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NOTICE
Tliis document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
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ABSTRACT
The limnetic zooplankton in lakes of the Naknek River system in
southwestern Alaska was sampled extensively during 1962-63. The numerically
dominant forms of limnetic zooplankton were Diaptomus sp., Cyclops sp.,
Daphnia longiremis, Boamina coregoni, Kellicotia longispina, and Conochilus
unicornis. Some littoral and benthic forms were also identified but not
studied in detail. Species composition and the relative abundance of each
species differed considerably among the four major lakes and also among
basins within the lakes. These differences were consistent with limnological
differences in physical and chemical characteristics. Iliuk Arm, contains
glacial flour from glaciers and pumice from volcanic activity and had the
lowest standing crop. South Bay of Naknek Lake receives turbid water from
Iliuk Arm and clear water from Brooks Lake and was more productive than Iliuk
Arm, but much less so than other basins in Naknek Lake and the other lakes.
The clear and warmer waters of the North Arm of Naknek Lake had the highest
standing crops. Seasonal pulses of zooplankton occurred in mid-July and
again in late-August. Annual changes were also studied and in nine out of
ten comparisons, zooplankton were more abundant in 1963 than in 1962. Diel
migrations of groups of zooplankton and individual dominant species were also
examined.
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INTRODUCTION
The sockeye salmon (Oncorhynchus nerka) resource of Bristol Bay in
southwestern Alaska is one of the most valuable in the world (Hartman 1971).
These anadromous fish spawn in lakes and rivers, then the young spend from 1
to 3 years in the lakes before migrating to the Pacific Ocean (Hartman and
Burgner 1972) . While in "nursery" lakes the young are pelagic zooplankton
feeders (Johnson 1961; Hoag 1972); yet, relatively little is known about the
zooplankton of Alaskan sockeye nursery lakes. Juday et al. (1932) sampled
the net plankton of Karluk Lake on Kodiak Island where they found that
rotifers constituted numerically by far the bulk of the net plankton. Nelson
and Edmondson (1955) and Raleigh (1963) studied the zooplankton of shallow
Bare Lake on Kodiak Island during and following artificial fertilization
experiments. The zooplankton increased threefold after fertilization.
Waters (1967) and Hoag (1972) reported general studies on some of the lakes
draining to Bristol Bay.
In 1962 and 1963 the limnetic zooplankton were stuflied in four lakes of
the Naknek River drainage system in Katmai National Monument on the Alaska
Peninsula. This paper reports the occurrence, distribution, and abundance of
zooplankton species during the growing seasons each year from June to
October. Zooplankton abundance and species composition differed between
basins within lakes, between lakes, within seasons and between seasons; the
die! migratory behavior of zooplankton is also noted.
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THE STUDY AREA
The Naknek River system consists of four major interconnected
Lakes—Coville, Grosvenor, Brooks, and Naknek—all draining through Naknek
liver to Bristol Bay (Figure 1). Naknek Lake has five relatively distinct
basin areas--Iliuk Arm, North Arm, South Bay, Northwest Basin, and the large
shallow West End. All these lakes and basins were formed or modified by
glaciation (Mertie 1938). The general limnology of these study lakes and
others around Bristol Bay was described by Burgner et al. (1969). They are
subject to an oceanic climate since they are in the path of prevailing winds
and storms from the Bering Sea. Therraoclines seldom develop in the summer;
when they do, stratification is destroyed by the next strong windstorm.
These lakes freeze over in November or early December and become ice free in
May.
The watersheds are mainly jedimentary rock with some igneous outcrops
and volcanic ash deposits (Keller and Reiser. 1959); substantial differences
occur between lakes in certain physical and chemical characteristics (Table
1). Summer transparency ranges from 0.5 m in glacial fed lliuk Arm to 10.8 m
in Brooks Lake. Summer mean high temperatures are lowest in Brooks Lake, and
nearly 5°C warmer in shallow Coville Lake. Total dissolved solids, and some
of the cation concentrations were severalfold higher in Naknek Lake which
receives drainage from glaciers and the pumice and mineral deposits in the
Valley of Ten Thousand Smokes.
The ichthyofauna of these lakes is subarctic with emphasis on the
Salmonidae (Heard et al. 1969). Its modifying effect on the composition of
the zooplankton by selective feeding has not been studied. In addition to
the very abundant young sockeye and other salmonlds, such competitors for the
3
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zooplankton as threesplne sticklebacks (Gasterosteus aculeatus), ninespine
sticklebacks (Fungi tins pungitlus), pygmy whitefish (Prosopium coulteri),
least cisco (Coregonus sardinella), and pond smelt (Hypomesus olidus) are
very abundant in some if not all of these lakes.
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MATERIALS AND METHODS
Small high-speed Hardy plankton samplers as modified by Miller (1961)
were used to sample the limnetic zooplankton. These samplers trail a long
attached net with a high ratio of effective filtering area to sample
aperature. Standard No. 10 bolting (.158 mm) silk nets with detachable
collecting cups were used.
