Terrestrial prey fuels the fish population of a small, high-latitude lake

The significance of terrestrial carbon subsidies in lake ecosystems has been under active research, but the contribution of terrestrial energy to the highest trophic levels has been explored less frequently. Here, we examined the terrestrial energy contribution to the ingested and assimilated diet of introduced brown trout (Salmo trutta) in a small, high-latitude lake using stomach content, stable isotope and fatty acid analyses. Stomach content analysis of brown trout indicated a terrestrial contribution of 29 % during the open-water season. Terrestrial prey was mainly composed of rodents (23 % in volume), but also amphibians and terrestrial insects. A longer term estimate, obtained with a mixing model (SIAR) for liver and dorsal muscle stable isotopes from 2010 and 2011, revealed a terrestrial contribution of 68.5 and 63.5 %, respectively. Through a similar model, fatty acid analysis on 2011 samples estimated a contribution of 71.5 %. Despite the relatively high proportion of rodents in the trout ingested diet, no correlation was evident between the long-term rodent cycles and terrestrial energy contribution estimated with stable isotopes of muscle. Terrestrial prey were an important long-term energy source for fish in small high-latitude lake, but its contribution was not directly dependent on the availability of pulsed resources such as small mammals.