Recovery of sub-alpine lake basin fauna following removal of introduced trout

We conducted a four-year (2003-2006) 16-lake experiment in the Trinity Alps Wilderness of northern California to assess whether changes in abundance of introduced trout in wilderness lakes could aid amphibian recovery. We also tested whether trout predation of larval amphibians and aquatic invertebrates suppresses prey subsidies from lakes to terrestrial predators. Treatments were: trout removal, stocking suspended, continued stocking, and historically fishless. We found that non-native trout suppress numbers of the declining Cascades Frog and other amphibians, as well as large-bodied aquatic insects such as mayflies and caddisflies. After trout removals, these groups show a marked increase in abundance. We found increased immigration, survival and recruitment of Cascades Frogs at the trout removal lakes compared to the trout-containing lakes and fishless control lakes. Over 100 species of birds and large numbers of bats used the lake basins during the snow-free season, and we will provide preliminary analysis of whether lake basin use by birds and bats is associated with trout abundances. Overall, results show that the species composition of the aquatic donor community can affect subsidies to the terrestrial recipient community.