- 314.9
- 321.5
- 245.7
- 338.8
- 327.7
- 353.0
M
224.8
241.6
192.9
238.6
235.1
255.8
S
77.3
69.3
47.2
67.9
50.5
54.2
                             73

-------
sampling was curtailed by inclement weather and temperature/salinity


values were accordingly depressed because of decreased air temperatures


and increased freshwater runoff.  Five days later, surface temperatures


had risen and salinity values had returned to pre-storm levels.


Throughout the 12-month period, hydrographic values did not vary


markedly between habitats during any given sampling period.  'As a


result, hydrographic parameters were not considered important factors


in comparisons of ichthyoplankton abundances between habitats.



General Composition and Seasonality


         Pushnet collections yielded 24,354 fishes and 8,631 eggs


representing 36 species and 20 families (Tables 2_4_, 2_5_ and 26) •  Fish


eggs were present in collections during the 6-month period March -


August 1979 (Table  25), but larval, postlarval or juvenile stages of


fishes were present during all months sampled (Table 24).  Mean


abundance of fishes in all habitats gradually increased throughout


the spring to a mid-summer peak, reflecting maximum densities of

                                    o
larval anchovies, of over 2000/100 m  in August 1979 (Table  27).


After September, mean abundance dropped to low, mid-winter levels


(18.8-43.7/100 m ) with the exception of a small peak in December


1979 when several large collections of larval croakers, Micropogonias


undulatus were taken.  Fish egg abundances were greatest between


May-August with peak spawning activity observed in July (Table  25).


         Eggs of six species of fishes were identified in pushnet


collections.  In addition, eggs of unidentified species of the


families Gobiidae and  Sciaenidae as well as other unknown species


were collected.  Eggs  of the windowpane flounder, Scopthalmus aquosus;
                                74

-------
      Table 24.  Species, common name, life history stage and months  of occurrence  of  fishes  in pushnet
      	collections. March 1979-March 1980.	
      SPECIES
                             COMMON NAME
                           STAGE
                    MAMJJASONDJM
Ul
Anguilla rostrata
Alosa aestivalis
Alosa pseudoharengus
Brevoortia tyrannus
Anchoa mitchilli
Anchoa hepsetus
Gobiesox strumosus
Hyporhamphus sp.
Membras martinica
Menidia menidia
Atherinidae
Gasterosteus
    aculeatus
Hippocampus erectus
Syngnataus fuscus
Cynoscion regalis
Sciaenops ocellatus
Menticirrhus americanus
Leiostomus xanthurus
Micropogonias undulatus
Bairdiella chrysoura
Sciaenidae
Tautoga onitis
Astroscopus guttatus
Hypsoblennius hentzi
Chasmodes bosquianus
Ammodytes hexapterus
Gobiosoma ginsburgi
Gobiosoma bosci
American eel
Blueback herring
Alewife
Atlantic menhaden
Bay anchovy
Striped anchoby
Skilletfish
HaIfbeak
Rough silverside
Atlantic silverside
silversides
Threespine stickleback

Lined seahorse
Northern pipefish
Weakfish
Red drum
Southern kingfish
Spot
Atlantic croaker
Silver perch
drums
Tautog
Stargazer
Feather blenny
Striped blenny
Sand lance
Seaboard goby
Naked goby
 elver
 juvenile
 juvenile
 postlarva-juvenile
 egg-adult
 postlarva-juvenile
 larva
 egg-juvenile
 egg-adult
 adult
 larvae
 juvenile

 young
 larva-adult
 larva-juvenile
-larva
 larva
 larva-juvenile
 larva-pos tlarva
 larva-postlarva
 egg
 egg
 postlarva
 larva-postlarva
 postlarva ,
 larva-pos tlarva
 postlarva
 postlarva
X
XX               X
        X
XXXX         XXXX
XXXXXXXXXXXX
        X X
    X
    X X XX
  xxxxxxxx
XXX           XXX
  X X X X X X
  X

        X
    XX X X X X X
    XXXX
          x
          X
  XXX             X
          XX   XXX
          X
    XXXX
  X
        X
    XXXX   X
        X
                      X
          XX     X
              X

-------
Table 24.   (continued)
SPECIES
Gobiosoma sp.
Microgobius
thalassinus
Gobiidae
Peprilus paru
Paralichthys dentatus
Scopthalmus aquosus
Pseudopleuronectes
americanus
Trinectes maculatus
Symphurus plagiusa
Sphoeroides maculatus
unknown
COMMON NAME
gobies
Green goby

gobies
Harvestfish
Summer flounder
Windowpane
Winter flounder

Hogchoker
Blackcheek tonguefish
Northern puffer
-
STAGE
egg- larva
larva-postlarva

larva
larva
postlarva
egg- larva
larva

egg- larva
larvae
larvae
eggs
M A M J J A
X X X X
XXX


X
X X
XXX
X

X X
X
X
X X
S 0 N D J M



X

X X X X








-------
Table 25.  Monthly and cummulative totals of fish eggs collected by
	pushnet, March-August 1979.	
SPECIES
M
M
TOTAL  % OF TOTAL
A. mitchilli '
M. martinica
Hy. unifasciatus
Sciaenidae
T. onitis 22
Gobiidae
S. aquosus 29 144
T. maculatus
unknown 75
1247 383 3347 249 5226
6 2 15 12 35
3 3
97 362 2580 44 3083
22
2 2
173
3 9 12
75
60.55
0.41
.0.03
35.72
0.25
0.02
2.00
0.14
0.87
Total
29  241
1352   753   5942   314   8631   99.99
                                      77

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Table 26.  Ranked numerical abundance of fish species captured
           by pushnet, March 1979 - March 1980.
Species
A. mitchilli
Gobiosoma sp.
B. tyrannus
S . f uscus
M. undulatus
M. martinica
L. xanthurus
atherinid larvae
A. hexapterus
C. regalis
M. menidia
A. hepsetus
M. thalassinus
S. aquosus
P. dentatus
H. hentzi
Hyporamphus sp.
A. rostrata
M. americanus
G. ginsburgi
G. strumosus
S. ocellata
C. bosquianus
B. chrysoura
T. maculatus
A. aestivalis
G. aculeatus
P. americanus
A. pseudoharengus
H. erectus
ฃ. bosci
gobiidae
P_. paru
S. plagiusa
S. maculatus
A. guttatus

Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22.5
22.5
24
25
26
27
28
32.5
32.5
32.5
32.5
32.5
32.5
32.5
32.5
Total
Total
17475
2177
1475
968
523
315
280
272
191
146
110
66
65
59
45
42
25
21
20
17
16
11
11
9
7
4
2
2
1
1
1
1
1
1
1
1
24,354
Percent Total
71.76
8.94
6.06
3.97
2.15
1.29
1.15
1.12
<1
<1
<1
. <1
<1
<1
<1
<1
<1
<1
<1
< 1
<1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
< 1
                               78

-------
Table 27.  Monthly pushnet fish catch summary, March 1979-March 1980.  Abbreviations,are:
          N - total number of individuals captured, M - mean abundance  (N/100m3) as calculated by
          N divided by total water volume filtered, Range - maximum and minimum densities (N/100m3)
          observed.  Daylight sampling periods are excluded.
MONTH

1979
MAR
APR
MAY
JUN
JUL
AUG
SEPT
OCT
NOV(l)
NOV(19)
DEC
1980
JAN
MAR
ALL HABITATS
N
181
668
1433
2483
1047
15139
1397
-
229
271
574

136
147
M
27.9
84.8
259.1
328.8
185.9
2052.2
361.6
-
31.0
43.7
67.2

29.4
18.8
RANGE
18.9-39.9
27.0-156.6
24.4-620.4
100.3-786.6
68.2-379.0
264.3-3597.5
191.1-512.3
-
0.8-69.9
18.6-76.9
3.5-186.9

18.8-50.1
4.8-36.5
VEGETATED
N
86
585
1387
955
707
8302
1090
170
221
91
122

100
42
M
22.9
113.4
372.3
192.3
177.2
1775.6
335.4
36.3
45.2
25.4
22.6

26.0
8.6
RANGE
18.9-26.2
27.0-156.6
86.9-620.4
100.3-377.5
68.2-228.4
264.3-3597.5
191.9-5123
33.6-41.6
11.7-69.9
18.6-34.2
3.5-47.9

18.8-50.1
4.8-10.4
SAND
N
95
83
46
1528
340
6837
307
-
8
180
452

36
105
RUPPIA
M
34.9
30.6
25.5
590.9
207.3
2531.0
500.9
-
3.2
68.6
143.5

46.5
35.5
N
45
278
1251
236
263
3.125
262
89
149
22
9

49
9
M
24.9
112.7
569.7
106.5
136.4
507.1
229.2
37.7
65.1
22.5
3.7

34.8
5.7
ZOSTERA
N
41
307
136
719
444
7177
828
81
72
69
113

51
33
M
21.1
114.1
88.9
261.4
215.3
2921.0
392.9
34.9
27.7
26.5
38.5

20.9
10.1

-------
the bay anchovy, Anchoa mitchilli; and the drums, family Sciaenidae,

dominated pushnet collections making up 98% of the total catch.  Eggs

of three species (Membras martinica; Hyporhamphus unifasciatus;

Gobiidae) are demersal, being attached to vegetation by chorionic

filaments (atheriniformes) or laid in open shell nest sites (Gobiidae).

As a result, density estimates of these species were not considered

quantitative.

         Of the 36 species occurring as larvae, post-larvae, juveniles

or adults in pushnet collections, eight species made up 96% of the total

catch (Table 26).  A single species, Anchoa mitchilli, the bay anchovy,

completely dominated collections, making up over 70% of all fishes

captured.  The remaining seven species, in order of decreasing abundance

were larval gobies (genus Gobiosoma); juvenile menhaden, Brevoortia

tyrannus; larval, juvenile and adult northern pipefish, Syngnathus

fuscus;  larval and postlarval croakers, M. undulatus; juvenile and

adult rough silversides, Membras martinica; postlarval spot, Leiostomus

xanthurus, and unidentified atherinid larvae.  Species names, common

names, life history stages encountered, months of occurrence and

numerical ranking of all species occurring in pushnet collections

are presented in Tables 24 and 26 .
    *

Day-Night Comparison Data

         Day vs. night pushnet catch comparison data are presented in

Tables 28 and 29 .  During both May and August sampling periods, mean

density  estimates for all species in each habitat as well as total

fishes captured in all habitats were greater in evening pushnet

collections, in most cases by at least one order of magnitude
                               80

-------
                                                         o
Table  28.  Day versus night pushnet catch  (numbers/100m ) comparisons,  May
            1979.  Pelagic egg abundance estimates are excluded.   Abbreviations
            are:  S-sand, R-Ruppia maritima-, Z-Zbstera marina, T-total  fishes
            captured in all habitats divided by total water volume filtered.
SPECIES
S
DAY
R
Z
T
S
NIGHT
R Z
T
B_. tyrannus        0

A. mitchilli       0

]>_. fuscus          0

M. martinica       1.4

L. xanthurus

H. unifasciatus

C^. regalis

^. aquosus        17.5

H. hentzi          0

jG. st^umosus       1.4

Gobiosoma sp.      0.5

ALL SPECIES        20.7
0    0.8

0    6.2

0.9  4.3

0.5  0.8
0.3

2.3

1.9

0.9
0    0     5.5

0.5  0     0.2

0    5.0   2.3

0    0.8   0.4

1.9  17.8  13.8
 2.8

16.6

 0.6

 1.7

 3.3

 0

 0.6
489.5  52.9  200.8

 62.4  41.9   41.8

  2.3   1.9    1.6

 15.0  21.6   12.5

  0     2.6    1.8
                              0.5   0.7

                              0     0
                                0.4

                                0.2
           25.5  569.7  88.9  259.0
                                        81

-------
                                                        3
Table   29.  Day versus night pushnet catch  (numbers/100m ) comparison, August
            1979.  Pelagic egg abundance..estimates are excluded.  Abbreviations
            are:  S-sand, R.-Ruppia-maritima>- Z-Zostera marina, T-total
fishes captured in all habitats divided by total water volume
filtered.

SPECIES
A. mitchilli
atherinid larvae
S. fuscus
Gobiosoma sp.
M. americanus
P_. paru
S. americanus
A. hepsetus
C. nebulosus
B . chrysoura
M. martinica
H. unifasciatus
M. uridxilatus
H. hentzi
S. plagiusa
G. girisburgi
M. thalassinus
T. maculatus
ALL SPECIES

DAY
S R Z T S
97.2 2.9 46.4 54.7 2378.8
2.8 3.9 1.0 2.6 1.5
1.2 0.6 0.5 0.8 10.0
0 0 0.5 0.2 65.9
4.1
0'
0.4
18.4
0.4
17.4
2.9
0
0.4
0
0.4
3.3
9.6
0
101.2 7.4 48.5 58.2 2513.1

NIGHT
R Z
283.0 2648.8
46.9 14.3
39.2 100.1
74.8 150.2
0.5 0
0.5 0
oo
7.7 0
0.9 3.3
0 38.3
10.4 9.4
0.9 0.4
0 0
0 0.4
0 0
0 2.4
6.3 7.3
0.5 2.4
474.1 2978.4

T
1838.3
19.4
48.8
96.7
1.6
0.1
0.1
8.9
1.5
19.1
7.3
0.4
0.1
0.1
0.1
2.0
7.9
0.9
2055.2
                                        82

-------
(Tables 28_ and 29_).   In May 1979, ten species of larval, juvenile and




adult fishes were recorded with equal numbers of species (n=7) occurring




in evening and daylight samples.  Four species occurred in both




evening and daylight collections but in all but one case, densities




and mean sizes of these species were lowest during the day (Tables 30




and 3L_).  Catches and size distributions of the northern pipefish, j^.




fuscus, appeared to be independent of time of collection (Table 30 ).




Three species (H. hentzi, (5. strumosus, Gobiosoma sp.) , were only




present in daylight collections as early larvae (3.4-6.6 mm NL).




Postlarvae and juveniles of spot, halfbeaks and weakfish were only




taken during evening hours in May.




         In August 1979, 19 species of larval, juvenile and adult species




occurred in day vs.  night comparison collections, but only four species




were taken in both day and night collections (Table 29).  The remaining




15 species occurred exclusively in evening collections.  Of the four




species occurring in both night and day samples, bay anchovies dominated




with density estimates of larvae in evening collections exceeding those




in daylight collections by several orders of magnitude  (Table 29).  In




addition, size frequency analysis of day vs. night caught larvae (Table




31) revealed extreme disparity in larval size distribution.  Anchovies




larger than 9.0 mm SL were not taken during daylight hours but were a




significant component of the evening anchovy catch.  In comparisons




between the remaining three species (Table 31)t size ranges did not




differ markedly, but density estimates of silverside, goby and pipefish




larvae were greater in evening collections.
                                83

-------
Table 30 .  Length frequency distributions of four species of fishes
           occurring in daylight and evening pushnet collections,
           May 1979.
         S. fuscus
Size
(mm)
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Over 30
D N








1 2
7 2
20 1
16
5


1














2 4
A. mitchilli
                                N
                         3
                        12
                         1
B. tyrannus
                         N
M. martinica
                  D
        N
                                                          1
                                                          2

                                                          1
                                                          2
                               165
                          1
                         14
                       1097
                       69
                               84

-------
    Table 31.   Length frequency distributions of four species of fishes
               occurring in daylight and evening pushnet collections,
               August 1979.
             A^  mitchilli     atherinidae     _ง_. fuscus     Gobiosoma sp.

    Size      D       N         DN       DN         DN
    (mm)
                                                                   111
      2       1       19              50                           186 .
      3       2       34        1     72                           219
      439        31                           104
      5      20       98        3                             1     53
      6      93      446        21            34              34
      7      98     1615               2           139              22
      8      11     2749               1      1    113              11
      9       1     2246                      1     17
     10             1895                      1     17
     11             1146        11             6
     12              825               .6
     13              589                             5
     14              431                             2
     15              344                             3
     16               70        1                    4
     17               96               1
     18               41               1
     19               46               1
     20               60
     21               32
     22               24                             1
     23               23
     24               34
     25               18
     26               20
     27               10                             1
     28               14
     29                9                             1
     30               14
Over 30              110                            10
                                    85

-------
Habitat Comparisons




         Distribution and abundance data from pushnet collections were




examined to determine the extent to which density estimates of fish




eggs, larvae and juveniles differed between sand and vegetated habitats




as well as between Zostera and Ruppia zones at Vaucluse Shores.




Comparison of density data for pelagic eggs of the three species




dominating pushnet collections is presented in Table 32.  Mean




densities and ranges for pelagic eggs of the windowpane flounder,




j>. aquosus, during March-April 1979 revealed no apparent distributional




trends, although highest mean densities and peak discrete estimates




were observed over vegetated habitats in each month.  In general, ^.




aquosus egg abundances were low and may reflect a lack of spawning in




nearshore habitats or the lower Chesapeake Bay proper (Olney 1978).




Smith et al. (1975) consistently found mid- and inner-shelf concentrations




of larval S^. aquosus in 1965-1966 and no evidence of estuarine dependence




for the species.




         Mean densities and ranges of observed densities of pelagic eggs




of A^. mitchilli were consistently higher (by at least one order  of




magnitude) over sand bottom than over either vegetated zone.  During




peak spawning activity in July 1979, mean densities of A. mitchilli




eggs exceeded 2000 eggs/100 m^ over sand bottom habitat while concurrent




estimates over Zostera or Ruppia habitats never exceeded 20 eggs/100 m^.




         Similar distribution and abundance patterns were observed for




eggs of the various species of sciaenid fishes  (Table 32).  Overlapping




identification characters and the probability that  two or more sciaenid




species spawn concurrently in the Bay prohibited separation of sciaenid




eggs to species level  (Olney, in press).  As with eggs of A, mitchilli,
                                 86

-------
               Table 32_.  Habitat  comparison of pelagic fish egg totals (N), mean densities (M) reported
                          as  eggs/100 m^ and range of density estimates (eggs/100 m3), March-August 1979.
oo
Species
Month
S. aquosus
Mar
Apr
A. mit chilli
May
Jun
Jul
Aug
Sciaenidae
May
Jun
Jul
Aug
Sand
N

11
47

1009
338
3310
238

53
328
1901
34
M

4.0
17.3

253.5
130.7
2018.3
45.7

13.3
126.8
1159.2
6.52
Range

2.
13.

48.
109.
211.
2.


94.
769.


2-5.1
6-21.2

9-597.4
9-157.3
3-3050.7
4-47.5

0-52.9
4-152.9
8-1381.6
0-27.5
N

3
57

215
45
23
11

19
33
664
10
Zostera
M Range

1.5
21.2

52.2
16.4
11.2
2.5

4.6
12.0
322.0
2.3

1.
16.


12.
6.
3.


9.
148.
1.

0-2.1
1-26.5

0-231.0
6-20.4
6-15.9
8-5.3

0-19.1
1-15.1
7-485.9
8-6.0
N

15
17

23
0
1
0

25
1
15
7
Ruppia
. M

8.3
13.5

5.3
0
0.5
0

5.8
0.5
7.8
1.8
Range

7.5-9.1
13.5

0-10.9
—
0-1.0
—

0-14.3
0-1.7
3.2-12.1
0-5.6

-------
 mean densities of sciaenid eggs were consistently highest over sand bottoms



and, during periods of peak density, sciaenid egg mean abundance and




peak observed density exceed those of vegetated zones by an order of




magnitude.  Sciaenids eggs, however, were taken in greater abundances




over Zostera than were those of A. mitchilli in July 1979.




         Eggs of the halfbeak (Hy. unifasciatus), the rough .silverside




(M. martinica) and gobies (Gobiidae) were taken in low densities but,




with the exception of a single silverside egg collected over sand bottom




in June, all eggs of these species (Table 25_) occurred in collections




over vegetated habitats.  Eggs of these species are not pelagic




(therefore not routinely collected by plankton net) but are demersal,




being attached by filaments to submerged objects or laid in shell nests.




In most cases, eggs of halfbeaks and silversides were found attached to




floating Zostera blades or other vegetable material.  Eggs of the




hogchoker, Trinectes maculatus, were taken in very low abundances over




sand habitat only.  Eggs of this species are major summer components




of lower Chesapeake Bay ichthyoplankton and ranked third in numerical




abundance in Bay channel areas  (Olney, in press).




         Monthly mean densities of fishes (larvae, postlarvae, juveniles




and adults) captured by pushnet in the evening over sand bottoms exceeded




mean estimates of fishes in vegetated habitats (pooled Zostera and




Ruppia catches) and density estimates of fishes in Ruppia zones during




all but three sampling periods  (Table 27).  Sand collections were not




made in October.  Monthly mean densities over sand bottoms ranged from




3.2-2531.0 fishes/100 m3, with peak abundances observed during the




period June-September 1979.
                                88

-------
         Monthly mean densities of pushnet caught fishes over Ruppia




beds ranged from 3.7-569.7 fishes/100 m3 with peak densities recorded




during the period April-September 1979.  Ruppia catches exceeded




densities observed over sand bottoms during spring and early summer




months (April, May) when large catches of IJ.  tyrannus were recorded




over Ruppia and in early November.  Densities observed in Ruppia beds




exceeded mean Zostera pushnet densities of fish in May, October and




November (19th) 1979 and January 1980.  In general, however, densities




of ichthyoplankton and pelagic juvenile fishes were lower in Ruppia




zones than in the other two habitats.




         Fish densities in Zostera zones peaked during the period




June-September 1979 with highest mean density recorded in August




(Table 27).  Monthly mean densities ranged from 10.1-2921.0 fishes/




100 m3.  Densities over Zostera beds exceeded those over sand bottom




in April, May, July, August and November (1st) 1979, but mean density




differences between these two habitats never exceeded 390 fish/100 m3.




Densities of pushnet catches over Zostera zones exceeded Ruppia




estimates during all but five sampling periods.  During the period




of maximum abundance of fishes and maximum density of vegetation




(April-September), catches over Zostera beds were only exceeded by




those over Ruppia beds in May 1979 when large numbers of menhaden were




taken.




