Risks of ignoring fish population spatial structure in fisheries management

Ignorance of spatial structures in fisheries management may lead to unexpected risks of overexploitation. Based on the information about small yellow croaker (Larimichthys polyactis) off the coast of China, we simulated a fish population consisting of three subpopulations mixing at intermediate levels, which was considered in the "true" spatial structure of the population in this study. Three scenarios of population spatial structure were assumed in assessing and managing this simulated fishery: (i) metapopulation, which has the same structure as the "true" population; (ii) three independent subpopulations, which overlook the exchanges among the subpopulations; and (iii) unit population, which completely ignores the population spatial structure. Corresponding approaches were applied to assess and manage each of these assumed fish populations. The management time period was assumed to be 10 years with two harvesting levels (i.e., maximum sustainable yield (MSY) and f0.1). Assessing and managing the metapopulation as several independent populations could lead to a high probability of overexploitation. Managing the metapopulation as a unit population could lead to local depletion. Use of MSY as a management target may be risk prone in the existence of a metapopulation, and use of a fishing mortality lower than f_0.1 as a management target is more desirable.