Population dynamics of the common shrimp, Crangon crangon (L.), in Port Erin Bay, Isle of Man, Irish Sea

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The population structure, growth, mortality, and size at sexual maturity of the common shrimp (Crangon crangon) were examined in Port Erin Bay, Isle of Man, Irish Sea between April 1995 and July 1998. For estimation of parameters of growth and mortality, monthly length–frequency data were analysed by ELEFAN. The population consisted mostly of the first year class, with a similar size composition each year. Regressions of body wet weight on carapace length indicated isometric growth (exponents very close to 3.0). Parameters of growth were estimated, using the modified von Bertalanffy growth function (VBGF) model incorporating seasonal variation in growth. Females grew faster and reached a larger size at age than males (K=1.09 yr −1 and L∞=18.5 mm CL for females, and K=0.90 yr −1 and L∞=15.1 mm CL for males). The maximum life span is estimated as 3.3 years. The recruitment pattern shows one major recruitment event per year. Total mortality (Z) by length-converted catch curve was estimated at 3.96 yr −1, fishing mortality (F) 0.36 yr −1, and natural mortality (M) 3.60 yr −1. The size at 50% sexual maturity for females ranged from 12.0 to 12.6 mm CL. Fecundity per recruit was 6.2×105. The exploitation rate (E) corresponding to 50% of the unexploited stock was 0.28 at L25, 0.32 at L50, and 0.35 at L75.