The relationship between spatial distribution and diet of Arctic charr, Salvelinus alpinus, in Loch Ness, UK

The pelagic fish community of Loch Ness, U.K., is dominated by Arctic charr, Salvelinus alpinus. Previous studies have shown that the distribution of zooplankton along the south-west to north-east axis of this elongate loch is very dynamic and determined largely by prevailing winds, but Arctic charr are consistently more abundant in the southern half of the loch. In July 1993, the diet compositions of 161 Arctic charr from 53 to 330 rum in length were determined and related to their spatial distribution and those of microcrustacean zooplankton and pelagic chironomid larvae and pupae. Diets were dominated by chironomid larvae, with chironomid pupae, Bythotrephes longimanus, Bosmina coregoni and Daphnia hyalina also frequently taken. Over the whole study period, B. longimanus were more important in the diet of fish from the northern half of the loch, while chironomid larvae were more important for fish from the southern half. As a result, per capita prey weight of fish from the south was greater than that of fish from the north. However, wind-induced changes in the distribution of zooplankton along the loch were accompanied by a change in the diet composition of Arctic charr from the south.