William J. Lissa, Gary L. Larsonb, Elisabeth K. Deimlinga, Lisa Ganioe, Robert Gresswella, Robert Hoffmana, Mihaly Kissa, Gregg Lomnickya, C. David McIntirec, Robert Truittd, and Torrey Tylera
March 1995
CA-9000-8-0006
Subagreement 11
National Park Service
Pacific Northwest Region
Science & Technology
909 First Avenue
Seattle, WA 98104
|
aDepartment of Fisheries and Wildlife Nash Hall Oregon State University Corvallis, OR 97331-3803
aNational Biological Service
eNorthwest Statistical Services |
cDepartment of Botany Oregon State University Corvallis, OR 97331
dDepartment of Forest Resources |
LAKE CLASSIFICATION AND CHEMICAL AND PHYSICAL PROPERTIES OF LAKES
CONCLUSIONS REGARDING EFFECTS OF STOCKED TROUT ON NATIVE BIOTA IN NOCA
LAKE CLASSIFICATION AND CHEMICAL AND PHYSICAL PROPERTIES OF LAKES
Figure 1. Interrelationships among components of watersheds and lakes
Figure 2. Location of the North Cascades National Park Service Complex in Washington. Westslope/Eastslope: relative to the hydrologic crest (Ageeand Pickford 1985)
Figure 3. Relationship between estimate date of ice-out (Julian days), elevation (m), and basin aspect for eastslope and westslope subalpine lakes in 1989
Figure 4. Relationship between epilimnion temperature (°C) and month for westslope vegetation zones. Each symbol represents the average temperature of all lakes sampled in a particular vegetation zone each month
Figure 5. Relationship between epilimnion temperature (°C) and elevation (m) for forest and alpine zones
Figure 6. Ordination of water chemistry variables for lakes sampled from 1989-1992. Groups defined by cluster analysis (Table 9) are shown. Discriminant analysis was used to graphically represent the clusters in ordination space. A total of 142 samples represent 58 lakes
Figure 7. Relationship between total Kjeldahl nitrogen (mg/l), total phosphorus (mg/l) and maximum lake for eastslope and westslope lakes
Figure 8. Relationship between total Kjeldahl nitrogen (mg/l) and an index of flushing ratio (watershed area/lake volume) for westslope vegetation zones
FISH
Figure 1a. Frequency of all fish caught in gill nets and recaptured fish (an indicator of the length of fish marked by angling) during the mark-recapture procedures in 13 lakes in North Cascades National Park Service Complex
Figure 1b. Number of all fish caught in gill nets and recaptured fish (an indicator of the length of fish marked by angling) during the mark-recapture procedures in 13 lakes in North Cascades National Park Service Complex
PHYTOPLANKTON
Figure 1. Ordinations of the phytoplankton divisions and the four lake types (alpine, subalpine, high forest and low forest) relative to the taxonomic composition of the phytoplankton at the division level during the period from 1988 to 1993
Figure 2. Relationships among elevation, temperature and pH, and the scores of the X axis of the ordination of the four lake types (Fig. 1)
Figure 3. Relationships among alkalinity, conductivity and Kjeldahl-nitrogen, and the scores of the X axis of the ordination of the four lake types (Fig. 1)
Figure 4. Relationships among ammonia-nitrogen and nitrate-nitrogen and the scores of the X axis, and the relationship between total phosphorus and scores of the Y axis of the ordination of the four lake types (Fig. 1)
Figure 5. Ordination of the phytoplankton community assemblages by lake and the position of each cluster of lakes for samples collected in 1989
ROTIFERS
Figure 1. Dendrogram from a hierarchical agglomerative cluster analysis of lakes which had mean rotifer densities > 1.0 per liter (30 lakes)
Figure 2. Graph of axis scores for each lake from detrended correspondence analysis. Axis one scores correlated positively with total Kjeldahl nitrogen (TKN), total phosphorous (Total P), temperature, and proportional abundance of adult Daphnids using Pearson product-moment correlation coefficients. Axis one scores correlated negatively with proportional abundance of large Diaptomids and Holopedium gibberum. Axis two scores correlated positively with elevation and ortho-phosphorous (Ortho P), but correlated negatively with temperature. Lakes are numbered according to cluster.
