Effects of Predation Refugia on the Sustainability of Linked Predator-Prey Fisheries

Many species have spatially complex life histories, which likely have important implications for management.  However, fisheries management often operates on large spatial scales and ignores much of the substructure of stocks.  This is especially true in predator-prey systems, where predation refugia have been hypothesized as an important stabilizing force for population persistence (i.e., foraging arena hypothesis).  We conducted a simulation study of a spatially-structured linked predator prey system to evaluate how spatial patterns of fishing on predators and prey affected population dynamics and resilience to perturbations.  The stochastic simulation model was fashioned after striped bass (Morone saxatilis) and Atlantic menhaden (Brevoortia tyrannus) in the western north Atlantic and included sub-stocks in several spatial areas that were linked with seasonal migration.  We explored the effects of alternative spatial and temporal fishing patterns on predator and prey sustainability and fishery metrics.  We also considered several scenarios of prey importance from the predator in which the primary prey species composed 10%, 25%, and 50% of the predator diet in the absence of fishing.  The spatial pattern of fishing on the prey had relatively little effect on the predator dynamics when the prey were only 10% of the predator’s diet.  Different spatial fishing patterns generally had the same effect on prey and predator populations when migration rates among areas were high.  However, when migration rates were low and the prey was highly important in the diet of the predator, the spatial and temporal pattern of fishing had an effect on prey and predator sustainability.