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Abstract Title: Risks and benefits of consuming fish upstream and downstream of a dam on the Wolastoq | Saint John River, New Brunswick
Presenter Name: Jenni Velichka
Company/Institution: McMaster University
Session: Mercury in Freshwater Ecosystems
Co-Authors: Jenni Velichka

Abstract Information :

Fish are recommended for consumption because they provide a rich source of nutrients, including the omega-3 fatty acids (FAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, fish also bioaccumulate several contaminants, such as mercury (Hg), which can undermine the nutritional benefits to consumers. Furthermore, contaminants and FAs can vary among species and spatially within species. For example, the construction of dams can change Hg speciation and availability in reservoirs, making Hg more bioavailable to fish. The Wolastoq | Saint John River, New Brunswick (Canada) has a large hydroelectric dam and supports the subsistence fishing of six First Nation communities. In 2020 and 2021, Smallmouth Bass, Yellow Perch, American Eel and Striped Bass were collected from locations upstream and downstream of the dam and analyzed for Hg, FAs, organic contaminants and trace metals. Of the contaminants measured in the fish to date, Hg poses the biggest risk to consumers. Mean total Hg varied among species (Striped Bass: 1.19, Smallmouth Bass: 0.62, American Eel: 0.38, Yellow Perch: 0.31 μg/g ww), and differed among sites. Hg concentrations (size-adjusted) were highest in the reservoir for Yellow Perch and highest farther downstream from the dam for Smallmouth Bass. Initial FA analyses indicate that Smallmouth Bass had higher DHA but lower EPA concentrations (mean = 1569 and 1041 μg/g ww, respectively) compared to Yellow Perch (mean = 1004 and 1584 μg/g ww, respectively). Within species, Hg increased with length while EPA and DHA either decreased or showed no trend with length, suggesting fewer health benefits and greater risks when consuming larger fish. Our results indicate that species, size and location influence contaminant and nutrient concentrations in fish. Overall, these data will help inform local recreational and First Nation fishers of the risks and benefits of consuming fish from the Wolastoq | Saint John River.

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