Predicting Eco-evolutionary Impacts of Fishing on Body Size and Trophic Role of Atlantic Cod

Abstract

Fishing has caused changes in abundance and demography in exploited populations, in part due to rapid decreases in age and size at maturation. Few models address how direct effects of fishing on age- and size-structure compare to indirect effects on the trophic role of predators. Using Atlantic Cod as example, we model the possible consequences of fishing for trophic roles, contrasting purely demographic effects with those that also include adaptive responses to fishing. While fishing decreases cod abundance in both scenarios, mean trophic level decreases more when there is an adaptive response in maturation. Adaptation also resulted more small fish, which supported the persistence of larger fish, even with heavy fishing. These large fish have a high trophic position, increasing variation relative to the demography-only case. Our model provides a proof-of-concept that eco-evolutionary feedbacks can change the trophic role of fished populations, altering food web dynamics in harvested ecosystems.