         A total of 23,875 fishes were captured in evening pushnet




collections March 1979-March 1980.  Of the total, 10,071 (42.2%) were




taken over Zostera zones; 10,017  (41.9%) over sand bottom; and 3787




(15.9%) over Ruppia zones.  Additional discussion-of habitat comparison




data for individual species will be presented in the following section.
                                .'7.





                                89

-------
Dominant Species




                         Anchoa mitchilli




         Bay anchovies dominated pushnet collections, ranking first in




numerical abundances and making up 71.8% (N=17,475) of all fishes




captured.  Table  33 summarizes monthly pushnet catch data, including




daylight samples in May and August 1979.  Peak monthly mean densities




of A. mitchilli were recorded in all habitats in June-September 1979,




a 4-month period including time of peak spawning (Table 32; Olney, in




press) and during which larval and postlarval stages dominated collections.




Bay anchovies were present in pushnet samples during all sampling




periods and in all habitats during each sampling period with the




exception of March 1979 Ruppia collections.  Densities at positive




stations ranged from 0.8-410.5 fish/100 m  over Ruppia beds; 0.7-3304.1




fish/100 m3 over Zostera beds; and 0.8-2672.1 fish/100 m  over sand




bottom habitat.  In general, monthly mean densities of bay anchovies




varied only slightly between habitats, with the exception of August




1979 data.  During this period of peak abundance, larval anchovies




were conspicuously less abundant over Ruppia beds at Vaucluse Shores.




Numerically, pushnet catches over Ruppia contributed only 9.6% of the




total anchovies taken during the 12-month period, March 1979 - March




1980.  Densities of anchovies over sand and Zostera beds appeared to be




habitat-independent.



         Length frequency distribution of pushnet catches of Anchoa




mitchilli are presented in Figures 11 - 22 .  Catches were dominated by




juvenile and adult anchovies (fishes >30 mm SL) in March-May 1979




 (Figures 11^ - 13), and October-December 1979 (Figures 18_ - 20) .   In
                                90

-------
Table 33.  Data summary of monthly catches of Anchoa mitchilli in pushnet collections, March 1979 -
           March 1980.  Abbreviations are:  N - number of specimens; M - monthly mean density (N/
           100 m3).
Month
1979
Mar
Apr
May
Jun
July
Aug
Sept
Oct
Nov (1)
Nov (19)
Dec
1980
Jan
Mar
Total
Percent Total
Sand
N
2
23
30
392
154
6647
301
M
0.7
8.5
7.5
151.6
93.9
1275.3
491.1


3.

142.
45.
41.

Range
0-3.6
6-13.6
0-19.8
5-163.4
9-177.8
3-2672.1
491.1
no samples
7
162
45

1
12
7776
44.4
2.8
61.7
14.3

1.3
4.1


0.
58.
8.


3.


8-4.9
9-64.7
6-19.6

1.3
3-4.8


N
4
12
123
206
174
6583
743
75
69
34
22

1
2
8048
45.9
Zostera
M
2.1
4.5
22.5
74.8
84.4
1497.8
352.6
32.3
26.5
13.0
7.5

0.4
0.6


Range
2.0-2.1
3.7-5.3
0-50.0
63.7-87.0
80.8-87.8
37.1-3304.1
294.1-483.1
31.7-32.8
10.3-44.5
7.8-18.2
5.4-9.6

0-0.7
0-1.2


N
0
44
137
207
122
706
239
79
131
14
1

1
2
1683
9.6
Ruppia
M
0
17.8
31.7
93.5
63.3
177.7
209.1
33.4
57.2
14.3
0.4

0.7
1.3


Range
. *,!***
15.

88.
37.
1.
172.
26.
49.




1.


—•ซ
7-19.9
0-78.3
8-97.6
3-87.9
8-410.5
4-266.3
7-39.9
8-64.6
14.3
0-0.8

0-1.6
2-1.3



-------
ERR  CHHPT
MIDPOINT
LENGTH
 DF LQbNDOl
                                                             LQGMD01
      4
      5
      6
      7
      8
      9
     10
     11
     1ฃ
     13
     14
     15
     16
     17
     18
     19
     ฃ0
     ฃ1
     •-1 •",
     cc
     ฃ3
     ฃ4
     ฃ5
     ฃ6
     ฃ7.
     ฃ8
     ฃ9
     30
     31
     34
     35
     36
     40
     41
     4ฃ
     43
     44
     45
     46
     47
     48
     49
     50
     51
     er •*•
     •Ju.
     53
 •*•ป*••ป•
                                                            0. 0 0 0 0 0 0
                                                            0. 0 0 0 01'.' U
                                                            0. 0 U 0 U 0 0
                                                            0. 0 0 0 U 0 0
                                                            0. 0 0 0 0 0 0
                                                            0. 0 0 0 0 0 0
                                                            0. 0 0 0 0 0 0
                                                            0. 0 0 0 U 0 0
                                                            0. 0 0 0 0 0 0
                                                            0. 0 0 0 0 0 0
                                                            0. 0 0 0 0 0 f.i
                                                            0. 0 0 0 0 0 0
                                                            0. 0 U 0 01J0
                                                            0. 0 0 0 U 0 0
                                                            0. 0 0 0 0 ft 0
                                                            0. 0 0 0 0 U 0
                                                            U. 00 0 0 0 0
                                                            0. 0 0 0 f 101 "•:
                                                            0. 0 0 0 0 0 0
                                                            0. 0 0 0 U 0 0
                                                            0. U 0 0 0 U 0
                                                            0. 0 0 0 0 u i".i
                                                            0.000000
                                                            0. 0 0 0 0 01'1
                                                            0.000000
'"••*••ป•**•*•*
	+	4	

    0. 3 0. b  0.
                                0. 0 0 0 0 0 0
                                0. 0 0 0 0 0.0
                                0. 0 0 0 0 0' j
                                0.
                                0.
                                0.000000

                                0. 0 0 0 0 0 0
                                0. 301 030

                                0. 301 030
                                0.000000
                                0. 0 0 0 0 0 0
                                0. 0 0 0 0 0 0
                                0. 0 0 011' 0 0
                                0. 0 0 0 0 0 0
                                0. 301 030
                                0. 0 01J 0 01J
                                0. 0 0 0 00 i.'1
                                0.
                                0. 0
                                0. 301 030
                                0. 0 0 0 0 0 0
                                0. 0 0 01'.' 0 0
                                0. 0 0 0 0 0 0
                                0.4771ฃ1
                          '  1.c 1.5  1.
8 ฃ'. 1  c . 4 ฃ. 7
      Figure 11.   Length frequency distribution of pushnet  catches of Anchoa
                  mitchilli in all habitats during March 1979.

-------
E'-RR CHflRT DF LDGNDOS
MIDPDIHT
LENGTH
/V
ฃ '-•
•-. s-. •
4
5
6
7
8
9
10
11
• 1 c! ""
; 13
14
15-
" 16
1 7
18
1 9
ฃ0
ฃ1
ฃฃ
ฃ3 -;'-
ฃ4
ฃ5
ฃ6
ฃ7
: ฃ8
ฃ9
3 0
3 1
3ฃ
33 •"•44+ 4
34
35
. 36
37
38
39
4 0
41 -•-44++
4ฃ
43 •-•4444-44
•44 -4444-
45

47 '-4-44444
43 •-•444444
. 49 '--444444
50 -'-444444444
. 51 '--44444-4
5ฃ '•"4444-444444444-I
53 --44444444444444
0 . 3 0 . 6 0 . 9
Figure 12. Length freqx


LOGNDOc'

0. 000000
0. 000000
0. 000000
0. 000000
0. 00000 U
n. nrrfifififi
0. 000000
0. 000000
0. OOOOO'i
0. 000000
U. OUOOOU
0. 000000
0 . 0 0 0 0 0 0
0. 000000
0. 000000
0. 000000
0. 000000
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
n. rififiiinfi
0. 000000
U. 000 OU i.i
0. 000000
0. 000000
0 . 0 0 0 0 0 0
0. 000000
0. 000000
0. 000000
U. UUIJUUU
0. 000000
0. 000000
0. 301030
U. U U U 1.1 I.I I.I
0 . 0 0 0 0 0 0
0. 000000
0. 000000
0. 000000
U . 0 U I.i U U U
0. 000000
0.301030
0. 000000
0.4771ฃ1
0. 301 030
n. fiTififififi
0.698970
0.4771ฃ1
0.4771ฃ1
0. 477121
0.698970
0.4771ฃ1
>4 1.1461ฃ8
^444444444444 1.949390
.1.2 1.5 1.3 ฃ.1 ฃ.4 ฃ.7 3 3.3 3.6
lency distribution of pushnet catches of Anchoa
mitchilli in all habitats during April 1979.

-------
ERR CHRRT
MIDPOINT."
LENGTH
DF LQGHD03
                                                           L06NQ03
ฃ '"•44'444444
>; ---444444444444444
4 ''-+4+4 .
5 'x -. . •-•
ฃ >--+4-44- . vv
"?••"•• •
8 '"• . ••:'-•
1 9 '"•
10
11
1 p "-
J. t.
13
14
-15 .A
16 :
17
18 •'••'••
19
ฃ0
ฃ1 > A
ฃฃ •-• ' .
ฃ3 A '
ฃ4
ฃ5
ฃ6
ฃ7
ฃ8
ฃ9 --4444
3 0
. 31 '--444444-
3ฃ '"• *• ซ•ซ•+
.33 '--4444
34 '-444444-44+
35 " '"-4444444-44444
36 '--4444444-44444
37 •••••444444444444444
33 "-44444444444-444444
39 •••"4444444444444444444
40 ••••44. + 444-*4444*444ป44
41 ••••4444**-4444444-
4g '•••ซ• *•ซ. 4.4- * +*•*•ปซ•*•*ป
43 ••'••4444'444'4*44-44
44 ••'• 4-444-4-44444444
45 •"••ป+>+•
4K '••44444444-4-4*4
47 '--444444
43 ''-444444
49 '--444444444
Slj '-44444444
51 '--4444
5ฃ ••'-44444444
53 '--4444444-444444
0. 60ฃ060
1. 113943
0. 301 030
0 . 0 0 0 0 0 0
0. 301 030
0 . 0 0 Li 0 0 U
0. OUUUMU
0 . 0 0 0 0 0 0
U . 0 IJ U U Li U
0 . 0 0 0 0 0 0
fl . f ! f! 0 I'l I'l fl

U . U U LI U U '.I
0. 000000
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 1 J 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 1 J
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
U . U IJ 0 0 LI IJ
ij . 0 ij fj ij ij ij
0 . 0 0 0 0 0 0
n. mniimii
f i . fi f i n n f i i~i
0. 301 030
ij. 000000
JJ.4771ฃ1
0. 301 030
0. 301 030
0.698970
0. 903090
0. 903090
1. 113943
1 . ฃ78754
1.414973
1.34ฃ4ฃ3
1 . 0 0 0 0 0 0
1. 041393
0.954ฃ43
1 . 0 0 0 0 0 0
0.301030
0. 903090
0.4771ฃ1
0.4771ฃ1
0. 698970
0. 60ฃ060
0. 301 030
0. 60 ฃ060
0. 954ฃ43
     -i
              0.3  0.6 0.9  1. ฃ 1.5  1.8 ฃ. 1  ฃ. 4 ฃ. 7
                                            3   3 . 3 3 . 6
  Figure  13.  Length frequency distribution of pushnet catches of Anchoa
             mitchilli in all habitats during May  1979.

-------
ERR CHHPT  DF LDGN004
MIDPOINT
LENGTH
                                                                   LDGNQ04
                                     '•     '    [  '                 0.OOOOOO
                                                                 0.477121
                                                                 1.361728
                                                                 1.778151
        ''••AAAAAAAAAAAAAAAA A.,*. A. .*. A. A. ^ A. A.                              •!  i~i C' •! "I ET .-•
                                                                 1 • O •_' 1 L_ •_' C'
                                                                 1.61ฃ784
                                     1 •  .                    :     1.255273
                                                                 1.ฃ30449
                                                                 0.477.121
                                                                 0. 602060
        ""*           .                                             0.00 0 0 0 0
        ""'-.'.                            •                 .0. OOOOOO
        '%'                                                        0.0 0 0 0 0 0
                                                                 0.OOOOOO
                                                                 0.OOOOOO
        "•                                                        0. OOOOOO
        x"                                                        0. OOOOOO
                                                                 0.OOOOOO
        f"                                                        0. OOOOOO
                                                                 0.0 0 0 0 0 0
        '''•                                      : •                 0. OOOOOO
                                                           •      0.OOOOOO
                                                                 o. o o o o o o
                                                                 0.OOOOOO
                                                                 0.OOOOOO
                                                                 0.OOOOOO
                                                                 0.OOOOOO
                                                                 0.OOOOOO
                                                                 o.oooooo
                                                                 o.oooooo
                                                     .0.OOOOOO
                                                                 0.OOOOOO
                                                                 0.OOOOOO
                                                                 0.OOOOOO
                                                                 0.OOOOOO
                                                                 o. oooooo
                                                                 o.oooooo
        '••                                                        0.000000
                                                                 0.OOOOOO
        ''"        .                         '                       0. OOOOOO
        ''••**•**•*•*•**•*+***•**•                                        1.113943
                                                                 1.518514
                                                                 1.707570
                                                                 1.770852
                                                                 1.716003
                                                                 1.7ฃ4ฃ76
                                                                 1.447158
                                                                 1.556303
                                                                 1.380211
                                                                 1.204120
                                                                 1.230449
                                                                 1.740363

           0.3 0.6  0.9 1.2 1.5 1.8,2.1  ฃ.4 ฃ.7   3  3.3 3.6

Figure 14.  Length frequency distribution of pushnet catches of Anchoa
           mitchilli in all habitats during June 1979.

                                95
     c.
     3
     4
     5
     6
     7
     8
     9
    10
    11
    1ฃ
    13
    14
    45
    -16
    17
    13
    19
    ฃ0
    ฃ1
    22
    ฃ3
    ฃ4
    ฃ5
    ฃ6
    ฃ7
    ฃ8
    ฃ9
    30
    31
    32
    33
    34
    35
    36
    37
    33
    39
    40
    41
    4ฃ
    43
    44
    45
    46
    47
    43
    49
    50
    51
    52

-------
ERR CHRRT  DF LDGNQ05.
MIDPOINT
LENGTH
                                                                LDbNDOS
   4
   •C"
   6
   7
   ft
   9
  10
  11
  IE
  13
  14
  15
 .16
  17
  18
  19
  ฃ0
  ฃ1
  ฃฃ
  ฃ3
  ฃ4
  ฃ5
  ฃ6
  27
  ฃ8
  ฃ9
  30
  31
  3ฃ
  Cj;~;
  34
  35
  36
  37
  38
  39
  40
  41
  4ฃ
  43
  44
  45
  46
  47
  48
  49
  50
  51
  5ฃ
  53
Figure 15.
'x + 4- + 4- 4- 4-4-4-
''•• + 4- + + 4- + 4- + 4- + + + 4-+4-4-4-4-4'4-4-4-
A 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4-
•"•4- + 4-4-4-4- + 4-4-4- + 4-4- + + 4-4-4-4-4-+4-4-
''•• + 4-4- + + 4 + 4-4-4-+4- + 4-4-4-4-4-4-4-4-
'x + 4-4- + 4-4- + + + + + + 4-4 + 4-4-+4-4-
^•4-4-4-4'4- + 44-4-4-4-4-4:4- + 4-4-4-4-
-"• 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4-
's + 4- 4- 4- + 44- 4- 4- 4- .
•••••4-4-4-4-4- + + + 4-4- + +
••"•4-4-4-4-4-4- + 4-4-4-
•"" + + 4-4-
-x*4-4-4- .
/'-. ' .
/••-;. .
'"'••-'
,':
,-\
-•••.
/'•-
S: , • -
*'•• •
S:
.•X • '
''" + 4-4-+.
•"*••
y>.
•-•4-4-4-4-
j.^
j-';.
f':
'x*4-4-*
y-.
'x4-4-4-4-
••'••4- 4- 4- 4-
t';
/'-.
^S

''%4-4-4-4-
--4-4-4-4- . .
.•••.
''••4- 4- 4- 4- + 4- + *
•'•4-4-4- + 4-4- + *
''" 4- 4- 4- 4- 4- 4- 4 * + 4- 4- 4-
''•• 4- 4- 4- + 4- 4- 4 + 4- 4- 4-
•"• + 4-4-4-4 + 44-4-4-4-4-
•-• + + + + + + + + + + + + +
•••• + + + + + + + + + + + + + +
'"- +++ + + + + + + + +
'•- + + + + + + + +
•-•+> + + + + + + + + + + + + + •
	 H 	 (. 	 H 	 + 	 H 	 H 	 4- 	 H 	 + 	 + 	 + 	 +
0 .3 0.6 0.9 1 . ฃ 1.5 1.8 E . 1 ฃ . 4 ฃ . 7 3 3 . 3 3 . 6
15. Length frequency distribution of pushnet catches of Anchoa
0.60E060
1.6 7' ฃ09 8
1.579784
1 . 732394
1.579784
1.531479
1.397940
1. 113943
0.778151
0. 903090
0.778151
0.301030
0. 301030
0 . 0 0 0 0 0 0
0. 00 on no
0 . 0 0 0 0 0 0
u . o n fnj 0 fi
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . U U U U 0 U
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0.3.01030
0. 000000
u . o o fi i"i n n
0 . 3 0 1 03 0
0 . U 0 U l.l U U
0 . 0 0 0 0 0 f i
n . n n n n r i n
0. 301030
0 . 0 0 0 0 0 0
0. 301 030
0. 301 030
o . n o n n n f i
0. 000000
•f i . n o n n f i n
0 . 0 0 0 0 0 0
0. 301 030
0.301030
0 . 0 0 0 0 0 0
0 . 6 02 06 0
0. 602060
0. 903090
0. 845098
0. 903090
1 . 0 0 U 0 1 j U
1. 079181
0. 845098
0. 602060
1. ฃ04 180



           mitchilli in all habitats during July 1979.
                                96

-------
ERR CHfiPT
MIDPOINT
LENGTH
   3
   4
   5
   6
   7
   8
   9
  10
  ii
  is
  1 3
  16
  17
  18
  19
  am
  ฃ1
  ฃฃ
  ฃ3
  ฃ4
  ฃ5
  ฃ6
  ฃ7
  ฃ8
  ฃ9
  30
  •-' 1
  •—• 4.
  3ฃ
  •Tซ O
  w1 •—'
  34
  35
  36
  37
  38
  39
  40
  41
  4ฃ
  43
  44
  45
  46
  47
  48
  49
  50
  51
  5ฃ
        DF LGGN006
          '•**•**•
 LOGND06

  3ฃฃฃ19
  568ฃ0ฃ
  176091
  075547
  73ฃ394
  ฃ34011
  441066
  351796
  ฃ77838
  059563
  916980
  77085ฃ
  635484
  537819
  851ฃ58
  98677ฃ
  6ฃ3ฃ49
  67ฃ098
  785330
  518514
  397940
  380211
  544068
  ฃ78754
  3ฃฃฃ19
  041393
  176091
  0 0 0 0 0 0
  176091
0.301030
0.301 030
0. 0 0 0 0 0 0
0. 301 030
0. 0 0 0 0 0 0
  0 0 0 0 0 0
  0 0 0 0 0 0
  0 0 0 0 0 0
  301030
  000000
  301030
  0 0 0 0 0 0
  0 0 0 0 0 0
  0 0 0 0 0 0
  0 0 0 0 0 0
  0 0 0 0 0 0
0. 0 0 0 0 0 0
0.301 030
0. 0 0 0 0 0 0
0.60ฃ060
0.698970
0.698970
1.9731ฃ8
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
             0.3 0.6  0.9  l.ฃ 1.5 1.8 ฃ.1 ฃ.4  ฃ.7
                                                     3.3 3.6
Figure 16.  Length frequency distribution of pushnet catches ฉf Anchoa
          mitchilli in all habitats during August 1979.
                               97

-------
BaP. CHftRT DF LDGND07
MIDPOINT
LENGTH
ฃ 'x
3 A • :

4 '"

5 '"• . '••'•'•• r
6 . . '• • • • .
7 - • ' .. • • •
8
9 '•-
10 '^++*
1 1 ^ + + + + + *ซ. + * +
1ฃ •••-4.*4-*****-ป-*-*-4-**-**-4-
13 '•••*+++*+ซ•*ซ••ป•*••ป++ซ•+*ซ• •
14 ^* + *4. + + + 4.* ++** + + *4-**** +
"15 • 'x + + + + + + + + + + * + + *-* + 4-+ + + + + *
16 '-- + * + + * + + + *ซ.+ + + * + + *+ซ.*.** + *** +
1 7 ^••••+*+++****++**++++**+*4.++
18 '•- + + 4-4-*4-** + + *ซ- + * + ** + * + *> + + ซ- + .ป* +
19 ^t^*******.*.**.***.***.**.**.****.**.
ฃ0 ••••• + + ซ + + * + + **ซ- + + + * + + 4- + * + 4-* + *ซ-***4-
81 '-•ป**4-****************-4-*******4-
ฃฃ '•••+ซ• + + + + + + + + +• + + + •ปซ•ซ• + + ซ• + + + + .ป•ซ.*
ฃ3 A*********.ป***************.
ฃ4 ^ + + *.* + + *ซ..ป4..ป**4.* + * +
ฃ•5 '•" + + 4. + 4.4. + * + 4. + + *ป + * + *. + * + *
ฃ6 '•" + * + *ซ.+"ป*.+++4-4-*4-+ซ-
ฃ7 ^** + * + + * + + + + + + 4.* + * +
ฃ8 '•••ซ•++ ++ซ•
ฃ9 ''•••• + + + ซ.ซ. + *. + *
30 •'••ซ•*+ ++++*•*ซ•ซ•ซ•*•
31 A4-*****
3ฃ •"• + + + 4- + + + +
•-'•-' •"•
34 ,.'•-
35 '. •-•****
36
37
38 "• '
39
40 -x-ป+++
41
4ฃ
43 -"-.*+++++
44 ''- .
45
46 A
47
48 '-•****
49 '-•****
50
5 1
5ฃ •"••.**•ป*•ป*

