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
-------
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
-------
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
-------
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.
-------
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
-------
R=RUPPIA
Z=ZOST£RA
S=SAND
/ = MIXED
ft-«^
= TRANSECTS
CHESAPEAKE -.'.••# /R /V
BAY _ :.Y# /..-..:.:•• R
M
Figure 1
5
-------
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
-------
5
3
>
•••
202u
NET
" 70cm—>
505pm
METER
NET
23cm
202 p
NET
B
Figure 2
-------
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 500°C) 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
-------
Figure 3
10
-------
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
-------
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
-------
Figure 4
-------
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
-------
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
-------
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 56°C 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
-------
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 56°C) 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
-------
Figure 5
18
-------
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 Purina®
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
-------
(.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 12°,
17°, 22°, and 27°C. 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
-------
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
-------
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, £. 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 (£. 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
-------
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 (£. regalis) spotted
seatrout (£. 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 «-•»-» 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
*-«*-•» 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
£. 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 (£. 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
£. 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. «6 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 °/oo; 1.5-28.0°C; 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
(n»3)
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 23« 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
-------
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
£. 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 _§_. 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.
—•«
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
-------
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lency distribution of pushnet catches of Anchoa
mitchilli in all habitats during April 1979.
-------
ERR CHRRT
MIDPOINT."
LENGTH
DF LQGHD03
L06NQ03
£ '"•44'444444
>; ---444444444444444
4 ''-+4+4 .
5 'x -. . •-•
£ >--+4-44- . vv
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8 '"• . ••:'-•
1 9 '"•
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11
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13
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34 '-444444-44+
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36 '--4444444-44444
37 •••••444444444444444
33 "-44444444444-444444
39 •••"4444444444444444444
40 ••••44. + 444-*4444*444»44
41 ••••4444**-4444444-
4g '•••«• *•«. 4.4- * +*•*•»«•*•*»
43 ••'••4444'444'4*44-44
44 ••'• 4-444-4-44444444
45 •"••»+>+•
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0. 60£060
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.4771£1
0. 301 030
0. 301 030
0.698970
0. 903090
0. 903090
1. 113943
1 . £78754
1.414973
1.34£4£3
1 . 0 0 0 0 0 0
1. 041393
0.954£43
1 . 0 0 0 0 0 0
0.301030
0. 903090
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0. 301 030
0. 60 £060
0. 954£43
-i
0.3 0.6 0.9 1. £ 1.5 1.8 £. 1 £. 4 £. 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'
1.61£784
1 • . : 1.255273
1.£30449
0.477.121
0. 602060
""* . 0.00 0 0 0 0
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'%' 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
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''" . ' 0. OOOOOO
''••**•**•*•*•**•*+***•**• 1.113943
1.518514
1.707570
1.770852
1.716003
1.7£4£76
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 £.4 £.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
1£
13
14
45
-16
17
13
19
£0
£1
22
£3
£4
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£6
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£8
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30
31
32
33
34
35
36
37
33
39
40
41
4£
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
£0
£1
££
£3
£4
£5
£6
27
£8
£9
30
31
3£
Cj;~;
34
35
36
37
38
39
40
41
4£
43
44
45
46
47
48
49
50
51
5£
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- + +
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•-•+> + + + + + + + + + + + + + •
H (. H + H H 4- H + + + +
0 .3 0.6 0.9 1 . £ 1.5 1.8 E . 1 £ . 4 £ . 7 3 3 . 3 3 . 6
15. Length frequency distribution of pushnet catches of Anchoa
0.60E060
1.6 7' £09 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
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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
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0. 301 030
0. 301 030
o . n o n n n f i
0. 000000
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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. £04 180
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
£1
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35
36
37
38
39
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43
44
45
46
47
48
49
50
51
5£
DF LGGN006
'•**•**•
LOGND06
3£££19
568£0£
176091
075547
73£394
£34011
441066
351796
£77838
059563
916980
77085£
635484
537819
851£58
98677£
6£3£49
67£098
785330
518514
397940
380211
544068
£78754
3£££19
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
0.60£060
0.698970
0.698970
1.9731£8
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.3 0.6 0.9 l.£ 1.5 1.8 £.1 £.4 £.7
3.3 3.6
Figure 16. Length frequency distribution of pushnet catches ©f Anchoa
mitchilli in all habitats during August 1979.
97
-------
BaP. CHftRT DF LDGND07
MIDPOINT
LENGTH
£ 'x
3 A • :
4 '"
5 '"• . '••'•'•• r
6 . . '• • • • .
