Modelling the response of size and diversity spectra of fish assemblages to changes in exploitation

In this paper we investigate whether single and multispecies fisheries models can be used to predict the response of size and diversity spectra of fish assemblages to changes in exploitation. Both types of models estimate that the slope of the size spectrum will steepen and the intercept will increase when fishing intensity increases, while the response of the slope and intercept of the diversity spectrum depend on the model used. The changes in the slope and intercept of the size spectrum are found to be proportional to the change in fishing intensity. The proportionality is insensitive to changes in natural mortality, but sensitive to changes in growth and to the relationship between stock and recruitment. The results agree well with results obtained from previous analysis of survey data from the North Sea and suggest that the slope of the size spectrum is a useful measure of fishing impacts.