Age and Growth of the Blacktip Shark, Carcharhinus 

 limhatuSy near Tampa Bay, Florida 



Kristie A. Killam and Glenn R. Parsons 



ABSTRACT: Age and growth of the blacktip 

 shark, Carcharhinus limbatus, was investigated in 

 the Tampa Bay area of Florida during May 1985- 

 February 1987. Two hundred and eighteen sharks 

 were captured, and vertebrae were examined from 

 86 females (52.4-183.0 cm TL) and 54 males (59.8- 

 160.5 cm TL). Minimum and maximum number of 

 translucent winter rings was and 11. Marginal 

 increment analysis on juvenile blacktips with one 

 to three translucent vertebral rings suggested an 

 annual ring deposition during December-January. 

 Length-frequency and length-month analyses sug- 

 gested three age classes for blacktips <120 cm TL. 

 Growth in length and percentage of size increase of 

 blacktips age and 1 was 21.0 (29.3%) and 19.0 

 (20.7%) cm/yr, respectively. Growth in weight and 

 percentage of size increase of age and I blacktips 

 was 3.09 (120.7%) and 3.29 (58.2%) kg/yr, respec- 

 tively. Age at maturity was 6-7 years (158-162 cm 

 TL) for females and 4-5 years (133-136 cm TL) for 

 males. Maximum age of blacktips captured was 10 

 years for two females 179.0 and 180.0 cm TL, and 9 

 years for a 160.5 cm TL male. Growth in weight 

 was fit with a logistic equation. Von Bertalanffy 

 growth parameters for females were estimated at 

 L, = 195.0 cm TL, k = 0.197 and t„ = 1.154 

 years and for males, L^ = 166.5 cm TL, k = 

 0.276, and ^n = -0.884 years. 



Blacktip sharks, Carcharhinus limbatus, are 

 distributed in all tropical and subtropical con- 

 tinental waters (Compagno 1984) and are very 

 common inhabitants of inshore coastal and estu- 

 arine regions in Florida and the Gulf of Mexico 

 (Springer 1940; Clark and von Schmidt 1965; 

 Dodrill 1977; Branstetter 1981; Killam 1987). Re- 

 cently, blacktip sharks have received commer- 

 cial interest because of their increased value as a 

 food fish. Commercial shark landings in Florida 

 have risen steadily from 170,740 pounds in 1979 

 to 1,910,222 pounds in 1986 (Florida Department 



Kristie A. Killam, University of South Florida, Department 



of Marine Science. 140 7th Ave. S., St. Petersburg, FL 



33701; present address; Maryland Department of Natural 



Resources, 580 Taylor Ave.. Room C-2, Annapolis, MD 



21401. 



Glenn R. Parsons, Department of Biologj-, The University 



of Mississippi, University, MS 38677. 



of Natural Resources 1979-86). In Cahfornia a 

 similar situation has occurred where landings for 

 the common thresher shark, Alopias imlpinus, 

 the blue shark, Prionace glauca, and the short- 

 fin mako, Isurus oxyrifichus, increased from 

 800,000 pounds in 1976 to 3,500,000 pounds in 

 1981 (Cailliet and Bedford 1983). 



Elasmobranch populations are thought to be 

 easily overexploited because of their relatively 

 slow growth rates, long gestation periods, and 

 low fecundity (Holden 1974, 1977). As apex 

 predators in complex estuarine and marine 

 ecosystems, blacktip sharks have an important 

 ecological role. Increased exploitation of blacktip 

 shark stocks may effect lower trophic levels in 

 the ecosystem, therefore sound life history infor- 

 mation is needed. At present, little information 

 is available concerning the biology of the blacktip 

 shark. Its reproductive biology has been ex- 

 amined in the northern (Branstetter 1981) and 

 east-central (Clark and von Schmidt 1965; Killam 

 1987) Gulf of Mexico. Killam (1987) provided 

 detailed informaton on the seasonal distribution, 

 reproductive biology, and feeding habits of C. 

 limbatus captured near Tampa Bay, FL. Dodrill 

 (1977) provided life history information on black- 

 tip sharks captured along the east coast of 

 Florida. Garrick (1982) reported that distinct 

 populations of C. limbatus may exist in different 

 geographic regions, because maximum attain- 

 able size and sizes at maturity differ markedly 

 between regions. 



At present only a single study has been com- 

 pleted concerning the age and growth of the 

 blacktip shark. Branstetter (1987a) estimated 

 gi'owth parameters of C. limbatus in the north- 

 western Gulf of Mexico. This study provides 

 additional information on the age and gi'owth of 

 C. limbatus by 1) providing a detailed exami- 

 nation of early growth rates using length-fre- 

 quency and length-month analyses, 2) utilizing 

 marginal increment analysis on juvenile C. 

 limbatus to determine periodicity of ring deposi- 

 tion, and 3) identifying differences in age and 

 growth rates between female and male C. 

 limbatus. 



Manuscript accepted May 1989. 

 Fishery Bulletin, U.S. 87: 845-857. 



845 



