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

Abstract

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 has a historic reliance on fisheries and seafood consumption, 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 for 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 unambiguous identification of 38 collected samples, which were either labeled as Shortfin Mako shark (Isurus oxyrinchus), Common Thresher shark (Alopias vulpinus), or swordfish (Xiphias gladius) in market. Mako, an IUCN Red List Endangered species and Thresher, an IUCN Red List vulnerable species, are additionally listed on the CITES Appendix II List. 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 Mako 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.