Stable isotope characterization of Rainy River, Ontario, lake sturgeon diet and trophic position

Abstract

Abstract Lake sturgeon ( Acipenser fulvescens ) are considered threatened and many populations have declined since the early 1890s. Limited food web studies have been conducted with lacustrine lake sturgeon populations while similar studies do not exist for riverine populations. We use stable isotope analysis to study the diet composition of lake sturgeon captured in the Rainy River, Ontario. Historical reports of lake sturgeon consumption of fish and fish eggs exist, but both prey have largely been considered as a minor contribution to the overall diet of lake sturgeon. More recent dietary studies have focused on juvenile sturgeon and report low or no incidence of fish or fish eggs in lake sturgeon diets. The results of the stable isotope studies of Rainy River lake sturgeon suggest they obtain a large portion of their energy from organic material derived directly or indirectly from fish. Results parallel those recently reported for adult sturgeon in Lake Winnebago, Wisconsin, and are important in the context of contributing modern technical verification to earlier historical reports of fish and fish eggs in lake sturgeon diets. The results of this study provide evidence of potential seasonal or temporal shifts in lake sturgeon diet and further evidence to the potential shift in resource use based on life stage. Estimates of isotopic niches for the Rainy River sturgeon establish an important baseline for future changes in food web structure that might accompany the introduction of invasive species or the addition of anthropogenic stressors that could have implications for lake sturgeon conservation.