0 ~: fi ^. f i ^ 1 . ฃ 1 c' 1 .' ft c! . 1 c! . 4 ฃ . 7 -•! :^ . •"! ~! . ^:-
Figure 17. Length frequency distribution of pushnet catches of Anchoa


LDSND07
U. UUUUUU
II 1 1 1 1 1 1 1 1 1 1 1 1

II IIIIMIillll

0 . U U I.I 0 U 1."
0 . 0 0 0 0 0 0
0 . 0 0 U 0 U 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0. 301030
0. 778151
1 . ฃ55ฃ73
1.3617ฃ8
1. 67ฃ098
1 . 7ฃ4ฃ76
1.991 ฃฃ6
ฃ. 1ฃ7105
ฃ. 15836ฃ
ฃ. 089905
ฃ.ฃ85557
ฃ. 15ฃฃ88
ฃ. 0043ฃ1
1.875061
1. 34ฃ4ฃ3
1.61 ฃ784
l.ฃ55ฃ73
1.380E11
0.4771ฃ1
0. 903090
0.954ฃ43
10. 4771 ฃ1
0. 60ฃ060
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0. 301030
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
U . U U 0 U 0 O
0 . 0 0 0 0 0 0
0. 301 030
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0.4771ฃ1
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
o . o n o o n o
0 . 0 0 0 0 0 0
0. 301030
0. 301 030
0 . U 0 U 0 LI U
0 . 0 0 0 0 0 0
0.4771E1!
1.3ฃฃฃ19


mitchilli in all habitats during September 1979.
                       98

-------
BRR CHftRT OF LDGHD08
MI
tiPDINT
LEHGTH . .-'••'.























































f~: ' • -• -.,
2
:-' • ' ' : L
4 .
5 '-• ' • -• • .'>•-. . ,
6 ~ ... >'•',..'!• '
l' ' -• * - • * ^ - .
8 ; '•""•"'•..•
9 .' '"•'*'•' ••
10.'"' i ;
1 1
' 1ฃ • " '
13
14 '-•
••is ..'••• .
16
17 'A '
18
19
ฃ0
ฃ1
ฃฃ
ฃ3 '">
ฃ4
ฃ5-
ฃ6
ฃ7 '•••4-4- + 4-
ฃ8 -•••+•++*++•
ฃ9 '"•4- 4- 4- 4- + 4-
30 '•••4- 4- 4- 4- 4- 4- 4- 4- 4-
31 •'••*4-4-4-4-4-4-4-4-
3ฃ ••"••4' 4- 4- 4- 4- 4- 4- 4-
33 ''••4-4-4-4-4-4-4-4-4-
34 's- 4-4- 4- + 4- 4- 4-4-4-
35 : •••••4-4-4-4- + 4-4-4- + 4 + 4- + 4-4-
36 •'••4- 4- 4- 4- 4- 4-* 4-** 4- 4- 4-*
37 •"•4- 4- + + 4- 4- 4- 4- 4- 4-
33 '"4- + + 44 + 4-4444.
39 '-•4-4-*4-**4-4-4-
40 '-•4-4-4-4-*4-4-4- +
41 •'•4-4-**4-4-4-4"ป4-4-
4ฃ '•- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4-4- 4-
43 A +•ซ> •*••* + •*•ป•ป 4>ซ-
44 ''••4-4-4-4-4'4-4-4-4-4-4-4-4-
45 •••• 4- 4- 4- 4- 4 4- 4- 4-4- 4-4-
46 •-•4-44444-4-4*44-4-
47 ••'••4-ป4'4-4-4-4-4-4-44-4-4'
48 ''-*4-****4-4-**
49 A4-4-4-4-4-4-4-**4-
50 -•••4-4-4-4>4-4- + 4-
51 '••4-4-44 + 4-*4*4-4-
5ฃ •"• 4- 4-4- 4- + 4-4-4-
53 - + * + + + + +++ + * + * + + 4,4.+ + + 4-
0.3 0.6 0.9 l.ฃ 1.5 1.8.. ฃ.1 ฃ.4 ฃ.7 3 3.3 3.6
TJicnire 18. Length frequency distribution of pushnet catches of Anchoa

LDGND08

0 . 0 0 0 0 0 0
0 . 0 0 0 iJ IJ IJ
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
II 1 1 1 1 1 t 1 1 1 1 1 1

IJ . IJ IJ IJ IJ IJ IJ
0 . 0 0 1 J 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
IJ . IJ IJ IJ IJ IJ IJ
0 . 0 0 0 0 0 0
ft. f 1 fl f 1 0 fl fl
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
IJ . IJ I.I IJ IJ IJ IJ
0 . 0 0 0 0 0 0
fl . fl f 1 fl fl fl fl
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0.301030
0.4771ฃ1
0.4771ฃ1
0.698970
0. 698970
0.60 ฃ060
fi. 69ft 9 7 fi
0.698970
1. 1461 ฃ8
1. 079181
0.778151
0.845098
0.698970
0.698970
0.845098
0.954ฃ43
0.778151
0.954ฃ43
0.845098
0. 903090
0.954ฃ43
0.778151
0.778151
0. 698970
0. 845098
0.60ฃ060
1.568ฃ0ฃ


mitchilli in all habitats during October 1979.
                        99

-------
t'.H* CHRRT DF  LDGND09
MIDPOINT
LENGTH
ฃ
3
4
5
6
7
8
9
10
11
1ฃ
13
14
15
16
17
18
19
ฃ0
ฃ1
22
ฃ3
ฃ4
ฃ5
ฃ6
ฃ7
ฃ8
ฃ9
3 0
31
•-•C.
33
34
35
36
37
38
39
40
41
4ฃ
43
44
45
46
47
48
49
50
51
5ฃ
53


*""'
.-.
A . -.
'
A .
• , . ' . '
••"••.....
.
.•X
s\ V
A . . ' - ' .
: -
A .
"'"••****
. -
. '•••
'"••******
'•'•****
•"••******
'""****** •
••'••************
'"••******
''-********** . ' '
•"•*************
''••**********
'-•
•'••**********
'"'************
''••********
--•***********
''••*****.********
'-•***************
:•••••**************
''-.**********
--•************
'x********** .
'•"***************
'x***********
•'-************
A*************
''•'***.********** .
•"•**********
•'"••************
'x****** ***********
"'****************
''-*****************
•••-,****** **********
--•*******************
'x*****************
'-•***************
"•********************•****
	 + 	 + 	 + 	 + 	 + 	 + 	 + 	 + 	 + 	 + 	 + 	 +
0 .3 0.6 0.9 1 . ฃ 1.5 1 . 8 ฃ . 1 ฃ . 4 ฃ . 7 3 3 . 3 3 . 6
0 . 0 0 0 0 0 0
fi . f i fi f i f 1 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0. 000000
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . U 0 0 U 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0.301030
0. 000000
0. 000000
0.4771ฃ1
0. 301 030
0.4771ฃ1
0.477121
f| C||y-;f|C|f!
0.4771ฃ1
0.773151
1 . 0 0 0 0 0 0
0.778151
0 . 0 0 0 0 0 0
0.778151
0. 903090
0 . 6 0ฃ 06 0
0.845098
0.954ฃ43
1. 1461ฃ8
1. 079181
0.778151
0. 903090
0.778151
1. 113943
0.845098
0. 903090
0.954243
0.954243
0.778151
0. 903090
1 . ฃ55ฃ73
1. ฃ3 044 9
1 . ฃ55ฃ73
1.204120
1.447158
1.301030
1. 113943
1.845098


    Figure 19.  Length frequency distribution of pushnet catches of Anchoa
               mitchilli in all habitats during November 1979.

-------
ERR CHRRT
MIDPOINT
LENGTH
   4
   5
   6
   7
   8
   9
   1 0
   11
   1ฃ
   13
   14
   1 5
   16
   17
   ฃ 0
   ฃ1
   ฃฃ
   ฃ3
   ฃ4
   ฃ5
   ฃ6
   ฃ7
   ฃS
   ฃ9
   30
   31
34
35
36
37
3 8
39
4ij
4 1
4ฃ
43
44
45

47
48
49
50
51
52
         DF LDGND1D
        " * * * *
          '••• 4. + 4. 4.
                                                                 0
 LDbHQlO

0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0.OOOOOO
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
  0 0 0 0 0 0
0.000000
0. 0 0 0 0 ill 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0.OOOOOO
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. OOOOOO
0.OOOOOO
0. 0 0 0 0 0 ill
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 0 0 0 0 0 0
0. 301 030
0. 0 0 0 0 ij 0
0. 0 0 0 0 00
0. 0 0 0 0 0 0
0. 301 030
  60ฃ060
  778151
  ';• IJ 1 I.I •J IJ
  4771ฃ1
  698970
  845098
  778151
                                                                  0 .
                                                                  0.
                                                                  0 .
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.
                                                                  0.698970
                                                                  0.773151
                                                                  0.4771ฃ1
                                                                  0.4771ฃ1
                                                                  0.4771ฃ1
                                                                  0.698970
           0.3  0.6 0.9 l.ฃ  1.5 1.8 ฃ.1  ฃ.4 ฃ.7  3   3.3 3.6
Figure 20.  Length frequency distribution of pushnet catches of Anchoa
           mitchilli in all habitats during December 1979.
                                101

-------
ERR CHHRT DF-LDGNDll"
MIDPOINT
LENGTH
f>.
ฃ
^"i f"m
•3 '
4
5 .'••.-.
6 - ..."'•••
7 '-' ' - ,'••'.
8 'x • '
9 .•#;.••
10 - •'-"•' * . '••' : . .
11 '" ' . • •-'. .'•• /:; - ' ' .
1ฃ . ' '' •-'••- :
13 ' • " •-.?•'. ••'.•••
14 - .'••
15 '-; •'"•'." -
16 '-• .
1 7 '' ' . ' .
18
19''-
ฃ0
ฃ1 -•****
ฃฃ'-• '
ฃ3
'ฃ4 •-• .
ฃ5 '--4.***
ฃ6
ฃ7. '-ซ. + ซ.+
ฃ8
ฃ9
30
31
3ฃ
33 "•
34
35 . •"•
36
37
1;ft
39
40
4 1
42 •-•'^
43
44
45
46
47
j*
48 '-• ซ
49
50
51
5ฃ
53 •-• ":
iiiiiiiiiiii
0.3 0.6 0.9 1 . ฃ 1.5 1.8 ฃ . 1 ฃ . 4 ฃ . 7 3 3 . 3 3 . 6

Figure 21. Length frequency distribution of pushnet catches of Anchoa


LDGN011

0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
U . 0 0 0 0 0 0
0. 000000
0. 000000
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
f 1 . 0 0 f 1 I'l 0 fl
0 . 0 0 0 0 0 0
0. OOOOO'O
0.000000
0 . U 0 0 0 l.i U
0 . 0 U IJ 0 0 '.I
0. 0 1." 0 0 0 l.i
ill . 0 0 0 0 0 0
0. 000000
0. 301030
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0.301030
0. 000000
0. 301030
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0. 000000
0. 000000
f 1 . fl fl f 1 f 1 fl I'l
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 ill 0 0
0 . 0 0 U 0 0 0
0. 000000
0 . 0 0 0 0 0 i.i
0 . 0 0 0 0 0 0
IJ . U I.I IJ 0 0 l.l
f ! . f 1 f! f 1 fl f I f 1
0 . 0 0 0 0 0 0

0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 0 0 0 0 0
0 . 0 i.i 1.1 U 0 1.1
0 . 0 0 0 0 0 0
0. 000000

t

mitchilli in all habitats during January 1980.
                        102

-------
ERR CHftRT
MIDPOINT
LENGTH
DF LOSN012
                                                        LQGH012
          ••****
          ••*ป**
   c.
   3
   4
   7
   8

  1 0
  11
  12
  13
  14
  15
  16
  17
  18

  2 0
  21
  22
  23
  24
  25
  26
  27
  28
  29
  3 0
  31
  32

  34
  35
  36
  37
  38
  •-i ฃ|    f''.
  40
  41
  42
  43
  44    -;-
  45    A
  46
  47
  48
  49
  50
  51    A     '     •
  52
  53                        '      .

           0.3 0.6 0.9  1.2 1.5 1.8 2.1  2.4 2.7  3  3.3 3.6

Figure 22. Length frequency distribution of pushnet catches of Anchoa
          mitchilli in all habitats during March 1980.
                                                                  0.
                                                                  0 .
                                                         OOOOOO
          '•• •ป * *•
                                                                  0
                                                                  0
                                                                  0
                                                                  0.
                                                                  0.
                                                                  0
                                                         0 1 J 0 0 0 U
                                                         0 0 0 fj ij 0
                                                       0. 000000
                                                       o . o o o o o o
                                                       0. 000000
                                                       0. 000000
                                                       0. 000000
                                                         OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                         OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                         OOOOOO
                                                         OOOOOO
                                                       0.301030
                                                       0. OOOOOO
                                                         OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0.301030
                                                       0.301030
                                                       0.477121
                                                       0.4771&1
                                                       0.4771c:l
                                                       0.602060
                                                       0. OOOOOO
                                                       0 . 3 0 1 0 3 0
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                         602060
                                                         OOOOOO
                                                         OOOOOO
                                                         OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                         OOOOOO
                                                         OOOOOO
                                                         OOOOOO
                                                         OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                                                       0. OOOOOO
                       103

-------
January and early-March 1980, few juveniles and no adult anchovies




were taken.  Larval anchovies appeared in collections in May 1979




(Figure 13), corresponding to the time of first occurrence of pelagic




eggs (Table 32) and ranged in size from 2-6 mm NL.  Catches exhibited




bimodal distributions in June and July 1979, (Figures 14_ - 15). but by




August 1979 (Figure 16) larval and postlarval anchovies (2 mm NL - 30




mm SL) completely dominated pushnet collections.  By September 1979




(Figure 17) spawning had ceased and no early larval stages appeared in




collections.  Young anchovies ranged from 10-32 mm SL and this larval




cohort dominated September catches.  Postlarval and early juvenile




stages (16-30 mm SL) remained in pushnet collections throughout the




remainder of sampling  (October 1979 - March 1980), apparently a period




of minimal growth.  This conclusion is supported by the presence of a




few juvenile individuals of the 1978 year class in March and April 1979




collections.




         August 1979 length frequency data  (Figur.e 16) from sand and




Zostera habitats was examined to determine  if sand vs. Zostera size




distributions were significantly different utilizing the Wilcoxon




signed rank test, a non-parametric distribution-free test  (Zar 1974).




Sand vs. Zostera size  distributions of larval A. mitchilli  (2 mm NL -




30 mm SL) were not significantly different  (T=17.15>TQ 05(2) 29^



during periods of peak abundance.






                           Gobiosoma sp.




         Larval gobies  (genus Gobiosoma) less than 8 mm SL  ranked second




in numerical abundance after anchovies and  constituted 8.9%  (n=2177) of




the total pushnet fish catch  (Table 34).  Identification of  gobies to
                                104

-------
 Table 34.  Abundance of larval gobies (Gobiosoma sp.) during months
            of occurrence in pushnet collections, 1979.  Abbreviations
            are N - number of specimens;  M - monthly mean abundance
            (N/100 m3).
Habitat
May
Months
June
X
July
August
Sand
      N
      M
    Range
Ruppia
0
0
   1071
   414.2
263.5-604.8
     8
   4.9
. 4.8-5.0
  218
  41.8
0-122.2
N
M
Range
Zostera
N
M
Range
0
0
2
0.5
0-1.5
8
3.6
0-6.8
346
125.8
51.1-206.5
10
5.2
1.1-9.1
5
2.4
0.9-3.9
161
40.5
0-105.5
370
84.2
0-198.5
                               105

-------
species level is not possible in specimens under 9 mm SL (Olney, in



press).  Postlarvae of two species, G_. bosci and ฃ. ginsburgi, occurred



in collections but ฃ. ginsburgi predominated numerically (Table 26 ).



Larval gobies appeared in pushnet collections during the period May-



August 1979 (Table 34).  Peak densities were recorded in June 1979



with a secondary peak in August.  Goby densities at positive stations



ranged from 4.8-604.8/100 m3 in sand; 1.1-105.5/100 m3 over Ruppia; and


               3
0.9-206.5/100 m  over Zostera.  Although the highest abundances occurred



over sand in June, density patterns did not reveal identifiable



distributional trends.  The abrupt appearance and disappearance of



larval gobies in collections and the polymodal nature of density, data



(May - low; June - high; July - low; August - high) suggested a highly



pulsed spawning behavior.





                        Brevoortia tyrannus



         Postlarval and juvenile menhaden ranked third in numerical



abundance and constituted 6.1%  (n=1475) of the total pushnet fish



catch (Table  26) .  Menhaden were present during March-June 1979 and



November 1979-March 1980 (Table 35).  Size frequency analysis (Table 36)



presented a bimodal distribution, which was interpreted as representing seperate



recruitment populations.  The first population, collected initially in



1979, appeared in collections as postlarvae 22-29 mm SL during;



March-April.  May 1979 catches were predominated by transforming



individuals (29-44 mm SL) and by June, all menhaden captured were



juvenile fishes (Table 36).  Curiously, a few specimens (n=7) captured



in May 1979 represented a distinct size cohort  (51-56 mm SL), apparently



independent of the majority of  the catch.  No explanation for the



presence of this size class was readily apparent.





                                106

-------
Table 35.  Abundance of menhaden, Ii. tyrannus, during months of occurrence in pushnet
           collections, March 1979 - March 1980.  Abbreviations are N - total number of
           specimens; M - monthly mean density (N/100 m^).  Daylight samples excluded.
Sand

1979
Mar
Apr
May (1)
May (31)
Jun
Nov (19)
Dec
1980
Jan
Mar
Total
Percent of Total
N
16
3
M
5.9
1.1
Range
2.4-10.2
0.7-1.5
no samples
5
42
16
1
17
2
102
6.9
2.8
16.2
6.1
0.3
21.9
0.7


2.3-3.2
9.6-21.6
0.8-11.6
0-0.6
21.9
0.7-0.7


N
9
11
70
31
1
17
0
16
1
156
10.6
Zostera
M Range
4.6 2.9-6.4
4.1 3.8-4.4
51.5 51.5
20.3 20.2-20.3
0.4 0-0.8
6.5 3.9-9.1
0
6.6 5.6-7.9
0.3 0-0.6



N
9
112

1075
2
5
0
11
1
1215
82.5
Ruppia
M Range
4.9 4.3-5.7
45.4 37.1-53.4
no samples
489.5 462.6-521.3
0.9 0-1.9
5.1 5.1
0
7.8 7.6-8.1
0.6 0-1.3



-------
Table 36.  Length frequency distribution of young menhaden, Brevoortia
          tyrannus, in pushnet collections, March 1979-March 1980.



SIZE CLASS
(ram)
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
above 53
M
N
FT


MAM






4
2
6 3
11 25
6 42
1 64
1 37
10 1
14
122
221
266
144
117
85
29
46
14
25
6
7
1
7






2
2
2
1


MONTH

J J A S



























4
1
4
3
4
5
5
2
2
3
3
9



ALL
0 N D J M MONTHS


1 1
1 1
41 5
4 4
9 13
7 1 1 11
2 1 12
2 6 44
5 53
12 2 79
13 1 52
1 5 17
14
122
221
266
144
117
85
29
46
14
25
6
7
5
8
4
3
4
5
5
2
4
5
5
10


                                       108

-------
         A second recruitment population appeared in late November 1979




and included postlarvae ranging in length from 18-29 mm SL.  Collections




in early November (1st) failed to detect the presence of postlarvae,




thereby pinpointing in time the fall entry of recruits to the study




area.  Postlarvae were sparse in December 1979 and early-March 1980




samples, but January collections (23-29 mm SL postlarvae) confirmed




the continued presence of menhaden in these nearshore habitats.




         Density data (Table 35) revealed generally equal distribution




of individuals among habitats.  May 1979 abundances, however, were




clearly greatest over Ruppia beds, but schooling behavior of this




species at size ranges above 25 mm SL likely contributes to extremely




patchy distribution.  The disproportionate percentage of total catch




over Ruppia is also related to this phenomenon, since 88% of all menhaden




captured in Ruppia zones were taken in two pushnet collections in May




1979.  Postlarval densities at positive stations ranged from 0.7-53.4




in all habitats in spring 1979 and 0.3-21.9 during the period 19




November 1979 - March 1980.






                         Syngnathus fuscus




         Northern pipefish ranked fourth in numerical abundance (n=968)




and represented 3.9% of the total pushnet catch (Table 26).  Recently




born pipefish are essentially adult-like when extruded from the male




brood sac, do not exhibit a larval stage typical of other teleostean




fishes, and, except for stages under 10 mm SL, are associated with a




substrate (Zostera blades, floating vegetation) and thus not generally




available to standard plankton gear.
                                109

-------
Table 37 .  Abundance of northern pipefish,    Syngnathus fuscus, during months of occurrence in
pushnet collections, March 1979 - March 1980.
specimens; M - monthly mean density (N/100 m3) .

May
Jun
Jul
Aug
Sept
Oct
Nov (1)
Nov (19)
Total
Percent of Total
Sand
N M Range
1 0.6 0-1.1
20 7.7 6.1-9.0
127 77.4 30.7-159.3
27 10.0 4.2-16.3
00 —
no samples
1 0.4 0-0.8
00--
176
18.6
Abbreviations are N - total number of
Daylight samples excluded.
Zostera
N
3
100
214
246
32
2
2
1
600
63.5
M
1.9
36.4
103.8
100.1
15.2
0.9
0.8
. 0.4


Range
1.2-2.9
23.1-50.7
99.8-107.6
76.0-128.5
4.6-19.9
0.8-0.9
0.7-0.8
0-0.8


N
5
2
61
87
14
0
0
0
169
17.8
Ruppia
M
2.3
0.9
31.6
39.2
12.3
0
0
0


Range
1.7-2.9
0.8-0.9
8.5-53.6
11.3-61.2
7.2-20.1
—
—
—



-------
         Young pipefish and adults were present in collections during



May-November 1979.  Pushnet catches peaked in June-August, during which



time a higher percentage of the total catch (88.6-92.0%) was under 10


mm SL.  Densities (Table 37) during periods of peak abundance ranged


from 0.8-159.3 fish/100 m^.  As expected, densities were generally


higher in pushnet collections over Zostera beds.  Over 80% of the total


pipefishes collected were taken in pushnet collections over vegetated



habitats.




