Canadian Journal of Fisheries and Aquatic Sciences
National Research Council Canada
under-ice, diel, vertical migrations, Oncorhynchus nerka, zooplankton, prey
We used stationary hydroacoustics and measures of environmental conditions (water temperature, dissolved oxygen, light levels, and zooplankton) to determine what factors, foraging or predation risk, influenced diel vertical migrations of Oncorhynchus nerka during winter in three high-mountain lakes. The Sawtooth Valley lakes are deep, oligotrophic, glacial lakes located in central Idaho, U.S.A., and historically contained populations of anadromous O. nerka. In general, low light intensities limited foraging opportunities of O. nerka under ice, especially at night. In Stanley Lake, O. nerka underwent diel vertical migrations to exploit available light to feed. Oncorhynchus nerka occupied shallow water at night, where there was still sufficient light to feed, but were found in deep water during the day. It is unknown whether O. nerka occupied deep depths during the day to feed on high densities of zooplankton or to avoid predators. In Alturas Lake, O. nerka remained in the top 25 m both day and night to feed high densities of zooplankton found near the surface. In Redfish Lake, O. nerka also showed little migration: O. nerka stayed in shallow water both day and night and occupied the same depths with the highest zooplankton densities. The vertical distribution of O. nerka during the winter appears to be determined by available food and light, but the deep daytime distribution found in Stanley Lake is still unexplained.
Steinhart, G.B. and W.A. Wurtsbaugh. 1999. Under-ice diel vertical migrations of Oncorhynchus nerka and their zooplankton prey. Can. J. Fish. Aquat. Sci. 56 (Supplement 1): 152-161.