1999
FINAL REPORT SUBMITTED TO
PacifiCorp
By
Marc Desjardins & Douglas F. Markle
104 Nash Hall
Department of Fisheries and Wildlife
Oregon
March 28, 2000.2
Abstract
The objectives of this two-year study (1998-1999) were to
document distribution, abundance, age class structure, recruitment success, and
habitat use by all life history stages of shortnose and Lost River suckers in
three lower Klamath River hydroelectric reservoirs (J. C. Boyle, Copco, and Iron
Gate). Lost River sucker catches were sporadic (only 3 adult individuals total)
and the focus of our analyses, therefore, shifted to shortnose suckers.
Adult and larval suckers were found in all reservoirs
both years. All life history stages (larvae, juveniles and adults) were found in
J. C. Boyle during both years and in Copco in 1999.
Juvenile suckers were not found in Copco in 1998. The number of adult
shortnose suckers was highest in Copco reservoir (n=165), followed by J.C. Boyle
(n=50) and
It appeared that recruitment of young-of-the-year suckers
only occurred in J. C. Boyle with downstream reservoirs recruiting older
individuals, perhaps those that had earlier recruited to J. C. Boyle. Tagging
studies could clarify adult recruitment dynamics and an additional study of
juvenile recruitment would be needed to confirm these patterns.
Predation pressure may be somewhat reduced in J. C. Boyle
in comparison to the other reservoirs as its fish community was dominated by
native fishes while communities in Copco and Iron Gate reservoirs were dominated
by exotic predators. J. C. Boyle also possessed.3
proportionally more littoral
habitat, which suggests it may provide a more stable environment for young
fishes. However, our sampling was inadequate to demonstrate such relationships
due to high variance in larval and juvenile catches and potentially confounding
habitat variables. One such variable was water level fluctuations, which could
interact with habitat and resource availability in complex ways. For example, water level
fluctuations, presumed to have a negative impact, were greatest in J. C. Boyle.
Extrapolation from the literature suggests it should have had the poorest
habitat for larval and juvenile suckers, but our results indicated J. C. Boyle
had the most young suckers. Additional study of the relationships between water
level fluctuations, habitat availability, the exotic fish community, and
juvenile sucker recruitment would be needed to better understand early life
history ecology of endangered lake suckers in these systems..4
Introduction
Among western North American Catostomids, the genera Deltistes
and Chasmistes are obligate lake dwellers. Their maximum distribution
and abundance came during pluvial periods between the Pliocene and Pleistocene
epochs. Since then, their habitats have been greatly reduced by desiccation and
populations have become fragmented and isolated. The
Currently, all four species of both genera are federally
listed endangered species (U.S. Department of the Interior 1973, U.S. Fish and
Wildlife Service [USFWS] 1986, 1988). Research has recently been initiated to
understand the basic ecology (habitat utilization, community level interactions,
influence of water quality, quantity and timing of water fluctuations) of the
lake suckers to help explain declining population abundances (U.S. Fish and
Wildlife Service 1993, Simon et al 1997). The USFWS recovery plan attributes the
decline of the
It is generally believed that the range of the lake
suckers has expanded due to the creation of reservoirs by the three
Both species of lacustrine suckers were once common in
Copco reservoir (Coots 1965). By the
1970’s very few
Description
of Sites
The mainstem
J.C. Boyle Reservoir
Located in south central
Power is generated at J.C. Boyle using daily peaking
operations (A.K.A. load factoring). Load
factoring is a technique used to conserve water for use during periods of
maximum economic gain. Water is run through the turbines when the price of
energy is high (i.e. during the day and during summer months). The resulting
water level profile shows drafts during daylight hours and refilling during the
night. Due to summer demand for power, fluctuations tend to increase during
summer months. Peak operations are usually initiated in May or June. This type
of operation causes the water fluctuations in J.C. Boyle to be greater than in
other reservoirs.
During the 1999 sampling period surface elevation
fluctuated between 3788.7 - 3793.5 ft. mean sea level and daily fluctuations
ranged from 0.04 – 3.53ft. The average daily water level fluctuation was
1.14ft.
