Density-dependent mortality in 0-group plaice (Pleuronectes platessa L.) populations

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Abstract
The 0-group plaice population size and mortality rates in Filey Bay, Yorkshire, were estimated during four separate years. Population density was estimated from beam-trawl catches and the area within density contours measured to estimate total population. In one year (1969) an estimate was also made by latex tagging fish in a capture-recapture experiment. The instantaneous rate of population decrease from the peak of recruitment (July) to the end of the sampling season (October) gave the best estimate of mortality. These data were combined with those from three other nursery areas (ten observations in all) to examine the relationship between mortality rate and population density. It is concluded that the mortality comprises a constant, density-independent component, and a curvilinear density-dependent component, which is asymptotic. A hypothesis is put forward describing how the mortality might be caused by two predator groups. The density-independent mortality being caused by predators normally resident in plaice nurseries, e.g., Trachinus vipera, Agonus cataphractus, and Callionymus spp; and the density-dependent mortality being caused by migrant predators, e.g. older flatfish, and gadoids.

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