Population dynamics of the brown shrimp Crangon crangon L., in shallow areas of the German Wadden Sea

Settlement, growth and mortality of the brown shrimp, Crangon Crangon L., were studied in the north Frisian Wadden Sea over a period of 19 months to fill existing gaps regarding the species' life cycle, and thereby to clarify points related to the fishery. Settlement of postlarval shrimp in the shallow areas occurred in three batches: in May; during summer; and an overwintering batch. Compared with an earlier model based on laboratory-derived data, a new growth model based on field data predicts similar growth rates for the earlier phase of the shrimp life cycle, but higher rates for the later stages of the cohorts. Mean growth rate of the different cohorts over the size range sampled was 0.23 ± 0.08 mm day^?1. Of the factors tested, only temperature significantly influenced growth rates. Preliminary estimates of instantaneous total mortality values for shrimp cohorts from these shallow areas ranged from 0.03 to 0.12 day^?1. Salinity explained most of the variation in mortality rates, but this most likely indicates an indirect effect of depth on emigration. The cumulative effects of growth rates estimated from the new model and lower losses through predation could imply a higher contribution of winter eggs to the autumn fishery. This, however, needs further evaluation to properly quantify the trade-offs between settlement and recruitment to the fishery, as well as the growth and mortality rates.