DNA barcoding reveals mislabeling of endangered sharks sold as swordfish in New England fish markets

Mislabeling of shark and swordfish meat poses a substantial challenge to conservation of rapidly declining pelagic shark populations in the North Atlantic, so routine market assessments are critical. New England’s southern region of Massachusetts, Connecticut, and Rhode Island is a region with historic reliance on fisheries and contemporary cultural demand for locally sourced seafood, including sharks and swordfish. The visual similarity of shark and swordfish meat is considerable, and as such, this study aimed to evaluate mislabeling of shark as swordfish meat collected from markets and grocery stores in New England in 2019. DNA barcoding was used on the mitochondrial cytochrome oxidase I (COI) gene to determine identification of 38 collected samples, which were either labeled as ‘mako shark’, ‘thresher shark’, or ‘swordfish’ in market. Barcoding and phylogenetic analysis revealed four mislabeled samples for a total substitution rate of 10.5%. One substitution, labeled ‘mako’ in the market, was identified as thresher shark. Three further substitutions, labeled as ‘swordfish’ in the market were identified as mako, Alopias spp., and a lamnid shark, all of which are endangered or threatened shark species. As samples were collected just before implementation of major import monitoring programs and a shortfin mako ( Isurus oxyrinchus ) fishing ban in the United States, this study has established a temporal baseline that can be used to determine if market mislabeling has decreased as a result of these conservation initiatives.