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 addressing the potential evolutive impacts of anthropogenic exploitation in fish populations. However, not many conclusions about the nature of long term changes in fish populations have been derived from wild population observations. Simulation models can help to identify factors that play important roles in the evolution of fish through genetic change. The objective of this paper is to present an individual-based model with a genetic component using parameters common to fish population dynamics. Such a model could help us gain insight in the impact of selective fishing mortality on the characteristics of the progeny through genetic based changes. The model deviates from quantitative genetics on its handling of trait inheritance. It also establishes a link between 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 simulate four exploitation scenarios. The results indicate that smaller length-at-maturity, slower growth to smaller sizes and higher fecundity would be advantageous traits for adult survival under exploitation. However, the magnitude of such evolutive trend was very small with deterministic recruitment. Moreover, the effect of the selective forces determining the successful traits to be passed to the offspring was weakened even further under stochastic recruitment.