Habitat, benthic prey, and distribution of juvenile lake sturgeon (Acipenser fulvescens) in northern Ontario rivers

The spatial and temporal distribution and relative abundance of juvenile lake sturgeon (Acipenser fulvescens) and benthic macroinvertebrates were examined in the Mattagami and Groundhog rivers, tributaries of the Moose River in northern Ontario, Canada. Relative density and diversity of the benthic fauna were low, the most common taxa being Ablabesmyia sp. (Diptera) and Hexagenia sp. (Ephemeroptera). Benthic organisms were most abundant in substrate dominated by sand and clay. An appreciable portion of the riverbed was strewn with wood chips and was particularly depauperate of macrobenthos. Lake sturgeon foraged exclusively on the benthos, especially taxa of Ephemeroptera, Diptera, and Trichoptera. Hexagenia was the only prey species in greater density in sturgeon stomachs than in the benthos. The largest concentration of juvenile lake sturgeon was found adjacent to substrate dominated by sand and clay. Gillnet catches of lake sturgeon suggest that they are more active at night, which may enhance their foraging success. In these northern rivers, the trophic status of juvenile lake sturgeon is marginalized by an impoverished food supply, in part the consequence of habitat loss resulting from anthropogenic activities.