12-17-2002, 09:57 PM
Lately there's been quite a bit of board traffic concerning Bear Lake, it's fish, and it's productivity. I read this informative summary a couple years ago and have found many other publications by Wurtsbaugh very informative. Break out your dictionaries, because if you take time to understand this publication summary, you'll have a better understanding of Bear Lake's productivity (or lack there of) and food web. Who knows, this information may even help you catch more fish.
Wurtsbaugh, W. and C. Hawkins. 1990. Trophic interactions of fish and invertebrates in Bear Lake, Utah/Idaho. Ecology Center Special Publication, Logan, UT.
SUMMARY
An intensive study of the limnology, invertebrates and fishes of Bear Lake was conducted in 1987 in order to define the productivity and food web of the community. Limnological parameters and invertebrates were measured at approximately monthly intervals while fish distribution and feeding was analyzed in February, June, August, and October. Samples were collected at three to eight stations along a transect running from the shallow littoral area on the west side of the lake, to the deep profundal zone.
During the study Bear Lake did not freeze, but it nevertheless was inversely stratified in winter. During summer stratification surface temperatures reached 19°C. Chlorophyll A concentrations were highest during fall and winter mixing. The mean summer chlorophyll concentration was only 0.5 mg/m3 indicating that Bear Lake is very oligotrophic.
The zooplankton assemblage was dominated by the calanoid copepod Epischura nevadiensis and by other small crustaceans and rotifers. Copepods and cladocera > 1 mm were rare. Crustacean abundance peaked in the spring and fall, but their mean annual abundance was only 2,000 organisms/m3 . The mean annual biomass of zooplankton (0.42 g dry weight/m2) was among the lowest yet recorded for a temperate zone lake.
The benthic invertebrate community was also characterized by low densities of small organisms. Chironomid larvae and ostracods dominated the biomass of the littoral zone, while oligochaetes were dominant in profundal areas. Mean annual dry biomass of benthic invertebrates in the littoral zone was 0.80 g dry wt/m2, but declined to 0.10 g/m2 in the profundal zone (35-45 m). The whole-lake mean annual biomass of 0.34 g dry wt/m2 is the lowest recorded for a temperate zone lake. Production of benthic invertebrates in the lake may be limited by the low primary productivity and by dominance of fine marl sediments.
The density and biomass of invertebrates in the surface film (neuston) of the lake was very low, but these organisms were generally larger than those in the plankton or benthic invertebrate assemblages. Chironomid pupae, aphids and ants contributed most to the biomass of the neuston. Biomass varied substantially over the year from a low of 0.000003 g dry matter/m2 in February to 0.0003 g/m2 in August.
Thirteen species of fish were captured in Bear Lake, four of which are endemic. Ninety-nine percent of the fish captured were native. Bear Lake sculpin, Bonneville cisco, Utah suckers and two species of whitefish dominated the catch. A large portion of the fish were concentrated where the metalimnion intersects the lake bottom. Only one species (Bonneville cisco) was captured in the pelagic region. Ontogenetic shifts in habitat preference occurred in most species, with small fish utilizing shallower, warmer regions than large fish.
Multivariate analysis of the diets of the fishes delineated three trophic groups: 1) benthivores; 2) a zooplanktivore; and, 3) fish feeding on forage fish and neuston. Eight species of fish in Bear Lake fed primarily on the relatively abundant benthic invertebrates, particularly chironomid larvae and ostracods. Only one species, Bonneville cisco, utilized significant amounts of zooplankton. Cutthroat trout fed on neuston when they were young and became primarily piscivorous after reaching 300 mm. Adult lake trout have a diet similar to large cutthroat.
The low fish yield in Bear Lake (0.5 kg/ha/yr) is consistent with its low intrinsic productivity. The paucity of large invertebrates in either the plankton,or benthic communities probably limits recruitment of juvenile trout. Predation by adult trout may also lower survival of juvenile cutthroat planted in Bear Lake.
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Wurtsbaugh, W. and C. Hawkins. 1990. Trophic interactions of fish and invertebrates in Bear Lake, Utah/Idaho. Ecology Center Special Publication, Logan, UT.
SUMMARY
An intensive study of the limnology, invertebrates and fishes of Bear Lake was conducted in 1987 in order to define the productivity and food web of the community. Limnological parameters and invertebrates were measured at approximately monthly intervals while fish distribution and feeding was analyzed in February, June, August, and October. Samples were collected at three to eight stations along a transect running from the shallow littoral area on the west side of the lake, to the deep profundal zone.
During the study Bear Lake did not freeze, but it nevertheless was inversely stratified in winter. During summer stratification surface temperatures reached 19°C. Chlorophyll A concentrations were highest during fall and winter mixing. The mean summer chlorophyll concentration was only 0.5 mg/m3 indicating that Bear Lake is very oligotrophic.
The zooplankton assemblage was dominated by the calanoid copepod Epischura nevadiensis and by other small crustaceans and rotifers. Copepods and cladocera > 1 mm were rare. Crustacean abundance peaked in the spring and fall, but their mean annual abundance was only 2,000 organisms/m3 . The mean annual biomass of zooplankton (0.42 g dry weight/m2) was among the lowest yet recorded for a temperate zone lake.
The benthic invertebrate community was also characterized by low densities of small organisms. Chironomid larvae and ostracods dominated the biomass of the littoral zone, while oligochaetes were dominant in profundal areas. Mean annual dry biomass of benthic invertebrates in the littoral zone was 0.80 g dry wt/m2, but declined to 0.10 g/m2 in the profundal zone (35-45 m). The whole-lake mean annual biomass of 0.34 g dry wt/m2 is the lowest recorded for a temperate zone lake. Production of benthic invertebrates in the lake may be limited by the low primary productivity and by dominance of fine marl sediments.
The density and biomass of invertebrates in the surface film (neuston) of the lake was very low, but these organisms were generally larger than those in the plankton or benthic invertebrate assemblages. Chironomid pupae, aphids and ants contributed most to the biomass of the neuston. Biomass varied substantially over the year from a low of 0.000003 g dry matter/m2 in February to 0.0003 g/m2 in August.
Thirteen species of fish were captured in Bear Lake, four of which are endemic. Ninety-nine percent of the fish captured were native. Bear Lake sculpin, Bonneville cisco, Utah suckers and two species of whitefish dominated the catch. A large portion of the fish were concentrated where the metalimnion intersects the lake bottom. Only one species (Bonneville cisco) was captured in the pelagic region. Ontogenetic shifts in habitat preference occurred in most species, with small fish utilizing shallower, warmer regions than large fish.
Multivariate analysis of the diets of the fishes delineated three trophic groups: 1) benthivores; 2) a zooplanktivore; and, 3) fish feeding on forage fish and neuston. Eight species of fish in Bear Lake fed primarily on the relatively abundant benthic invertebrates, particularly chironomid larvae and ostracods. Only one species, Bonneville cisco, utilized significant amounts of zooplankton. Cutthroat trout fed on neuston when they were young and became primarily piscivorous after reaching 300 mm. Adult lake trout have a diet similar to large cutthroat.
The low fish yield in Bear Lake (0.5 kg/ha/yr) is consistent with its low intrinsic productivity. The paucity of large invertebrates in either the plankton,or benthic communities probably limits recruitment of juvenile trout. Predation by adult trout may also lower survival of juvenile cutthroat planted in Bear Lake.
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