341 



Abstract. ^The sandbar shark, Car- 

 charhinus plumbeus, is the most com- 

 mon large coastal shark in Virginia 

 waters and is an important component 

 of recreational and commercial fisher- 

 ies along the east coast of the United 

 States. Sandbar shark demographic 

 analyses, using known and estimated 

 life history parameters, including fish- 

 ing mortality (F) at ages and levels es- 

 timated in a recent stock assessment, 

 were used to estimate potential popu- 

 lation growth and exploitation. Life his- 

 tory tables were constructed by using 

 best estimates of natural mortality (M) 

 of 0.11 or 0.07 for maximum ages of 30 

 or 60 yr, respectively. Natality was fixed 

 at 2.1 female pups/yr. Fishing mortal- 

 ity (F=0.05, 0.10, 0.15, 0.20, or 0.25) 

 was simulated to begin at age 8, 10, 15, 

 20, or 29. The annual population 

 growth rate was highest under a "best- 

 case" scenario of M=0.05 (V2 best esti- 

 mate) and maximum age of 30 yr, but 

 was only 11.9%/yr. At A/=0.11 for all 

 ages, the population increase rate was 

 6 1' yr, and the generation time was 

 about 20 years. At higher juvenile mor- 

 tality rates, the population growth rate 

 decreased to 2.6%/yr. Adding fishing 

 mortality at immature ages caused the 

 population to decline unless F levels 

 were <0.10 and 0.05 at maximum age = 

 30 and 60, respectively. It is apparent 

 that sandbar shark populations will 

 decline under any substantial fishing 

 mortality on immature ages and that 

 mature fish can be exploited only at 

 very low levels. 



Demographic analysis of the sandbar 

 shark, Carcharhinus plumbeus, 

 in the western North Atlantic* 



Thomas R. Sminkey 



Florida Marine Research Institute. Department of Environmental Protection 

 100 Eighth Avenue SE. St Petersburg. Florida 33701 



John A. Musick 



Virginia Institute of Marine Science. School of Marine Science 

 College of William and Mary, Gloucester Point. Virginia 23062 



Manuscript accepted 4 December 1995. 

 Fishery Bulletin 94:341-347 ( 1996). 



The sandbar shark, Carcharhinus 

 plumbeus, ranges from Cape Cod to 

 Brazil in the western North Atlan- 

 tic (Bigelow and Schroeder, 1948; 

 Springer, 1960; Garrick, 1982) and 

 is the most common large coastal 

 shark in Virginia waters (Musick et 

 al., 1993). It comprises 20% of the 

 large-shark fauna of the U.S. east 

 coast and is an important compo- 

 nent of recreational and commercial 

 fisheries (Hoff, 1990; Musick et al., 

 1993; Anonymous 1 ). Age and growth 

 (Casey et al., 1985; Casey and 

 Natanson, 1992; Sminkey and 

 Musick, 1995), seasonal distribu- 

 tion (Bigelow and Schroeder, 1948; 

 Springer, 1960; Musick etal., 1993), 

 and reproductive biology (Colvo- 

 coresses and Musick 2 ) of the sand- 

 bar shark have been studied, but 

 population studies have been lim- 

 ited to a time series of relative abun- 

 dance in Virginia waters (Musick et 

 al., 1993) and to a demographic 

 analysis based on previously pub- 

 lished life history parameters (Hoff, 

 1990). 



The recent increase in fishing 

 pressure on sandbar sharks and 

 subsequent decline in abundance 

 (Musick et al., 1993), revised age 

 and growth studies (Casey and 

 Natanson, 1992; Sminkey and 

 Musick, 1995), and a reexamination 

 of fecundity data presented in 



Colvocoresses and Musick 2 have 

 provided updated parameters nec- 

 essary for a demographic analysis 

 of the sandbar shark. This analysis 

 uses estimates of longevity, age-spe- 

 cific survival, and age-specific na- 

 tality to construct a life history table 

 which generates estimates of the 

 net reproductive rate per genera- 

 tion, the generation time, and the 

 intrinsic rate of increase of the 

 population (Krebs, 1985). These 

 parameters are useful for manage- 

 ment purposes and for input into 

 population models (Krebs, 1985; 

 Hoenig and Gruber, 1990). The ob- 

 jective of this study is to provide an 

 updated demographic analysis of 

 the sandbar shark by estimating 

 population parameters under vary- 

 ing conditions of natural mortality 

 and fishing mortality (i.e. mortal- 

 ity caused by fishing). 



Contribution 1983 of the Virginia Insti- 

 tute of Marine Science, School of Marine 

 Science, College of William and Mary, 

 Gloucester Point, VA 23062. 



1 Anonymous. 1992. Fishery manage- 

 ment plan for sharks of the Atlantic 

 Ocean. U.S. Dep. Commer., NMFS, 

 NOAA, 10 December 1992. 



2 Colvocoresses, J. A., and J. A. Musick. 

 1989. Reproductive biology of the sand- 

 bar shark, Carcharhinus plumbeus, in the 

 Chesapeake Bight. Abstract, 69th annual 

 meeting. Am. Soc. Ichthyology and Herp.; 

 17-23 June 1989, San Francisco. CA. 



