Fisheries‐induced Evolution

AbstractModern fisheries have drastically changed the level and size dependence of mortality faced by fish populations: commercial fishing usually targets medium‐sized and large individuals, which often are relatively invulnerable to natural predators. Life‐history theory predicts that fish adapt to these changes through evolutionary alterations in their life histories. Experiments and models predict that such fisheries‐induced evolution is potentially fast: significant evolutionary adaptations may occur over time scales of just a few generations. A growing body of observational studies of wild fish populations is supporting this theoretical prediction. So far, fisheries‐induced changes in maturation schedules are best documented, but several studies are also pointing to changes in growth and reproductive investment. Although fisheries‐induced evolution can render fish populations more robust against high exploitation levels, uncontrolled fisheries‐induced evolution is likely to reduce both the quality and the quantity of fisheries yields, calling for management strategies that can mitigate such undesirable effects.Key concepts:Fisheries management: Management of fish resources for the common good, typically by restricting the quantity and quality (e.g. size) of fish captured directly or indirectly, by restrictions to fishing methods and areas and times when fishing is permitted.Precautionary principle: A principle according to which uncertainty should not be used as a reason for postponing mitigating management measures when the absence of such measures would risk severe and unrecoverable damage to the environment or human well‐being.Life‐history theory: Evolutionary theory predicting how life histories are expected to be shaped by the ambient environment. Predictions often focus on key life‐history traits such as maturation, growth, and reproductive investment, and thus on the main determinants of an individual's expected reproductive success.Fisheries‐induced evolution: Genetic change of the population‐level distribution of heritable characteristics of individuals, with mortality caused by fishing as the selective agent driving the change.Fisheries‐induced adaptive change: Change of the population‐level distribution of phenotypic characteristics of individuals, caused by fishing and reflecting both genetic changes and changes due to adaptive phenotypic plasticity.Phenotypic change: Change of the population‐level distribution of phenotypic characteristics of individuals. Although such changes are often observed readily and unambiguously, the challenge is to disentangle genetic changes from other changes and fisheries‐induced causes from other causes.Probabilistic maturation reaction norm: A conceptual and statistical tool accounting for the effects of growth conditions on maturation. This tool has helped to establish that maturation changes widely observed in exploited fish stocks can usually not be explained by changes in growth conditions alone. Once this major component of maturation plasticity has thus been isolated from the total phenotypic change in maturation, potentially remaining maturation changes must have other explanations, among which fisheries‐induced evolution often appears as being the most parsimonious.