Methylmercury Levels in Commercially Harvested Spiny Dogfish Captured off the Coast of Massachusetts

Spiny DogfishSqualus acanthiasare small sharks that are harvested for seafood, primarily off the Eastern Seaboard of the United States. For the purposes of establishing seafood consumption advisories with regard to methylmercury (MeHg) content, the U.S. Food and Drug Administration (FDA) classifies Spiny Dogfish as "sharks," an overly broad taxonomic grouping with a mean MeHg content of 0.98 mu g/g wet weight. Because the FDA mean includes fishes of different species that have been collected internationally over the last four decades, there is reason to believe that the FDA mean value is not reflective of the fish harvested in the Spiny Dogfish fishery. To evaluate how closely Spiny Dogfish match the values in the FDA's generic shark category, we collected muscle samples from 102 commercially harvested Spiny Dogfish caught off Cape Cod, Massachusetts, during the 2018 fishing season. Among the fish we sampled, 100% had MeHg concentrations lower than the FDA mean for sharks and 77.5% had MeHg concentrations that the FDA considers safe for consumption at a frequency of once per week. The mean MeHg concentration in our samples was 0.378 mu g/g wet weight, less than half of the value for the generic shark category. Moreover, through a comparison with data from the 1970s, we documented a 30% decline in MeHg concentrations for select size categories of Spiny Dogfish captured off the coast of New England. Exposure simulations indicated that to minimize risk, Spiny Dogfish should be consumed no more than twice per month by most people.