| Summary: | Arctic lakes provide a unique natural laboratory where changes of fish behavior can be studied. NE 12 and GTH 156 are a pair of connected tundra lakes located within the Toolik Lake Long Term Ecological Research Site (LTER) study area, on the North Slope of the Brooks Mountains in Alaska. NE 12 is a deep lake at 24 meters and provides a liquid layer for fish to live year round. GTH 156 is a shallow lake at 2 meters and freezes solid during the winters. In addition to depth, the lakes have different quantities of zooplankton biomass with GTH 156 containing three times the amount of zooplankton food for fish compared to NE 12. Data collected using mark-recapture methods indicated that during the summer grayling migrate to GTH 156 the return to NE 12 to over winter. Analysis of 15N content of grayling tissue indicated that 30% of the grayling in GTH 156 had recently migrated from NE 12. While the Arctic Grayling are the same population, they have significantly different feeding habits in the different lakes. Fish stomach contents indicated that approximately 80% of prey in grayling from GTH 156 consisted of zooplankton, while zooplankton comprised less then 10% of the grayling from NE 12. In NE 12 grayling diets were primarily composed of benthic or terrestrial insects. Results from these studies suggest that grayling use shallow lakes as summer feeding habitats and return to deeper lakes to persist through the winter.
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