Small-scale biocomplexity in coastal Atlantic cod supporting a Darwinian perspective on fisheries management

Abstract

Harvesting of marine resources raises concerns about how to identify andpreserve biocomplexity, including the diversity of life histories foundwithin and among wild populations of a species. In order to fullyaccomplish this, there is a need to elucidate the underlying causes ofphenotypic variation, and how this variation responds to environmentalchanges. In general, both evolutionary (genetic) and nonevolutionary(plastic) responses may occur. Plastic responses to environmental changeare expected to shift the phenotype along a reaction norm, while anevolutionary response is expected to shift the reaction norm itself.Here, we assess the maturation patterns of coastal Atlantic cod (Gadusmorhua) in Skagerrak, where studies using neutral markers have revealedgenetically differentiated populations of this harvested fish withintens of kilometres of coastline. Our results suggest that physiologicalstate prior to the spawning season, as well as juvenile growth, bothinfluence the probability of completing sexual maturation at a givenage. Furthermore, our results point towards a spatial structuring ofthis plasticity (i.e. the maturation reaction norms) comparable withpopulation connectivity inferred from neutral markers. We argue thatsuch fine-scale biocomplexity calls for a Darwinian approach tofisheries management.