Resource Partitioning in Summer by Salmonids in South-Central Lake Ontario

Abstract

During the summers of 1981 and 1982, we studied resource partitioning by stocked lake trout Salvelinus namaycush, brown trout Salmo trutta, and chinook salmon Oncorhynchus tshawytscha by fishing vertical gill nets at six distances from shore in south-central Lake Ontario. The nets were set at depths of approximately 15-45 m (nearshore stations,offshore) and more than 55 m (offshore stations, 4-24 km offshore). Salmonids were concentrated near shore, where they partitioned available habitat and, thus, food resources. Horizontal habitat was partitioned with respect to distance from shore; vertical habitat was partitioned in relation to temperature and the thermocline. Salmonids foraged for the most available prey items within their habitat. Overlaps in both food use and horizontal habitat use were inversely related to overlap in use of vertical habitat. There was increased habitat separation between sexes for those species caught farther from shore. At the salmonid stocking and prey density levels existing during our study, lake trout, brown trout, and chinook salmon appeared to partition resources and minimize deleterious trophic interactions during thermal stratification.