Mitochondrial DNA diversity and divergence among sharpnose sharks , Rhizoprionodon terraenovae , from the Gulf of Mexico and Mid - Atlantic Bight

-The Atlantic sharpnose shark, Rhizoprionodon terraenovae, is a small coastal shark that is harvested in both directed and nondirected fisheries throughout its range. Because pups of this species are found both along the southeastern U.S. Atlantic coast and the Gulf of Mexico, it is possible that multiple isolated breeding stocks exist. Restriction fragment length polymorphism analysis ofmitochondrial DNA was used to test the hypothesis that Atlantic sharpnose sharks from the U.S. Atlantic coast and the western Gulf of Mexico have identical mitochondrial haplotype frequencies and therefore no apparent genetic stock structure. Seven mitochondrial haplotypes were detected among 52 individuals. The distribution of haplotypes between samples did not differ significantly from homogeneity (P= 0.694), indicating that the null hypothesis of a single breeding population could not be rejected. Manuscript accepted 14 May 1996. Fishery Bulletin 94:664-668 (1996). The Atlantic sharpnose shark, Rhizoprionodon terraenovae, is a small (maximum length 110 cm total length) coastal shark that inhabits the east coast of North America from New Brunswick, Canada, to Yucatan, Mexico (Compagno, 1984). This species is abundant along the southern U.S. Atlantic coast and is second only to the sandbar shark, Carcharhinus plumbeus, in longline catches in Virginia (Musick et al., 1993). It supports a large recreational fishery offTexas (Parrackl ) and is an important species in the Mexican shark longline fishery (Applegate et al., 1993). In addition to being caught in directed fisheries, the Atlantic sharpnose shark is frequently taken by shark longliners targeting large coastal species (Branstetter and McEachran, 1986; Russell, 1993) as well as by commercial shrimp trawlers (Branstetter, 1981; Parrackl ); however, the implementation of turtle excluder devices (TED's) has produced the additional benefit of reducing bycatch of sharks (Branstetter2). Atlantic sharpnose sharks travel in sex-segregated schools, as noted by the disparate sex ratios of adults captured by longlines (Branstetter, 1981; Musick et al., 1993). The gestation period for this species is about ten to twelve months, and parturition takes place from April to June in the northern Gulf of Mexico (Branstetter, 1981; Parsons, 1983) and from May to June in South Carolina (Castro, 1993). The most recent fishery management plan for sharks in the coastal Atlantic waters ofthe United States (NMFS3) divides sharks into three categories for management purposes: pelagic species, large coastal species, and small coastal species. Currently catches of small coastal species (predominantly the Atlantic sharpnoseshark) are not regulated * Contribution 1933 of the Virginia Institute ofMarine Science, School ofMarine Science, College of William and Mary, Gloucester Point, Virginia 23062. ** Present address: Department ofWildlife and Fisheries Sciences, 'Thxas A&M University, College Station, Texas 77843-2258. E-mail address: [email protected]. 1 Parrack, M. L. 1990. A study ofshark exploitation in U.S. Atlantic coastal waters during 1986-1989. NOAA, Natl. Mar. Fish. Serv., Southeast Fisheries Science Center, Miami, Florida. 2 Branstetter, S. 1995. Gulf and South Atlantic Fisheries Development Foundation, Suite 997, Lincoln Center, 5401 W. Kennedy, Tampa, Florida 33609. Personal commun. 3 NMFS. 1993. Fishery management plan for sharks of the Atlantic Ocean. U.S. Dep. Commer., NOAA, Southeast Regional Office, St. Petersburg, FL, p. 1-167. Heist et al.: Mitochondrial DNA diversity and divergence among Rhizoprionodon terraenovae 665