Taking animal breeding into the wild: regulation of fishing gear can make fish stocks evolve higher productivity

Harvesting of living resources involves conflicting objectives between profits, human consumption, population sustainability and ecological impacts. These trade-offs are often complex, as harvesting affects demography and productivity of wild populations immersed in rich ecological interactions, and consequences may extend to the evolutionary dimension. In a life-history model of a commercially harvested fish stock, the Northeast Arctic stock of Atlantic cod Gadus morhua, we show how fishing mortality and gear selectivity affect evolution of maturation age, population dynamics and fisheries yield. We focus on common management objectives, and show that taking more of the catch with gillnets that select for intermediate sizes has the potential to increase yield and reverse undesirable evolutionary effects that have taken place over the past century. We compare the high fishing pressure of past decades with the current management plan and alternative scenarios that maximize (1) food production, (2) product quality (size of individual fish in the catch), or (3) evolutionary reversal. Directing more of the catch towards individuals below or at maturation size improves sustainability and food production from fisheries while reversing evolutionary impacts. This demonstrates that evolutionarily enlightened management of size selectivity, based on existing gear types and technology, can reconcile seemingly conflicting management objectives.