                      Micropogonias undulatus


         Larvae and postlarvae of the croaker, Micropogonias undulatus,


ranked fifth in numerical abundance and made up 2.2% (n=523) of all


fishes taken in pushnet collections.  Data on pelagic larvae and


postlarvae of croakers in the Chesapeake Bay are sparse and, with


the exception of a small collection of M. undulatus larvae (n=lll) at


the bay mouth by Pearson (1941), no additional larval or postlarval


records exist (Olney 1978, Chao and Musick 1977).  Croakers were taken


in pushnet collections during the period August 1979-January 1980.


Abundance data (Table  38) revealed peak densities from the latter part



of November 1979 through January 1980 with the highest recorded mean


density (122.3 postlarvae/100 m^) OVer sand bottom in December 1979.


During the period of peak abundance, density estimates at positive

                                               *3
stations ranged from 0.8-170.4 postlarvae/100 m  .  Postlarvae were


generally evenly distributed in all three habitats, although December


1979 catches over sand were exceptionally high.  Larval croakers (less


than 10 mm SL) were only taken over sand in late summer (August,



September) and only over vegetated habitats in January 1980.
                                Ill

-------
                Table 38.  Abundance of young croakers, Micropogonias undulatus, during monthes of occurrence
                           in pushnet collections, March 1979 - March 1980.  Abbreviations are:  N - total
                           specimens collected; M - monthly mean density (N/100 m ).   Daylight collections
                           excluded.
K>
Sand

1979
Aug
Sept
Oct
Nov (1)
Nov (19)
Dec
Jan
Total
Percent of Total
N
1
1
0
0
2
385
15
404
77.5
M
0.4
1.6
0
0
0.8
122.3
19.4


Range
0-0.7
1.6
—
—
0.8-0.8
77.7-170.4
19.4


N
0
0
0
1
16
26
34
77
14.8
Zostera
M Range
0
0
0
0.4 0-0.7
6.1 6.1-6.2
8.9 6.1-11.6
13.9 12.6-15.9


Ruppia
N
0
0
0
1
3
0
36
40
7.7
M
0
0
0
0.4
3.1
0
25.6


Range
—
	
—
0-0.9
3.1
—
15.2-38.8



-------
         Length frequency data (Table 39) indicated that croakers




greater than 18 mm SL were unavailable to surface pushnet collections.




During the period of peak abundance, postlarvae ranged from 10-17 mm SL




with only a few (n=4) larvae less than 10 mm SL taken.  The presence of




small specimens in both late summer and early 1980 indicate a protracted




period of recruitment into the Bay from offshore spawning grounds.






                         Membras martinica




         Juvenile and adult rough silversides, Membras martinica, ranged




in size from 16-87 mm SL, ranked sixth in numerical abundance and con-




stituted 1.3% (n=315) of the total fishes collected by pushnet (Table 26).




Rough silversides were captured by pushnet during the eight month




period April-November 1979.  Densities at positive stations ranged




from 0.8-34.8 fish/100 m^ and peak mean densities were observed between




May and June 1979 with a secondary peak in September 1979 (Table 40).




Rough silversides were more available to pushnet capture over vegetated




habitats than sand bottoms.  Over 93% of all M. martinica collected




occurred in Zostera and Ruppia collections.  In addition, mean densities




of silversides over Zostera or Ruppia beds always exceeded density




estimates over sand during any given sampling period.  Peak densities




over vegetation coincided with peak abundances of M. martinica egg




collections and summer peaks in abundance of atherinid larvae (Tables 25




and 43).
                                 113

-------
Table 39.  Length frequency distribution of young croaker, Micropogonias
	undulatus,  in pushnet collections, March 1979-March  1980.	

                                  MONTH
                                                                          ALL
SIZE CLASS    MAMJJASONDJM    MONTHS
   (mm)                                 1
    5                                  1                                  1
    6
    7
    8
    9                                        1
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20



1
3
3
4
3
1





9
17
63
100
100
39
45
14
1
1
2
10
21
24
15
5
1
3

1
1
3
20
41
90
119
108
41
48
14
                                       114

-------
Table 40.  Abundance of rough silversides, Membras martinica, during months of occurrence
           in pushnet collections, March 1979 - March 1980.  Abbreviations are N - number of
           specimens; M - monthly mean abundance  (N/100 m^).  Daylight collections are
           excluded.
                            Sand
                              Zostera
                                Ruppia
                      N   M
              Range
   N    M
Range
N    M
Range
1979
April

May (1)

May (31)

Jun

Jul

Aug

Sept

Oct

Nov (1)

Total

Percent of Total
  3  1.1      0-2.3

    no samples

  3  1.7      0-3.2

  0    0

  5  3.1      0-4.8

  8  2.9    2.1-3.9

  5  4.9       4.9

    no samples

  0  0

 22

6.8
   8   2.9   2.9-3.0

  32  23.5     23.5

  33  21.6  10.7-34.8

  47  17.1  13.3-21.2

   9   4.4   2.8-5.9

  23   9.4   5.3-12.8

  33  15.7  13.1-21.5

   2   0.9     0-1.6

   00--

 187

57.5
               2   0.8   0.8-0.8

                  no samples

              33  15.0  12.6-17.8

              13   5.9   5.1-6.8

              16   8.3   7.1-9.6

              23  10.4   6.2-13.7

               8   7.0   2.2-10.1

               4   1.7   1.6-1.7

              17   7.4   5.2-9.6

             116

            35.7

-------
                        Leiostomus xanthurus


          Postlarval and juvenile spot ranked seventh (n=280) in numerical


abundance and constituted 1.2% of the total fishes captured by pushnet


(Table 26).  Length frequency data (Table 41) indicated an extremely


abbreviated period of recruitment into the grass beds (March-April)


and high growth rates during spring months.  Postlarval spot appeared


in April 1979 in a size range of 13-24 mm SL.  By May 1979, spot were


far less available to pushnet collection and ranged from 30-41 mm SL.


Only a few juveniles (n=4) over 50 mm SL were taken after May.  April


1979 densities ranged from 12.9-49.4 fish/100 m3 with generally equal


distribution of young fish among the three habitats.  Although' over 78%


of all spot taken occurred over vegetated bottoms, a single, large


collection taken on 1 May 1979 (Table 42) in Zostera with no concurrent


samples in the other habitats biased these totals.



                          Atherinid Larvae


          Larval silversides of undetermined identity ranked eighth in


numerical abundance and constituted 1.1% (n=272) of all fishes taken by


pushnet (Table 26).  Silversides under 18 mm SL could not be identified


with certainty (Olney, 1978), however, with the exception of April 1979


collections (Table 43), silverside larvae taken in June-August 1979


co-occurred with eggs and adults of M. martinica.  Eggs or adult M.


menidia were not taken during this period suggesting that the majority


of unidentified atherinid larvae in pushnet collections may be referable


to only one species, M. martinica.


          Atherinid larvae peaked in abundance in July and August  1979.

                                                                 o
Densities at positive stations ranged from 0.8-78.9 larvae/100 m  and
                                 116

-------
Table4L  Length frequency distrubution of young spot,  Leiostomus
          xanthurus, in pushnet collections, March 1979-March 1980.


SIZE CLASS
(mm)
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
Over 50
MONTH
MAMJJAS ONDJM

4 1
4 .1
11
27
48
63
50
34
14
2
3
1
1





2
2
2
1 1

1
1




1








6
                                                                            ALL
                                                                            MONTHS
                                                                              5
                                                                              5
                                                                             11
                                                                             27
                                                                             48
                                                                             63
                                                                             50
                                                                             34
                                                                             14
                                                                              2
                                                                              3
                                                                              1
                                                                              1
                                                                              2
                                                                              2
                                                                              2
                                                                              2

                                                                              1
                                                                              1
                                   117

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               Table 42.   Abundance of spot,  Leiostomus xanthurus,  during months of occurrence in pushnet
                          collections, March 1979 - March 1980.  Abbreviations are N - number of specimens;
                          M - monthly mean abundance (N/100 m^).
oo
1979
Apr

May (1)

May (31)

Jul
                                           Sand
                                                     Zostera
                                                        Ruppia
                       N
                                           M    Range
 N    M
                                    Range
 N     M    Range
53  19.5  12.9-25.8

   no samples

 6   3.3   2.3-4.2

 00--
65  23.4  16.1-31.0

47  34.6    34.6

 4   2.6     0-4.8

 2   0.9     0-1.9
102  41.4  33.0-49.4

    no samples

  00--

  4   2.1   2.0-2.1
               1980
               Mar                    0

               Total                 59

               Percent of Total    20.9
                                                1   0.3

                                              117

                                             41.5
                                      0-0.6
                          0

                        106

                       37.6

-------
Table 43.  Abundance of atherinid larvae during months of occurrence in pushnet collections,
           March 1979 - March 1980.  Abbreviations are N - number of specimens; M - monthly
           mean abundance (N/100 m3).  Daylight samples are excluded.


1979
Apr
Sand Zostera
N M Range N M Range

0 0 — 1 0.4 0-0.8

N

14
Ruppia
M Range

5.7 2.4-9.1
Jun

Jul

Aug

Total

Percent of Total
   00     —

  23  14.0  11.5-18.5

   4   1.5   0.8-2.1

  27

10.8
  11   4.0     0-8.3

  27  13.1   8.5-17.9

  35  14.3  10.5-18.6

  74

29.6
   00--

  31  16.1  6.4-25.3

 104  46.9  6.2-78.9

 149

59.6

-------
                                                        o
mean density estimates ranged from 1.5-46.9 larvae/100 m  during these


months.  Over 88% of all larvae were taken over vegetated habitats


although July 1979 densities over sand bottom exceeded Zostera estimates.



Notes on Additional Species


         Postlarval striped anchovies, A. hepsetus, ranging in size from


13 to 41 mm SL (n=66), appeared in pushnet collections during July and


August 1979.  Greatest densities were recorded in August 1979.  Abundance

                     3
estimates  (fish/100 m ) in all habitats during peak density were:  sand -


24.9, 33.9; Ruppia - 7.2, 8.0; and Zostera - 2.7, 12.8.  Postlarval


striped anchovies were conspicuously absent from previous collections


in the lower Chesapeake Bay (Pearson 1941; Massman et al. 1961, 1962;


Olney, in  press).  Massman et al. (1961, 1962) provided the only reports


of postlarvae north of Cape Hatteras, North Carolina; one 19 mm SL


specimen taken in the Atlantic Ocean off the Bay entrance and one 23 mm


SL postlarva in the Pamunkey River, Va.  The present collections confirm


Hildebrand and Cable's (1930) suspicion that larvae of this species


occur in areas which have received low sampling intensity, such as


estuarine  shallows and grassy areas.


         Juvenile and adult Atlantic silversides (n=110), Menidia menidia


were collected in March, April and June 1979 and during  the period


December 1979 - March 1980.  Monthly mean density fish/100 nr during


months of  occurrence were:  March 1979, 0.5; April 1979, 0.1; June 1979,


0.5; December 1979, 10.4; January 1980, 0.4; and March 1980, 1.4.


Atlantic silversides were considerably less abundant than rough


silversides, M. martinica, (Table 40) and collections indicated strong


temporal discontinuity between these two atherinid species.  In addition,
                                 120

-------
eggs of M. menidia were conspicuously absent from collections, whereas




M. martinica eggs were relatively common, especially considering their




demersal nature.




         Eggs (n=3) early larvae (n=19) and juveniles  (n=6) of the




halfbeak, Hyporhamphus sp., were taken in pushnet collections during




the period May - August 1979.  Late larval stages of Hyporhamphus sp.




are reported from the Chesapeake Bay region (Hardy and Johnson 1974),




however eggs and early larvae are undescribed and the  importance of




submerged aquatic vegetation as a spawning habitat for this species has




not been investigated.  Eggs and larvae were taken over vegetated




habitats in June, July and August but did not occur in .pushnet samples




over sand bottom during this period.  Peak larval density  (ll.l larvae/




100 m3) was observed in Ruppia beds in July 1979.




         In addition to M. undulatus and L_. xanthurus, four sciaenid




species were represented as larvae in pushnet collections.  These were




the weakfish, Cynoscion regalis, (n=146); southern kingfish Menticirrhus




americanus, (n=20); red drum, Sciaenops ocellata (n=ll); and the silver




perch, Bairdiella chrysoura, (n=9).  Monthly pushnet density data for




these species are presented in Tables 44 and 45.




         JC. regalis larvae were taken by pushnet during the period May -




August 1979, with peak densities in August 1979  (Table 44).  Larval




weakfish are important components of lower Chesapeake  Bay  summer




ichthyoplankton (Pearson 1941, Olney 1978) ranking second  in numerical




abundance after anchovies.  The infrequent occurrence  of C^. regalis




larvae in nearshore habitats is indicative of the minimal  importance




of SAV as a spawning habitat for this species.
                                 121

-------
Table 44 .  Monthly mean density and size ranges of Cynoscion regalis




           captured by pushnet in evening collections, March 1979 -




           March 1980.










                        May          Jun         Jul           Aug





Total Specimens          1            3           1          -  141




Size Range (mm)        3.8 NL   3.1 NL-5.3 SL   4.3 NL   2.0 NL-51.0 SL




Zostera (N/100 m3)       0            0           0           38.3




Ruppia  (N/100 m3)       0            0           0              0




Sand    (N/100 m3)     0.6           1.2        0.6           17.4
                                 122

-------
Table 45.  Monthly mean density and size ranges of Sciaenops ocellata




           Menticirrhus americanus and Bairdiella chrysoura in evening




           pushnet collections in August 1979.










                       j>. ocellata     M. americanus     ]J.. chrysoura





Total Specimens             11              20                 9




Size Range (mm)       2.0 NL-5.2 SL    3.8 NL-9.2 SL    2.0 NL-5.1 SL




Zostera (N/100 m3)         3.3             3.3                1.2




Ruppia  (N/100 m3)         0.9             0.5                2.7




Sand    (N/100 m3)         0.4             4.1                 0
                                123

-------
         Larvae of M. americanus, jS_. ocellata and _B. chrysoura were




taken in August 1979 in low abundance (Table 45).  The presence of




larval red drum over grass beds is consistent with previous 'studies




(Powles and Stender 1978 and references therein) but these specimens




represent the first record of spawning activity  for the species in




Chesapeake Bay.  The absence of large numbers of silver perch larvae




is surprising considering the importance of this species in previous




studies of SAV ichthyofauna (Orth and Heck,  1980).      Apparently,




JB. chrysoura (as well as all sciaenid species) only utilize SAV as a




nursery and refuge but not as a spawning habitat.  M. americanus larvae




were infrequent in pushnet collections as they were in previous lower




Bay ichthyoplankton surveys (Pearson 1941, Olney 1978).




         Occurrence of larvae and postlarvae of  the sand lance,




Ammodytes hexapterus, was consistent with previous collections in




the lower Chesapeake Bay (Pearson 1941, Norcross et al. 1961, Olney




1978, Grant and Olney 1979).  A. hexapterus  larvae  (n=191) were captured




by pushnet in March 1979, 1980.  Monthly mean density  (N/100 m3) in




each habitat during each year were:  Sand -  19.8 (1979), 24.7  (1980);




Ruppia - 12.2  (1979), 1.9 (1980); Zostera -  8.7  (1979), 5.2  (1980).




Larvae ranged  from 9.0 mm NL to 27 mm SL.






Seasonal assemblages




         Numerically dominant species during each month of pushnet




sampling are listed in Table 46.  Patterns of dominance are  related  to




water temperature in Table 4h7 and then listed in seasonal patterns of




occurrence.
                                124

-------
Table 4^.  Numerically dominant species of ichthyoplankton, listed
           in order of abundance, taken by pushnet in evening
           collections, March 19.79 - March 1980.  Eggs are excluded.

1980
Mar
Apr
May
Jun
Jul
Aug
Sept
Oct
Nov (1)
Nov (19)
Dec -
Sand
A. hexapterus
B . tyrannus
A. rostrata
L. xanthurus
A. mitchilli
A. mitchilli
L. xanthurus
B . tyrannus
Gobiosoma sp.
A. mitchilli
B . tyrannus
A. mitchilli
S. fuscus
atherinidae
A. mitchilli
Gobiosoma sp.
A. hepsetus
A. mitchilli
M. martinica
no samples
A. mitchilli
A. mitchilli
B. tyrannus
M. undulatus
M. undulatus
A. mitchilli
Ruppia

A. hexapterus-
B. tyrannus
A. rostrata
B . tyrannus
L . xanthurus
A. mitchilli
B . tyrannus
A. mitchilli
M. martinica
A. mitchilli
M. martinica
Gobiosoma sp;
A. mitchilli
S. fuscus
atherinidae
A. mitchilli
Gobiosoma sp.
S. fuscus
A. mitchilli
S. fuscus
M. martinica
A. mitchilli
H. hentzi
M. martinica
A. mitchilli
M. martinica
A. mitchilli
B . tyrannus
M. undulatus
M. menidia

Zostera

A. hexapterus
B . tyrannus
P. dentatus
L. xanthurus
B. tyrannus
A. mitchilli
A. mitchilli
M. martinica
B. tyrannus
Gobiosoma sp.
A. mitchilli
S. fuscus
A. mitchilli
S . fuscus
atherinidae
A. mitchilli
Gobiosoma sp.
S . fuscus
A. mitchilli
M. martinica
S . fuscus
A. mitchilli
A. mitchilli
S. fuscus
A. mitchilli
B . tyrannus
M. undulatus
M. menidia
M. undulatus
              M. menidia
A. mitchilli
                                125

-------
Table 46 (continued)
                   Sand               Ruppia             Zostera
1980
Jan           M. undulatus        M.  undulatus       M. undulatus
              B^. tyrannus         li.  tyrannus        JJ. tyrannus

Mar           A. hexapterus       A.  hexapterus      A. hexapterus
              P_. dentatus                            M. menidia
              A. mitchilli              .             P. dentatus
                                126

-------
Table 47.  Summary of seasonal ichthyoplankton assemblages in nearshore
           habitats in Chesapeake Bay.  Species life history stages
           (E - egg, L - larva, P - postlarva, J - juvenile, A - adult),
           surface temperature range and months of collection are
           reported from pushnet collections, March 1979 - March 1980.
     Surface
Temperature Range    Season
     (ฐC)              (months)
                           Characteristic Species
                            (life history stage)
1-12 Winter . A.
(November - March) B.
P.
A.
M.
A.
M.
15-22 Spring L.
(April - May) B.
M.
A.
S.
hexapterus
tyrannus
dentatus
rostrata
undulatus
mitchilli
menidia
xanthurus
tyrannus
martinica
mitchilli
aquosus
atherinidae
tj • j_uSCilo
(L, P)
(P)
(P)
(elver)
(L, P)
(J, A)
(J, A)
(P, J)
(P, J)
(J, A)
(J, A)
(L)
(L)
(A)
    20-28
Summer
  (June - August)
    13-21
Fall
  (September - October)
A. mitchilli
Gobiosoma sp.
A_. hepsetus
j^. fuscus
Sciaenidae
M. martinica
atherinidae
M. thalassinus
Hyporamphus sp.
H. hentzi

A. mitchilli
M. martinica
S^. fuscus
H. hentzi
(E,  L,  J,  A)
(L)
(P)
(L)
(E,  L,  J)
(E,  J,  A)
(L)
(L)
(E,  L)
(L)

(P,  J,  A)
(J,  A)
(J,  A)
(P,  J)
                                  127

-------
         Winter Assemblage - Winter pushnet collections (November -




March) were characterized by the occurrence of postlarvae of five




species of offshore spawners:  A. hexapterus, IJ. tyrannus, ฃ. dentatus,




A. rostrata and M. undulatus.  Larval and postlarval stages of these




fishes (elvers in the case of American eel) enter the Chesapeake. Bay




when surface water temperatures range from 1-12ฐC.  Patterns of




immigration into the Bay are unknown, but the presence of these




stages in nearshore habitats along the eastern Bay margin likely relates




to Bay salinity patterns.  The eastern Bay margin is characterized




by high salinity salt wedge intrusion.  Postlarvae are believed to




utilize the non-tidal, upriver vector of this intrusion as a mechanism




in estuarine dependence.  The absence of dense Zostera or Ruppia beds




during this period precludes utilization by these species of SAV




habitat.  In addition to immigrant postlarvae resident populations




of A^. mitchilli and M. martinica occupy the nearshore waters during




winter periods.




         Spring assemblage - With increasing surface temperatures




(15-22ฐC), pushnet collections revealed the continued presence of




IJ. tyrannus postlarvae and juveniles; the introduction of postlarval




and juvenile spot, L^. xanthurus to the SAV system; the continued




presence of resident populations of juvenile and adult anchovies and




rough silversides and the spawning activity of atherinids and windowpane




flounder, S^. aquosus.  Atherinid spawning, and the presence  of adult




_S_. fuseus and young spot in collections was interpreted to relate  to




initiation of SAV growth.
                                128

-------
         Summer Assemblage - The summer ichthyoplankton assemblage was




dominated by egg and larval stages of resident lower Chesapeake Bay




spawners including anchovies, gobies, pipefish, sciaenids (ฃ. regalis,




M. americanus, j[. ocellata, and IJ. chrysoura), atherinids, blennies and




halfbeaks.  In addition, some immigration of offshore (or coastal)




spawned larvae was observed, namely postlarval ^. hepsetus.  Summer




pushnet collections revealed peaks in density and diversity of nearshore




ichthyoplankton populations but habitat comparison data (see earlier




section) confirmed that these peaks were independent of the presence




of dense SAV beds.  However, the high numerical rank abundance of goby




and pipefish larvae was clearly a function of water depth and the




presence of vegetation.  This conclusion is based on the relative




importance of the species in ichthyoplankton surveys of deeper waters




in the Bay (Pearson 1941, Olney 1978).




