Salvelinus namaycush Walbaum, 1792

Several lines of evidence suggest that lake trout (Salvelinus namaycush) and cutthroat trout (Oncorhynchus clarki) are competing for the prey fish. First, the low growth rates and P-values of the piscivores suggests that they are food-limited. Second, the data suggest that lake trout may be competitively excluding cutthroat trout from feeding on Bear Lake sculpin. In 1987, when lake trout abundance was very low, Bear Lake sculpin made up 67% of the diet of cutthroat trout between 250 and 350 mm TL (Wurtsbaugh and Hawkins 1990). During our 1993–1994 diet analysis, when the lake trout were abundant, almost no identifiable fish were observed in the 91 cutthroat trout smaller 400 mm TL that we examined, indicating a major change in feeding. The substantial population of large lake trout, coupled with the small population of large cutthroats could be interpreted as competitive exclusion of the larger sizes of cutthroats by lake trout.... Beginning in 1988, when lake trout were recruiting through small size-classes, cutthroat trout were absent at similar sizes, suggesting they had poor recruitment during these years (Figure 7). As these lake trout cohorts grew, reaching approximately 400 mm TL (1992), cutthroat trout of smaller size-classes were again captured in gill nets. This pattern may be due to competitive exclusion of similar- sized cutthroat trout by lake trout. (Ruzycki et al., 2001)

Two principal sport fish—the indigenous Bonneville cutthroat trout Oncorhynchus clarki utah and the introduced lake trout Salvelinus namaycush—are the dominant piscivores in Bear Lake, a 282-km2 oligotrophic system. These piscivores rely predominantly on four endemic prey fish species that make up a major portion of the unique Bear Lake fish assemblage.Lake trout predation on juvenile cutthroat trout, combined with competition with other age-classes, also contributes to the poor survival of cutthroat trout. Although prey fish abundance appears to be largely influenced by bottom-up factors related to water elevation, lake trout exert a decoupled predatory threat to the endemic prey fish populations and have the potential to suppress endemic fishes during unpredictable periods of poor prey fish production. Four endemic species: Cottus extensus, Prosopium gemmifer, P. spilonotus, and P. abyssicola sustain the salmonine sport fishery. (Ruzycki et al., 2001)