Abstract
Although mercury (Hg) in polar ecosystems has been well-studied, there is little information on Hg in the Arctic during low-productivity seasons like the polar night. We quantified Hg concentrations, carbon, and nitrogen stable isotope ratios (δ13C and δ15N) in the muscle of polar cod (Boreogadus saida), Atlantic cod (Gadus morhua), and capelin (Mallotus villosus) sampled from the North-West and North-East Barents Sea during November–December 2019. Hg concentrations varied between species (14–175 ng/g dw), dependent on region, but were well below the toxicity threshold for fish health and the EU-accepted threshold for human consumption. Interspecific differences were observed only in the North-East region, with Atlantic cod having highest Hg concentrations, explained by its larger size, higher trophic position and benthopelagic feeding. Spatial differences in polar cod with higher Hg concentrations in the North-East than the North-West were likely due to a combination of differences in food web structure and Hg exposure.
Highlights
There is a growing concern regarding the increasing concentrations of mercury (Hg) in some areas in the Arctic (Dietz et al, 2021; AMAP, 2018)
Our results of stable isotope signatures showed that each species from each region occupied a specific dietary niche, with little spatial and species overlap (Fig. 2)
Polar cod and capelin are ice-assocated and pelagic forage fishes respectively, that feed on zooplankton, and occupy similar dietary niches in Arctic and boreal ecosystems (Mecklenburg et al, 2018; McNicholl et al, 2016; Hop and Gjøsæter, 2013; Walkusz et al, 2013), while Atlantic cod's habitat and omnivorous diet becomes increasingly benthopelagic with size (Berge et al, 2020)
Summary
There is a growing concern regarding the increasing concentrations of mercury (Hg) in some areas in the Arctic (Dietz et al, 2021; AMAP, 2018). Hg is a naturally occurring metal found worldwide, global human activity has led to a several-fold increase of Hg emissions into the atmosphere, oceans and rivers (AMAP, 2018; Obrist et al, 2018; Pacyna et al, 2006; Lamborg et al, 2014). Hg is recognized as a “chemical of global concern”, because of its long-range transport, subsequent bioaccumulation and biomagnification in marine food webs, and toxicity when reaching high concentrations causing adverse behavioural, neurochemical, hormonal, and reproductive ef fects in predators at higher trophic levels (AMAP, 2003; Dietz et al, 2013; Douglas et al, 2012; Driscoll et al, 2013; Rice et al, 2014; Scheuhammer et al, 2007). Variation in lipid concentration of tissue is known to dilute Hg uptake into the muscle tissue of fish and have an impact on measured Hg content, especially in the Hg found in higher trophic levels (Jardine et al, 2009)
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