Mercury Concentrations in Lake Sturgeon from Six River Systems in Manitoba, Canada

Mercury is a toxic trace metal that bioaccumulates to concentrations potentially affecting human and environmental health. Lake sturgeon are large, long-lived fish, characteristics conducive to mercury bioaccumulation. This study measured total mercury (THg) in the axial musculature of 256 sturgeon captured between 2002 and 2019 from primarily five river systems (Winnipeg, Saskatchewan, Nelson, Hayes, and Churchill) in the province of Manitoba, Canada. These systems occur within traditional resource use areas of Indigenous people. Since the 1900s, all sampled rivers except the Hayes were impacted by hydroelectric impoundment, which can increase fish THg concentrations for decades following inundation. Concentrations of THg in sturgeon of 97-1390-mm fork length and aged 0+ to 51 years ranged from 0.008 to 0.67 ppm wet weight and were positively related to fish length and age. Mean length-standardized THg concentrations ranged from 0.06 to 0.18 ppm, differing significantly among some populations. Of the 35 sturgeon also analyzed for diet composition, 34 had identifiable gastrointestinal contents. Ten different prey taxa were identified, including fish. Chironomids dominated diet numerical abundance. However, as the number of taxa increased with fish length to include larger, THg-rich organisms, chironomid abundance significantly decreased, suggesting a link between sturgeon diet and mercury concentrations. A paucity of historical data precludes the isolation of effects of hydroelectric impoundment on THg levels in lake sturgeon, but concentrations are not particularly high post 2002 in any of the waterbodies we examined. However, as lake sturgeon populations recover and harvest rates potentially increase, resource users may consider the tendency of mercury to bioaccumulate in this fish and limit the consumption of larger (>1000-mm fork length) individuals. Environ Toxicol Chem 2023;00:1-13. (c) 2022 SETAC

Automated summary

This study measured total mercury concentrations in lake sturgeon from five river systems in Manitoba, Canada. The concentrations were positively related to fish length and age, and the composition of fish diet was found to affect mercury concentrations. The study suggests that as lake sturgeon populations recover and harvest rates potentially increase, consumption of larger individuals should be limited.