A study of stock/recruitment processes in model form suggests that the natural mortality of fishes is a density dependent function of age. With an estimate of the
larval mortality of the plaice in the Southern North Sea, the trend of natural mortality with age was estimated. A critical age was defined as that at which the specific
growth rates and specific mortality rates become equal and it was suggested that in older age groups mortality might become senescent. In the models used, mortality rate
in the larval stage depends upon the variability of food and there is a sense in which subsequent recruitment is determined by the patchiness of the food. There is a distinction between such an exploratory character in the density dependent mortality that may establish the magnitude of recruitment and the conservative character of the stock dependent on which the initial numbers are based. Difierences in the ratio of specific growth rate and specific mortality rate during larval life might express competitive differences which would afiect the magnitude of recruitment and eventually the quantity in the stock. A consequence is that possibly high diversity is the result of low competitive pressures and vice versa