Figure 3. Plot of densities (number per liter) of adult Cladocerans against densities of: a) Kellicottia lonpispina; b) and all loricated rotifers combined. Data used are sample means.
CRUSTACEAN ZOOPLANKTON
Figure 1. Cluster analysis of 53 lakes based on proportional abundance of crustacean zooplankton species, North Cascades National Park Service Complex
Figure 2. Ordination of lakes based on proportional abundance of crustacean zooplankton species in each lake. Lake clusters (Table 2) are shown. Arrows indicate direction of increase of abiotic variables along axis one
Figure 3. Relationship between the concentration of Kjeldahl nitrogen and lake depth relative to the occurrence of D. kenai, D. tyrrelli, and lakes inhabited by both species
Figure 4. Relationship between the concentration of total phosphorus and lake depth relative to the occurrences of D. kenai, D. tyrrelli, and lake inhabited by both species
Figure 5. Crustacean zooplankton communities at high and low elevation on the east and westslope of the crest of the Cascades, North Cascades National Park Service Complex. Dominant species indicated by an *
Figure 6. Conceptual model of the possible interactions of lake morphometry, water, temperature, water chemistry, and invertebrate and vertebrate predation in determining distribution and abundance of diaptomid copepods in NOCA
MACROINVERTEBRATES
Figure 1. Generalized model of the organization of nearshore macroinvertebrate communities in the lakes of the North Cascades National Park Service Complex, with Substrate Preference Groups (after Faunal Categories, Ward 1992) and Functional Feeding Groups (after Merritt and Cummins 1984)
Figure 2. Relationship of the number of taxa per lake and maximum water temperature
Figure 3. Ordination of benthic substrates (A) and lakes by vegetation zone (B) based on axes derived from DECORANA analysis of substrates matrix
Figure 4. Factors affecting the presence of macroinvertebrates in high mountain lakes
RESEARCH DESIGN
Table 1. Sampling frequency of NOCA lakes from 1989 to 1993
LAKE CLASSIFICATION AND CHEMICAL AND PHYSICAL PROPERTIES OF LAKES
Table 1. Processes or events controlling systems on different spatiotemporal scales in North Cascades National Park Service Complex
Table 2. Analytical procedures used by the Cooperative Chemistry Analytical Laboratory, Oregon State University. (Cameron Jones, personal communication)
Table 3. Vegetation zones for lake basins with corresponding cover types (Agee & Pickford 1985) and cover type mean elevations for open and closed forest, lake elevations (min & max), habitat notes and NOCA lakes. Sampled lakes in bold type. Lake acronyms given in Appendix I
Table 4. Elevations (EL), precipitation (PREC), and date of ice-out for NOCA lakes by position east or west of the Cascade crest and vegetation zone
Table 5. Morphogenetic lake classes listed with general descriptors associated with each class. Temporal frame of reference and depth for North Cascades lakes (Maximum age to approx. 7000 yrs.)
