Fisheries-Induced Changes in Age and Size at Maturation and Understanding the Potential for Selection-Induced Stock Collapse

Abstract

Fishing is very likely to create selective pressures inducing adaptive changes in the life histories of harvested stocks. Using field data and adequate statistical methods, such alterations can be demonstrated. However, in order to understand underlying causes and to evaluate alternative management practices, past selective pressures must be quantified and predictions of future evolutionary changes are needed. In this respect, modelling the ecological and evolutionary dynamics of exploited stocks is a critical challenge. To illustrate this point, we studied the evolution of age and size at maturation induced by fishing using adaptive dynamics theory – a framework that allows modelling long-term evolution of quantitative traits under density- and frequency-dependent selection. Specifically, we investigated the evolutionary implications of alternative management policies. As a novel contribution to the discussion of fisheries-induced adaptive change, we showed that frequency-dependent selection, arising from fishing mortality under some particular management policies, can not only reduce the age and size at maturation and thus stock biomass, but can ultimately even induce the extinction of entire stocks. The potential for such phenomena of ‘evolutionary suicide’ is overlooked in models that do not incorporate life history evolution. Our findings thus highlight the importance of considering evolutionary trends in the management of exploited stocks.