7 - • ' .. • • •
8
9 '•-
10 '^++*
1 1 ^ + + + + + *«. + * +
1£ •••-4.*4-*****-»-*-*-4-**-**-4-
13 '•••*+++*+«•*«••»•*••»++«•+*«• •
14 ^* + *4. + + + 4.* ++** + + *4-**** +
"15 • 'x + + + + + + + + + + * + + *-* + 4-+ + + + + *
16 '-- + * + + * + + + *«.+ + + * + + *+«.*.** + *** +
1 7 ^••••+*+++****++**++++**+*4.++
18 '•- + + 4-4-*4-** + + *«- + * + ** + * + *> + + «- + .»* +
19 ^t^*******.*.**.***.***.**.**.****.**.
£0 ••••• + + « + + * + + **«- + + + * + + 4- + * + 4-* + *«-***4-
81 '-•»**4-****************-4-*******4-
££ '•••+«• + + + + + + + + +• + + + •»«•«• + + «• + + + + .»•«.*
£3 A*********.»***************.
£4 ^ + + *.* + + *«..»4..»**4.* + * +
£•5 '•" + + 4. + 4.4. + * + 4. + + *» + * + *. + * + *
£6 '•" + * + *«.+"»*.+++4-4-*4-+«-
£7 ^** + * + + * + + + + + + 4.* + * +
£8 '•••«•++ ++«•
£9 ''•••• + + + «.«. + *. + *
30 •'••«•*+ ++++*•*«•«•«•*•
31 A4-*****
3£ •"• + + + 4- + + + +
•-'•-' •"•
34 ,.'•-
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37
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40 -x-»+++
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4£
43 -"-.*+++++
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45
46 A
47
48 '-•****
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50
5 1
5£ •"••.**•»*•»*
0 ~: fi ^. f i ^ 1 . £ 1 c' 1 .' ft c! . 1 c! . 4 £ . 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 . £55£73
1.3617£8
1. 67£098
1 . 7£4£76
1.991 ££6
£. 1£7105
£. 15836£
£. 089905
£.£85557
£. 15££88
£. 0043£1
1.875061
1. 34£4£3
1.61 £784
l.£55£73
1.380E11
0.4771£1
0. 903090
0.954£43
10. 4771 £1
0. 60£060
0 . 0 0 0 0 0 0
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0. 301030
0 . 0 0 0 0 0 0
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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!
1.3£££19
mitchilli in all habitats during September 1979.
98
-------
BRR CHftRT OF LDGHD08
MI
tiPDINT
LEHGTH . .-'••'.
f~: ' • -• -.,
2
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30 '•••4- 4- 4- 4- 4- 4- 4- 4- 4-
31 •'••*4-4-4-4-4-4-4-4-
3£ ••"••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"»4-4-
4£ '•- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4- 4-4- 4-
43 A +•«> •*••* + •*•»•» 4>«-
44 ''••4-4-4-4-4'4-4-4-4-4-4-4-4-
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0.3 0.6 0.9 l.£ 1.5 1.8.. £.1 £.4 £.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
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0 . 0 0 0 0 0 0
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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
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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
0.4771£1
0.4771£1
0.698970
0. 698970
0.60 £060
fi. 69ft 9 7 fi
0.698970
1. 1461 £8
1. 079181
0.778151
0.845098
0.698970
0.698970
0.845098
0.954£43
0.778151
0.954£43
0.845098
0. 903090
0.954£43
0.778151
0.778151
0. 698970
0. 845098
0.60£060
1.568£0£
mitchilli in all habitats during October 1979.
99
-------
t'.H* CHRRT DF LDGND09
MIDPOINT
LENGTH
£
3
4
5
6
7
8
9
10
11
1£
13
14
15
16
17
18
19
£0
£1
22
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£4
£5
£6
£7
£8
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3 0
31
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33
34
35
36
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39
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43
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45
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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
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0.301030
0. 000000
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0.4771£1
0. 301 030
0.4771£1
0.477121
f| C||y-;f|C|f!
0.4771£1
0.773151
1 . 0 0 0 0 0 0
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0 . 0 0 0 0 0 0
0.778151
0. 903090
0 . 6 0£ 06 0
0.845098
0.954£43
1. 1461£8
1. 079181
0.778151
0. 903090
0.778151
1. 113943
0.845098
0. 903090
0.954243
0.954243
0.778151
0. 903090
1 . £55£73
1. £3 044 9
1 . £55£73
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
1£
13
14
1 5
16
17
£ 0
£1
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£3
£4
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30
31
34
35
36
37
3 8
39
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43
44
45
47
48
49
50
51
52
DF LDGND1D
" * * * *
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0. 0 0 0 0 0 0
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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
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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
60£060
778151
';• IJ 1 I.I •J IJ
4771£1
698970
845098
778151
0 .
0.
0 .
0.
0.
0.
0.
0.698970
0.773151
0.4771£1
0.4771£1
0.4771£1
0.698970
0.3 0.6 0.9 l.£ 1.5 1.8 £.1 £.4 £.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>.
£
^"i f"m
•3 '
4
5 .'••.-.
6 - ..."'•••
7 '-' ' - ,'••'.
