Food Habits and Trophic Ecology of Native and Introduced Fish from Nahuel Huapi Lake, Northern Patagonia, Argentina

Since the introduction of salmonids in Argentine Patagonian water bodies the concern has been to elucidate the effect they might have on native fauna. Lake Nahuel Huapi is the biggest lake in northern Patagonia and the center of the Nahuel Huapi National Park, for which there are no studies about impacts and trophic relationships between native and introduced salmonids. Based on gillnet samplings we examine diet and trophic relationships of native fish and exotic salmonids in this lake. We used the Relative Importance index, Levins index and multivariate approaches to describe and test diet overlaps and to find seasonal and ontogenetic patterns in relation to natives and introduced fish. Ten prey groups were identified, diet varying according to predator and size, being mainly based on two prey items: larvae and adults of native galaxiids and the crayfish Samastacus sp. Diet overlaps occurred depending on predator size class and season, possibly following prey availability. Trophic relationships based on diet composition showed that fish community is highly dependent on energy fluxes from the littoral through galaxiids and from the benthos through the crayfish. This study represents a first approach to food web comprehensive analysis in this enormous glacial lake.