Spatial limitation of population size; The concentration hypothesis

The long-term dynamics to be expected of fish populations controlled by density-dependent processes in the early life-history compared with in the adult phase are explored. It is suggested that those species (as exemplified by European plaice, Pleuronectes platessa) which tend to concentrate spatially into nursery grounds during their early life-history may be ‘saturating’ the carrying capacity of those juvenile habitats though the adult part of the population is still relatively small and not limited by the adult habitat. This is called the concentration hypothesis and, if valid, it would explain some features of the long-term dynamics of different species. Tests based on the characteristics of the stock and recruitment data series to be expected from ‘concentrating’ vs ‘non-concentrating’ species are proposed, with some provisional results.