Modeling co-occurring species: a simulation study on the effects of spatial scale for setting management targets

Many species of marine fish are found in similar habitats and display similar vulnerability to fishing pressure, although their sustainable exploitation rates may differ considerably. Managing and setting harvest limits is challenging for such co-occurring species because the management targets for the less productive species may affect the fishing opportunities for the more productive species. We used simulation modeling to explore the effects of setting multi-species management targets and harvest regulations at local area or coast-wide levels. Setting management targets over the entire coast, and identifying optimal harvest rates within each local area, consistently led to the same or higher yields than setting management targets for each area. Essentially, the global conservation goal can be achieved by protecting areas in which the less productive species is abundant and by taking most of the harvest from other areas. The increases in yield do not increase the coast-wide probabilities of either species being overfished or severely depleted, but do increase these probabilities at the local area level for the less productive species. These results are magnified with increased spatial variation in the ratio of abundance and differences in intrinsic rates of growth among the fished species.