Table 6. Distribution of morphogenetic classes of NOCA lakes by vegetation zone. Number in parentheses
Table 7. Means and standard deviations (in parenthesis) for water chemistry variables 1989-1992. LF= Low Forest; HF= High Forest; SA= Subalpine
Table 8. Summary of lake groups developed using cluster analysis, based on water chemistry variables, 1989-1992. Each lake sample was considered an individual point. Two lakes with multiple samples had a single sample in a second group. Lakes occurring in more than one group were placed in the group containing the majority of samples for that lake. Lake acronyms given in Appendix I
Table 9. Cluster group means of selected water chemistry variables, 1989-1992
FISH
Table 1. Mean length, weight, and condition factor (K) for fish captured in gill nets set in lakes of North Cascades National Park Service Complex, 1990-1993
Table 2. Age distribution (%) estimated from an age-length key for fish captured in gill nets from lakes in North Cascades National Park Complex, 1991-1992
Table 3. Mean length and number of otolith samples (n) of each age group of fish captured in gill nets from lakes in North Cascades National Park Service Complex, 1991-1992
Table 4. Trout population estimates (N) and upper and lower confidence limits (LCL and UCL; p=0.05) for lakes in North Cascades National Park Service Complex, 1990-1993
Table 5. Trout density in lakes that do not support reproducing populations, North Cascades National Park Service Complex, 1990-1992
Table 6. Trout density and biomass (mean weight per fish estimated from weight-length equation) estimates for lakes in North Cascades National Park Service Complex, 1990-1993
Table 7. Stomach contents of fish in 1990
Table 8a. Percentage of major food groups in trout diet determined from numbers of organisms found in stomachs
Table 8b. Macroinvertebrate and vertebrate organisms recovered from trout-stomach samples (NOCA lakes, Summer 1990). Average number of prey organisms per fish for each food grouping arrange by vegetation zone
Table 8c. Percent of prey organisms per fish for each food group arranged by vegetation zone
AMPHIBIANS
Table 1. Average and range interval (in parenthesis) of larval densities of A. macrodactylum, years each lake was sampled and total number of snorkel surveys in each year (in parenthesis) in North Cascades National Park Service Complex, WA, USA
Table 2. Average and 95% confidence interval (in parenthesis) of physical and biological variables in fish and fishless lakes in North Cascades National Park Service Complex, WA, USA. P-values are for comparisons of fish and fishless lakes using the Mann-Whitney U test (a=0.05). P-values for comparisons among all lakes and for eastslope lakes (Pyramid Lake omitted) are given
Table 3. Physical characteristics of westslope lakes and number of times each lake was sampled annually, North Cascades National Park Service Complex, WA, U.S.A.
Table 4. Density estimates (see Fish section) and average total length (TL) of trout in four westslope lakes, North Cascades National Park Service Complex, WA, U.S.A
Table 5. Occurrence of Ambystoma and Taricha in westslope lakes, North Cascades National Park Service Complex, WA, U.S.A.
Table 6. Annual average densities of salamander life stages determined by snorkel surveys in five westslope lakes, North Cascades National Park Service Complex, WA, U.S.A.
Table 7. Anuran taxa found in NOCA Lakes (A=adult, L=larva, T=tadpole)
PHYTOPLANKTON
Table 1. Number of NOCA phytoplankton samples collected by month and year and the number of lakes sampled each year from 1988 to 1993
Table 2. NOCA phytoplankton data: 1988-1993. List of taxa with division and codes
Table 3. Average proportional abundances (>= 5%) for phytoplankton taxa in the 178 samples collected during the period from 1988 to 1993, number of samples in which each taxon was present, and average proportional abundance in all samples in which each taxon was present
Table 4. Proportional abundances in samples with 500 cell counts, proportional cell densities and cell biovolumes for each taxonomic division and class during the period between 1988 and 1993
Table 5. Average number of phytoplankton taxa by taxonomic division and class in alpine, subalpine, high-forest and low-forest lakes during the period from 1988 to 1993
Table 6. Proportional abundances in samples with 500 cell counts and proportional cell densities and biovolumes by taxonomic division and class in alpine, subalpine, high-forest and low-forest lakes during the period between 1988 and 1993
Table 7. Samples in each cluster of the lake ordination relative to the taxonomic composition of phytoplankton in samples collected in 1989