         Fall Assemblage - Late postlarval, juvenile and adults of




four species, all resident lower Bay fishes were present in fall




(September, October) pushnet collections.  During this period, density




and diversity of catch was low and little evidences of SAV dependence




was observed.
                                 129

-------
Laboratory analysis




Food Habits




        Nonempty stomachs from 669 resident fishes and 348 migratory




predators were collected, sorted, contents•identified (Table 48).




Gravimetric and numerical analyses were then undertaken to define the




relative importance of prey items.  Spot, silver perch, and pipefish




stomachs were examined for ontogenetic shifts in food preference and monthly




changes in prey selectivity.




    Three different indices were computed to define the relative "importance"




of prey items to each species of fish.  Percent frequency of occurrence




was calculated by recording the number of stomachs containing one or more




individuals of each food category and then expressing this number as a




percentage of all non empty stomachs from a single species of fish.  Percent




number was determined by counting the number of individuals in a food




category and the total is expressed as a percentage of the total individuals




in all food categories.  Percent dry weight was calculated by summation




of the dry weights of individuals in a food category and expressing  the




results as a percentage of the dry weight of the total individuals in




all food categories.  Three indices were utilized since no one food  index




properly describes the relative  importance of prey items to the predators.




Frequency of occurrence demonstrates the regularity at which an  item is




fed upon, but gives no indication of quantity or number of food  items  eaten.




Percent number gives an indication of the  amount of effort exerted in




selecting and capturing different organisms.  However percent number




overemphasizes the importance of small prey; is difficult  to use because




of mastication of  the  food before  it reaches the stomach;  and is not suitable




for dealing nondiscrete food  items such as macroalgae and  detritus.  Percent
                                      130

-------
           Table 48




Feeding Analysis of SAV Fishes
Resident Species
Centropristis striata
Micropogonius undulatus
Clupea harengus
Morone americana
Pseudopleuronectes americanus
Orthopristis chrysoptera
Scophthalmus aquosus
Urophycis regius
Prionotus evolans
Leiostomus xanthurus
it it
n ii
Bairdiella chrysoura
n n
n it
Syngnathus fuscus
n n
it n
Migratory Species
Paralichthys dentatus
Cyno scion regalis
Pomatomus saltatrix
Morone saxatilis
Sciaenops ocellata
Rachycentron canadum
Cynoscion nebulosus
Carcharhinus milberti
Dasyatis sayi
Tylosurus acus
Strongylura marina
Number
4
1
1
1
8
19
2
10
6
56
103
36
51
118
38
93
103
19
Number
24
26
63
2
2
1
20
199
2
7
2
Length Range
72-158
305
132
204
47-100
29-107
221-246
49-113
35-105
20-50
60-100
110-150
20-50
60-100
100-150
60-100
110-150'
160-180
Length Range
131-140
320-580
122-870
286-307
384-765
490
400-595
435-852
700-710
970-1140
380-403
               131

-------
weight demonstrates  the bulk of food items and is related to caloric




content.  This  index tends to overestimate the contribution of items with




heavy exoskeletons such as molluscs and crabs.




    Figure  23 and 24 ,  illustrate, and Table  49 and  50 describe  the food




habits of resident fishes captured in the SAV study area.  Prey categories




were composed of members of the benthic, epibenthic and planktonic communities




in the Zostera  and Ruppia  areas .  The dominant prey  items  (by all three




food indices) of the resident fishes were the mysid shrimp
americana) ,  the  sand  shrimp  (Crango n septemspinosa) , and calanoid copepods.




Isopods, amphipods, and  polychaetes were very  important for certain




species of  fishes  but were not  eaten regularly by all resident fishes.  Spot




 (L. xanthurus) ,  croaker  (M.  undulatus) and hogchoker  (T. maculatus) demon-




strated benthic  feeding  behavior  by the abundance of harpacticoid copepods,




nematodes,  bivalves,  polychaetes,  and detritus found  in their stomachs.




Epibenthic  feeding in black  seabass  (C . striata) , pipefish  (ฃ. fuscus) ,




pigfish  (0.  chrysoptera) and white perch  (M. americana) occurred as shown




by  the presence  of amphipods and  shrimps  in  their stomachs.  B. chrysou ia




and ฃ. harengus  were plankton  feeders that  consumed calanoid copepods,




mysids, and occasionally larger shrimps.




    The food habits of  the three  dominant resident  species  (L. xanthurus ,




 IJ.  chrysoura and S^. fuscus)  were  analyzed for  monthly changes  in prey




 selectivity and  ontogenetic  shifts in  food preference.  Frequency of




 occurrence (Table  51) indicated that plant detritus,  nematodes, polychaetes,




 ostracods,  harpacticoid  and  calanoid copepods  were  frequently  consumed




 by  all sizes of  spot.  By percent number  (Figure 25)  all  sizes of spot




 consumed a large number  of harpacticoid copepods and  nematodes while  the




 largest  spot consumed primarily N. americana.  Figure 26  indicates  that
                                      132

-------
PERCENT NUMBER OF PREY  ITEMS FOUND IN THE STOMACHS  OF RESIDENT SPECIES

PCNUMBER SUM

     100
      90 -
      30 -
      70 -i
      60 -
      50 r-
      40 -
      30 -
      20 -
      10 -
  LEG-END: TRXCCDE2
                          .'/
                         


-------
PERCENT WEIGHT OF  PREY ITEMS FOUND IN THE  STOMACHS OF RESIDENT SPECIES
PCWEIGHT SUM

     100 -



      90 -



      80 -



      70 -



      60 -



      50 -



      40 -



      30 -



      20 -



      10 -

      
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    LEGEND:  TRXCODE
                                    PREDRTOR

                              RNIMRL FKRGMENTS
                              OTHER
                              POLYCHREIR
                              G.  DIBRRNCHIRTfi
                              HRRPRCTICOID
                              N .  RMERICRNR
                              1DOTER SRLTHICR
                              R.  LONGIMRNR
                              M.  RRNEYI
                              P VULGRRIG
                              C.  SflPIDUS
                              FISH EGGS
                              L .  XRNTHURUS
      UN I DENT DETRITUS
      PLRNT DETRITUS
      NEREIS REMfllNS
      TECEl.u'G PLEBEIUG
fe. ^ '• CRLRNOID
'///////. F. - RTTtlNJRTR
•SS'j RMPHIPODfi
      G. MUCRONRTUS
      c. PENRNTIS
LXXXi C . SEPTEMSPINOSR
K 3K'-^ UNIDENT. FISH
      ENGRHULICRE
                                    Figure 24
                                       134

-------
                                                     Table 49
                                         Resident Fishes of SAV Study Area
uv
Syngnathus Leiostomus Bairdiella
fuscus (214) xanthurus (170) chrysoura(161)

Animal Fragments
Unid. Detritus
Bryophyta
Algae
Plant Detritus
Zostera marina
Ruppia maritima
Foraroinifera
Hydro zoans
S tylo chus ellipticus
Trematoda
Nemertea
Nematodes
Polychaeta
Phyilodocidae
Eteone heterodpoda
Phyllodoce arena
Syllidae
Nereis remains
Nereis succinea
Glycera dibranchiata
Glycera solitaria
Capitellidae
Heteromastus filiformis
Maldanidae
Clymenella torquata
Spinodiae
Poly dor a longni
Polydora pinnata
Orbinidae
Tharys setigera
% Wt % Occ % N % Wt
10.8 46.9 1.2 3.0
.1 2.8 .1 9.6
.5
trace
2.4 2.8 .1 12.5
.1 .5 trace trace

.1 2.3 .2 .1
trace 0.5 trace 1.7
trace
trace
.2
1.7
.7 1.4 trace 3.1
.1
1.2

trace
3.8 .7 ,1 .1
.1 0.9 trace .8
.2
.5
.5
trace
1.3
2.1
.2
.9
trace
trace
trace
% Occ % N % Wt % Occ % N
26.5 0.2 0.2 2.4 trace
27.6 0.2 1.1 13.0 0.2
14.7 5.3
1.8 trace
24.7 0.2 .1 2.4 trace
.6 trace .2 0.5 trace
trace 0.5 trace
4.1 0.1
5.9 trace
.5 trace
.5 trace
.5 trace
52.5 45.6
20.4 .3 .9 .5 trace
1.0 trace
16.8 .8
.9 .5 trace
5.1 0.1
2.0 trace
4.6 trace
2.6 trace
6.1 0.1
3.0 .1
1.1 trace
1.1 trace
.5 trace
2.6 .1
7.1 0.1
.5 trace
1.5 trace
.5 trace
Orthopristjs
chrysoptera (19)
% Wt % Occ % N
1.8 26.3 0.3
2.2 15.8 0.2


1.1 21.1 0.3



0.3 5.3 0.1



trace 5.3 0.1





0.7 10.5 0.1

5.3 5.3 0.1











-------
                                                 Table 49  (Continued)
                               Syngnathus
                               fuscus (214)
                             % Wt % Occ  % N
                          Leiostomus
                          xanthurus (170)
                       % Wt % Occ  % N
                                        Bairdiella
                                        chrysoura(161)
                                     % Wt % Occ  % N
                                                       Orthopristjs
                                                       chrysoptera (19).
                                                      Wt % Occ  % N
Mollusca
Gastropoda
Crepidula convexa
Nudibranchia
Hamindae solitaria
Re^usa canaliculata
Doridella obscura
Pelecypoda
Anadora transversa
Gemma gemma
Crustacea
Ostracoda
Copepoda
Harpacticoid
Calanoid
Cennipedia
Balanus improvisus
Neonrysis americana
Mysidopsis bigelowi
Cumacea
Cyclaspis varians
Oxyurostylis smith!
Isopoda
Chirodotea caeca
Erichsonella attenuata
Idotea balthica
Edotea triloba
Paracerceis caudata
Amphipoda
Ampeliscidae
Ampelisca abdita
Ampelisca radorum
Ampithoidae
Ampithoe
Ampithoe longimana
trace    .5  trace
   .4   9.3

   .1   2.3
 15.1  39.5
  4.3
  2.4
trace
trace
  3.0
12.6
15.8
 3.7
 0.9
14.4
        0.7

         .7
       71.1
   .1   1.9     .1
 18.4  25.6    7.0
trace    .5  trace
  1.3
  0.8
  0.1
trace
  1.7
   .7   1.4  trace

  3.0  15.3    1.6
                       1.1 trace
                       6.1   0.1
                       3.1 trace
                        .5 trace
                        .5 trace
         trace
           0.2
            .4
         trace
         trace

         trace
            .2
         trace
           0.5
         trace
           0.8
         trace
           3.2
            .6
            .1
           1.4
          46.7
            .3
         trace
         trace
         trace
         trace
trace   0.5 trace

   .1  10.7   0.2

   .1   3.1 trace
trace   0.5 trace
trace    .5 trace

  0.2   1.5 trace
                                                                   .3   5.3   .1
                                                                   .6   5.3   .1
.5
6.6
1.1
1.1
1.1
25.6
1.0
51.5
23.5
1.1
8.6
37.2
2.1
3.6
0.5
5.1
.5
trace
0.1
trace
0.1
trace
2.7
0.1
31.1
4.8
trace
.2
6.6
0.1
trace
trace
0.1
trace
                                             0.1    2.9  trace
                       1.1  26.6  25.7
                      64.6  77.8  70.9
                       0.2   3.9   0.1

                       0.3   1.4   0.1
                     trace    .5 trace
  0.1
  0.3
  0.9
  0.1

   .7
  0.1
  0.2

trace
trace
  0.2
0.5 trace
6.7   0.1
5.3    .2
1.0 trace

9.7   0.2
1.0 trace
3.9   0.2

1.4 trace
 .5 trace
3.9    .1
                                                                  0.9    5.3   .1
                     trace  10.5  0.1
                       0.5  10.5  0.2

                       2.8  47.4 65.2
                                                           8.7   42.1  23.8
                                          trace    5.3  0.1

                                            1.6   15.8  0.4
                                            5.9   42.1  1.1
  1.9  21.0  0.4

trace   5.3  0.1



  1.4  21.1  0.5

-------
                                                  Table 49  (continued)
            Food  Items
                                Syngnathus
                                fuscus (214)
                             % Wt % Occ  % N
                         Leiostomus
                         xanthurus (170)
                      % Wt % Occ  % N
                                       Bairdiella
                                       chrysoura(l61)
                                    % Wt  %  Occ   % N
                                               Orthopristls
                                               chrysoptera (19)
                                            % Wt  % Occ  %  N
to
Ampithoe valida_
Cymadusa compta
Batea catharinensls
Corphiidae
Cerapus tubularis
Corophium
Corophium acherusicum
Corophium simile
Corophium tuberculatum
Erichthonius brasiliensis
Gammaridae
Gaimnarus sp. A
Gammarus palustris
Gammarus mucronatus
Microprotopus raneyi
Microprotopus edwardsi
Caprellidae
Caprella penantis
Caprella equilibra
Paracaprella tenuis
Decopoda
Lucifer faxoni
Crangon septemspinosa
Callinectes sapidus
Pinnixa chaetopterana
Pinnixa sayana
Insecta
Polydesmida
Unid. Fish
Fish Eggs
Engraulidae
Anchoa mitchilli
  1.4

   .1
trace

   .1

  1.0

  1.8

  1.1
 10.0
  4.6

trace
 12.9
trace
   .6
  .8  0.1

 0.9 trace
 0.5 trace

  .5 trace

  .9 trace

12.1  1.6

 1.9   .1
16.7  6.3
 9.3   .4

 2.3   .1
31.1  4.0
  .5 trace
 7.4  0.4
                                    .1    .5  trace
                                   1.0     .5  trace
                                    .1     .5  trace
                                                     trace
                                                     trace

                                                       0.1
                                                     trace
   .5
  1.0
trace
trace
  0.2

trace
                      2.5
                      0,1

                      0..2
         1.0 trace
         1.0 trace

         1.5 trace
          .5 trace
                                                     trace    0.5  trace
                                                     trace    1.0  trace
 8.2   .1
13.3  0.5
 0.5 trace
 2.0 trace
 4.6   .1

 4.1   .1
                      2.6  trace
                       .5  trace

                       .5  trace
                                                    trace    1.0 trace
                                                    trace      .5 trace
                0.1  204  trace
                0.1  3.9    .1
              trace   .5  trace

                0.1  2.9  trace
                 .8  4.3   0.1
                0.1  1.4  trace

                0.1   .5  trace
                0.1  1.0  trace
              trace  1.0  trace
   .3  8.7    .3
  1.2 15.9    .3
trace   .5  trace

  1.1 17.4   0.4

trace   .5  trace
  0.2   .5  trace
trace   .5  trace
 18.3 24.8   0.6
trace   .5  trace
trace  1.0  trace
                                           1.0  1.9  trace

                                           4.7   .5  trace
                                           0.5  1.4  trace
  2.7  36.8  1.0

trace   5.3  0.1



  0.9   5.3  0.1

trace   5.3  0.1
trace   5.3  0.1
  0.8  10.5  0.2

  1.3  31.6   .5
  1.2  26.3  0.5


  2.0  31.6   .9

  0.3  15.8  0.5


  6.1  36.8  2.8


trace   5.3  0.1


 48.4  10.5  0.1

-------
                                                                    Table 50

                                                        Occasional Fishes of SAV Study Area
Urophycis Pseudopleuronectes
regius (10) americanus (8)
Food Item
Animal Fragments
Unid. Detritus
Plant Detritus
Polychaeta
Nereis remains
Glycera dibranchiata
Gastropoda
Crepidula convexa
Pelecypoda
Mya arenaria
Limulus polyphemus
Calanoid
Neomysis americanus
Mysidopsis bigelowi
Erichsonella attenuate
Idotea balthica
Edotea triloba
Amphidpoda
Ampithoe longimana
Cymadusa compta
Gammaridea
Gammarus sp. A
Gammarus macronatus
Microprotopus raneyi
Caprella penantis
Decapoda
Paleomonetes vulgaris
Crangon septemspinosa
Callinectes sapidus
Unid. Fish
Fish Eggs
Brevoortia tyrannus
Anchoa mitchilli
% Wt % Occ % N % Wt % Occ
0.0008 10 4.5455
6.0487 25.0
5.8514 25.0
2.3011 12.5
2.6298 12.5
19.3294 25.0
2.3669 12.5
0.7688 20 18.1818 3.0901 12.5
3.9448 25.0
0.5952 10 4.5455
6.5889 10 9.0909 54.4379 25.0
79.2073 100 54.5455
% ,N
1.0417
1.0417
1.0417
0.5208
90.6250
0.5208
0.5208
1.0417
3.6458
Prionotus
evolans
% Wt % Occ
12.2735 16.6667
0.0039 16.6667
0.1059 16.6667
0.2000 16.6667
0.7843 16.6667
1.2156 16.6667
13.9754 83.3333
0.1372 33.3333
0.6274 16.6667
0.0039 16.6667
0.7215 50.0000
2.1489 66.6667
0.0078 33.3333
67.4496 83.3333
0.3451 16.6667
(6)
% N
0.7463
0.7463
0.7463
3.7313
0.7463
0.7463
21.6418
2.9851
0.7463
10.4478
29.8507
7.427
1.4925
17.1642
0.7463
Centropristjs Scophthalmus
striata (4) aquosus (2)
% Wt. % Occ % .U % Wt % Occ . .%. N...
3.6191 25 2.7027
3.8564 25 2.7027
2.7588 50 56.7568 54.8167 100 97.561
2.2249 25 5.4054
, 8.9588 50 5.4054
51.5574 75 18.9189
27.0246 25 8.1081
51.5574
45.1833 50 2.439
Atherinidae
Leiostomus xanthurus
                          12.8388   10   9.0909

-------
Table 51

FREQUENCY OF OCCURRENCE  FOR DOMINANT PREY ITEMS FOUND IN THE STOMACHS OF LEIOSTOMUS XANTHURUS

	__.	L L20=20MM LENGTH (SL)J	

       TAXCODE      L20  L30  L40  L50  L60  L70  L80  L90  L100 L110 L120 L130  L140 L150

   ANIMAL FRAGMENTS    .  23-5 50.0 55.6 72.7 58.8 14.3   ....   14.3  33ซ3
   UNIDENT DETRITUS    	  53-630.838.1 41.741.771.4
   BRYOPHYTA           .  17.6 15.4 33-3 54.5 41.2        .    .     .     .
   PLANT DETRITUS   50.0 47.1 15-4 11.1   .    .  17.9 38.5 23-8 33.3 75.0 71.4  66.7 50.0
   FORMANIFERA         .    .    .    .    .    .  10.7   .    .     .   16.7
   HYDROZOANS          	17.6 21.4	
   TREMATODA           .    .    .    .    .    .    .    .    .     .     .     .     .   50.0
   NEMATODES        50.0 70.6 57.7 66.7 63.6 29.4 57-1 46.2 52.4 66.7 50.0 42.9
   POLYCHAETA       25.035.323.1 33.3   •  11.821.423-1   •   25.025.042.9
   E. HETEROPODA    50.0 58.8 46.2 44.4   	
   SYLLIDAE            	16.7   .   14-3
   NEREIS SUCCINEA     .    .    .11.1	
   G. DIBRANCHIATA     .    .    .11.1   .    .    .    .    .     .     .     .
   G. SOLITARIA        .	16.7 41.7 28.6    .     .
   CAPITELLIDAE        .  11.8 11.5 11.1   .    .    	
   H. FILIFORMIS	28.6
   SPIONIDAE           .    .11.5   	     	
   POLYDORA LIGNI      .  23.5 15-4 44.4   .    .    .    .    ...     .   •  .
   P. PINNATA          ...........   14-3
   ORBINIDAE           .    ...    '.    .    .    .    .    .     .   25.0   .     .
   GASTROPODA          	14-3 16.7 16.7 14.3    .   50.0
   C. CONVEXA          	14.3	
   PELECYPODA          .  11.8   .  11.1   .    .    	
   OSTRACODA        25.0 47.1 19-2 44.4   .    .  35.7 34-6 28.6 41.7 50.0 28.6
   HARPACTICOID     50.0 58.8 19-2   .    .    .  67.9 84.6 76.2 66.7 91-7 71.4  66.7
   CALANOID         25.0   .*...'   .    .  28.6 42.3 38.1 25.0 66.7 42.9  66.7  100
   B. IMPROVISUS       .  23.5 19.2 11.1 36.4 11.8   .	
 '  N.AMERICANA        ....  18.2   .  35.757.771.475.091.7.71.4.  100  100
   M. BIGELOWI	 .     .     .   14.3  33.3

-------
Table  51.  (continued)
          TAXCODE      L20  L30  L40  L50  L60  L70  L80  L90   LlOO LllO L120 L130 L140 L150

      CUHACEA             ......   10.7   .    .    ...
      0.  SMITHI           .     .     .     .     .    .    .  15.4   .    .  16.7
     'AMPHIPODA           	14.3 26.9   .  16.7 16.7
      AMPELISCA  ABDITA   .     .     .   11.1  18.2   	
      A.  LONGIMANA       .     .     .     .     .    .    .    .    .    .    .  14.3
      GAMMARIDEA       25.0   .          	
      G.  MUCRONATUS    25.0   .   15-4  55-6    .    .    .    .    .    .    .  14-3
      M.  RANEYI           .     .     .   — .     .    .   17.9 23.1 23-8 41.7 25.0 28.6
      CAPRELLIDAE      25.0	
      C.  PENANTIS        .     .11.5	
      P.  TENUIS           	11 .5        ....

