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The long-term effects of water resource development on blood mercury levels and the trophic ecology of Namew (lake sturgeon, Acipenser fulvescens)

Lescord, G., Simard, J., Johnston, T., Seguin, J., Farrell, C., O'Driscoll, N. & O'Connor, C.

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We studied total (THg) and methylmercury concentrations in whole blood sampled non-lethally from namew (Moose Cree L-dialect, lake sturgeon, Acipenser fulvescens), an endangered and culturally important subsistence fish.

Key points

• Namew from the free-flowing river had higher mercury in their blood than fish from the river with hydroelectric facilities, which was likely because they were eating more different prey than Namew from the river with hydroelectric facilities.
• Namew’s diet changed downstream of the hydroelectric facilities, and our team had trouble finding bugs along the shoreline downstream of the hydroelectric facilities; this was unlike the free-flowing river, or sites upstream of the hydroelectric facilities, where many bugs were found. Since the hydroelectric facilities in this study are decades old, our results suggest that any initial increase in mercury levels that may have happened during the reservoir creation have now ceased in this river, and diet is likely a more important factors driving mercury burdens in Namew now.
• We will need to do more research to fully understand these differences in diets, and to understand what Namew are eating downstream of the hydroelectric facilities.

Abstract

Water resource development can alter the movement and ecology of sturgeons. We studied total (THg) and methylmercury concentrations in whole blood sampled non-lethally from namew (Moose Cree L-dialect, lake sturgeon, Acipenser fulvescens), an endangered and culturally important subsistence fish. Namew were sampled from two tributaries within the Moose Cree Homeland: the Lower Mattagami River (an impacted system with four hydroelectric generating stations) and the North French River (a reference system that is free-flowing system with no development). Results indicated namew from the North French River had higher blood [THg] than those from the Mattagami River. Further modeling showed that trophic position was the primary driver of these differences, with North French namew having the highest nitrogen isotope ratios. Based on further isotope modeling, crayfish were major components of namew diet at all sites, while other prey items differed between sites. Specifically, namew with unobstructed access to the lower watershed had notably more enriched isotope values when compared to the freshwater benthic macroinvertebrates sampled, implying that other prey not captured herein may contribute to their diets and [THg]. Overall, we found differences in namew’s trophic ecology but no elevation in blood mercury levels at a site impacted by hydroelectric operations 60+ years post-impoundment.

Recommended citation

Lescord, G., Simard, J., Johnston, T., Seguin, J., Farrell, C., O'Driscoll, N. & O'Connor, C. (2024). The long-term effects of water resource development on blood mercury levels and the trophic ecology of Namew (lake sturgeon, Acipenser fulvescens). Facets. https://doi.org/10.1139/facets-2023-0151