Abstract
Walleyes Sander vitreus are ecologically and recreationally important. A non-native population of Walleyes has recently been established in the Lake Pend Oreille system in northern Idaho. Walleyes are piscivorous and the new population raises concerns regarding their potential effect on the system particularly regarding consumption of salmonids. The objective of my research was to evaluate the trophic ecology of Walleyes throughout the system, identify factors related to growth of Walleyes, and relate individual variability in growth to variability in isotopes (i.e., d15N, d13C). Food habits were diverse, and Walleyes consumed various fishes and macroinvertebrates. Kokanee Oncorhynchus nerka was the most frequently consumed prey item, and abundance of kokanee was related to growth of Walleyes in the system. Fast-growing individuals consumed prey items at higher trophic positions and from pelagic habitats. These results suggest that Walleyes will likely have negative effects on the kokanee population. This research provides valuable information regarding the direct and indirect effects of an established Walleye population in the Lake Pend Oreille system.