Background/Question/Methods Arctic landscapes contain a mosaic of lakes, streams and ponds. We examined seasonal movement patterns, feeding habits, and potential predation risk of arctic grayling Thymallus arcticus in a watershed near the Toolik Lake Field Station. Individuals in a deep central lake were marked using pit tags from 2000-2008. Individuals were captured using gill nets in both deep lakes, and shallow summer-residence lakes. Gastric lavage was used to collect stomach contents.

Results/Conclusions Greater than 20% of these individuals left the resident lake each summer to feed in shallow pond habitats. These shallow ponds did not provide winter habitat as these froze solid each year. Grayling in shallow ponds fed extensively on zooplankton, particularly the large cladoceran Daphnia middendorffiana. Grayling that remained in the winter resident lake consumed benthic and terrestrial insects and experienced lower growth. The size distribution of emigrant grayling was dominated by smaller individuals, suggesting that risk of predation by resident lake trout was a factor in the movement of this species. Results of this study help explain the disparate observations that most omnivorous fish gain their energy from benthic prey, but exert large influences on zooplankton assemblage structure. When resident grayling eliminate Daphnia middendorffiana, they switch to feeding on benthic invertebrates. The short-term residence of grayling in shallow ponds allows these Daphnia to persist.