DEMOGRAPHIC-ANALYSIS OF THE SANDBAR SHARK, CARCHARHINUS-PLUMBEUS IN THE WESTERN NORTH-ATLANTIC

The sandbar shark, Carcharhinus plumbeus, is the most common large coa stal shark in Virginia waters and is an important component of recreat ional and commercial fisheries along the east coast of the United Stat es. Sandbar shark demographic analyses, using known and estimated life history parameters, including fishing mortality (F) at ages and level s estimated in a recent stock assessment, were used to estimate potent ial population growth and exploitation. Life history tables were const ructed by using best estimates of natural mortality (M) of O.11 or 0.0 7 for maximum ages of 30 or 60 yr, respectively. Natality was fixed at 2.1 female pups/yr. Fishing mortality (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 po pulation growth rate was highest under a ''best-case'' scenario of M=0 .05 (1/2 best estimate) and maximum age of 30 yr, but was only 11.9%/y r. At M=0.11 for all ages, the population increase rate was 6.4%/yr, a nd the generation time was about 20 years. At higher juvenile mortalit y rates, the population growth rate decreased to 2.6%/yr. Adding fishi ng 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 ca n be exploited only at very low levels.