8 'x • '
9 .•#;.••
10 - •'-"•' * . '••' : . .
11 '" ' . • •-'. .'•• /:; - ' ' .
1£ . ' '' •-'••- :
13 ' • " •-.?•'. ••'.•••
14 - .'••
15 '-; •'"•'." -
16 '-• .
1 7 '' ' . ' .
18
19''-
£0
£1 -•****
££'-• '
£3
'£4 •-• .
£5 '--4.***
£6
£7. '-«. + «.+
£8
£9
30
31
3£
33 "•
34
35 . •"•
36
37
1;ft
39
40
4 1
42 •-•'^
43
44
45
46
47
j*
48 '-• «
49
50
51
5£
53 •-• ":
iiiiiiiiiiii
0.3 0.6 0.9 1 . £ 1.5 1.8 £ . 1 £ . 4 £ . 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
••****
••*»**
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 £| 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
'•• •» * *•
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 £. ginsburgi, occurred
in collections but £. 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
-------
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
(°C) (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, £. 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 1-12°C. 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
(15-22°C), 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 (£. 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 (£. 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 £. 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 -
<*?
<*>
<*>
1
i
1
S
T
R
I
R
T
R
U
N
r
U
L
R
T
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G
H
n
n
R
F
N
G
u1
S
R
M
E
R
i
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R
X
R
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T
H
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R
U
S
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H
R
Y
S
0
P
T
E.
R
Q
U
Q
G
U
G
R
E
G
I
;j
S
E
V
0
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G
f
U
G
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. G
L
R
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 33«3
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 r« 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 « 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? «
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 13«6 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
£ 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^^»; OTHER
U*/*J HRRPRCTICOID
A\\\ N. RMERICRNR
-.X^N: IS30TER BRLTHICfl
&k. ^ •*« 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
^
1§
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
.
. . .«
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
E
C
R
S
I
T
R
T
R
T
1
M
R
X
R
T
i
I
L
0
C
E
L
L
R
T
r
R
N
R
D
U
M
i
C
R
N
N
E
B
U
L
n
L
B
F
R
R
T
R
Y
I
T
Y
L
Q
r
•j
U
R
U
f
J
R
r
N
R
LEG-END: TRXCODE2
DREDRTOR
OTHER
RUPPIR rfiRIT
N. RMERICRNR
DECRPODR
. \N
SEPTEMSPINQSR
SRD!DUG-HRRD
C
C
C. SRDIDUS-SOFT
FISH F.CC-S
RNCHOR M. ITCH ILL
S, FUSCUS
L . XRNTHURUG
,vv\N \
,.V\ X
^. ^. ^
ZOSTLRR
/'/
•////.
RRENRRIR
BIC-El.OWI
VULGRR
COO
_>n.
iS
I f.
! DUG-PR1
•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
E"
N
T
R
T
R
E
7771
5
R
I
T
R
T
R
i
l
X
R
X
R
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E
i
L
fi
T
R
N
R
D
E
n
C
R
c
R
U
L
n
L
B
f
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r
R
T
n
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LEG-END: TRXCCCt:
SiXXSK
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,s\ AN \\ \
u *\ V
/ / / / .
r« T
U 1
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HER
REIG REARING
'RMERICRNR
MUCRONRTUG
CR°ODR
GEPTLf^iP'NOGR
C.
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FI
GH EGGS
XRNTHURUG
•,VV\. M
PQLYCHRETR
M. RRENRRIR
M. BiGELOWI
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« P \i' n r> n p T r
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WtSSlSSi UN ICE NT - PISH
\v.\x. B . TYRRNNJS
XXX, MDGIL CEPMRLu'G
•Figure 38
161
-------
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
£. 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
-------
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
-------
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 £. 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
17°, 22°, and 27°. 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
O
a:
u
a.
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
-------
4.0-1
3.5H
o
X
S2
ui
o
o
CD
3.0 H
2.5 =
2.0-
UJ
O
tr
LJ
a.
± 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
-------
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
^£ = 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 22° was .032. The daily ration for pipefish was 4.4% dry
body weight per day at 22°C. 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 22°C 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 22°C 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 (£. 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
-------
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 CftTCH»TIME
RVEWT I
2.25
SYMBOL USED IS *
SYMBOL USED IS «•
2.00
1.75
1.50
1.25
1.00
0.75
0.50 •»•
0.25 •»•
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
-------
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 « « «
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 27° 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
(£. 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+ 2°C 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
-------
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
-------
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
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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
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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
-------
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 £. milberti, ^. saltatrix, and jC. regalis start
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to move into the shallow areas in the afternoon. £. milberti and £.
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 £. milberti, £. saltatrix, P. dentatus, and
£. nebulosus indicated that these migratory predators were feeding in the
SAV bed. Spot was heavily preyed upon by £. regalis and £. 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 27°C. 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 £. 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
(£. 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 (§.- 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
29° 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
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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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