A standard plankton tow was for 1 minute and 43 seconds with the cable
maintained at a 45° angle. Six samplers were towed simultaneously at depths
of 1, 5, 10, 15, 25, and 35 meters. A Scripps 40-pound depressor was used to
depress the cable. The six samplers towed for 1 minute and 43 seconds
covered 152.4 m (500 ft) and each sampler theoretically strained 1.245 cubic
meters of water. The sampler aperature is 10.2 cm in diameter. By
maintaining a constant cable angle and towing in a Iar3e circle effects
between tows of differences in boat weight, outboard motor sizes, water
currents, and wind and wave conditions were minimized.
After collection, zooplankters were poured ir.to glass jars and preserved
in 3% formalin. In the laboratory, the preservative was carefully decanted
to leave one volume of zooplankton to four volumes of preservative. After
mixing by inversion, a 0.5 ml subsample was taken with a calibrated
wide-mouth pipet and placed into an etched Sedgwick-Rafter cell. Al ]
organisms in the subsample were counted. At least 200 organisms we; >unted
and identified under a compound microcope for each sample. The counts were
expanded to estimate numbers per cubic meter of lake water in the usual
manner relating sample size to the volume of water strained.
The following factors place some constraint on interpretations from the
samples. Significant local differences in horizontal distribution related to
5
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the swarming of zooplankters was reported by Kangas (1964) and others. The
aperture of the samplers was only 10.2 cm in diameter, so swarming may have
been a problem. Vertical stratification and diel migration which existed
tended to complicate comparisons of standing crop estimated between basins
and especially lakes. However, by basing comparisons on average numbers from
six depths sampled simultaneously this complication was minimized.
The 0.158 mm mesh size used for collections also placed limitations on
zooplankton counts. Many of the rotifers, smaller nauplii and all protozoans
passed through the nets and hence were not quantitatively sampled.
Contamination introduced during the vertical retrieval haul from sample
depth to the surface was probably insignificant because tows were made for
nearly 2 minutes at depth and then brought rapidly to the surface.
Furthermore, the diel samples show little if any contamination of deep water
tows with primarily surface forms. There was no contamination while casting
the samplers because they were lowered cup end first which effectively back
flushed them.
Special sets of data collected demonstrate levels of statistical
reliability that give confidence in mr.king comparisons between samples and
lakes. Samples were collected at the six depths six times at 2-hour
intervals betwen 0600 and 1600 hours 1 day at Brooks Lake and 1 day at South
Bay in Naknek Lake. Mean numbers, standard deviations and coefficients of
variation of these samples for the six depths combined for Copepoda,
Cladocera, Rotifera and the dominant species in these groups are given in
Table 2. The coefficients of variation are relatively small for most of the
dominant organisms. As the sampling was conducted throughout the day
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covering time sampled at. other stations and lakes, the results give
confidence in comparing differences in zooplankton numbers between stations,
lakes and seasons.
A paired T-test was used on eight samples from Brooks Lake and eight
samples from South Bay of Naknek Lake to find if population estimates of each
species were identical (Table 3). The samples were collected at similar
times throughout the season. The results show that the major species
(Diaptomus sp., Cyclops sp. and Daphnia longiremis) constituting the bulk of
the standing crop were significantly more abundant in Brooks Lake than in
South Bay of Naknek Lake. Bosmina coregoni and Kellicotia longispina were
not significantly different in the two lakes.
Several forms were not enumerated to species because of taxonomic
similarities and difficulties in identifying copepodite stages. Diaptomus
gracilis and Diaptomus pribiloferisis were not enumerated separately and are
presented collectively as Diaptomus sp; Cyclops strenuus and Cyclops
capillatus were also not enumerated separately and are presented here as
Cyclops sp.
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RESULTS AND DISCUSSION
Limnetic samples from the four Naknek River lakes and their basins
consisted of five species of Copepoda, five species of Cladocera, and 10
species of Rotifera. Two other copepods and two other cladocerans were
identified in littoral areas (Table A). The dominant limnetic forms common
to all lakes were Diaptomus sp., Cyclops sp., Daphnia longiremis, Bosmina
coregoni, Kellicotia longispina, and Conochilus unicornis.
Distribution
Certain differences were found in the distribution of species between
lakes. Leptodora kindtii was only found in Coville and Grosvenor Lakes.
Holopedium gibberum was found in these two upper lakes and Brooks Lake. The
rotifer Ploesoma sp. was only found in the South Bay of Naknek Lake. The
rotifer Conochiloides natans was only found in Brooks Lake, wherear. the
rotifer Conochilus unicornis was found In all areas except Iliuk Arm.
Eurytemora yukonensis was rare in Brooks Lake where it was found in only one
of 138 samples taken from there.
Investigators of other subarctic lakes (e.g., Reed 1964) concluded that
plankton communities of large subarctic lakes are relatively rich in species
and relatively poor in numbers. Most of the species of cladocerans and
rotifers found in the lakes of the Naknek River system are widely distributed
and abundant in Northern United States, Canada, and Alaska. However, species
of copepods from the Naknek River lakes tend to be more restricted to
Northern Canada and Alaska. Yeatman, in Ward and Whipple (edited by
Kdmondson 1959) reported that Cyclops strenuus and Cyclops capillatus were
generally relatively rare in North America. However, these two species were
numerically the moat abundant zooplnnkters In the Naknek River system lakes.
