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

The population structure, growth, mortality, and size at sexual maturity of the common shrimp (Crangon crangon) were examined in Port Erin Bay, Isle o f Man, Irish Sea between April 1995 and July 1998. For estimation of parame ters of growth and mortality, monthly length-frequency data were analysed b y ELEFAN. The population consisted mostly of the first year class, with a s imilar size composition each year. Regressions of body wet weight on carapa ce length indicated isometric growth (exponents very close to 3.0). Paramet ers of growth were estimated, using the modified von Bertalanffy growth fun ction (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-in finity=18.5 mm CL for females, and K = 0.90 yr(-1) and L-infinity = 15.1 mm CL for males). The maximum life span is estimated as 3.3 years. The recrui tment pattern shows one major recruitment event per year. Total mortality ( Z) by length-converted catch curve was estimated at 3.96 yr(-1), fishing mo rtality (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 x 10(5). The exploitation rate (E) corresponding to 50% of the unexploited stock was 0.28 at L-25, 0.32 at L-50, and 0.35 at L-75. (C) 1999 International Council for the Exploration of the Sea.