Interannual Variability in Trophic Relationships of Fish in a Pristine North Temperate Lake

The study of trophic interactions in freshwater lakes is often complicated by an abundance of species to characterize and anthropogenic impacts such as nutrient loading and invasive species.  We used ¹³C and ¹⁵N stable isotopes to describe trophic relationships of fish in Lake Hövsgöl, a pristine north temperate lake in Mongolia.  The lake is home to only eight species of fish, offering a unique opportunity to characterize trophic dynamics of all of the fish species in a system with minimal human impacts.  δ¹⁵N values indicated that the lake has a food chain length (FCL) of 3.4-3.9, with all fish occupying a trophic level between 2.8 and 3.9.  This FCL is low for such a large lake, and the narrow trophic range suggests extensive omnivory.  δ¹⁵N increased with body size in burbot but not lenok or perch.  Fish dependent on benthic productivity showed less variability in their δ¹³C values than did those dependent on pelagic and mixed sources.  Grayling δ¹³C values suggested a reliance on mixed sources regardless of body size and pelagic or littoral collection location.  These data provide an overall picture of a short lake food chain characterized by substantial omnivory and greater variability in benthic- than pelagic-dependent species.