Biomagnification of Mercury in Wolves and Their Prey in the Northwest Territories, Canada

Due to its neurotoxicity and tendency to bioaccumulate, mercury (Hg) is a risk to both human and environmental health. Most Hg studies focus on aquatic systems due to their longer food chains and predatory fish. Yet opportunistic terrestrial predators such as wolves (Canis lupus) are less studied despite the potential for high-Hg prey in their diets that could lead to high concentrations and subsequent health effects. Here, we studied the movement of Hg to wolves from their prey across two regions of the Northwest Territories (NWT), Canada between 2006 and 2024 by combining stomach content data with stable isotope analysis of over 350 individuals. While terrestrial prey such as caribou dominated the diet of wolves in both regions (>55% of stomachs), a small number of wolves in both regions recently consumed aquatic prey (5%) and these aquatic prey had significantly higher Hg concentrations than terrestrial prey (P < 0.001). This led to higher Hg concentrations in wolves that had eaten aquatic prey relative to those eating semi-aquatic and terrestrial prey, and is likely responsible for Hg trophic magnification factors (TMFs) that matched or exceeded those typically observed in aquatic systems. These findings highlight the transfer of Hg from aquatic to terrestrial food webs and the potential for health risks to terrestrial predators. Mercury concentrations in wolves remained well below expected animal health effect thresholds and there was no evidence for an increase in concentrations in either region over the last decade, but the high concentrations in some prey species and trophic magnification in wolves illustrate the vulnerability of terrestrial predators to Hg exposure when their diets contain aquatic prey.