Influence of feeding ecology on mercury accumulation in turtles and fish of the Rideau Canal, Ontario, Canada

Pollution is a major cause of biodiversity declines worldwide. Therefore, understanding exposure and uptake mechanisms for contaminants such as mercury (Hg) is a crucial step in our efforts to understand the causes of species decline. I investigated the influence of dietary reliance on the benthic food chain, and the influence of the proportion of zebra mussels in the diet, on the accumulation of Hg in freshwater fish and turtle species. I collected turtle blood samples and fish muscle samples in 2012 and analyzed these tissue samples for carbon and nitrogen isotope ratios (delta 13C and delta15N), and for Hg concentrations. Isotopic ratios were used to calculate trophic level, dietary reliance on the benthic food chain, and the proportion of zebra mussels in the diet. Reliance on the benthic food chain was a good predictor of Hg concentration in fish muscle, but not in turtle blood. The proportion of zebra mussels in the diet was not a good predictor of Hg in turtles or in fish. My results indicate that dietary reliance on the benthos should be considered in future tissue Hg modelling studies for fish, and that this predictor variable could be used to identify other fish species likely to be burdened by high concentrations of Hg.