Copco Reservoir
In northern
With the possible exception of J. C. Boyle, both
Methods
PacifiCorp conducted a pilot trammel net survey in the
reservoirs once a month from June through October, 1997. In 1998, we increased
effort by trying to sample more available habitat and multiple life history
stages. In 1999, knowledge gained from the previous two years was used to modify
sampling strategies to better target larval, juvenile, and adult suckers. The
targeting of multiple life history stages required many gear types used
differently through the season to capture life stages, as they became vulnerable
to the gears. Only the most successful techniques and gears were utilized in
1999. Sampling locations within the reservoirs were adjusted seasonally to
target different life history stages. For example, adults would be sampled early
in the year in deeper habitats with trammel nets while juveniles were sampled
late in the year in shallow habitats with seine nets. During 1998, sampling
trips were scheduled every three weeks and each reservoir was sampled during a
given week (Table 1). In an effort to more efficiently sample larval sucker
peaks in abundance, the schedule was altered in 1999 and reservoirs were
intensively sampled weekly from mid May to mid June (Table 1). Locations of
adult, juvenile and larval sampling sites for each reservoir are presented in
the Appendix figures A1-A12.
Adult sampling
Adult sampling commenced the last week of March 1998 and
the second week of April 1999 (Table 1). Three 300-ft trammel nets were set
non-randomly to sample depths less than approximately 20 feet. Nets were
deployed in an attempt to maximize sucker catches and sample a wide variety of
habitats. Areas that held suckers on previous sampling trips were often sampled
more than once. Trammel nets were deployed both during day and night in 1998.
Nets were set only during the night in 1999 as they proved to be more
successful. Fish species, size and condition were recorded for all individuals.
In addition, spawning condition and weight data were collected for endangered
suckers. Endangered suckers were also PIT-tagged to determine recapture rate.
Adult suckers that were difficult to identify were recorded as sucker species
and were not included in the analyses.
Juvenile sampling
Beach seines, cast nets, trap nets, backpack
electrofishing, and otter trawls were used to sample the three reservoirs for
juvenile suckers in 1998 (Table 1). Only beach seines and trap nets were used in
1999 because the other techniques were unsuccessful in 1998. Sampling sites were
non-randomly chosen with an attempt to maximize sucker catches and sample all
available accessible habitats. Areas that held suckers on previous sampling
trips were often sampled more than once. A 6.1 m beach seine (2x2x2m bag and a
4.8mm bar mesh) was used to sample all possible depths and substrates in
vegetated and non-vegetated areas.
Two trap nets (5x1.0m (4.8mm mesh) trap and a 25 m lead)
were deployed at various depths (1-7m) during day and night in 1998. However,
traps were only used late in the 1998 field season. In 1999, night trap nets
were used extensively to target juvenile suckers and effort was continuous
throughout the sample period (Table 1). Fish species, size and condition were
recorded for all individuals. In addition, spawning condition (for adult suckers
taken in trap nets) and weight data were collected for endangered suckers. Adult
endangered suckers were PIT-tagged to determine recapture rate. An arbitrary
length of 30mm was used to separate larval suckers from juvenile suckers. Due to
taxonomic difficulties, juvenile suckers could not be identified to species.
Larval sampling
Drift nets, larval trawls, and dip nets were used to
sample larval suckers. Drift nets were set for variable periods in 1998 and
because night sets were more successful, only night sets were used in 1999.
Half-meter diameter (1000-micron mesh) drift nets were set in areas of visible
flow, usually at the inflow to the reservoirs. Due to high flow rates, the lack
of a place to secure drift nets, and poor drift net accessibility at the inflow
to J.C. Boyle, drift nets were deployed from the Highway 66 and
The larval trawl consisted of a 2.5 m (1000 micron mesh)
net with a 0.8x1.5m opening. It was mounted on an aluminum frame with runners,
similar to that described by Labolle et al. (1985). Sites were selected based on
accessibility, coverage with the gear type, depth, substrate, slope, and
vegetation density. Both vegetated and non-vegetated sites were sampled. Larval
trawls were set 3-15 m from shore in water 0.5 to 1.5 m deep. Trawls were
allowed to sit for about twelve minutes to allow the site to recover from the
disturbance of setting the trawl and then pulled to shore with ropes.
Dip net sites were selected based on suitable habitat
(around macrophytes in shallow embayments) for larvae and were used to
supplement trawl data and to sample areas not easily sampled with the larval
trawl. For example, dip net sampling was very useful in
Habitat data
Habitat attributes of adult catches (trammel nets) were difficult to quantify due to depth and poor visibility. The following habitat data were collected at all larval and juvenile sampling locations: substrate type, vegetation cover, vegetation type, depth, and distance to shoreline.
