Effects of Spawning Pacific Salmon on the Trophic and Population Ecology of Stream-Resident Sculpins

Across the North Pacific coast, marine and freshwater ecosystems are linked by annual spawning runs of Pacific salmon. Although past research has highlighted the importance of these nutrient subsidies to freshwater food webs, their effects on the trophic and population dynamics of freshwater fish remain poorly understood. In this thesis I examined the relative influences of pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon and habitat on the diets, individual condition, and population densities of freshwater prickly sculpins (Cottus asper), and coastrange sculpins (C. aleuticus). I found that sculpin condition and salmon nutrients in sculpin diets increased with the availability and density of spawning salmon, and were influenced by season, sculpin species, body size, and habitat. I also found that salmon density, pH, and habitat were related to sculpin population densities, but that their effects differed between sculpin species. This is the first study to test such relationships for freshwater fishes across wide, natural gradients in salmon spawning density and habitat.