SIMULATION ANALYSIS OF EVOLUTIONARY RESPONSE OF FISH POPULATIONS TO SIZE-SELECTIVE HARVESTING WITH THE USE OF AN INDIVIDUAL-BASED MODEL

Many studies have been devoted to analyze data and/or discuss theory a ddressing the potential evolutive impacts of anthropogenic exploitatio n in fish populations. However, not many conclusions about the nature of long term changes in fish populations have been derived from wild p opulation observations. Simulation models can help to identify factors that play important roles in the evolution of fish through genetic ch ange. The objective of this paper is to present an individual-based mo del with a genetic component using parameters common to fish populatio n dynamics. Such a model could help us gain insight in the impact of s elective fishing mortality on the characteristics of the progeny throu gh genetic based changes. The model deviates from quantitative genetic s on its handling of trait inheritance. It also establishes a link bet ween large scale population dynamic processes such as recruitment and the contribution of individual fish to the spawning stock biomass (SSB ) and the resulting distribution of trait inheritance. The model uses parameter values for cod (Gadus morhua) from the literature to simulat e four exploitation scenarios. The results indicate that smaller lengt h-at-maturity, slower growth to smaller sizes and higher fecundity wou ld be advantageous traits for adult survival under exploitation. Howev er, the magnitude of such evolutive trend was very small with determin istic recruitment. Moreover, the effect of the selective forces determ ining the successful traits to be passed to the offspring was weakened even further under stochastic recruitment. (C) 1998 Elsevier Science B.V. All rights reserved.