Table 8. Number of alpine, subalpine, high-forest and low-forest lakes relative to the eastside (E) and westside (W) of the park in each cluster of the lake ordination in 1989
Table 9. Dominant phytoplankton taxa in each cluster of the lake ordination for samples collected in 1989
Table 10. Average number of taxa and phytoplankton cell densities per sample in each cluster of the lake ordination, east-side (E) lakes, west-side (W) lakes, and all lakes collectively for samples collected in 1989
Table 11. Total number of phytoplankton taxa, average number of taxa per sample, and the ranges of cell densities in lakes in Quebec, Finland, Olympic National Park, Mount Rainier National Park, and NOCA (1989)
Table 12. Dominant phytoplankton assemblages (proportional abundances) at the division level in lakes at high latitude or elevations
ROTIFERS
Table 1. Number of times each lake was sampled in each year. Lakes with an asterisk were used in cluster analysis and to examine effects of crustacean zooplankton on rotifers
Table 2. Twenty-seven east-slope lakes grouped according to vertebrate predation category. Kruskal-WalIis tests were used to test for differences between categories in rotifer taxa
Table 3. Percent of 66 lakes in which taxa and proportional abundance of taxa among all lakes in which vertical tows were taken
Table 4. Characteristics of lake clusters: Dominant taxa in each cluster with means of their proportional abundance among lakes in that cluster; other taxa in each cluster which had means of proportional abundance greater than 0.01 per liter. Lakes in each cluster are listed
Table 5. Means of chemical and physical variables from lakes within each cluster. Asterisks indicate those variables that had statistically significant correlations with ordination axes scores from a detrended correspondence analysis
Table 6. Means (and ranges) of crustacean zooplankton density from lakes within each cluster. Asterisks indicate those taxa whose proportional abundance had statistically significant correlations with ordination axes scores from a detrended correspondence analysis
Table 7. Means (and ranges) of densities (no/l) of rotifer taxa within each vertebrate predation category for twenty-seven east-slope lakes. P values of Kruskal-Wallis tests are listed
CRUSTACEAN ZOOPLANKTON
Table 1. Aspect (east or west of Cascade crest), vegetation zone (F=forest, S=subalpine, A=alpine), and sampling frequency of lakes used in analysis of crustacean zooplankton
Table 2. Lake clusters based on proportional abundance of crustacean zooplankton species in North Cascades National Park Service Complex. Dominants are species with >= 50% proportional abundance. Subdominants are species with >= 5% proportional abundances. Average number of species in each cluster is in parenthesis
Table 3. Percentage similarity of lake clusters based on proportional abundance of crustacean zooplankton species in North Cascades National Park Service Complex
Table 4. PCA component loadings for each abiotic variable. Heavily-loaded variables in each component are indicated in bold type
Table 5. Average length of crustacean zooplankton species and the number of individuals measured (N) in North Cascades National Park Service Complex
Table 6. Relative occurrence of crustacean zooplankton taxa in 53 lakes in North Cascades National Park Service Complex
Table 7. Chemical and physical properties of lake clusters
Table 8. Distribution of adult diaptomid copepods in North Cascades National Park Service Complex, 1989-1993. Based on vertical and horizontal net tows
Table 9. Pearson correlation coefficients and associated P-values (in parenthesis) between densities of D. kenai, D. tyrrelli, D. rosea and H. gibberum and selected environmental variables for all lake samples
Table 10. Pearson correlation coefficients and associated p-values (in parentheses) between TKN and TP and selected environmental variables for all lake samples
Table 11. Average temperatures of D. tyrrelli lakes, and lakes inhabited by D. tyrrelli and D. kenai, and the temperature range of D. kenai lakes
Table 12. Density of D. tyrrelli and large copepods in lakes where TKN >= 0.04, TP >= 0.004, and temp >= 11.4d°C
Table 13. Vertebrate predators in eastslope lakes, North Cascades National Park Service Complex, 1989-1993
Table 14. Body length of crustacean zooplankton taxa and density of larval salamanders (A. macrodactylum) in fishless eastslope lakes, North Cascades National Park Service Complex
Table 15. Densities (no/l) of adult copepods Diaptomus kenai and Diaptomus tyrrelli in eastslope lakes with reproducing trout, non-reproducing trout, and no vertebrate predators