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Of the six species mentioned as common in Lake Iliamna by Lenarz (1966) only
Cyclops scutifer was not found in the Naknek lakes. Lake Iliamna is over 100
miles east of the Naknek River system and enters Bristol Bay via a separate
drainage.
Relative Abundance
Differences were also found between lakes in the relative abundance of
various species. Looking first at major groups of zooplankton (Figure 2)
rotifers were more abundant in the uppermost major lake, Coville, in July
when they equaled nearly half of the zooplankton. Cladocerans were most
important numerically in Grosvenor Lake in both July and August. In all
other lakes and Naknek Lake basins, copepods dominated the zooplankton.
Dominance of one species of copepod, cladoceran, or rotifer was evident
in almost all samples. Usually one species in each group constituted the
bulk of any given sample. For copepods it was usually Cyclops s_p_.; for
cladocerans usually Daphnia longiremis; and for rotifers usually Kellicotia
longispina or Conochllus unicornis (Tables 5-8). However, some differences
in dominance occurred between lakes. The cladoceran Daphnia longiremis was
dominant in Brooks and Coville Lakes in both July and August, 1962 (Tables 5
and 7). In Grosvenor Lake, Daphnia rosea was more abundant than Daphnia
longiremis in July and strongly dorai..ant in August. These observations
support the report by Fsnnak (1957) that two species from the same genus
present at the same time as dominants in a limnetic community is ur.usual,
although chis occasionally happens. He further stated that the periodicities
of two species of the same genus may be different, or they may occupy
different water strata, yet invariably one is always much more abundant.
Diversities in limnological conditions (Burgner et al. 1969) and the
species composition of zooplankton between lakes in the Naknek River system
9
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have been noted. There were also differences within each lake in the
relative abundance of species and overall standing crops.
In Brooks Lake, Station 2 was located nearer the major tributary
entering the lake, and Station 1 nearer the outlet. Standing crops of
zooplankton in July and August in 1962 were essentially the same at both
stations but species differences occurred. Diaptomus sp. was twice as
abundant downlake at Station 1, whereas Cyclops sp. occurred in virtually
identical numbers at both stations. Cladocerans were more abundant at
Station 2 in July, and at Station 1 in August (Tables 5 and 7).
The diversity of limnological conditions in the many areas of Naknek
Lake was reflected in differences in the zooplankton (Tables 6 and 8). This
lake had the highest and lowest standing crops in different basins on similar
sampling dates. North West Basin in Naknek Lake is a relatively shallow bay
almost completely separated from the rest of th« Naknek Lake complex (Figure
1). It was sampled in July during a heavy Anabaena sp. bloom. The standing
crop of zooplankton was very low, dominated by Bosmina coregoni and several
rotifers. Perhaps, as Ryther (1954) suggests, the dense phytoplankton
populations created conditions incompatible or actually lethal to many other
aquatic organisms in North West Basin in July.
Illiuk Arm receives glacial flour, pumice, and silt from the Valley of
Ten Thousand Smokes. Secchi disc readings seldom exceed 0.9 meters.
Zooplankton were very low in numbers at both stations with little difference
in species composition. No other lake or basin had such low standing crops.
Copepods dominated the zooplankton.
South Bay receives turbid water from Iliuk Arm and clear water from
Brooks Lake. Zooplankton were two to three times more abundant here than in
Iliuk Arm but lower than in any other area in the Naknek River system.
10
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Stations 3 and 4 were only 4 miles apart and had essentially the same
standing crops and species composition; Cyclops sp., Diaptomus sp., and two
species of rotifers dominated.
The water in North Arm Stations 7,8, and 9 was clear and warm and had
the largest standing crops of zooplankton in the Naknek Lake complex.
Copepods dominated the 2:.">oplankton at all three stations. Rotifers were also
important, at Stations 8 and 9 in July and 7 and 9 in August.
Only one station (12) was sampled in warm and shallow Coville Lake. The
standing crop in July and August was high; Cyclops sp. were especially
abundant but Diapf.omus sp., cladocerao.s, and rotifers were well represented
(Tables 5 and 7).
Grosvenor Lake is deep and slightly colder than most of the other lakes
or basins. Station 14 in the middle of this long, narrow lake had the
highest standing crop in both July and August. At the upper end, which
receives water from Coville Lake, the standing crop was somewhat less. At
the lower end of the lake, the water is relatively turbid due to a silty
effluent from Hardscrabble Creek, and the standing crop was quite low (Tables
5 and 7).
Seasonal Changes in Standing Crop
Seasonal changes in the standing crop of zooplankton were documented at
Brooks Lake (Station I) and Naknek Lake (Station 3) in 1962 from early July
through early October. The occurrence of two pulses of abundance was noted
in Brooks Lake, whereas it was less pronounced in Naknek Lake (Figure 3).
The highest number of zooplankton occurred in July in both lakes; then a
midsummer depression occurred in both lakes at virtually the same time around
mid-August. The late-summer pulse peaked about the first of September in
both lakes; the subsequent rapid decline was similar in both lakes.
