Coexistence and alternative stable states in the bioeconomics of fisheries and aquaculture

The growing shortfall in wild seafood and expansion of aquaculture can involve ecological and economic feedback between wild and farmed fish populations such as disease transmission and market competition. Here, we investigate the resilience of bioeconomically interacting fisheries and aquaculture systems by developing and analyzing mathematical models that capture the ecological suppression of wild fish survival by aquaculture, the management of fisheries for maximum sustainable yield, and aquaculture growth via two regulatory scenarios: perfect competition or rent optimization. Stability analysis of the models indicates that coexistence of productive fisheries and aquaculture is stable if the ecological impacts of aquaculture on wild fish are held below a bioeconomic threshold. Otherwise, the dynamics involve regime shifts between alternative stable states of fishery dominance with little aquaculture versus aquaculture dominance with collapsed fisheries. These regime shifts are difficult to reverse due to hysteresis. Coexistence and alternative stable states occur in both regulatory scenarios, but resilience is higher under rent optimization than perfect competition. Our results indicate that bioeconomic feedback can have important consequences for the resilience of aquaculture-fishery systems.