A survey of the fishes of Lake Winnipeg and interactions of the introduced white bass with the native ichthyofauna of Hudson Bay drainage : with emphasis on young-of-the-year fishes in nearshore environments

Abstract

This project examined the littoral zone fish communities of Lake Winnipeg and adjacent waterways to determine 1) the distribution of all nearshore fishes, 2) the seasonal use of nearshore habitat by pelagic fish, 3) the food resources used by nearshore fish, 4) the fish species that are sympatric with white bass and 5) the diet similarity among fish species in sympatry with the invading white bass. Four basic distribution patterns were identified for the fishes of the Red River, Lake Winnipeg and their tributaries, and these are presented as individual species maps. Fish move inshore in early to late June and remain there until September. All combinations of pelagic fish occured in samples, suggesting no spatial or temporal habitat shift in the presence of white bass. Pelagic insectivorous, pelagic piscivorous, pelagic zooplanktivorous and benthic insectivorous feeding guilds were defined from analysis of the diets of nearshore fishes. Feeding guilds appeared stable throughout the summer with the exception of emerald shiners, which ate zooplankton and insects in varying proportions. Diet analysis determined that yellow perch, emerald shiner, goldeye, juvenile walleye and sauger and cisco feed on the same zooplankton species as juvenile white bass. Adult white bass feed on the same fish as adult walleye and sauger. Pelagic fish commonly found in sympatry with the white bass include goldeye, mooneye, walleye, sauger, emerald shiner, and yellow perch. These fish are found throughout the lake with no northward range retreat in response to invasion of white bass. Segregation by time occurs in this lake and minimizes contact between white bass, cisco and lake whitefish. There is no evidence of abundance decline, habitat shift or diet shift in native fish in relation to the presence of white bass and therefore there is no evidence for competition resulting from the white bass invasion. The success of white bass is due to exploitation of abundant food items (calanoid copepods and leptodorid cladocerans when young and emerald shiners and perch as adults) thereby eliminating competition with native piscivores. The rapid growth, and the lack of potential predators (walleye and sauger) in Lake Winnipeg also contributed to the success of the white bass.