11
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Seasonal changes In the species composition of the zooplankton (Figures
4 and 5) also occurred. The copepods comprised a large percent of the total
plankton at all times. Cyclops sp. decreased in relative abundance whereas
Diaptomus sp. tended to increase as the season progressed in both lakes. In
Brooks Lake nauplii decreased whereas in Naknek Lake they remained relatively
constant during the sampling period. Daphnia longiremis were most abundant
in mid and late su Ar in both lakes. The relative peak abundance of
Kellicotia longispina and Conochilus unicornis differed in the two lakes
(Figures 4 and 5). No one dominant species showed two strong pulses. The
pulses were largely a result of certain species peaking in abundance early in
the summer, then declining, while other species, low in abundance early in
the summer, peaked in late summer.
Miscellaneous species not included in either Figures 4 or 5 were common
for relatively short time periods only. In Brooks Lake Holopedium gibberum
and Daphnia rosea were common at certain times but virtually absent from
South Bay of Naknek Lake. In South Bay Asplancha priodonta and Eurytemora
yukonensis were co-nmon at certain times, but not in Brooks Lake.
Annual Difference in Standing Crop
Annual differences in the standing crop of zooplankton for four of the
lakes were also noted. Zooplankton were collected at the same stations in
Brooks and Naknek Lakes on three dates and in Coville and Grosvenor Lakes on
two dates in 1963 corresponding to sampling dates in 1962. Even with limited
data seasonal variations in abundance and the timing of species dominance was
observed. Copepods w«re more abundant in 1963, especially so in Grosvenor
Lake where they were nearly double (Table 9). In only two of the 10
comparisons were numbers in 1962 larger. Cladocerans were also more abundant
in 1963. Only in July in Grosvenor Lake were they more abundant in 1962. In
12
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all remaining nine comparisons, numbers in 1963 were from 17 to 96 percent
higher, averaging 27 percent higher.
Rotifers, however, were less abundant on the average in 1963 in Brooks
and Naknek Lakes. They were about the same density both years in Grosvenor
Lake. Only in Coville Lake were they more abundant in 1963, as were
cladocerans and copepods.
The composite zooplankton showed larger numbers in nine cases out of 10
in 1963 (Table 9). Unpublished data show that solar radiation and primary
productivity were higher in 1963 than in 1962, a condition under which larger
populations of phytoplankton, and subsequently, zooplankton, were expected.
Did Vertical Migrations
Diel vertical migrations of many marine and freshwater species of
zoonlankton have already been described. Most investigators agree that light
is the primary environmental factor responsible for diel movements. However,
Pennak (1944) reported that diel movements of zooplankton cannot be predicted
in an uninvestigated lake and that factors other than light must play an
important role. Other contributing factors suggested by many workers
include: temperature, wind, gravity, oxygen depletion, carbon dioxide
accumulation, and age or condition of the individual organisms.
The diel distributions of zooplankton were studied in clear Brooks Lake
on July 30, 1962 and in somewhat turbid South Bay of Naknek Lake on August
15, 1962. July 30 was bright, clear, and calm; August 15 was a dark day with
rain most of the time. Samples were taken at depths of 1, 5, 10, 15, 25, and
35 meters every 2 hours from 0000 to 2200 hours. Figures 6, 7, and 8 show
the percent of organisms occurring at each depth.
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Cladocerans and rotifers exhibited substantial vertical migrations
during the 24-hour periods at both Brooks Lake and Naknek Lake (Figures 6 and
7). Large proportions of these zooplankton ascended near to the surface
waters at night and descended to depths of 5, 10, and 15 meters during the
day. The diurnal descent went deeper in the more transparent Brooks Lake
than in Naknek Lake while the nocturnal ascent reached closer to the surface
in Naknek Lake. Almost no cladocerans or rotifers^were found at 1 meter
below the surface between 0600 and 1600 hours at Brooks Lake and between 1000
and 1600 hours at Naknek Lake. The typical summer secchi disc reading at
Naknek Lake Is 4.4 m and at Brooks Lake is 10.8 m (Burgner et al. 1969);
consequently diel vertical migrations in Brooks Lake were more pronounced.
The median values are plotted for each sample distribution In Figures 6 and
7. They essentially divide distributions described above.- The deep
distribution of copepods, especially during mid-day in Naknek Lake, exceeded
the deepest sampling depth of 35 meters. However, the population of
cladocerans and rotifers was distributed nearly entirely above 35 meters.
Copepods in Naknek Lake also showed a substantial diel migration as both
the shape of the depth distribution and plot of median values illustrate
(Figure 7). In both Naknek and Brooks Lakes copepods were distributed deeper
In the water column than cladocerans and rotifers. In «^p groups in either
lake, however, was midnight sinking of entoraostraca observed as reported
elsewhere by Gushing (1951) for example. However, our sampling depths of 1,
5 and 10 meters precluded noting vertical changes between these depths.
