LAKE TROUT (SALVELINUS-NAMAYCUSH) CONTROL OF SNAIL DENSITY AND SIZE DISTRIBUTION IN AN ARCTIC LAKE

In arctic Alaskan lakes the density and size distribution of the snail Lymnaea elodes appear to be greatly affected by the presence or absence of lake trout (Salvelinus namaycush). Snail densities were much lower and size distributions depressed in lakes where trout were present. During the summer of 1986, lake trout were introduced into an arctic lake to test the effects of their predation on the dominant snail Lymnaea elodes. During July and early August, snail densities in the experimental lake remained stable in the deepwater areas of the lake, but increased significantly in the deepwater areas of an adjacent, troutless control lake, probably due to snail migration from the lake periphery in the absence of predation pressure. These experimental results suggest that the observed pattern of snail distribution and size in lakes containing trout is due to lake trout predation.