Substrates were qualitatively separated into fines, sand,
gravel, small mix (a mix of the previous three categories), cobble, boulder,
large mix (a mix of the previous two categories), and intermediate mix (a mix of
both small and large substrates). Sites containing more than approximately 80%
of any one substrate were scored as being dominated by that substrate (100%).
For a description of the substrate classifications used see Appendix Table A.1.
Vegetation was qualitatively categorized as present –
absent, submerged or emergent, and vegetation cover or density categorized as
low (1%-33.3%), medium (33.3%-66.6%), or high (66.6%-100%).
A Hydrolab ® was used to collect water quality data. In
1998 water quality data were collected during reservoir profiling and from
surface waters at each sample site. Comparisons of the 1998 water quality data
between variables taken at sampled sites and at fixed reservoir profiling showed
no statistical difference. As a result, water quality data were only collected
at fixed sites during reservoir profiling in 1999. Only the 1998 water quality
data was used to compare sucker catch rates and water quality. Reservoir level
fluctuation data were collected by Pacificorp for each reservoir.
Analyses
Catch per unit effort (CPUE) for each gear type was
compared across reservoirs to quantify abundance and distribution of sucker life
history stages and to examine reservoir community structure (1998 and 1999
only). To reduce the effect of large single catches, we used a ranking system
weighted to more diverse catches. For example, the most abundant species in a
sample with five species captured was ranked 5 whereas the most abundant species
in a sample with three species captured was ranked 3. The least abundant species
in a sample was ranked 1.
Ranks were summed for each gear and the five most
dominant species given grand ranks in the intuitively more obvious notation of 1
for most dominant. Species from larval drift were not ranked. Length frequency
distributions were generated for each life history stage to examine recruitment
potential for each reservoir. Differences in methods made interannual
comparisons problematic and only trends could be described.
The highly variable larval catches, qualitatively defined
habitats, and the presence of many confounding variables made statistical
comparisons difficult. As a result, the timing of peaks and declines in larval
sucker catches were compared to the timing of critical water quality events and
water level fluctuations.
Results
Distribution and Abundance of Suckers
Adults
Total number and species of suckers caught differed
between years (Table 2). In part this is due to differences in effort. The total
trammel net effort (soak time) was 40.01 hr in 1997, 201.4 hr in 1998 and 120.31
hr in 1999. In 1997 most trammel net sampling in Copco and J.C. Boyle was during
September and October, while most sampling in
Juveniles
Juvenile suckers were captured from lake habitats in J.C.
Boyle in 1998 and J.C. Boyle and Copco in 1999 (Table 2). The highest numbers
were taken in J. C. Boyle both years (Table 2). Only 3 juveniles were found from
lake habitats in Copco reservoir in 1999. An additional 9 were captured from the
Larvae
Most larval suckers were captured in 1999, possibly
reflecting increased effort (Table 2) or a good year class since high larval
abundance was also seen in Upper Klamath Lake in 1999 (D. Simon, O.S.U, personal
communication, 2000). Catches were highest in Copco and lowest in J. C. Boyle
(Table 2). Shortnose sucker staging, migration, and spawning behaviors have been
documented in Copco (Beak Consultants, 1987, Buettner and Scoppettone 1991) and
suggest that these larvae could be shortnose suckers. Evidence of adult lake
sucker spawning behavior is lacking from the other two reservoirs.
Community Structure
Due to differences in sampling effort in 1997, only
trammel net surveys from 1998 and 1999 were compared. Adult CPUE from trammel
nets differed between reservoirs (Figure 3). Shortnose suckers made the largest
percent contribution to the adult fish community in Copco during both years
(Figure3). The percent of exotics increased downstream from 40 % in J.C. Boyle
to 78% in
Trap net catches were more uniformly dominated by exotics
with four exotics in the top five species in J. C. Boyle and Copco while all
five of the top species in
Juvenile fish CPUE from beach seines also differed
between reservoirs (Figure 4). Juvenile suckers were a numerically important
part of the beach seine fish community in J.C. Boyle. Juvenile suckers were
important in the dominant rankings in J. C. Boyle and the only native species in
the beach seine dominance ranking in Copco in 1999 (Table 3). Again, the
proportion of exotic species in the community increased downstream (Figure 4 and
Table 3) and the proportion of predators among exotics increased from 14% in J.