The diel distributions of individual species that dominated the
zooplankton in Brooks Lake during July help explain the character of the
migrations when the species are grouped. Neither the two species of Cyclops
nor the two species of Dlaptomus sp. exhibited much diel migration (Figure
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8), which was essentially the same situation when all copepods including
nauplii were grouped (Figure 6), although if all four species had been
considered independently this may not have been so. Daphnia longiremls was
the most abundant cladoceran and its diel vertical migrations (Figure 8)
characterized that of the grouped cladocerans. The less abundant Holopedium
glbberum exhibited diel migrations, but they were less pronounced and
confined to depths of less than 10 meters. The rotifers, Kellicotia
longlsplna and Conochilus unicornis, were about equally abundant and the
grouped pattern of diel distributions of all rotifers reflects the
combinations of the separate and different behaviors. Both rotifers showed
vertical migrations but utilized different levels in the water column.
Kellicotia longispina migrated mainly between 5 and 20 meters with some
individuals reaching the surface at night. Conochilus unicornis migrated
between the surface and 10 m. At night when both species were nearer the
surface, the grouped distribution shows primarily one bulge of abundance
around 5 meters, but by mid-day the grouped distribution (Figure 6) shows two
strata of abundance at 5 and 15 meters representing the differential diurnal
distribution of the shallower Conochilus unicornis and the deeper Kellicotia
longispina.
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ACKNOWLEDGMENTS
The support of this research by the U.S. Bureau of Commercial Fisheries
(now the National Marine Fisheries Service), Auke Bay, Alaska is gratefully
acknowledged. I especially want to thank Dr. Wilbur L. Hartman for valuable
advice and assistance during this study and for help with the manuscript.
Appreciation is extended to Mr. Terrence Hartnan and Mr. William Emison for
their assistance with collecting and enumerating zooplankton.
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LITERATURE CITED
Burgner, R. L., C. J. Di Costanzo, R. J. Ellis, G. Y. Harry, Jr., W. L.
Hartman, 0. E. Kerns, Jr., 0. A. Mathisen, and W. F. Royce. 1969.
Biological studies and estimates of optimum escapements of sockeye
salmon in the major river systems in south-western Alaska. U.S. Fish
Wildl. Serv. Fish. Bull. 67: 405-459.
Gushing, D. H. 1951. The vertical migration of plankton crustacea. Biol.
Rev. 26: 158-192.
Hartman, W. L. 1971. Alaska's fishery resources-—the sockeye salmon. Nat.
Mar. Fish. Serv. Fish. Leaf. 636, p. 8.
Hartman, W. L., and R. L. Burgner. 1972. Limnology and fish ecology of
sockeye nursery lakes of the world. J. Fish. Res. Board Can. 29:
699-715.
Heard, W. R., R. L. Wallace, and W. L. Hartraan. 1969. Distribution of
fishes in fresh water of Katmai National Monument, Alaska, and their
zoogeographical implications. U.S. Fish. Wildl. Serv. Spec. Sci. Rep.
Fish. 590. 20 p.
Hoag, S. H. 1972. The relationship between the summer food of juvenile
sockeye salmon, Oncorhynchus nerka, and the standing stock of
7,ooplankton in Iliamra Lake Alaska. U.S. Fish. Wildl. Serv. Fish. Bull.
70: 355-362.
Johnson, W. E. 1961. Aspects of ecology of a pelagic zooplankton eating
fish. Verh. Intl. Ver. Limnol. 14: 727-731.
Juday, C., W. H. Rich, G. I. Kemmarer and A. Mann. 1932. Liranological
studies of Karluk Lake, Alaska: 1926-30. Bull. U.S. Bur. Fish. 47:
407-435.
17
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Kangas, I. 196A. On the horizontal distribution of some plankton species in
a small eutrophic lake. Verh. Intl. Ver. Limnol. 15: 745.
Keller, S., and H. N. Reiser. 1959. Geology of the Mount Karroai area,
Alaska. U.S. Geol. Surv. Bull. 105R-G. 298 p.
Lenarz, W. H. 1966. Population dynamics of Cyclops scutifer and an
evaluation of a sampling program for estimating the standing crop of
zooplankton in Iliamna Lake. M.S. Thesis, Univ. Washington, Seattle.
120 p.
Mertie, J. B., Jr. 1938. The Nushagak District, Alaska. U.S. Geol. Surv.
Bull. 903. 96 p.
Miller, D. 1961. A modification of the Small Hardy Plankton Sampler for
simultaneous high-speed plankton hauls. Bull. Mar. Ecol. 5: 165-172.
Nelson, P. R., and W. T. Edmondson. 1955. Limnological effects of
fertilizing Bare Lake, Alaska. U.S. Fish Wildl. Serv. Fish. Bull. 56:
415-436.
Pennak, R. W. 1944. Diurnal movements of zooplankton organisms in some
Colorado mountain lakes. Ecology 25: 387-403.
Pennak, R. W. 1953. Fresh Water Invertebrates of the United States. Ronald
Press Co., New York. 769 p.
Pennak, R. W. 1957. Species composition of limnetic zooplankton
communities. Limnol. Oceanogr. 2: 222-232.
Raleigh, R. F. 1963. The composition, abundance, and depth distribution of
the 1957 summer net zooplankton of Bare Lake, Alaska, after
fertilization. U.S. Fish Wildl. Serv. Spec. Sci. Rep. Fish. No. 423.
14 p.
