Abstract. — Age and growth of 

 the dusky shark, Carcharhinus 

 obscurus, was estimated from 

 bands in the vertebral centra of 122 

 individuals and from length-fre- 

 quency data from 341 individuals. 

 The von Bertalanffy growth func- 

 tion parameters from the vertebral 

 analysis were considered more ro- 

 bust (L =373, #=0.038, < =-6.28, 

 male; zT=349, #=0.039, * =-7.04, 

 female). Comparison of male and 

 female growth curves generated 

 from vertebral data indicate a sta- 

 tistically significant difference; 

 however, these differences are due 

 primarily to larger sizes attained 

 by adult females. Estimates of age 

 at maturity indicate that dusky 

 sharks follow the typical carchar- 

 hinid pattern of slow growth and 

 late age at maturity. The size at 

 maturity is reported at 231 cm FL 

 and 235 cm FL for males and fe- 

 males, respectively. These lengths 

 correspond to approximately 19 

 years for males and 21 years for fe- 

 males. The oldest fish aged from ver- 

 tebrae was a 33+ year-old female. 



Age and growth estimates for the 

 dusky shark, Carcharhinus obscurus, 

 in the western North Atlantic Ocean 



Lisa J. Natanson 

 John G. Casey 

 Nancy E. Kohler 



Narragansett Laboratory, Northeast Fisheries Science Center 



National Marine Fisheries Service, NOAA 



28 Tarzwell Drive 



Narragansett, Rhode Island 02882-1 199 



Manuscript accepted 15 July 1994. 

 Fishery Bulletin 93:116-126 (1995). 



Sharks have become increasingly 

 important in U.S. commercial fish- 

 eries in the western North Atlantic 

 Ocean in recent years. U.S. landings 

 of large coastal sharks, represented 

 primarily by several species in the 

 family Carcharhinidae, increased 

 from 135 to 7,122 metric tons (t) 

 from 1979 to 1989 (Anon., 1993). 

 Musick et al. (1993) reported that 

 annual recreational catches are es- 

 timated to be 35,000 U.S. tons and 

 related annual mortality is over 

 10,000 U.S. tons (9,074 1). As a group, 

 sharks tend to exhibit slow growth, 

 late age at maturity, and low fecun- 

 dity (Holden, 1973). As a conse- 

 quence of these life history charac- 

 teristics, recruitment in sharks is 

 directly dependent on stock size 

 (Holden, 1973). This direct relation- 

 ship means that elasmobranchs may 

 not be able to recover readily from 

 overexploitation (Holden, 1973). 



The dusky shark, Carcharhinus 

 obscurus, is part of the species com- 

 plex presently managed under the 

 Secretarial Shark Fisheries Manage- 

 ment Plan (FMP) for the Atlantic 

 Ocean (Anon. 1993). Currently, dusky 

 sharks are harvested in commercial 

 fisheries off the southeastern United 

 States and in the Gulf of Mexico. Rec- 

 reational fishermen off the northeast- 

 ern United States also catch dusky 

 sharks (Casey and Hoey, 1985; 

 Musick et al., 1993). The shark FMP 

 (Anon. 1993) details the need for ac- 



curate life history information on in- 

 dividual species taken in the shark 

 fishery. Proper management at the 

 species level requires specific infor- 

 mation on age and growth. 



The dusky shark is a common 

 coastal pelagic species with a world- 

 wide distribution in temperate and 

 tropical waters (Compagno, 1984). 

 In the western North Atlantic, it 

 ranges from as far as Banquereau 

 Bank off Nova Scotia, Canada, to 

 southern Brazil, including the Gulf 

 of Mexico and Caribbean Sea (Hoey, 

 1983; Compagno, 1984). Tagging 

 studies show dusky shark move- 

 ments from southern New England 

 to Yucatan, Mexico (Casey et al. 1 ; 

 Hoey, 1983). 



Age and growth studies of large 

 sharks are difficult because many 

 species are highly migratory, mak- 

 ing them available for only short 

 seasonal periods, and different ele- 

 ments of the population segregate 

 spatially by size and sex (Hoenig 

 and Gruber, 1990). In addition, the 

 large size attained by adults makes 

 them difficult to sample. Recent lit- 

 erature has discussed the benefits 

 of growth and longevity estimates 

 attained from tag and recapture 



1 Casey, J. G., H. L. Pratt Jr., and C. E. 

 Stillwell. 1980. The shark tagger summary. 

 Newsletter of the Coop. Shark Tagging 

 Program. U.S. Dep. Commer., Northeast 

 Fish. Sci. Cent., Natl. Mar. Fish. Serv., 28 

 Tarzwell Rd., Narragansett, RI, 02882-1199. 



116 