C. Boyle in 1999 to 99 % in Copco and 87 % in
Larval fish CPUE from larval trawls was highest in 1999.
Larval suckers were the second most abundant category (e.g., exotics, suckers,
other natives) in all reservoirs in 1999 (Figure 5) and first or second in the
larval trawl catch dominance rankings for all reservoirs in 1999 (Table 3). In
1999, exotic species increased downstream from 15% in J.C. Boyle to 67% in
Adults
The smallest C.
brevirostris were captured in J.C. Boyle reservoir and the largest in Copco.
Within each reservoir, the mean length of adult C. brevirostris in trammel nets was similar between years. Mean
lengths of J.C. Boyle C. brevirostris in
trammel nets were 301 +/-16 mm in 1998 and 327 +/- 27 mm in 1999 (Figure 6).
When the 1999 trap net data is combined
with the 1999 trammel net data the mean length of C.
brevirostris drops to 262 +/- 16 mm. There appears to be several size
classes of relatively young suckers in J.C. Boyle reservoir (Figure 6). In the
1997 survey only one C. brevirostris (405
mm) was captured.
Mean adult lengths were similar to one another in Copco
and
Juveniles
J.C. Boyle and Copco were the only reservoirs in which
juvenile suckers were collected. Juvenile
suckers were occasionally captured with larval trawls and dip nets but the most
effective gear was the beach seine. The average length of juveniles taken in J.
C. Boyle was 33 mm in 1998 and 35 mm in 1999 (Figures 9 and 10). In Copco, the
average size of juveniles taken in 1999 was 34mm (Figure 10). Juveniles were not
taken from lake habitats in Copco reservoir during 1998.
Larvae
Larval suckers were captured with larval drift nets, dip
nets, larval trawls, and beach seines. In 1998, the average length of sucker
larvae was 25 mm in J.C. Boyle, 14 mm in Copco, and 13 mm in
Habitat Comparisons
Because habitat attributes of adult trammel nets catches
were difficult to quantify, only habitats associated with juvenile and larval
catches were analyzed. Non parametric statistical comparisons were made between
larval trawl catches and habitat type (substrate type, vegetation type, and the
presence / absence of vegetation, Table 4). There were no significant
relationships between habitat variables and sucker catch rates in part because
sucker catches were highly variable across habitats.
Juveniles
In 1999 all juve nile suckers from J. C. Boyle were
captured in areas devoid of vegetation near the inflow, where macrophytes were
not abundant. In 1998 by contrast, all juvenile suckers were captured in areas
with medium to high vegetation densities. In 1999 85% of juvenile suckers were
caught over fine substrates and in 1998 75% were caught over fine substrates.
The juvenile suckers in Copco reservoir were occupying flooded terrestrial
habitats characterized by grasses and other terrestrial plants with fine and
intermediate substrates.
Larvae
In 1999, 58% of larval suckers (excluding the drift net
samples) were caught over small substrates (small mix see methods). In 1998, 83%
of the larval sucker catch was collected over small substrates. The patterns may
have been driven by the relative proportions of substrates sampled. In 1999 69%
of all sites sampled had small substrates and in 1998 78% of all sites sampled
had small substrates.
Across reservoirs, catches of larval suckers were similar
in vegetated (54%) and non-vegetated (46%) areas in 1999, despite collections
being skewed toward vegetated sites (71%). This
apparently even distribution in vegetated and non vegetated areas is largely
driven by the sucker catches in Copco reservoir. High catches from non vegetated
areas in Copco reservoir were common. Furthermore, larval sucker catches in
Copco far exceed those in the other reservoirs. In Copco reservoir, 38% of the
collections were from non-vegetated sites but those sites produced 48% of all
sucker larvae caught. In contrast, 88% of larval suckers from J.C. Boyle and
100% from
Seventy four percent of the larval catch was collected in
non-vegetated sites but these non vegetated sites made up only 33% of samples
taken from Copco. All larval catches in J.C. Boyle and
Water
Quality Parameters
Average lake-wide water temperature profiles for the
three
Lake-wide average pH profiles were similar until August
(Figure 12). The range of pH was 7.71 - 9.00 in J.C. Boyle, 7.79 - 9.19 in Copco,
7.71 – 9.63 in
The dissolved oxygen profiles were similar until early
August when values dropped in
Water
Level Fluctuations
Water fluctuations in J.C. Boyle tended to be greater
than the other reservoirs (Figures 14, 15, and 16). During the 1999 sampling
period, mean sea level surface elevations ranged 3788.7 -3793.5 ft in J. C.