-------
PERCENT  NUMBER OF PREY PER SIZE CLASS OF LEIOSTOMUS XANTHURUS


  PCNUMBER SUM
         90 H
         70 H
         50 -J
         40 -1
         30 J
         10 -\
                                               2




20  30  40  50
                                   70  50   30  100  110  120  130 140 150
   LEGEND: TRXCODE2
                        K X
                        \xVx\
               SIZE  CL.RSS  IN hH

               RNIMRL  FRRGMENT'S
               BRYOPHYTR
               POLYCHRETfi
               CRPJTELLIDflE
               POLYDORR LIONI
               HRRPRCTICOID
               B.  IMPROVISUG
               C-.  MUCRONHTUS
               CflPREl.LIDRE
                                               < r-1  i
                                               i oL i
      OTHER
      NEMRTQDES
      E .  HETEROPODR
      SPJQNIDRE
^ ^, ^ GSTRRCCDR
V//////, CRLRNOID
' S J* A N.  RMERICRNR
ES22S2SS M .  RRNEYI
                              Figure 25


                                    141

-------
PERCENT WEIGHT OF PREY  PER  SIZE CLASS OF  LEIOSTOMUS MNTHURUS
  Fr i ' c T rซ LJ T  c
  L w I i v n i  o
UM
        90 -\
        80 H
         70  -J
         60
         50  H
         40  -H
         30 H
         20 -J
         10



                                   \
                               Kl
                                                   X
               20  30  40  50  SO  70 . 8
                                90  100  110 120 130 140 150
                  SIZE CLRSS
                                         IN nr. ISL
   LEGEND: TflXCODE
  RNIhfiL
  OTHER
3 PLRNT
                         RRGMENTS
                                   DETRITUS

                             E, HETL:ROPODR
                             G. DIBRRNCHIRTR
                             MRLCIDRE
                             POLYDORR LI ON I
                             HflRPRCTICCID
                             N- RhERICRNR
                           fc* H. RRNEYI
      UNIDENT DETRITUS
      BRYOPHYTR
    \ HYDROZORNS
    V POLYCMRETR
i,. ^ % NEREIS SUCCINER
•///////. CRPITtl.LICRF
' SS <• C - TORQURTR
rflWiTFfnwpFr f^*"TP'^f^'^'~;Q
lijau,uju!auiUAi U-J I i\ n ซ o ui n
      B. IMPR-QVI5UG
      RMPEt.ISCR R3DITR
      C. SEPTEMSPJNOSR
                                 Figure 26

                                      142

-------
by percent weight, as spot increased in size, the amount of unidentified




material in their stomachs increased.  Frequency of occurrence (Table 51)




suggests that polychaetes are frequently eaten by most sizes of spot.




Percent number and percent weight may not adequately define the importance




of polychaetes to spot.  Mastication of polychaetes creates difficulty in




counting and polychaetes digest quickly so that their true weight is often




underestimated.  As early juvenile spot enter the SAV bed in April  (Figures




27 and 28, Table 52) planktonic feeding on calanoid copepods quickly




switched in May to epibenthic and benthic feeding on amphipods, isopods,




harpacticoid copepods, and polychaetes.  August and September spot




stomachs contained a large portion of animal fragments in their stomachs




(Figure 28) and Table 24) and indicate a large difference in prey




selectivity between October of 1978 and 1979.  Unlike October 1979, in




October 1978 swarms of Neomysis americana covered the study area.   In




1979, spot switched to preying on mysid shrimps in November instead of




October.




           Percent number, percent weight and frequency of occurrence  (Figure




29 and 30, Table 53) indicate a large reduction in consumption of calanoid




copepods as silver perch grows from 20mm. to 70ram.   Silver perch also




increase consumption of Neomysis americana from 30mm to 150mm.  Crangon




septemspinosa was also a dominant prey item by weight for 50mm to 110mm 13.




chrysoura.  Monthly changes in percent number  (Figure 31) and frequency




of occurrence  (Table 54) of prey items consumed by silver perch indicate




a gradual  shift from a predominantly calanoid copepod consumer  (August to




October to a diet of mysid shrimp by November.  However, percent weight  (Figure 32)




indicates  that C. septemspinosa is also a dominant food item from August
                                      143

-------
MONTHLY CHANCE IN THE PCNUMBER OF PREY ITEMS FOUND IN THE STOMACHS OF LEIOSTOMUS XANTHURUS
PCN'JMBER  SUM

        100 -




         90 -




         80 -
            60 -
            50 -
            40 -
            30 -
             !0 -
            10 -
                                    ~
                                     A
        r^S
        tf
                                    V
                                              EZ3

                                                    \
                            I

                                  \

                                   |
                               8  31011
                             73
                           79
                                                           10 11    MONTH

                                                           	1    YERR
      LEGEND: TRXCCDE2
      flNIMRL  FRRGMENTS
OCXX.V OTHER
c .as; 3 PLRNT DETRITUS
\^NV\VX POLYCHRETR
w^/V POLYDORR  LIGN1
/.'//. HRSPRCTICOID'
      B.  IMPROVISUS
    '4 GRMMRRIDER
      C.  PENflNTIS
                                                           UNIDENT DETRITUS
                                                           BRYOPHYTR
                                                           NEMRTQDES
                                                           E, HETL'ROPODR
                                                           OGTRRCODR
                                                     ' f j? ซ
                                                              N - RflERICRNR
                                                              CRPRELL1DRE
                                    Figure 27


                                        144

-------
MONTHLY CHANGES IN THE PCWEIGHT OF PREY ITEMS FOUND IN THE STOMACHS OF LEIOSTOMJS" XANTHURU:
P CWEIGH

   100 -



    90 -



    30 -



    70 -



    60 -
SUM
    40 H
    30 H
    !0 -J
    10 -1

                        8

                       73
                  3.10  11
                                            79


           10  11'
MONTH

YERR
   LEGEND: TRXCCDE
                    RNIMRL
                    OTHER
                    PLRNT DET
                                       R,
                    NEMRTQDES
                    E. HETEROP03R
                    CRPJ TEL. LIDRE
                    POLYDORR LIGNI
                    HRRPRCTICCID
                    B. IMPROVISUS
                    GRMMRRiDER
                    CRPRElLIDRE
       UN I DENT DETRITUS
       BRYOPHYTR
,\\\\  HYOROZORNG
=.XX^-  POLYCHRETR
& ^ *•-  NERE1G SUCCINER
///////.  MRLCIDRE
• S f .*  C -  CONVEXR
52J2ESES5S  CRLRNOID
       N-  RMERICRNR
                                                           C.  SEPTt:r.SPJNQSfl-
                                 Figure 28

                                     145

-------
                                        Table 52




FREQUENCY OF OCCURRENCE OF DOMINANT PREY ITEMS FOUND IN THE STOMACHS OF LEIOSTOMUS XANTHURUS
TAXCODE
ANIMAL FRAGMENTS
UNIDENT DETRITUS
BRYOPHYTA <
PLANT DETRITUS
HYDROZOANS
NEMATODES
POLYCHAETA
E. HETEROPODA
SYLLIDAE
NEREIS SUCCINEA
G. DIBRANCHIATA
G. SOLITARIA
CAPITELLIDAE
POLYDORA LIGNI
GASTROPODA
C. CONVEXA
PELECYPODA
OSTRACODA
HARPACTICOID
CALANOID
B. IMPROV1SUS
N. AMKH1UANA
AMPHIPODA
AMPELISCA ABDITA
GAMMARIDEA
G. MUCRONATUS
M. RAWEYI
CAPRELLIDAE
C. PENANTIS
JULY78 OCT78
.
42.7
. .
50.0
. .
59.8
19.5
.
12.2
. .
. .
14.6
• *
. .
14.6
. .
. .
42.7
96.3
53.7
. .
75.6
17.1
. .
. .
.
31-7
• •
* •
APRIL79 MAY79
38.8
. .
18.4
50.0 28.6
. ,
71.4
32.7
55.1
. .
. .
10.2
. .
12.2
22.4
. .
. .
10.2
38.8
34.7
50.0
24. b
. .
. .
. .
50.0
24.5
.
50.0
.
JUNE79 JULY79 AUG79
61.5 • 87.5
.
23.1 • 62.5
. . .
. . .
15.4 . 87.5
50.0
15.4
. . .
12.5
. . .
. . .
. . .
23-1
• • *
. . •
12.5
. . .
. . .
100
30. a
37.5
. . 12.5
. . . 12.5
. •
. . .
.
. . .
23-1
SEPT79 OCT79 NOV79
69.2
43.8 41.7
61.5
...
15-4 43.8
30.8 31.3
16.7
.
. .
. .
. . .
.
. . •
• .
...
18.8
.• * •
12.5
31.3
.
. . .
58.3
. . 16.7
...
.
.
.
.
.

-------
PERCENT NUMBER OF PREY PER SIZE CLASS OF  BAIRDIELLA CHRYSOURA
   PCNUMBER SUM

        IOC -




         90 -




         80 -




         70 -
          50 -\
          40  H
          30  4
          10

                           I *^

                20  30  40  50  60   70  SO  30 100 110  120  130 140 150
    LE&END:  TRXCODE2
      SIZE  CLRSS IN MM ISL )

      OTHER               :
      N.  RKERiCRNR        •
K m> a G-  MUCRONRTU5
:-\\\v\\ C.PENRNTIS
                                      147

                                Figure 29
QV. CRLRNQID
U IDOTER SRLTHICR
\\ .M .  RRNEYI
                                                          SEPTTKSPJNQSR

-------
PERCENT WEIGHT OF PREY PER SIZE  CLASS OF  BAIRDIELLA CHRYSOUR;

  PC WEIGHT  SUM

     .  100  H
        90 -4
        80 -A
        70 -\
        60 -J
        40 -J
        20 H
        10 -J

                      NN
1
I





           1






  LEG-END: TfiXCODE
                  30  40   50   60  70  80  30 100 1 10 120 130 140  150

                             SIZE: CL.RSS IN MM ISL )
v OTHER
J POLYCHRETR
                            IDOTEfi SflLTHICR
                            CYMROUSR COMPTR
                            G.  MUCRONflTUS
                            C.  PENRNTIS
A UN I DENT
                                       H
                            PLRNT DETRITUS
                            CRUSTRCER
                            N. RhERICRNR
                      •,V\*\: RMFHIPOCR
                      *. ^ ^ COROPHIUtl
                      ///////. M-. RRNEYI
                      '^//•.,^C. SEPTEMSPJN05R
                            ENGRRULIDRE
                            RNCHOR HITCH ILL I
                               Figure 30

                                   148

-------
                                             Table 53

FREQUENCY OP OCCURRENCE FOR DOMINANT PREY ITEMS FOUND IN THE STOMACHS OF BAIRDIELLA CHRYSOURA

	I L20=20MM LENGTH (SL)J	

       TAXCODE      L20  L30  L40  L50  L60  L70  L80  L90  L100  L110 L120 L130 L140 L150

   UNIDENT DETRITUS	19.0 22.7 23-3 13-0  26.3 16.7    .     .
   PLANT DETRITUS     .    .  11.1   .  -  .    	
   CRUSTACEA   -       .    .    .11.1	     .   .
   CALANOID          100 54-5 27.8 27.8 22.7 33.3 31.8 20.0   .21.1   .  25.0  100 100
   N. AMERICANA     50.0 54.5 61.1 55-6 68.2 71.4 77.3 93.3 95.7  94.7 83.3  100  100 100
   M. BIGELOVI        .         .    .    .    .    .    .  13.0    .....
   E. ATTENUATA       .    .    .  16.7   .    .  13.6   ....  25.0    .
   IDOTEA BALTHICA    .    .    .11.1 22.7   ...    	
   AMPHIPODA          .    .  16.7 11.1 13.6   .  13.6 13.3   .   10.5   •     •     •
   AMPITHOIDAE	50.0  .
   A. LONGIMANA       	13.6   .    .     .    ....
   CYMADUSA COMPTA  25.0   .  11.1   	
   COROPHIUM          	14.3	
   G. MUCRONATUS      .    .  22.2 11.1 22.7	•     •     .100
   M. RANEYI          .    .  11.1        .  23.8 50.0 20.0 13.0  15.8   ....
   C. PENANTIS        .    .11.1 16.7 13ซ6 19.0 31.8 33-3 13-0  10.5 16.7
   C. SEPTEMSPINOSA   .    .    .  22.2 36.4 38.1  40.9 23-3 26.1  36.8   .    '.     .
   UNIDENT. FISH	16.7
   ANCHOA MITCHILLI   .    .11.1	     .   .

-------
 MONTHLY CHANGES IN THE PERCENT NUMBER OF PREY ITEMS FOUND IN THE STOMACHS OF BAIRDIELLA CHRYSOUR

PCNUM6ER  SUM

    100-1
    90  -
     80  -
     70  -
     50
     40 -
     30 -
     20 -
     10 -
    LEGEND: TRXCODE2
                             10
11
       OTHER
CKXX; CRLRNOID
K X 2) E. <  RT.TE.NJRTR
XN\\\\\ RtfPMJPODR
i/W' G.  MUCRONRTUS
/,'//. C .  SEPT
                                       150
                                   Figure 31
                                                           y///
                                    10
11
MONTH

YERR
                        ,  CRUSTRCER
                          N .  RMERICRNR
                      xs  IDOTER BflLTHICR
                        -  CYMRDUSR tOMPTR
                          C •  PENRNTIS

-------
MONTHLY CHANGES IN THE PCWEIGHT OF PREY ITEMS FOUND IN THE STOMACHS OF BAIRDIELLA CHRYSOURA
PCWEIGHT SUM

  IOC -



   90 -



   80 -.



   70 -



   60 -



   50 -



   40 -



   30 -



   20 -



   10 -
                          10
      1 1
                      78
  LEGEND:  TRXCODE
                       ฃ X.
  UN I DENT  DETRITUS
  PLRNT  DETRITUS
  CRUSTRCER
  N-  RI1ERICRNR
:  IDOTER BRLTHICR
.  M.  RRNEYI
*t-  SEPTEMSPJNOSR
*  ENGRRULIDRE
       10
1 1
                          73
MONTH

YERR
 XXXXK OTHER
      POLYCHRETR
      CRLRNQID
      E . RTTENURTR
      G- ftUCRONRTUS
      C- -PENRNTIS
• J * * UN I DENT -  FISH
      RNCHOR  HITCHILLI
                                      Figure 32


                                        151

-------
                                                          Table 54
              FREQUENCY OF OCCURRENCE OF DOMINANT PREY ITEMS FOUND IN THE STOMACHS OF BAIRDIELLA CHRYSOURA
to
TAXCODE
:DENT DETRITUS
LNT DETRITUS
fSTACEA
,ANOID
AMERICANA
ATTENUATA
ITEA BALTHICA
'HIPODA
1ADUSA COMPTA
MUCRONATUS
RANEYI
PENANTIS
SEPTEMSPINOSA
JULY78 OCT78
23.5
. .
. .
28.7
95-7
. .
. .
11.3
. .
. .
25-2
26.1
23.5
APRIL79 MAY79 JUNE79 JULY79 AUG79 SEPT79 OCT79
. . . . . . ' •
. 17.4
. . . . . . •
44.4 19-4 17.4
55.6 67.7 26.1
17.4
... . . 34.8
. . . . . 17.4
17,4
14.8 . 34.8
. •
.21.7
14.8 16.1 52.2
NOV79
.
.
18.2
.
81.8
.
.
.
.
18.2
.
.
27.3

-------
to November.  Percent number (Figure 31) points out that as with spot,




B. chrysoura  food habits during October 1978 were more like November




1979 than October 1979.




    Syngnathus fuscus feed upon a wide variety of amphipods as well as




calanoid copepods, mysids, and polychaetes.  Percent number (Figure 33)




and frequency of occurrence (Table 55) indicate that calanoid copepods




were the dominant prey item.selected by 60-160mm pipefish.  Figure 34




illustrates that although calanoid copepods were important prey items,




Neomysis americana and several species of amphipods were more important




in terms of weight to this size range of pipefish.  All three food in-




dices indicate that 120-180mm pipefish have a diverse diet dominated by




Caprella penantis and Gamnarus mucronatus.




    Pipefish food habits were analyzed from July 1978 to November 1979




(Figures 35 and 36, Table 56).  Calanoid copepods were the most consistently




consumed prey (Figure 22 and Table 28).  All food indices showed large




variations in preferred species of amphipods.  The variations may be due




to changes in available prey sizes as well as prey density.  Pipefish




prey items of July and October of 1978 and 1979 were very different.  Unlike




October 1978, in October 1979 N. americana was not an important food item.




N. americana was an important prey item in November 1979.




    The migratory predators fed primarily on fishes, blue crab, and sand




shrimp (Figures 37 and 38, Tables 57 and 58).  Summer flounder  (P. dentatus)




under 200mm SL preyed almost exclusively on mysids and Crangon  septemspinosa.




Larger specimens preyed almost primarily on fishes  which included Leiostomus




xanthurus and Syngnathus fuscus. Spotted seatrout  (Cynoscion nebulosus)




and weakfish (C_. regalis) demonstrated similar feeding habits.  Diets were




comprised primarily of fishes (including Brevoortia tyrannus, L. xanthurus,




Anchoa mitchilli, and Mugil cephalus) and several invertebrates (Crangon






                                      153

-------
PERCENT  NUMBER OF PREY  PER  SIZE CLASS OF SYNGNATHUS FUSCU!
  PCNUMBER  SUM

       100  -I
        90 -
        80 -
        70 -
        60 -
        40 -
        30 -
        !0 -
        10 -
               60
      LEGEND:  TRXCODE2
                                   \

                                                                   1


SO   90   \QG   110  120  130  140   150   160  170  18!

         SIZE  CL.RSS IN M^ (SU

  .XXXX,  RNIMRL FRRGMENTS
  CXXXJ  CSTRRCCDR
  K X a  CRLRNQIC
  \\\\\\v.  E.  RTTENJRTR
  t-W-  EDOTER TRILOBR
  .////,  R-  LONGIMRNR
  'SSS*  G.  MUCRONRTUG
K^^ป; OTHER
U*/*J HRRPRCTICOID
A\\\ N.  RMERICRNR
-.X^N: IS30TER  BRLTHICfl
&k. ^ •*ซ RMPHIPODR
•///////. GRfir.RRICER
• * J j> C .  PENRNTIS
                                   Figure 33
                                      154

-------
                                        Table 55

  FREQUENCY OF OCCURRENCE FOR DOMINANT PREY ITEMS FOUND IN THE STOMACHS OF SYNGNATHUS FUSCUS

 	_[  L20=20MM LENGTH (SL)J	

    TAXCODE       L60   L70   L80  L90   L100 L110  L120  LI 30  L140  L150  LI 60  L1?0  L180

ANIMAL FRAGMENTS  66.7  35.7  58.8 57.7  39-4 37.5  30.4  53-3  37.5  64.7  45.5   100  75.0
UNIDENT DETRITUS    .     .     .     .     .  12.5    .......
PLANT DETRITUS      .     .     .     .     .     .      .     .   12.5    •   18.2
FORMANIFERA         .     .   23.5    .     .     .
NEREIS REMAINS      .     .     .     .     .     .      .   13.3     .....
OSTRACODA         33.3        11.8          .     .      .   13.3  12.5  17.6    .   50.0
HARPACTICOID        .     .17.6	     .
CALANOID          66.7  78.6  52.9 46.2  48.5 54.2  39-1  26.7  20.8  17.6    .
B. IMPROVISUS       .     .     .     .     .     .      .     .         11.8        25.0
N.AMERICANA        .   14.3    •  30.8  33.3 54-2  47.8  13-3  16.7  17.6
E. ATTENUATA        .     .   29.4  15-4    .     .    13.0  13-3  16.7  11.8    .
IDOTEA BALTHICA     .     .   17.6  15-4    .  16.7    .   26.7  20.8  11.8  18.2  25.0  75.0
EDOTEA TRILOBA    66.7    .   11.8    .     .     .      .     .      .
AMPHIPODA           .   28.6  58.8 30.8    .     .           .      .11.8  18.2
A. LONGIMANA      33-3    •   11.8    .     .     .    21.7  26.7  29.2  23..5  27.3  50.0  75.0
GAMMARIDEA          .   14.3  11.8 15.4  -  .     .      .   26.7  25.0    .     .   50.0
G. PALUSTRIS        .     .     .     ,.     .     .      .     .      .     .   18.2
G. MUCRONATUS     33-3    .     .  11.5    •     •    13-0  13.3  25.0  41.2*27.3   100   100
M. RANEYI           .     .     .  11.5    •     •    17.4    .   12.5  23.5    .   25.0
C. PENANTIS       33.3    •   1.1.8  11.5  18.2 16.7  21.7  60.0  50.0  64.7  81.8  50.0  75.0
P. TENUIS           .     .   23.5 11-5    .....   11.8    .     .   25.0

-------
PERCENT WEIGHT OF  PREY  PER  SIZE  CLASS OF  STNGNATHUS FUSCUS
PCW EIGHT  SUM
   i n o
   1 J u —
    90 -
    80 -
    70 -
     6n
     u —
    40 -
    30 -
    20 -
    10 -
CV
I
1
I

                         XggX
                         5500

    I
    1
    ss
    Vs
    I
I
1
                                  ^
                                  1ง

                                       oooo
                                       xxxx
                                       5555

           60   70   80
  LEG-END: TflXCODE
                             sizt CLRSS IN nn  ISD
A. RNIMRL FRRGtlENTS
 i PLRNT DETRITUS
2 NEREIS REMRINS
,\ CRLRNOID
,' E - RTTENURTR
••. RMPHIPODfl
 .- R. LONGIMRNR
     TUBERCULRTUM
      90  100   110   120  130  140  150   ISC   170  180
                      x-6!^^l M. RRNEYi
                                  OTHER
                                  POLYCHRETR
                                  OSTRRCODR
                                  N,  flMERICRNR
                                  IDOTER  5RLTHICR
                                  RMFITHOIDRE
                                  CYMRDUSR CCMC1TR
                                  GRMMRRICER
                                  G.  MUCRONRTUS
                                  C.  PENRNTIS
                                  Figure 34


                                     156

-------
MONTHLY CHANGES IN THE PCNUMBER OF PREY ITEMS FOUND IN THE STOMACHS OF SYNGNATHUS FUSCU:
  PCNUMBER SUM

           100 -



           90 -



           80 -



           70 -
           50  -
            40  -
           30  -
            !0  -
            10  -
      LEGEND:  TRXCODE2


                                             I
Z
                     %
                                                 •i^A
                               9   10   11
                            78
      RNIMRL  FRRGME'NTS
    3 G5TRRCCDR
E JE 3 CRLRNQIC
\N*:\VX E.  RTTL'NJRTR
•u^'V-EDOTER  TRILQBR
/'///. fl •  LONGIMRNR
    O G.  MUCRONRTUS
    A p •  TE:NUIS
            I
            I
                 i
                                                                  562
                      6   7    91011

                      	 79  	\
                      MONTH

                      YERR
             OTHER
             HRRPRCTICOID
       A.\\\ N-  RMERICRNR
       ^VX'V IDOTER  BRLTH-ICR
       tx. ^. •> R^PHIPODR
       •///////, GfihMRRIDER
       ' S S s C.  PENRNTIS
                                        Figure 35


                                          157

-------
MONTHLY CHANGES IN THE PCWEIGHT OF PREY ITEMS FOUND IN THE STOMACHS OF SYNGNATHUS FUSCUS
PCWEIGHT  SUM

      100  -



      90  -



      80  -



      70  -   '



      60  -



      50  -



    -  40  -



      30  -



      20  -



       10  -
              5   6
   LEGEND:  TRXCODE

                                             I
                               10   11
                        78
                                                  79
                             RNIMRL PRRGMENTS
                           ; PLRNT  DETRITUS
                      C 385: * CRLRNOID
                      ;\\\\\vs E,  RTTENJRTR
                      u'W- RMPHIPODR
                             R-  LONGIMRNR
                             G.  MUCRONRTUS
                      r ST s, C .  PENRNTIS


10  11
         MONTH

         YERR
OTHER
NEREIS REMRINS
N. RtlERICRNR
IDOTER BRLTHICR
RflPJTHOIDRE
GRMMRRIDER
M. RRNEYI
                                    Figure 36
                                        158

-------
VO
                                                     Table 56                  .       .