Reed, E. B. 1964. Crustacean components of the limnetic communities of some
Canadian lakes. Verh. Intl. Ver. Verein. Limnol. 15: 691-699.
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Ryther, J. H. 1954. Inhibitory effects of phytoplankton upon the feeding of
Daphnia magna with reference to growth, reproduction, and survival.
Ecology 35: 522-533.
Ward, H. B., and G. C. Whipple. 1959. Freshwater Biology. 2nd ed. Ed. W.
T. Edmondson. John Wiley and Sons Inc., New York. 1248 p.
Waters, B. F. 1967. Abundance, distribution, and species composition of
zooplankton in the lakes of the Nashagak District, Alaska, 1961-1965.
Fisheries Research Institute, Univ. of Washington, Seattle. Circular
No. 67-2. 27 p.
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Table 1. Physical and chemical characteristics of four lakes in the Naknek
River system and lliuk Arm (Burgner et al. 1969, and unpublished
data).
Units
Area knr
Maximum depth m
Mean depth m
Volume km
Altitude m
Shoreline development
Total dissolved solids ppm
PH
Total alkalinity ppm
Sodium ppm
Potassium ppm
Magnesium ppm
Calcium ppm
Silica ppm
Summer secchi disc m
Summer high mean temp. °C
Brooks
Lake
75
79
45
3.39
19
1.70
75
7.3
27
4.3
1.0
2.2
8.9
10.5
10.8
10.7
Grosvenor
Lake
73
107
50
3.68
31
2.54
54
7.2
25
3.0
0.5
1.9
6.9
7.7
8.4
14.5
Coville
Lake
33
53
19
0.64
33
1.86
52
7.1
25
3.2
0.5
1.2
7.8
9.0
5.4
15.6
Naknek*
Lake
516
71-167
13-63
16.15
10
1.41-2.07
140
7.4
29
10.4
1.2
4.2
18.2
9.3
4.4
13.4
lliuk
Arm
94
173
96
9.00
10
1.71
7.3
0.5
11.0
* Includes several basins.
20
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Table 2. Mean number of zooplankton per cubic meter, including standard
deviations and coefficients of variation, for diurnal samples
collected from Brooks Lake, 30 July 1962 and the South Bay of
Naknek Lake, 15 August 1962.
Brooks Lake
Copepoda
Cyclops sp .
Diaptomus sp.
Cladocera
D. longiremis
B . coregoni
Rot if era
K. longispina
X*
3786
2032
900
1014
849
57
459
297
SD**
+ 413
-1- 322
-1- 146
+ 83
+ 67
+ 30
+ 101
+ 62
C***
11%
16%
16%
8%
8%
53%
22%
21%
X*
1782
946
472
132
48
89
1219
481
South Bay
SD**
+ 315
+_ 156
+ 104
± 15
+ 13
+ 19
+ 220
+ 172
C***
18%
16%
22%
11%
27%
21%
18%
35%
* Mean
** Standard deviation
***Coefficients of variation
21
-------
Table 3. Paired T-test on plankton in Brooks Lake and Naknek Lake to find if
populations are identical.
d
SDg
t
df
Diaptomus
1020
200
5.10**
7
Cyclops
1115
338
3.30*
7
Daphnia
533
127
4.20**
7
Bosmina Kellicotia
19 6
30 93
0.62 0.07
7 7
d = Average difference (Brooks - Naknek).
SDg = Standard deviation of the difference.
t = T-value
df = Degrees of freedom
* p < .05
** p < .01
22
-------
Table 4. Zooplankton species found in lakes of che Naknek River system in
southwestern Alaska, 1962-63.
Organisms
Habitat*
Copepoda
Calanoida
Diaptomus gracilis. Sars, 1863
[FAidiaptomus gracilus (Sars) 1863]+
Diaptomus pribilofensis. Juday and
Muttowski, 1915.
[Leptodiaptomus pribilotensis (Juday and
Muttowski) 19157*
Eurytemora yukonensis. M.S. Wilson, 1953.
Cyclopolda
Cyclops strenuus. Fischer, 1851.
Cyclops capillatus. Sars, 1863.
[Acanthocyclops capillatus (Sars) 1863]
Harpacticoida
Attheyella nordenskiolkii. (Lilljeborg),
1902).
Bryocamptus nivalis. (Willey), 1925.
Limnetic
Limnetic
Limnetic
Limnetic
Limnetic
Littoral, Benthic
Benthic
Cladocera
Haplopoda
Leptodora kindtii. (Focke), 1844.
Eucladocera
Holopedium gibberum. Zaddach, 1855.
Daphnia longiremis. Sars, 1861.
Daphnia rosea. Sars, 1862 emend.
Richards, 1896.
Scapholeberis kingi. Sars, 1903.
Bosmina coregoni. Baird, 1857.
Polyphemus pediculus. (Linne1), 1761.
Limnetic
Limnetic
Limnetic
Ponds and Lakes
Ponds and Lakes
Ponds and Lakes
Ponds and Marshes
Rotifera
Kellicotia longispina. (Kellicotia, Ahlstrom) Limnetic
Keratella~hiemali8. Carlin, 1943. Limnetic
Keratella cochleares. (Keratella, Bory Limnetic
de St. Vincent)
Gastropus sp. Imhof Limnetic
23
-------
Table 4. (Continued)
Organisms
Habitat
Asplanchna priodonta. Gosse, 1850.
