Evaluation of a dietary methylmercury dosing method for use in elasmobranch toxicology studies

As mid to upper trophic level predators, elasmobranchs (sharks, skates, and rays) are known to have elevated levels of a potent neurotoxicant, methylmercury (MeHg). The lethality of MeHg across different vertebrate taxa is well established, but its sublethal effects have only been investigated in depth at the scope of human health. The sublethal effects of exposure to MeHg, which are known to impact animal physiology and behavior, remain largely undescribed in elasmobranchs. In this study, a new approach was tested for assessing bioaccumulation and the sublethal effects of MeHg in a coastal shark species over extended time periods (five months) in a spatially constrained research setting. By the end of the experiment, shark muscle in the high-dose treatment had 24.03 μg/g MeHg, while low-dose shark muscle had 10.11 μg/g MeHg, compared to the 1.18 μg/g MeHg in the muscle of control sharks. Regardless of treatment, the highest concentrations of MeHg were found within the muscle, brain, heart, and kidneys while the lowest concentrations were found in the liver, intestine, and stomach. This work provides insight into how biological processes may respond to MeHg exposure, a widespread contaminant in aquatic environments.