The Effects of Fish Spatial Segregation on the Mixed Stock Fishery

U.S. law requires that overfishing be stopped while achieving the optimum yield for each fishery. This is especially difficult in a mixed stock fishery where several species of different life histories share the same habitat. The problem becomes even harder when overfished species (weak stocks) are caught together with healthy stocks (strong stocks), hence limiting the overall fishing effort in order to comply with the catch limits of the weaker stock. However, this requires giving up some sustainable yield of strong stocks. In this study we use a spatially explicit bio-economic model of a weak stock and a strong stock to explore the consequences of species spatial segregation on the biological yield and economic rent of the fishery under several management scenarios. We compare the results between a race-to-fish scenario, a total allowable catch scenario with marine reserves, and an individual quota system scenario. Trend in revenue, cost and potential lost yield is compared across the management scenarios for the varying level of spatial overlap between the weak and strong species. Model sensitivity to fish movement, MPA size, and uncertainty in movement of fishing fleets is also tested.