                 FREQUENCY OF OCCURRENCE OF DOMINANT PREY ITEMS FOUND IN THE STOMACHS OF SYNGNATHUS FUSCUS
TAXCODE
ANIMAL FRAGMENTS
FORMANIFERA
NEREIS REMAINS
OSTRACODA
HARPACTICOID
CALANOID
B. IMPROVISUS
N. AMERICANA
E. ATTENUATA
IDOTEA BALTHICA
EDOTEA TRILOBA
P. CAUDATA
AMPHIPODA
A. LONGIMANA
GAMMARIDEA
G. PALUSTRIS
G. MUCRONATUS
M. RANEYI
C. PEN ANT IS
P. TENUIS
JULY78 OCT78
25.0
. .
15.4
. .
. .
57.7 28.8
. .
82.7
. .
11.5
. .
. .
23.1
. .
11.5
15.4
11.5
30.8
50.0
. .
APRIL79 MAY79
95-5
. .
. .
31 .8
. .
. .
18.2
. .
. .
. .
. .
. .
. .
27.3
31.8
. .
90.9
13.6
86.4
. .
JUNE79
48.0
.
..
.
.
52.0
.
•
.
36.0
.
.
.
16.0
36.0
.
44.0
.
56.0
.
JULY79 AUG79 SEPT79
14.3 • 73-0
. . .
. • .
21.6
10.8
92.9 . 37.8
. .
. . .
37.8-
14.3 • 32.4
.
. . .ซ
21.6
40.5
18.9
. .
. . .
. . .
. 45-9
24-3
OCT79
78.9
10.5
.
10.5
.
42.1
.
.
47.4
26.3
15.8
10.5
52.6
10.5
.
.
.
.
.
21.1
NOV79
50.0
.
.
.
.
25.0
.
50.0
.

.
.
30.0
.
.
.
.
.
.
.

-------
     PERCENT NUMBER OF PREY ITEMS FOUND IN THE STOMACHS OF MEGAPREDATORS
PCNJMBFR  SUM
      100  -I
      SO
      60  -
       40  -
       20  H
              0
              E.
              N
              T
              R
R
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                   S
                         I
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                              M
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0
C
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L
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                          i
                          C
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                          N
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                                    R
                                    T
                                                             R
                                                             Y
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  LEG-END:  TRXCODE2
                                      DREDRTOR
            OTHER
            RUPPIR  rfiRIT
            N.  RMERICRNR
            DECRPODR
                           . \N
               SEPTEMSPINQSR
               SRD!DUG-HRRD
      C
      C
      C. SRDIDUS-SOFT
      FISH  F.CC-S
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      S, FUSCUS
      L . XRNTHURUG
                       ,vv\N \
                       ,.V\ X
                       ^. ^.  ^
                                  ZOSTLRR
                                                    /'/
                         •////.
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                                                                   iS
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                                                                         •ER
                                                           UN I DENT - F ISt
                                                           B. TYRRNNUS
                                                           RTHERINOICE:I
                                                    ,XXX, SCIRENIDRE
                                 ' //• ,/7 ,<
                                 fmTtnmwfr'
                                 :,iLlUi.najJ4i4,U
                                   Figure 37


                                       160

-------
     PERCENT WEIGHT OF PREY ITEMS FOUND IN THE STOMACHS OF MEGAPREDATCRS
p r LI c T n u T c : i M
i L. HL i on .  oUn
     i no
     i J u —
      40  -
              D
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              N
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                       XXX, MDGIL  CEPMRLu'G
                                   •Figure 38
                                       161

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                                                                       Table 57
                                                                Dominant Megapredators
Carcharhinus Pomatomus
mtlberti
Food Item
Plant detritus
Zostera marina
Ruppia maritima
.Invertebrates
Gastropoda
Crepidula convexa
Nassarius obsoletus
Retusa canaliculate
Pelecypoda
Squilla empusa
Neoraysis americana
% Wt
1.4
trace
0.5
trace
0.1
trace
0.2
% Occ
32.2
5.0
1.5
0.5
0.5
0.5
0.5
(199) saltatrix (63)
% N % Wt % Occ % N
trace 3.2 ' 1.4
14.7
2.3
0.7
0.2
0.2
0.2
0.2
Cynoscion Paralichthys
regalis (26) dentatus (24)
% Wt % Occ % N % Wt
0.8
trace
trace
15.7
% Occ
16.7
4.2
4.2
58.3
% N
0.1
trace
trace
99.2
Cynoscion
nebulosus (20)
% Wt % Occ • % N
0.2 10 3.2
Isopoda
Amphidpoda
Decapoda
Paleomonetes vulgaris
Crangon septemspinosa
Callinectes sapidus
C, sapidus - hard
ฃ. sapidus - paper
(^. sapidus - soft
Ovalipes ocellatus
Libinia dubia
Fishes
Anguilla rostrata
Brevoortia tyrannus
Engraulidae
Anchoa mltchilli
Opsanus tau
Rissola marginata
Fundulus majalis
Atherinidae
Syngnqthus fuscus
Sciaenidae
Cynoscion regalis
Leiostonus xanthurus
Mugil cephalus
Blenniidae
Hypsoblenitius hentzi
Trinectes maculatus
Paralichthys dentatus
Unid. Fish
Animal fragments
0.1 .
trace
0.1
5.6
11.0
6.0
43.3
0.1
0.8
0.3
3.6
0.1
0.2
0.2
1.5
2.0
0.5
2.5
9.5
9.5
5.5
56.8
0.5
2.0
1.0
2.5
1.0
0.5
1.0
0.5
0.9
0.2
1.0
6.5
5.6
3.3
38.6
0.5
0.9.
0.5
1.2
0.7
0.2
• 0.5
0.2
                          trace

                           0.1
                           0.1
                           0.1.
                            1.6

                            4.8
                            1.6
                            1.6
                           0.7

                          27.1
                           5.0
                           0.7
trace

 3.9
 0.6
 3.8

30.8
11.5
 0.9

31.6
 2.6
trace
trace

  5.0
 4.2
 4.2

41.7
                                                                                            trace
                                                                                            trace
                  0.5
41.5     10
trace    10
                          59.3     41.3   24.3
                          trace     1.6    0.7
 0.1
 0.2

 2.4
 4.0
 0.1
 2.3

10.3
trace
 1.0
 1.5

 0.5
 6.4
 0.5
 2.0

28.1
 0.5
 0.5
 0.7

 0.2
 3.0
                 0.2
14.0
 0.2
                           0.1
                           5.9
                          12.3
                                    3.2     5.0
                    6.3    4.3
                    4.8    2.1
          21.9     34.9   23.6
30.3

 1.4



 0.3



46.3





16.0
23.1   13.7

26.9   18.8



 3.8    0.8



19.2   22.2





19.2    5.1
                                                                                                        0.3
                                                                                                        2.3
           1.0     4.2   trace
          46.4    16.7     0.1
                                                              30.6      4.2    trace
                                     6.8
                                    32.1
                                     1.4
                                    13.6
3.2
7.9
                                                                                                                       1.6
                                                                                                                  5     14.3
                                    25
                                     5
                                                                                                  5
                                                                                                65
                                 11.1
                                  1.6
                                           1.6
                                          47.6

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                                                                 Table 58

                                                        Occasional Megapredators
      Food Item
    Tylosurus
    acus (7),
% Wt % Occ  % N
   Strongylura
   marina (2)
% Wt % Occ  % N
    Dasyatis
    sayi (2)
% Wt % Occ  % N
    Iforone             Sciaenops         Rachycentron
    saxatilis (2)       ocellata (2)      canadum (1)
% Wt % Occ  % N    % Wt % Occ  Z  N    % Wt % Occ % N
Zoster a marina
Ruppia maritima
Mya arenaria
Decapoda
Crangon septemspinosa
Callinectes sapIdus
C_. sapidus - hard
Fishes
Syngnathus fuscus
Leiostomus xanthurus
Unid. Fish
Fish Eggs
                                      100   100   100
 9.1 14.3   7.7


8a.8 71.4  76.9.

 0.3 14.3   7.7
24.3  50   85.7
                   75.7  50   14.3
                                                                             0.1    50    7.1
                                                                           trace    50    7.1
                   19.3  100  66.7      0.4   100   35.7

                                      99.5   100   50.0




                   80.7  100  33.3
                                                                                              100    100  100

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septemspinosa, Palaemonetes vulgaris, and Callinectes sapidus).  The




dominant migratory predator after May was the sandbar shark (Carcharhinus




milberti) for which the dominant food item was clearly soft shell blue




crab.  A wide variety of fishes were also consumed.  Ponatomus saltatrix,




fed almost exclusively on fish.  The dominant prey species was Brevoo.itia




tyrannus  (59.3% by weight).  The portion of the stomachs of ฃ. mllberti,




P. dentatus, C. ."ebulosus, and P_. saltatrix contained fragments of Zoster a




marina  or Ruppia maritima.  This indicates that these species were feeding




in the SAV bed.




Feeding periodicity and daily ration




  . MFceding periodicity was determined for spot, silver perch, and pipefish.




The geometric means  (+ one standard error) of the percent dry body weight  .




found in  the gastrointestional tracts of six fish captured every three to




four hours over a twenty-four hour period were plotted against time




(Figure 26, 27 and 28).  Spot and pipefish fed during daylight hours in-




dicating  that they are sight feeders.  Silver perch  is predominantly a




nocturnal feeder.  It's dominant food items  (Neomysis americana and Crangon




septemspinosa) were most abundant in the SAV area after sunset.




    The daily ration of spot and pipefish were estimated by the evacuation




method of Peters and Kjelson  (1975).  The ingestion  rate may be determined




from stomach or gastrointestinal evacuation rate, because the  average




ingestion rate must  equal  the rate at which material leaves, whether by




assimilation or  expulsion  (Bajkov, 1935).  Evacuation rates for pipefish




fed a single meal of juvenile amphipods were obtained in the  laboratory at




17ฐ, 22ฐ, and 27ฐ.   Regression analysis on the data  yielded rate constants




which were used  to calculate  instantaneous evacuation rates.   The  feeding




periodicity  (figures  39,  40,  and 41) determined  the  quantities of  food
                                       164

-------
    7-
    6-
52
u


s
o
CD


I
u
o
a:
UJ
a.
    5-
4-1
          LEIOSTOMUS XANTHURUS


               Mean Size = 75 mm(SL)

              Size Ranges 58-92mm
3-
               0400
                     0800       1200      1600


                          TIME  OF DAY
2000
2400
                            Figure 39


                              165

-------
'::•:   U"




    10-



o


g  9-




6  8-


z



K  "


O

UJ  fij
Q

O
CD



cr
Q
u
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                                   BAIRDIELLA  CHRYSOURA
              Mean Size = 35mm (SL)

             Size Range =24 -50 mm
                    B.
 Mean Size = 71 mm (SL)

Size Range = 59-96mm
                           T
                                       T
                           T
               0400
                           0800       1200       1600



                                 TIME  OF  DAY
                                    2000
                                                                     2400
                             Figure 40



                                166

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   4.0-1
   3.5H
o
X

S2
ui
o
o
CD
   3.0 H
   2.5 =
   2.0-
UJ
O
tr
LJ
a.

ฑ   1.5-
    1.0
         SYNGNATHUS FUSCUS

          Mean Size = 135mm (SL)

         Size Range = 83- 208 mm
                0400      0800       1200       1600


                                 TIME OF  DAY
2000
2400
                              Figure 41


                               167

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present in the guts of selected species at 4 hour intervals throughout a


24 hour cycle.  Instantaneous evacuation rates were calculated for each


of the 4 hour intervals by the following equation




                       ^ฃ = 2.303BC         where
                       dt

B = evacuation rate constant and


C = content of gastrointestinal tract +1.


Summing the evacuation during each of these periods produced an estimate


of total evacuation of daily ration.  The evacuation rate constant (B)


for pipefish at 22ฐ was  .032.  The daily ration for pipefish was 4.4% dry


body weight per day at 22ฐC.  A graduate student at VIMS is utilizing


this information to construct a model that will describe the effects of


pipefish predation on the epifauna of the SAV bed.  The evacuation rate


of juvenile spot at 22ฐC has been reported to be .033 (Peters et al, 1974).


Using this information and figure 26 our estimate of daily ration for


juvenile spot at 22ฐC was 7.7% dry body weight per day.  We are still in


the process of determining evacuation rates for silver perch.


    Feeding periodicity  for JP. saltatrix and (3. regalis are illustrated in


figures 42, 43A, and 43B.  These figures are composites of one and a half


years of gill net data.  Weakfish  (ฃ. regalis) appeared to utilize the SAV


bed from dusk to dawn  (figure 42).  The dashed line indicates that during


this time  they were feeding.  Maximum feeding occurred around dawn.  Bluefish


exhibited  different feeding  patterns in the sand area and SAV bed  (figure


43A and 43B).  On  the  sand bar, bluefish were typically schooling and eating


menhaden.  Bluefish were captured  during mid-day and their stomachs were


also fullest  at  this  time.   In the  SAV bed bluefish were captured alone or


in small groups.   They were  twilight feeders with  the main feeding -peak


at dawn.
                                       168

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PLOT OF CflTCH PER  UNIT EFFORT FIND ftVEPfiGE WEIGHT PER STOMfiCH DF
C. REGRLIS CAPTURED IN THE EELGRRSS BEDS VERSUS TIME
PLOT DF ftVEUIT*TIME
PLOT OF CftTCHปTIME

RVEWT  I
 2.25
SYMBOL USED IS *
SYMBOL USED IS ซ•
 2.00
 1.75
 1.50
 1.25
 1.00
 0.75
 0.50 •ป•
 0.25 •ป•
 0.00
                   *
                   i N
                                     .CftTCH
                                       0.36
                                                             0.33
                                       0.30
                                                             0.27
                                                             0.24
                                                             0.21
                                                            0.18
                                       0.15
                                                            0.12
                                                            '0.09
                                                            0.06
                                                            0.03
                                                            0.00
                                                      22
                               Figure 42
                                  169

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PLOT OF CRTCH PER EFFORT  RND RVERR6E UIEI6HT PER STOMHCH W f.  J>ru-ipiKi
CRPTURED IN THE EELGRRSS  BED

PLOT OF RVEtJTVriME   SYMBOL USED IS ซ     ซ     ซ
PLOT OF CRTCH^TIME   SYMBOL USED IS *-	-*—	*
RVEUT  !

 0.0
                                                        0.05
                          TIME
                        Figure 43A                  — -

 PLOT OF CRTCH  PER EFFORT RMD RVERRGE UT. PER STOMRCH OF P.  SRLTRTRIX
 IN THE SfiND  RRER
 PLOT OF RVEU)T*TIME  SYMBOL USED IS
 PLOT OF CRTCH^TIME  SYMBOL USED IS
 RVEWT
                            TIME

                          Figure 43B
                             170
CRTCH
 0.7
                                                           0.6


                                                           0.5


                                                           0.4


                                                           0.3


                                                           0.2


                                                           0.1,
                                                             >



                                                           :  5

-------
    Feeding periodicity and catch per gill net pull for the sand bar shark




in July of 1980 is shown in figure 44.  The solid line (catch/effort)




indicates that the main increase of sharks in the SAV bed occurred from




dusk to 4 am.  The dashed line in the figure is a feeding .model described




by Lane et al., (1979).  The model indicates that feeding started at




10 pm and continued until 1 pm the following day.  As.the ingestion rate




started to plateau around 8 am catch per effort of sand bar shark dropped




quickly.  It therefore appears that sand bar sharks enter the SAV




beds to feed and leave the area as they become satiated.  The feeding model




estimated daily ration for a typical 1800 g (wet wt.) shark in July 1980



at a water temperature of 27ฐ as 10.5 grams dry weight per day



Predator-prey experiments




    Laboratory experiments were conducted to determine the effect of




artificial Zostera marina on predator-prey relationships of migratory




predators and resident fishes.  The migratory predators were the weakfish




(ฃ. regalis) and summer flounder (P. dentatus).  The two resident prey




species chosen for the experiments were spot (L. xanthurus) and the




Atlantic silverside (Menidia menidia).  Salinity varied between 16 and




20% while water temperature was maintained at 22+ 2ฐC over the duration




of the experiments.



    Figure 45 illustrates the number of prey consumed in each of the three




replicates of five vegetative substrate treatments.  The average number of




prey consumed over each of these treatments is shown in Table 59.




Flounder consumed all 12 silversides  in each replicate of the bare sand,




average density vegetation, and high density vegetation experiments.  In the




increased complexity  treatment, flounder consumed an average of 11 silversides,
                                      171

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Figure 44.  Feeding periodicity of Carcharhinus milbert.  Circles are
            arithmetic mean (+ one standard error) of dry weight of
            stomach contents of C_. milberti.  The number beside each
            mean is the number stomachs represented by the mean.
                                       172

-------
4.0 T
               T 10.0
        Carcharhinus milberti
           	Feeding Model

               Catch/Effort
                                                                o
                                                                o
                                                         --5.0  -
                                                                i

                                  12
16
20
                              Timt
                           173

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                        EXPERIMENTAL  RESULTS
                                                                 WtAKFISH
                                                                    VS.
                                                                  SPOT
   O —
                                                                 FLOUNDER
                                                                    VS.
                                                                   SPOT
O
u
z
3
V)
O
u
O -
    N _
                     T      T
                                                       _L
                                                                 WCAKFISH
                                                                    VS.
                                                                SILVERS1DES
    O -
                                                       J
    to-
                                                             FLOUNDER
                                                                 VS.
                                                            SILVERSIDES
    O —
                    \'    '     'H'     '   '1A'
                    VEGETATIVE TREATMENT
                                                        '1C'

-------
                               Table 59

                       Average Number Prey Consumed
Prey
Menidia
menidia
Leiostomus
xanthurus

Treatment
Predator N A H IA 1C
Cyno scion
regalis 12 11.3 11.3 97 8.7
Paralichthys
dentatus 12 12 12 10 11
Cyno scion
regalis 12 10.7 10 8 6
Paralichthys
dentatus 6 9.3 10 8 9

Numbers represent average for 3 replicates

N  = no artificial grass
A  = average density, 1m, 875 blades/m2, 7.5% area covered
H  = high density, 1 m2, 1750 blades/m2, 7.5% area covered
LA = increased area, 3 m2, 1450 blades/m2, 22% area covered
1C = increased complexity, 3-1 m2 evenly spaced, 1450 blades/m2, 22% area
     covered
                                  175

-------
The lowest average (10) captured over the three replicates occurred in the

increased area treatment.  Weakfish consumed all silversides in all three

replicates of the bare sand substrate experiments.  In both the average

and high density experiments weakfish consumed all prey in two replicates

and ten in the other.  Eight, nine and twelve silversides were consumed

over the increased area vegetated substrate.  At least two M. mendia

survived in each replicate of the increased complexity treatment.  This

vegetative arrangement also yielded the lowest average number of prey

consumed, 8.66.

    An average of six spot were consumed by summer flounder in the non-

vegetated treatment.  This was the lowest average of spot consumed for any treatment.

The average number of spot consumed for average density and high density

vegetation increased area and increased complexity treatments were 9.3,

10, 8, and 9.  Weakfish consumed all spot in each replicate of the non-

vegetated treatment.  In both IA and 1C no replicate exceeded 9 prey con-

sumed; the average number of spot consumed were 8 and 6, respectively.  The

average number of spot consumed was 10.6 for the average density treatment

and 10 for the high density treatment, both of which contained at least one

replicate in which all 12 prey were consumed.