Table 16. Averages, ranges (in parenthesis) and P-values for statistical comparison (Wilcoxon rank sum test) of lakes with reproducing and non-reproducing fish
MACROINVERTEBRATES
Table 1. Lake classification categories developed by Lomnicky (unpublished manuscript; Liss et al. 1991) and the number of lakes sampled in each category
Table 2. The distributions of 15 taxa examined for predator impacts
Table 3. Taxonomic groups in NOCA lakes
Table 4. Results of multiple regression analyses of the relationship of number of taxa per lake and maximum temperature, elevation, surface area and maximum depth. (Level of Significance p <0.05)
Table 5. Non-hierarchical clustering of lakes (NCSS, k-means algorithm) by number of taxa per lake, maximum temperature and lake elevation
Table 6. The mean number of taxa per lake, maximum temperature, and elevation for lakes in each classification category
Table 7. Percent of inorganic and organic substrates and combined substrate preference groups in NOCA lakes
Table 8. Pearson product-moment correlations between predictor variables and the first two canonical variates calculated during discriminant analysis
Table 9. Functional Feeding Groups in NOCA lake classification categories
Table 10. Vertebrate predation category comparisons for three macroinvertebrate taxa in NOCA lakes (Fisher's Exact Test, p <0.05)
Table 11. Parameters of habitat and taxa in NOCA lake classification categories
Research in remote and rugged terrain is difficult under the best of circumstances. This research would not have been possible without the co-operation and logistical support provided by personnel of North Cascades National Park Service Complex. In particular we thank Jonathan Jarvis, former Chief of Natural and Cultural Resources, and Bruce Freet, who presently holds that position. We also thank Park management biologist Bob Wasem, now retired, and aquatic biologist Reed Glesne for their interest and support. We also are grateful for the support and assistance provided by the National Park Service Regional Office in Seattle, particularly Jim Larson, former Regional Chief Scientist, and Shirley Clark, Assistant Regional Chief Scientist. National Park Service Personnel at the Marblemount Ranger Station, especially Gary Mason and Lee Smith, provided quality logistical support, and Kelly Wildman provided outstanding administrative, accounting, and clerical support at Oregon State University. We thank James Hall for assistance in fish sampling and for useful suggestions pertaining to fish data analysis. Tony Reece of Hi-Line Helicopters deserves special thanks for prompt and efficient flight services.
We are deeply grateful to the former and present members of our Scientific Advisory Panel: Stanford Loeb (Chair), Stanley Dodson, Robert Hughes, William Neill, W. John O'Brien, James Petranka, William Platts, and H.B. Shaffer. They were extremely helpful in establishing direction for the research, reviewing our annual reports and proposals, and suggesting improvements in research design and interpretation. The research benefitted tremendously from their involvement. Notwithstanding, any shortcomings of the research are solely the responsibility of the Principle Investigators.
The National Park Service provided support for this project to Oregon State University through cooperative agreement CA-9000-3-0003, Subagreement 21 and cooperative agreement CA-9000-8-006, Subagreement 11.
This research project was initiated in response to a directive from the Director of the National Park Service (NPS), dated June 12, 1986, which related to the stocking of fish into lakes of North Cascade National Park Service Complex (NOCA). The directive was an official response to a January 1986 request from the NPS Pacific Northwest Regional Office (PNRO) for a clear statement regarding fish-stocking policies of the NPS. Stocking of non-native animals, including fish, is not allowed in units of the National Park System (NPS, 1991). Although high-mountain lakes in NOCA were originally devoid of fish, the park and the State of Washington co-signed in 1979 a variance to the NPS policy of no fish stocking so that selected lakes could continue to be stocked with non-native trout at regular intervals. Although the policy variance did not have a termination date, NOCA drafted a new memorandum of understanding (MOU) in 1985 in which the policy variance was dropped. This proposal resulted in considerable debate by the public and Congress. A supplemental agreement to the 1985 MOU was prepared in 1988 and specified the stocking levels of selected lakes to the year 2000. The stipulation also was present that the practice of stocking could be discontinued by mutual consent.
