Modelling, theory and multigenerational experiments to study warming and fishing induced changes in fish life-histories
In the age of Anthropocene humans have become a major evolutionary force. Through fishing and global warming we are changing selection pressures and evolutionary trajectories of life in the ocean. How fast is this change? We have reviewed empirically reported and theoretically expected rates of life-history change in fished stocks and found that many moderately fished stocks are changing at a rate of ca 1% per year. These observed rates are about four times faster than those expected from evolutionary models, suggesting that either the models miss something or that observed changes are caused by more factors that fisheries-induced evolution only. For example, the observed changes might be driven by the interplay of warming and fishing, as suggested in this study.
One thing is clear, to study human induced evolution on life-history traits we need models that allow for dynamically emergent maturation size and age, and account for the trade-offs that are likely to be important in the wild. Together with Shane Richards we developed an optimal allocation model where maturation size, age and reproductive output emerge as a result of size-specific energy intake, metabolism and – very importantly – reproduction cost. This model produces more realistic results about the evolutionary trajectories of fished species (Baltic Sea cod), because it assumes that maturation size cannot decrease indefinitely despite high fishing mortality, because there must be some minimum size below which reproduction cost cannot be met.
We also need to incorporate dynamic and selection driven evolutionary responses into multi-species models. This is not necessarily easy due to model complexity and longer computational times. Note, we are talking here about selection driven changes in traits, because some models add evolution as random trait change at certain time steps, which can simulate random genetic drift but not response to selection. Romain Forestier’s PhD is adding adaptive evolution into trait-based size spectrum models to explore how maturation size or temperature tolerance are changing in response to fishing and warming. Lots of exciting stuff is coming soon, so stay tuned
Models and revisions are all very good, but we also want good experimental data! I am collaborating with John Morrongiello to study the interplay of warming and fishing driven evolution. Henry Wootton’s PhD project uses multi-generational zebrafish experiment to study evolutionary effects of two temperature and three size selection regimes. Our goal is to understand whether and how warming and fishing might reinforce or cancel each other out when it comes to fish growth, maturation, reproduction and metabolism. New papers are coming out soon!