Seasonally Dependent Movement of Lake Trout between Two Northern Idaho Lakes

Abstract

The diel and seasonal movements of lake trout Salvelinus namaycush between Upper Priest Lake and Priest Lake, Idaho, were studied in 2000. Gill nets were used to capture and detect fish movements between the lakes. Lake trout were caught in the outlet of Upper Priest Lake and in the Thorofare (the narrow channel connecting the two lakes) primarily in the spring and fall, when water temperatures were cool. No lake trout were caught when the water temperature exceeded 15°C. Lake trout were primarily caught at night (94%). Multiple regression analysis indicated that nighttime lake trout catch per unit effort (CPUE) was significantly higher at lower lake surface water temperatures than at higher temperatures (P < 0.01). Daytime lake trout CPUE was significantly higher at low Priest Lake surface temperature than high temperature and at high Thorofare depth than at low depth (P < 0.01). Nighttime CPUE was significantly higher than daytime CPUE (P < 0.01). These results indicate that warm summer water temperatures function as a natural thermal barrier to movement between the lakes in July and August, and that it may be necessary to block lake trout movements between the two lakes at other times to effectively control the population in Upper Priest Lake.