The 1986 memorandum from the Director of the National Park Service contained several key points and conclusions. The key points were: (1) fishing is an acceptable recreational activity in NOCA, (2) stocking of selected naturally fish-free waters is a practice that existed prior to the creation in 1968 of the park, and (3) the act of stocking naturally fish-free lakes or streams is to be avoided in areas managed as natural zones. Based on these points, the Director concluded that NOCA waters are to be aggregated into three categories: natural fish-free waters, waters containing self-sustaining fish populations, and waters in which fish stocking is to be continued. The Director further concluded that all NOCA waters that are presently without fish will not be stocked, NOCA waters that are potential candidates for continued fish stocking are to be reviewed, and those NOCA waters selected to be managed as enhanced recreational fisheries are the only ones that may be stocked now and in the future. The Director also suggested that it would be desirable for the PNRO to develop and implement research to establish current fish and aquatic habitat baseline conditions, monitor the impacts of the fish stocking on fish and wildlife, and determine changes over time referenced against current baseline conditions or against undisturbed natural conditions.
Several meetings were convened in 1987 between staff of NOCA, the Washington Department of Game, and the Oregon State University Cooperative Park Studies Unit to discuss the Director's memorandum and appropriate plans to carry-out his directives. Based on these meetings, park management and the PNRO determined that the existing lake and fish data from the park would be reviewed and summarized, a literature review and synthesis would be prepared on the effect of stocked fish on native biota in temperate lakes, and a lake classification system would be developed. The focus of the first two tasks was to determine what was already known about park resources and the role of fish in lakes at other locations. The latter task was needed so that study lakes could be selected and compared relative to physiographic conditions (climate, geology, topography and vegetation) and lake morphometry.
Work on the literature review and synthesis, and the development of the lake classification system were funded in 1988 by the PNRO. Initial sampling of a few lakes and ground-truthing of park physiography for the lake classification system were conducted in the summer of 1988. The literature review and synthesis (Goetze et al., 1989) and a preliminary lake classification system (Lomnicky et al., 1989) were completed in 1989.
Review of information available from the park revealed that much was known about fish stocks and certain aspects of lakes, but the available information was not sufficient to assess the effect of stocked fish on native biota. The literature review and synthesis of information about the role of fish in temperate lakes clearly demonstrated that little was known about the effects of stocked fish on communities of native species in naturally fishless high-mountain lakes. Most research had focused on growth, reproduction, and harvest of introduced fish, although elimination of prey species of fish in high-mountain lakes had been documented in a few studies (Nilsson, 1972; Reimers, 1958; Dawidowicz and Gliwicz, 1983; Walters and Vincent, 1973). In particular, fish were shown to alter the size structure, species composition, and species abundance of zooplankton by selectively preying on the largest species, and thereby causing the zooplankton community to be dominated by smaller species (e.g., Brooks and Dodson, 1965; Zaret, 1980). Such changes in the zooplankton community also could alter the species composition, abundance, and size-structure of phytoplankton assemblages. Fish also were shown to affect benthic macro-invertebrate communities by shifting the relative proportions of taxa (Post and Cucin, 1984; Blois-Heulin et al., 1990). In some cases benthic macro-invertebrate species (Reimers, 1958; Nilsson, 1972; Blois-Heulin et al., 1990) and amphibian species (Taylor, 1983; Bradford, 1989) were eliminated from lakes. Besides these examples of the impacts of fish on native prey species, some general patterns emerged from the literature:
1. The kinds and abundances of native species (community structure) that were in a lake before stocking fish and the types and intensities of complex interactions among species (community organization) were not the same after stocking. Changes in community composition involved phytoplankton, zooplankton, benthic macro-invertebrates and amphibians. Extinctions of some native prey species can occur in lakes.