Boyle, 2600.4 - 2607.3ft. in Copco, and 2324.8 - 2329.7 ft in
In all reservoirs, the timing of increased hydroelectric
production resulting in larger water level fluctuations coincided with times of
high larval abundance (Figures 15-17).
Discussion
Reservoir Summaries
J.C.
Boyle
J.C. Boyle reservoir was the only reservoir in which all
life stages of suckers were collected during both survey years (Table 2). Higher
numbers of adult Ca. rimiculus were
taken in J.C. Boyle with almost 10 times the numbers of the other two reservoirs
(Table 2). Although the CPUE for adult C. brevirostris was low (Figure 2), J.C. Boyle appeared to have
younger year classes of C. brevirostris (Figure
6) than downstream reservoirs and was the only reservoir in which juvenile
suckers were captured in any numbers (Figures 10 and 11). Even though larval
sucker catches were lowest in this reservoir (Table 2), the average size of the
larvae were greater than those from the other two reservoirs (Figure 9 and 10).
J.C. Boyle had the highest CPUE for native species
assemblages (Figures 3 –5) and usually the percentage of natives was greater
than the percentage of exotics. Despite J. C.Boyle having the most dramatic
water level fluctuation, there did not appear to be any relationship between
water level fluctuation and larval sucker catch rates although the period of
increased water fluctuation coincided with peak larval abundance (Figure 15).
Water quality did not exceed
known LC50 values.
Fine substrates and vegetated habitats predominated and J. C. Boyle reservoir
appeared to have more littoral habitat than the other two reservoirs. Its water
quality more closely followed pH and dissolved oxygen trends in
Proximity to
Copco
The largest numbers of larval suckers and adult shortnose
suckers were caught in Copco reservoir both years (Table 2). Adult shortnose
suckers were dominated by larger, older individuals (Figure 7) than in J.C.
Boyle while larval suckers were smaller (Figures 9 and 10).
Larval suckers were absent by early July and few juveniles were collected
from the reservoir. Species
assemblages for all life history stages in Copco were dominated by exotics
(Figures 3 – 5), and many were potential predators of larval and juvenile
suckers. Despite the dominance of exotics, C.
brevirostris made a significant contribution to both adult and larval
catches. Like J.C.Boyle, peak larval catches occured during periods of increased
water level manipulation. (Figure 16). Non-vegetated sites were 38% of the
larval sampling sites and produced 48% of the larval suckers. Since most Copco
sites sampled had small substrates, the majority of larval suckers were
collected over this substrate type.
Only C.
brevirostris and Ca. rimiculus were
collected in
Species assemblages were dominated by exotics and many
were potential predators on larval and juvenile suckers. Again, the period of
increased water level manipulation coincided with peak larval abundance (Figure
17). Critical water quality levels were encountered in mid and late July after
larval catches of suckers had declined. Larval sucker habitat reflected habitat
available for sampling with 93% associated with vegetation and 92% on fine
substrates. The shoreline in
Taxonomic problems
The taxonomic identifications used have an unknown,
though we believe small, potenetial for mis-identification. The taxonomic status
of the
Andreasen (1975) and Buettner and Scoppettone (1991)
found the Copco shortnose population was similar to those in
Resolution of species taxonomy is imperative for better
understanding the roles of the reservoirs in the life cycles of
Important Ecosystem Processes and Future Studies
There were no significant relationships between habitat
or environmental variables and larval and juvenile sucker catch rates. Despite
these results we believe these variables may be important. The nature of our
sampling plus the patchy distribution and high variance of sucker catches (0 -
1030 individuals per sample) may have made it impossible for us to detect
differences. A structured sampling regime, stratified on variables of interest,
rather than such a broad scale survey would be needed to address these types of
relationships.
