Evaluating the Reintroduction Potential of Lahontan Cutthroat Trout in Fallen Leaf Lake, California

We evaluated the potential for reintroducing Lahontan cutthroat trout Oncorhynchus clarkii henshawi. a species listed under the Endangered Species Act, into a lacustrine system where the biotic community has changed dramatically since the species' extirpation there. Since 2002. 76,547 Lahontan cutthroat trout have been reintroduced into Fallen Leaf Lake, California; we used creel surveys. diet data, mark-recapture methods. bioenergetics modeling, and netting data across seasons to evaluate the habitat use, growth, and relative abundance of Lahontan cutthroat trout and the abundance. diet. habitat use, and predation by nonnative species. Sampling totals (n = 2) and survey observations (n = 3) indicate low survival and abundance of reintroduced fish and together with creel data indicate the importance of epilimnetic habitats across size-classes. Despite substantial growth. Lahontan cutthroat trout exhibited low condition factor values (average = 0.69). We found substantial predation pressure front a large population of lake trout Salvelinus namaycush ((N) over cap = 8.799 fish: 95% confidence interval [CI] 4,990-16,530 fish): analysis of lake trout diets showed an increase in piscivory and in the percentage of stomachs containing Lahontan cutthroat trout anchor tags with increasing predator size. Overall. we estimated that lake trout consumed over 38% of reintroduced Lahontan cutthroat trout (mean number consumed = 7,736 Fish: 95% CI = 4,388-14,534 fish). With bioenergetics modeling, however. we estimated that lake trout consumed considerable amounts of salmonid biomass during this period (mean biomass = 3,137 kg: 95% Cl = 1 779 5,993 kg), which greatly exceeded the biomass of Lahontan cutthroat trout reintroduced in 2006. During the stratification period, there was little overlap in habitat use between lake trout and Lahontan cutthroat trout, but overlap was high during the spring and autumn. We found moderate-sized populations of nonnative brown trout Salmo trutta, kokanee O. nerka (lacustrine sockeye salmon), and rainbow trout O. mykiss. Together, our results suggest that Lahontan Cutthroat trout have few refugia front direct and indirect negative interactions with normative species and that alternative approaches are needed.