2. The kinds of effects depended on species composition and species interactions in the communities into which fish were introduced. In particular, the level of invertebrate predation can be important in influencing fish impacts on lake communities.
3. Habitat conditions can strongly influence community organization. Prey refuges can mediate effects of predation. Fluctuations in chemical and physical conditions may reduce, enhance or even override effects of fish predation.
4. Effects on native prey communities may be influenced by the age, size structure, and densities of stocked fish. Fish of different ages and sizes may use different habitats and consume different species and sizes of prey.
5. The effects of introduced fish on the biota in naturally fishless high-mountain lakes could not be predicted with much certainty from data available for NOCA. Some of this uncertainty results from the variability among lakes in physical, chemical, and biological characteristics, as well as the complexity of interactions within lake communities. The lake classification system was developed to account for some of this natural variation by grouping lakes into classes based on watershed and lake characteristics.
1. Salamander larvae are the top vertebrate predators in many fishless lakes in NOCA. Larvae of Ambystoma macrodactylum appear to be relatively sensitive to predation from introduced trout. There were statistically significant differences in larval densities between lakes with fish and fishless lakes. We found few or no larvae in lakes with trout with the exception of MR 11, a lake with sporadic history of trout stocking. However, larval density in fishless lakes was variable indicating that abiotic factors possibly related to lake size were influencing larval abundance. Limited sampling of lakes with A. gracile suggests that this species may be less vulnerable to trout predation than A. macrodactylum. In lakes with trout, A. gracile maintained higher densities of embryo masses and larvae than A. macrodactylum. Ambystoma macrodactylum may persist in the same geographic area as stocked trout by utilizing habitats that are unsuitable or inaccessible to trout such as smaller, shallower lakes and ponds. These habitats can support relatively high densities of larvae. Ambystoma gracile may persist in the same geographic region as trout by possessing behavioral and morphological adaptations such as noxious skin secretion, more reclusive or nocturnal behavior, or large size that enable it to live in lakes with fish.
2. Effects of introduced trout on the limnetic food web appear to be influenced by trout density and size structure and lake nutrient levels. In general, reproducing trout maintain higher densities and a more complex age and size structure than lakes in trout which do not reproduce are periodically stocked as fry. The large copepod Diaptomus kenai is the most ubiquitous crustacean zooplanktoer in NOCA, It is apparently able to persist across a wide range of abiotic factors in NOCA lakes, but may be limited by higher temperatures in some lakes. The small copepod, D. tyrrelli, was found only in lakes with higher nutrient levels. These lakes tended to be smaller, shallower lakes. Large copepods appear to negatively affect D. tyrrelli, probably through predation. In eastslope lakes, densities of D. kenai were significantly lower in lakes with reproducing fish than in lakes with non-reproducing trout. We were unable to determine if there were differences in D. kenai densities between lakes with non-reproducing trout and lakes with no vertebrate predators since most eastside lakes maintained either trout or salamander larvae. We hypothesize that reproducing trout at high densities can reduce or eliminate large copepods. In smaller, shallower lakes with nutrient levels suitable for D. tyrrelli, the small copepod may increase in abundance following reduction or elimination of large copepods by trout predation.
3. Three of 15 taxa of nearshore macroinvertebrates were found in significantly fewer lakes with vertebrate predators (trout and salamanders) than in lakes with no vertebrate predators. The distribution of only one of these taxa, Desmona, may be limited solely by trout. Distribution and abundance of rotifer taxa appear largely unrelated to vertebrate predators.
http://www.nps.gov/noca/trout1.htm