J.C. Boyle contains fewer exotic predators than the lower
two reservoirs, Copco and
Littoral
Zone Habitat
J.C. Boyle possesses proportionally more littoral
habitats than the two lower reservoirs, although cross reservoir comparisons
have not been quantified. The utilization of aquatic plants as fish habitat has
been extensively documented. Janecek (1988) compiled a list of 112 different
species representing 19 families that were collected in aquatic macrophytes in
the upper
Fish community structure and stability have been
associated with the presence, abundance, species composition and structural
heterogeneity of macrophytes (Hinch et al 1991, Benson and.Magnuson 1992,
Brazner and Magnuson 1994, Weaver et al 1997). In addition, the effects of
predation risk on habitat use in vegetated and nonvegetated areas has been
extensively investigated (Savino and Stein 1989, Wahl and Stein 1989, Jordan et
al. 1996). Jordan et al. (1996) showed in laboratory experiments that pinfish
used seagrass and open sand habitats equally in the absence of predators.
However, in the presence of predators, pinfish avoided nonvegetated areas.
Vegetated and complex habitats are advantagegous for prey species for they can
reduce predator efficiency through increases in handling times and visual
constraints.
However, increased habitat complexity can also decrease
foraging success of prey species (Kieffer and Colgan 1993, Tatrai and Herzig
1995). This can lead to a trade-off between mortality and growth. Dill and
Fraser (1984) found that starved juvenile coho were less responsive to the
presence of predators and willing to take more risks while foraging.
Competition and predation could effect habitat selection of prey species
and could be an important ecological process effecting sucker survival and
habitat choice in the reservoirs.
Water
Level Fluctuations
Water level fluctuations may further complicate the
interactions of predation and habitat availability. Theoretically, fish will
distribute themselves within and among lakes and reservoirs according to their
physiological and behavioral requirements and the availability of preferred
habitat (Werner 1986). Individuals are expected to choose habitats where
environmental conditions are optimal. However, habitats are multi-dimensional
(Magnuson et al. 1979) and environmental variables are interrelated. A site with
optimal physical conditions becomes less optimal habitat when species densities
become excessive. Similarly, the magnitude and frequency of water level
fluctuations can blur otherwise straightforward habitat relationships. Vegetated
sites where suckers were captured during one week may be dry the next week due
to water drawdown. Water level fluctuation can act as a disturbance through
changes in littoral zone cover and substrate (Gasith and Gafny 1990, Dibble
1993, Beauchamp et al. 1994, Irwin and Noble 1996). However, prior studies of
this phenomenon were conducted on flood control reservoirs where fluctuations
are less frequent and drawdown periods extend for longer periods than in the
lower Klamath reservoirs. The relevance of these studies to the suckers in the
lower Klamath reservoirs is speculative, but suggestive that the seasonal and
daily dynamics of habitat changes could be important.
Changes in water levels can also alter nutrient
concentrations, light, temperature, and razing pressure and indirectly effect
phytoplankton and zooplankton abundance (Lötmarker 1964, Rodhe 1964, Benson
1968, Mitchell 1975). Direct effects on phytoplankton and zooplankton can
include physical removal from the system during release of water from reservoirs
and dessication from stranding of organisms during drawdown (Benson and Cowell
1967, Clafin 1968, Barman and Barada 1978). Changes in phytoplankton and
zooplankton communities can effect higher trophic levels.
Benthic invertebrates can be indirectly or directly
affected by water level fluctuations through export out of the system, exposure
and desication, and reduction in community diversity (Grimås 1961, Davis and
Hughes 1966, Fillion 1967, Swanson 1967, Cowell and Hudson 1967, Hunt and Jones
1972, Benson 1973, Kaster and Jacobi 1978). Because some macro invertebrates
have specific habitat requirements such as soft mud or macrophytes, loss or
additions to their habitats greatly alters their species composition and can
potentially change fish foraging success (Benson 1973, Wegener et al. 1975).
If water level fluctuations force larval and juvenile
fishes to abandon refuge littoral areas, they can be more vulnerable to
predators. Increased foraging by predators during or immediately after drawdown
has been extensively documented (Heman et al. 1969, Beard and Snow 1970, Johnson
and Andrews 1974, Heisey et al. 1980). The
potential impacts documented here would suggest that reservoirs with greater
absolute water level changes and more frequent fluctuations would be less
desirable habitats. If true, we would predict that Copco would have the best
habitat for larvae and juveniles because water levels tended to rise over the
season (Figure 15). We would also predict that J. C. Boyle should have the worst
habitat because the total change in lake level was greatest (Figure 14) and the
frequncy of fluctuations greater than
J.C. Boyle reservoir is closer geographically to
One interpretation of the patterns seen in this study is
that the
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