    Figure 46 shows the general trend in percentage of prey survival

versus percentage vegetative cover.  Weakfish captured progressively

fewer prey, of both species, as the amount  (% area) of artificial grass

increased.  The  trend  is most pronounced in the weakfish vs. spot experi-

ments where the  percentage of prey surviving rises from zero for non-

vegetated to 15  for 7% covered to 40 for 22?0 covered.  A similar, but  less

pronounced trend is evident with flounder vs. silversides.  Here, percentage

prey survival rises from zero at both 0 and 7% vegetative cover  to  12%

survival at the  227, area covered treatment.  For  the flounder vs. spot

experiments the  trend  is reversed.  A greater percentage of prey survived

in the rion-vegetated than at either of the vegetated treatments.
                                      176

-------
                  PREY  REMAINING vs. % VEGETATIVE  COVER
    5OT
z

z

<
2
UJ
(T
UJ
cc
a
                                        PREDATOR-PREY


                                         W= WEAKFISH

                                         F= FLOUNDER

                                         M= MENlDlA

                                         SrSPOT
                                                    WVSS
                       VEGETATIVE  COVER
                           Figure 46
                              177

-------
    The median test, a nonparametric procedure was employed for statistical


examination of data.  The null hypothesis (HQ) states there is no difference,


among the treatments, in the median number of prey consumed.  Table 60


summarizes the results of the median test for the four predator-prey


combinations.  Test results indicate HQ is rejected (p=0.95) for the weak-


fish vs. spot experiments.  Statistical analysis can not, legitimately,


be employed to isolate differences between specific treatments (Conover, 1971),


However, visual inspection of illustrated data (figure 31) revealed most


apparent differences occur between the non-vegetated and increased area
                                                   t

treatments and the non-vegetated and increased complexity treatments.  No


significant differences, at alpha =0.05 or alpha - 0.10, occur among


treatments for the other predator-prey combinations.  The calculated value,


7.49, for the weakfish vs. silverside experiments falls just below the


alpha =0.10 critical value of 7.779.  Again, visually, most apparent


differences"here occur between the non-vegetated and the increased complexity


treatments.  These experiments were part of a VIMS graduate student's


Masters Thesis entitled "Fish predator-prey interactions in areas of


submerged aquatic vegetation."


Respiration measurements


    Figure 47 illustrates the routine respiration of the silver perch,


Bairdiella chrysoura.  The routine respiration of 300 silver perch were


measured in flow through respiration chambers.  These measurements are part


of a VIMS graduate student's dissertation thesis on the bioenergetics of


Bairdiella chrysoura.
                                      178

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                                  Table 60


                         Predator - Prey Experiments


                             Median Test Results
Critical value at a
Calculated gA8 7>7g
Predators vs. Prey Statistic a_ Q.05 d= 0.10
Paralichthys dentatus
Cyno scion regalis vs.
Paralichthys dentatus
Cyno scion regalis vs .
vs. Menidia menidia
Menidia menidia
vs. Leiostomus xanthurus
Leiostomus xanthurus

6.64
7.49
4.24
10.27
NS ' NS
NS NS
NS . NS
* *
•i
  indicates median number of prey consumed differed significantly among
  regetative treatments


NS - not significant
                                      179

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ROUTINE  RESPIRATION OF  BAIRDIELLA  CHRYSOURA
RESP
6.690075 A
 3.345037
        30
                                                         22
                                                     WEIGHT
                 TEMF
1 1-
          LOG(RESPIRATION)=(TEMPERATURE*.03130) + (LOG(WEIGHT)*.85337)-1.2802
              COEFFICIENT OF DETERMINATION = .92 SIGNIFICANCE LEVEL = .001
       TEMP-TEMPERATURE (C), RESP=RESPlRATION MG 02/G/HR,WEIGHT=WET WEIGHT (G)
                          Figure 47
                              180

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                                DISCUSSION









          The trends in distribution and abundance of migratory predators




and resident fishes recorded in the present study generally show agreement




with other studies in shallow-water habitats in the lower Chesapeake Bay (Orth




and Heck, 1980).       Migratory predators occurred sporadically with the




exception of the sand bar shark, J2. milberti. which was consistently abundant




from June through October.  Although gill nets are selective (Hamley, 1975),




the catch in this study appeared to give an estimate of relative abundance




of most species with the probable exception of the rays Rhinoptera bonasus




and Dasyatis sayi.and the summer floundei; Paralichthvs dentatus.  Of the




three gill net mesh sizes employed to capture migratory predators, 12.7 cm




and 8.8 cm stretched mesh gill nets were most effective.  However, 17.8 cm




mesh gill nets entangled rays to a greater extent than did the other




two mesh size gill nets.  Although the nets foul visibly with jellyfish,




large ctenophores, and drifting aquatic vegetation due to current flow,




the catch is not markedly greater at night when visual detection would be




less effective.  This may be due to the low water clarity during most




months.  Fifty-two to fifty-seven percent of the bluefish, sandbar shark,




and spotted sea trout catch were captured at night.  Seventy-seven




percent of the weakfish captured were taken at night.  This contrasts with




Pristas and Trent (1977), who found 93% of the most abundant species




taken at night in gill nets.




          Availability of most species arises from populations moving




through the area or coming from adjacent deep water areas.  Temporal




analysis indicates that ฃ. milberti, ^. saltatrix, and jC. regalis start
                                      181

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to move into the shallow areas in the afternoon.  ฃ. milberti and ฃ.




regalis were most abundant around midnight while P^. saltatrix left the




area after twilight.  These megapredators were also captured in greater




numbers on flooding tide stages than ebbing tide stages.  Sandbar shark,




spotted sea trout, and weakfish were captured primarily in the vegetated



areas while bluefish were captured in the sand area.  Feeding periodicity




indicated that  bluefish, weakfish and sandbar sharks entered the vegetated




area with very little material in * their stomachs and left the eelgrass bed




after feeding.  Weakfish were twilight feeders with maximum feeding




occurcingat dawn.  Two other sea trouts (C_. nebulosus and C_. arenarius)



have been found to possess a tapetum lucidum or reflective layer in their eyes




which increases dim-light vision (Arnott et al, 1970).  This adaptation




would give C^. regalis a great advantage when feeding at twilight periods.




Sandbar sharks fed from midnight to midmorning.  Bluefish exhibited




two feeding strategies; twilight feeding in the vegetated area and mid-




morning  to late afternoon feeding in the sand area.  In the vegetated




area bluefish were found in small groups  but on the sandbar bluefish




were in larger schools typically preying on menhaden.  Bluefish are predators




that use vision as a primary sense in feeding  (Olla et al, 1970).  It has




been demonstrated that cone movements of the retina of young bluefish




Cwhich are related to light-dark adaptation) may be under internal control




(Olla and Marchioni, 1968).  Through internal  control, the retina might




be predisposed to the coming of light or dark.  This preconditioning




would effectively lessen the time for the eyes  of  the bluefish to adapt




to the change in light and represent   a significant adaptation for a




predator which is highly active during morning  twilight  (Olla, 1972).




Since bluefish and weakfish hunt by sight one would also expect feeding




from mid morning to late afternoon when light  intensities permit the





                                     182

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highest visual acuity.  However, schooling by prey that would enhance a




confusion effect on the predator should be most effective under bright




light.  This may explain why schooling fishes appear relatively safe




from predators during most of the day (Hobson 1968).  Observations of




tropical reefs have indicated that small fishes (especially schooling




fishes) are most vulnearble at twilight periods (Hobson, 1979).  As light




diminished at twilight, the schools fall into disarray.  The eye




adaptations of bluefish and weakfish allow prey capture to reach maximum




efficiency during this time of day as seen in bluefish and weakfish feeding




periodicity data.  The highly streamlined and deeply forked tail-fins




of bluefish indicate that they are built for high speed chase and capture




of prey.  They are known to charge schools of menhaden, killing many




more than can possibly be eaten (Hildebrand and Schroeder, 1928).  This




type of feeding by bluefish has been witnessed in the sand area at the




Vaucluse Shore site.  The bluefish may be disrupting the school of men-




 Jiaden by chasing it from deep water on the abrupt shallow sand bar




surrounding the eelgrass bed.  If disruption of the school occurs one




would expect that individual menhaden could be captured with maximum




efficiency when light intensity is highest typically from midmorning to




late afternoon.  This may explain why there were two feeding strategies




exhibited by bluefish in the SAV study area.




           The occurrence of plant detritus and Zostera and/or Ruppia




fragments in the stomachs of ฃ. milberti, ฃ. saltatrix, P. dentatus, and




ฃ. nebulosus indicated that these migratory predators were feeding in the




SAV bed.  Spot was heavily preyed upon by ฃ. regalis and ฃ. dentatus.




A daily ration of 10.5g  (dry wt.) per day was calculated for the sandbar




shark in July 1980 when the average water temperature was 27ฐC.  The




diet of the sandbar shark was 66% blue crab of which 43.370 was soft shell
                                      183

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crab; 6% was paper shell crab; and 16J70was hard shell crab.  These crab




molt stages were distinct in the shark stomachs because the shells of




hard shell crabs were  compressed and shattered but remained thick in the




stomachs.  Through even late stages of digestion, hard shell blue crabs




were discernable from the soft and very thin shells i.pf recently molted




blue crabs.  Premolting blue crabs are by weight 67% water while postmolt




blue crabs are 86% water (Lewis and Haefner, 1976).  The resident




fishes averaged 79% water by weight.  If one converts the daily ration of




^. milberti to wet weight it becomes 3.3% body weight per day.  This figure




may be low due to regurgitation while the sharks were in the gill nets.




          The impact of predation by sandbar shark on blue crabs is significant.




In July 1980, the relative abundance estimate for the sandbar shark in the




SAV bed was 105.  Density estimates in July 1979 (Orth, this manuscript) for




blue ,crab indicated that the bed contained  9394g dry wt of blue crab.




This implies that every day,  7.7% of the blue crab biomass of the SAV bed




is consumed by sandbar sharks.  Orth has stated that his density estimates




are probably not accurate for crabs larger than 60 mm.  The sharks




ate crabs that ranged from 35mm to 115 mm and averaged 60 mm carapace width.




One must also realize  that gill nets did not capture every shark in the




SAV bed.  The daily ration calculated for the sandbar shark is not




unreasonable when compared to daily rations of large piscivorous teleosts




(Gerking, 1978).  The sharks leave  the SAV area with full stomachs and




enter the bed with their stomachs empty.  Since ฃ. milberti were found to




be very mobile in tagging experiments, sand bar sharks which feed and pass through




the study area may be a significant loss of energy  from the SAV system.




          Resident fishes were sampled with a haul  seine, otter trawl, and




push net.  The nekton push net was  the least successful in capturing resident
                                      184

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fishes.  Kriete and Loesch (1980) utilized this gear in the channels




of major tributaries of the Chesapeake Bay.  It appears that in shallow




areas, this gear is not suitable for sampling pelagic fishes.  The differences




between haul seine and trawl collections indicate the selectivity of each




gear.  The haul seine stressed the importance of pelagic species (B.




tyrannus, A. mitchilli, M. menidia. and M. martinica) with the numerical




dominant being A. mitchilli.  The numerical dominants, of the trawl




survey were spot (L. xanthurus), silver perch QJ. chrysoura). and pipefish




(ฃ. fuscus).  The 16 foot otter trawl was towed behind an outboard vessel




which fishes effectively only one meter off the bottom; thus both avoidance




and fishing of the net below the depth of occurrence of pelagic species




suggests that their relative abundance was underestimated.  Gear comparisons




by simultaneous haul seine and trawl collections indicated that juvenile




spot and silver perch effectively avoided the haul seine.  To accurately




sample both benthic and pelagic fishes in shallow SAV areas, a multiple




gear approach is necessary.




           Adams (1976a) showed dominance of pinfish (Lagodon rhomboides) and




pigfish (Orthopristes chrysoptera) in North Carolina eelgrass beds.  In the




present study, these species were seen in very low numbers in the 1980




trawl catch.  Spot and silver perch were recruited to Adams (1976a) eelgrass




bed approximately 2 months earlier than they entered the Vaucluse Shore study




area.  With the exception of A. mitchilli Adams  (1976a) drop net density




estimates  (per species) in North Carolina eelgrass beds were higher than




either the haul seine or trawl density estimates in the study area.




           Within the assemblage of resident fishes, two subgroups are apparent.




The first is comprised of the pelagic and/or schooling group ("pelagic residents")




including B. tyrannus, A. mitchilli, M. martinica, and M. menidia.
                                      185

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Adams  Q-976a) did not consider these  species as true residents of the bed.




Although  the  same is probably true  in the present study for all four




of  the above  species, they are considered with the residents  in terms of




ecological  impact upon  the ecosystem  due to their relatively high  biomass




in  the vegetated areas.   In  the  night collections these  species were




taken  in  all  three  habitats  without clear trends  in abundance.  Comparing




day and night haul seine collections  the abundance of ji. tyrannus showed




no trend,  ty.  martinica and _A. mitchilli were typically taken in low




abundance during the day and high abundance during the



night.  The other atherinid, M. menidia, however,showed an opposite pattern.




No M. menidia were captured  at night  except in March and April when




Membras densities were low.  In the day collections Menidia was common.   Trawl




collections indicated that _A. mitchilli was more abundant at night than




during  the day.




          The second group of resident fishes ("true residents") was




dominated by spot (L. xanthurus), pipefish (ง.- fuscus), and silver perch




(J5. chrysoura). Members of this component of the resident fish group were




captured most frequently in  the vegetated areas.  Day-night sampling by




haul seine and trawl suggested that spot and silver perch are more a abundant at




night.  Haul seine collections indicated that pipefish were abundant




during  the day while trawl samples  suggest that pipefish are more abundant




at night.  Orth and Heck  (1980) observed increased catch of spot in all




habitats  at night as observed in the  present study.  It remains to be




determined, however, whether the increases at night are due to increased




daytime avoidance or to actual movements to the bed from other areas.
                                      186

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In general the hiomass reported in the presjent study for the seyen majqr


species falls within the range of total fish-biomass for Zostera marina beds


in New England by Nixon and Oviatt (1972) but is less than that reported in


.studies to the south (North Carolina, Adams 1976 a; Texas, Hoese and


Jones 1963).


          Feeding periodicity collections determined that spot and


pipefish feed during daylight hours indicating that they are sight feeders.


However, Peters and Kjelson (1975) reported that juvenile spot fed continuously.


Silver perch is predominantly a nocturnal feeder.  Adams (1976) also


found that silver perch fed during the night.    Like the weakfish, silver


perch also has an unusual tapetum lucidum (a reflecting layer) in it's eyes


which increases dim-light vision (Arnott et al, 197Q).  The daily ration

     o
at 22  C for spot and pipefish were 7.7% and 4.4% body weight per day,


respectively.  Peters and Kjelson (1975) estimated a daily ration at


29ฐ C for spot as 10.1% body weight per day.


          Feeding relationships of fishes within the Vaucluse Shores


study site are generally similar to those of dominant species observed


in other studies in vegetated habitats (Carr and Adams 1973; Adams 1976c).


The lack of the dominant species from North Carolina (Lagodon rhomboides


and Orthopristis chrysoptera), however, may alter the feeding behavior of


L^. xanthurus  through availability of other food sources.  Although      .


plant material and detritus occur frequently gravimetric data suggests


that they are less important in the diet than in North Carolina Zostera beds


(Adams 1976c).  Spot are initially planktivorous, after which they switch


to predominantly benthic feeding (Kjelson et al, 1974; Sheridan 1978).


In the present study, spot collected in April were planktivorous, but


this shift in feeding strategy is not clearly seen in the feeding analysis


of different sizes of spot.  This may be due to the small number of


15-25 mm spot analyzed in April.  Cathy Meyer is conducting a more indepth




                                     187

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study of feeding of early juvenile spot and her results will be sent to




EPA later this year.  Spot exhibited benthic feeding on ostracods,




harpacticoid copepods and,..:    nematods as well as planktonic feeding




on mysids.  The importance of mysids in the diet are likely evidence of




high availability, since L. xanthurus has a subterminal mouth primarily




adapted   to feeding on infauna and benthic organisms  (Chao and Musick 1976).




Bairdiella chrysoura immigrates to the vegetated areas in Aguust.  This




species has a terminal mouth and is adapted for pelagic feeding, although




some epibenthic feeding takes place.  Most feeding studies of this species




(summarized in Chao and Musick, 1976) show fish, mysids, and decapod




shrimp to be the predominant dietary items.  Adams (1976c), by contrast,




observed no mysids in the diet of this species in North Carolina eelgrass




beds.  A clear ontogenic switch from consumption of calanoid copepods by




20 mm to 70 mm silver perch to consumption of predominantly mysids by




30 mm to 150 mm ^. chrysoura^ was noted.  Pipefish (S. fuscus) was the major epi-




faunal predator of the SAV bed.  However, as observed by Adams (1976c),




planktonic food items such as calanoid copepods and mysids were as important




as epifaunal components in the pipefish diet.




          Predator-prey experiments indicated a general trend of reduced




predator success with increasing artificial eelgrass density.  The three




dominant resident fishes appear to rely more upon planktonic and benthic




food sources than prey specific to the SAV bed.  The planktonic food




items were typically as abundant or more abundant in the adjacent sand




area.   (Unfortunately no meiofaunal comparisons between habitats were




analyzed to compare densities of spot's benthic prey items).  It therefore appears




that the major attraction of the SAV bed to the resident fishes  (at




least pipefish and  silver perch) is the protection from major predators




offered by the bed.







                                     188

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                           Summary



          A major objective of the SAV research component



relating to higher level consumer.interactions.was the



qualitative and quantitative definition of the community



of resident and migratory biota utilizing the SAV area.



To accomplish this objective  a drop net,nekton pushnet,



otter trawl> haul seine, ichthyoplankton and zooplankton



pushnet, and three different mesh size gill?nets were tested



to determine the most efficient sampling gears to monitor



shallow water nekton, zooplankton and ichthyoplankton



communities.  The ichthyoplankton and zooplankton pushnet



was an effective method to collect zooplankton and ichthyoplankton



in the SAV area.  The sampling of resident fishes required an



enclosing gear such as a haul seine to capture pelagic



species as well as an otter trawl for benthic species that



escaped under the haul seine as it was lifted by the eelgrass



in the pursing operation.  Megapredators were sampled



effectively with 3%" and 5%" stretch mesh gill nets.  A



thorough, description of seasonal changes in SAV nekton',



zooplankton, and icfithyoplankton communities was compiled




through monthly field sampling over a one and a half year



period.  Comparison sampling between the SAV bed and adjacent



"open" bottom areas indicated that the resident SAV fish



community was more diverse and superior in number and biomass



to the "open" bottom fish community.  Day-night sampling



found more resident and migratory fishes in the SAV bed at
                              189

-------
night than during the day.  However, this night-time increase



may be due as much to gear avoidance as actual nightly movements



of fishes onto the eelgrass bed.  These numerical and biomass



estimates for zooplankton, ichthyoplankton, resident fishes,



and megapredators also provide an essential data base for the



Wetzel SAV model (this manuscript).



     The other major goals of the higher consumer interactions



group.were to define the trophic importance and refuge function



of SAV to migratory consumers.  The trophic importance of SAV to



migratory consumers was addressed by stomach analysis, feeding



periodicity studies, and calculation of daily ration for the



dominant resident fishes and megapredators.  Stomach analysis



defined the components of the SAV that were preyed upon by these



fishes.  Prey preference varied seasonally as well as with



predator size.  Consumption of only SAV origin food was not



found and resident fishes relied heavily upon planktonic food



sources.  Feeding periodicity studies indicated that mega-



predators were entering the bed during twilight and night-time



periods and then leaving with full  stomachs during the day.



Estimates of daily ration for spot, pipefish and the sandbar



shark were calculated to  later model the effects of these



predators upon the SAV invertebrate community.  The daily



ration calculated for the sandbar shark indicates that intense



predation by this species may have  severely impacted the density



of the blue crab population in the  SAV bed.  Our analysis also



suggests Orth's (this manuscript) blue crab biomass and



secondary production estimates for  the study area are under-



estimations.
                              190

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     The refuge function of different densities of eelgrass was



experimentally tested in large swimming pools.  Megapredators



(C_. regalis and P_. dentatus) became less efficient at capturing



prey (M. meriidia and L. xanthurus) with increasing eelgrass



density.  Since resident .fishes (except pipefish) did not rely



heavily upon SAV origin food sources, the primary advantage



of SAV to resident fishes appears to be refuge rather than of



trophic importance.



     Several questions posed in the initial proposal could not be



answered due to cancellation under adverse weather conditions of



one third of our planned sampling trips and discontinuation of



funding:estimation of secondary production, mortality rates and



residence time of the resident fishes in the SAV bed.  Due to



escapement from the haul seine, reliable secondary production



estimates could not be determined for spot and silver perch.



Residence time was investigated for the sandbar shark through a



tagging program.  Through, a Virginia Commonwealth University



mini-grant, Brooks and Weinstein are currently sampling the study



area (with multiple gears) to determine secondary production of



resident fishes in the SAV bed.  Two intensive marking programs



for spot and silver perch will define their residence times and



mortality rates in the SAV area.



     One of the most significant and nagging management questions



not addressed by this study is relative habitat value for



commercial and recreationally important resources.  The importance



of SAV beds cannot be assessed without concurrent or parallel



studies of marshes,  mudflat areas and other nursery zones.
                                 191

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The primary objectives of the comparison program should be:
1.  To define community structure and secondary production for
individual species within each habitat; 2. Relative benefits
of each habitat to fishes from a-trophic and refuge stand point;
3.  Via an intensive marking program, determination of the period
of residency for selected species and definition of microhabitat
partitioning.  Do the dominant species of each habitat view a
marsh, tidal creek, mudflat or eelgrass bed as separate habitats
or is there a free exchange between them?
     Weinstein and Brooks efforts address a portion of the intra-
habitat objectives through comparison sampling and tagging studies
at the Vaucluse Shores site and a tidal creek area less than
.2 km from the SAV bed.  Initial spring sampling indicated that
the density of early juvenile spot in the tidal creek area was
at least four  times higher than the spot density found in the
SAV bed.  Tidal creek spot were also larger than SAV bed spot
which indicates a higher residency time for spot in the tidal
creek than on the eelgrass bed.  Without comparison studies
between primary shallow water nursery habitats, the relative value
of SAV to "resident" and migratory species cannot be determined.
                                  192

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