Alewives and Rainbow Smelt in Lake Huron: Midwater and Bottom Aggregations and Estimates of Standing Stocks

Abstract

Abstract The continued availability of adequate amounts of forage fish, primarily alewives Alosa pseudoharengus and rainbow smelt Osmerus mordax, is critical to the success of ongoing programs aimed at rebuilding lake trout Salvelinus namaycush populations and maintaining other salmonid stocks in Lake Huron. These forage species are distributed at middepths as well as on or near the bottom. Acoustic methods were integrated with midwater and bottom trawling to characterize the population and estimate the biomass of the forage stocks. The average sizes of alewives and rainbow smelt caught at middepths were smaller than those caught in bottom trawls; however, most size ranges in the bottom trawl catches were also present in the midwater catches. Subadult and adult fish (both species) were rarely caught concurrently in midwater and when they were caught together the fish were invariably large subadults and small adults. Biomass estimates for the pelagic component were determined from trawl catches and echogra...