Ploesoma sp. Herrick.
Polyarthra sp. Ehrenberg.
Fillnia terminalis. (Plate), 1886.
Conochiloides natans. (Conochiloides, Hlava).
Conochilus unicornis. (Conochilus, Hlava).
Limnetic
Limnetic
Limnetic
Limnetic
Limnetic
Limnetic
* Mostly as adapted from Pennak (1953) and Ward and Whipple (1959) 2nd ed.
+ Names by G. E. Hutchinson accepted by many workers as discussed (B. Tork,
personal communication) in Treatise on Limnology, Vol. II, p. 625.
24
-------
Table 5. Standing crop of zooplankton by species at different stations in
Brooks, Coville, and Grosvenor Lakes in July 1962 (mean number per
cubic meter for six sampling depths).
Brooks
Station No.
Date
Species
Eurytemora yukonensis
Diaptoraus sp.
Cyclops sp.
Nauplii
Copepoda total
Leptodora kindtii
Molopedium gibberum
Daphnia longiremis
Daphnia rosea
Bosmina coregoni
Cladocera total
Kellicotia longispina
Asplanchna priodonta
Conochilus unicornis
Misc. rotifers
Rotifera total
Total zooplankton
1
7/14
1198
4046
1615
6859
30
574
30
634
320
303
22
645
8138
2
7/14
2146
3737
993
6876
205
976
25
115
1321
242
599
25
866
9063
Coville
12
7/20
6
502
2815
623
3946
3
66
200
40
197
506
336
22
3469
8
3835
8287
Grosvenor
13
7/19
462
3599
649
4710
194
380
399
973
625
116
1398
27
2166
7849
14*
7/19
8
1650
5006
930
7594
1162
1752
1912
4826
1146
535
1334
52
3067
15487
15*
7/19
46
1354
46
1446
60
31
100
191
64
4
30
5
103
1740
* Mean of four depths only.
25
-------
Table 6. Standing crop of zooplankton by species at different stations in
Iliuk Arm and other basins of Naknek Lake in July 1962 (mean number
per cubic meter for six sampling depths).
Area
Station No.
Date
Species
Eurytemora yukonensis
Diaptomus sp.
Cyclops sp.
Nauplii
Copepoda total
Daphnia longiremis
Bosmina coregoni
Cladocera total
Kellicotia longispina
Keratella cochlearis
Asplanchna priodonta
Conochilus unicornis
Misc. rotifers
Rotifei'a total
Total zooplankton
South
3
7/11
216
518
1352
343
2474
56
35
91
127
1
28
74
4
234
2799
Iliuk
Bay Arm
4 5
7/11 7/4
216
692 20
932 1560
636 175
2476 1755
21 1
33 3
54 4
63 14
4
30 5
68
65
230 19
2760 1778
North Arm
7
7/5
6
553
4129
819
5507
83
44
127
74
77
10
161
5795
8
7/11
19
1918
7193
1183
10313
239
190
429
192
9
8
831
14
1054
11796
9*
7/11
35
1712
7058
1000
9805
769
368
1137
115
56
596
88
855
11797
N.W.
Basin
10**
7/26
111
128
202
181
622
972
972
133
1
215
1141
8
. 1498
3092
West
End
11***
7/26
99
1261
4084
644
6088
653
130
383
437
437
6908
* Mean of five depths only.
** Mean of four depths only.
.*** Shallow water - mean of 1- and 5-meter samples only.
26
-------
Table 7. Standing crop of zooplankton by species at different stations in
Brooks, Coville, and Grosvenor Lakes in August 1962 (mean number
per cubic meter for six sampling depths.)
Brooks
Coville
Grosvenor
Station No.
Date
1
8/17
2*
8/28
12
8/20
13 14
8/21 8/21
15
8/21
Species
Eurytemora yukonensis
Diaptoraus j3£.
Cyclops sp.
Nauplii
Copepoda total
903
1838
447
1671
1805
156
3188 3632
16
1013
4097
686
5812
373
1652
55
1170
2076
174
2080 3420
558
1165
58
1781
Lept:odora kindtii
Holopedium gibberum 153 95 3
Daphnia longiremis U18 608 460
Daphnia rosea 38 51 58
Bosmina coregoni 153 158 332
Cladocera total 1462 912 853
318
935
536
11
22
323
1846
620
1798 2822
2
4
434
1388
639
2467
Kellicotia longispina 251 150 275
Keratella cochlearis 5
Asplanchna priodonta 102 38
Conochilus unicornis 33 53 279
Misc. rotifers 31 1
125
28
66
266
146
43
151
15
73
33
1
Rotifera total
284
336
598
219
455
273
Total zooplankton
4934 4880
7263
4097 6697
4521
* Mean of five depths only,
27
-------
Table 8. Standing crop of zooplankton by species at different stations in
liuk Arm and other basins of Naknek Lake in August 1962 (mean
number per cubic meter for six sampling depths.)
