Feeding ecology of juvenile Lake Sturgeon, Acipenser fulvescens, in Northern Ontario

Dietary analyses of juvenile Lake Sturgeon in a resource-poor habitat showe d them to be a general predator. Cladocera dominated numerically the prey t axa, but were recorded in only four of the individual sturgeon examined and therefore excluded from stomach content analyses. Mayfly larvae (Ephemerop tera), primarily Hexagenia, were numerically the next most abundant (34% of all prey items) and the most widely taken (75% of all sturgeon) of the 10 prey categories. Others were Odonata, Annelida, Mollusca, Diptera and Trich optera, each at 5-8% of all prey items. The remaining dietary categories re presented < 3% of all prey items. No dietary partitioning was found over th e length range of juvenile sturgeon, suggesting that fish throughout this s ize range are almost certainly competing for food. Lake Sturgeon diet did n ot differ from that for suckers, Lake Whitefish and, to some extent, Burbot , but was different from that for Northern Pike and Walleye. Extremely low invertebrate densities (95 individuals x m(-2)) and occurrence of all benth ic species in the diet of juvenile Lake Sturgeon and several of the other d ominant fishes suggests niche breadth to be wide and thus competition for f ood to be severe. The low food abundance is reflected in the comparatively slow growth rate of sturgeon in our study area. Apparently sturgeon are at survival threshold in this area. Further depletion of their food base likel y would have serious repercussions for their growth and survival.