Exploring individual and population eco-evolutionary feedbacks under the coupled effects of fishing and predation

Intensive fishing that selects for large and old individuals can have pervasive effects on traits directly associated with the fecundity and survival of the target species. The observed reduction in fish body size can result in earlier sexual maturity at a smaller body size, leading to a lower individual reproductive output and population productivity in the long term. In addition, increased predation can induce similar responses in age and size at maturity due to the release of intraspecific competition and the lower population density. Thus, the combined impact of fisheries and predation is more difficult to predict due to their competition for fish, ultimately limiting and directing the prey size selectivity of each competitor. This can lead to various responses of fish on individual and population levels, depending on how the impacts of fisheries and predation affect each other. To explore this topic, we used an individual-based model to investigate the responses of the European hake (Merluccius merluccius) to the coupled pressures of the prevailing fishing regime and predation by bottlenose dolphins (Tursiops truncatus) as a study system. By simulating the growth trajectories of hake with consideration to its pronounced sexual size dimorphism (SSD), we applied Holling’s Type II and III functional responses (FRII and FRIII, respectively) and the Rosenzweig-MacArthur predator model to describe prey–predator dynamics. Our results demonstrate how the intensity, duration, and prey sizes selected by predation and fisheries determine the potential for evolutionary changes in hake life-history traits. Additionally, pronounced SSD in hake as well as the predation type play a pivotal role in hake resilience and recovery following a period of overexploitation. Different types of predation reveal the discrepancy in the intensity of competition between predators and fisheries for fish, as well as predator survival, which is relevant for sustainable fisheries management and effective predator conservation strategies.