The role of sex change, growth and mortality in Pandalus population dynamics and management

Sex change, growth. and mortality of Pandanus populations are important to stock management. To investigate the importance of these life history trait s in setting management strategies, we performed a variety of simulatoins u sing a length-based model. Wa compared three populations: a Kachemak Bay. A laska type (K_pop): a hypothetical one with the same growth but without sex change (H_pop): and a northern Barents Sea type (B_pop). The main differen ce between K_pop and B_pop is growth rate: K_pop has faster growth and a sh orter live span, whereas B_pop lives farther north, and therefore has faste r growth and greater longevity. We found that populations with sex change w ere more sensitive to fishing pressure. Continuous fishing was detrimental to K pop when instantaneous fishing mortality was above 0.3. but threshold management. i.e. closing the fishery at low population level, greatly impro ved the population performance. B_pop, the slower-growing. longer-lived pop ulation required larger mesh sizes than K_pop. but increasing mesh size cou ld not prevent collapse under high fishing mortality, and fishery closure u nder threshold management was necessary to sustain the population. Abrupt d ecrease of age one and two males caused populations with sex change to fluc tuate in spawning biomass. Seasonality in growth and natural mortality is a lso pertinent to shrimp management. Given taster growth in summer, higher n atural mortality in summer means fishing after spring hatching tends to res ult in higher cumulative yield than fishing after fall mating. and vice ver se. In addition, fishing after hatching is in general mure robust to overfi shing. From the simulation analyses, we concluded that both sex change and seasonality of growth and mortality of Pandalus populations should be taken into account in shrimp management. (C) 2001 International Council for the Exploration of the sea..