Area
Station No.
Date
Species
Eurytemora yukonensis
Diaptomus sp.
Cyclops sp .
Nauplii
Copepoda total
Daphnia longiremis,
Daphnia rosea
Bosmina coregoni
Cladocera total
Kellicotia longispina
Keratella cochlearis
Asplanchna priodonta
Conochilus unicornis
Misc. rotifers
Rotifers total
South
3
8/15
101
411
797
286
1595
30
95
125
229
90
582
121
1022
Bay
4
8/27
131
513
1062
252
1958
166
191
357
658
1
28
365
17
1069
Iliuk Arm
5 6
8/9 8/9
69 73
373 429
154 269
596 771
2 10
1 8
3 18
62 126
31 184
1
93 311
North Arm
7
8/9
18
1685
3043
368
5114
823
622
1445
300
84
612
3
999
8
8/13
21
890
2054
204
3169
387
8
231
626
239
4
24
1
1
269
9
8/31
2
504
1074
249
1829
270
218
488
516
1
280
1140
1
1938
Total zooplankton
2742 3384
692 1100
7558 4064 4255
28
-------
Table 9. Standing crop of zooplankton in lakes of the Naknek River system in
1962 and 1963 on similar dates (mean number per cubic meter for six
sampling depths).
Lake
Brooks
(Station 1)
Naknek
(Station 3)
Coville
(Station 12)
Grosvenor
(Station 13)
Date
7/3/62
7/5/63
7/30/62
7/29/63
9/9/62
9/6/63
7/5/62
7/6/63
8/5/62
8/6/63
9/7/62
9/6/63
7/20/62
7/13/63
8/20/62
8/12/63
7/19/62
7/13/63
8/21/62
8/12/63
Copepods
4108
6066
4054
5234
3452
4131
4192
2030
2141
2876
1465
1830
3945
4378
5812
5004
4710
7421
2080
5672
Cladocerans
516
616
854
1086
483 '
586
97
113
293
374
104
621
507
1819
853
2443
972
825
1797
3368
Rotifers
297
1294
440
360
739
277
245
243
864
411
449
165
3835
5965
597
1232
2166
2060
218
3177
Total
4921
7976
5348
6690
4674
4994
4534
2386
3298
3661
2018
2616
8287
12162
7262
8679
7848
10306
4095
12217
29
-------
10
MILES
IS 2O
Figure 1. Lakes and lake basins of the Naknek River system in southwestern Alaska showing stations where
zooplankton were sampled, 1962-63.
-------
10
IO
E 8
cn 6
n
o
± 4
C/)
o:
LU
GO
•i
m
WWWC-ttMW
•»»X«>tAV.
S»»WK«y.w
WS
MS
ll!
m
>XvX*»X
-------
10
C/)
Q
IS
I
2
eo
bJ
10
8
V
_L
_L
1
J_
_L
_L
10 20
JULY
30
10 20
AUGUST
_L
30 10 2O
SEPTEMBER
30 10
OCTOBER
Figure 3. Standing crop of zooplankton during 1962 In Brooks Lake ( —) and
Naknek Lake ( ) shown as mean number per cubic meter for six
sampling depths.
32
-------
0L _
1 i
10
,
20
JULY
1
31
10 20
AUGUST
1
31
l .
10 20
SEPTEMBER
, ,
30 10
OCTOSEN
Figure A. Seasonal changes of zoo^lanlcton in Brooks Lake during 1962 with
all six sampling depths combined.
33
-------
Cipepods
TIME oooo 0200 DAGO oeoo oeoo 1000 1200 1400 1600
PEICEIT O 2O 4O O 2O 4O O2O 4O O 2Q 4O O 2O 4O O 2O 4O O 2O 4O O 2O 4O O 2O 4O O 2<
30
2000 2200 i
O 2O 4O O 2O 4O
7
Cladocerans
Rotifers
10
20
3O
r-
Figure 6. The diel depth distribution by percent of copepods, cladocerans, and rotifers in Brooks Lake on July
30, 1962.
-------
Copcpods
10
20
3O
10- •
20
3O
THE oooo 0200 0*00 oeoo oeoo
KICEIT O2O4O O2O4O O2O4O O2O4O O 2O
o
10
20
3O
1OOO 12OO 14OO 16OO 18OO 2OOO 22OO
O2O4O O2O4O O2O4O O2O4O O2O4O O2O4O O2O4O
\
i
7
Cladocerans
Rotifers
Figure 7. The diel depth distribution by percent of copepods, cladocerans, and rotifers in Naknek Lake on
August 15, 1962.
-------
Cyclops sp.
TIME O2OO O6OO 1OOO 14OO 18OO 220O
PERCENT O 2O 4O 0 2O 40 O 2O 4O O 2O 40 O 20 4O 0 2O 4O
Figure 8
3O
Ol—,
1O
20
3O
0
1O.
20
30
O
10
•
20
3O
Diaptomus sp.
Bosmina c
(V
Daphnia I.
Holopedium g.
Kellicotia I.
Conochilus u.
10
20
30
The rUel depth diatrlbution by percent of Important species of
zooplankton In Brooks Lake on July 30, 1962.
37
------- |