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 [f.sub.0.1]) 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.sub.0.1] as a management target is more desirable. Ne pas tenir compte des structures spatiales dans la gestion de la peche peut mener a des risques imprevus de surexploitation. En utilisant des donnees sur la courbine jaune (Larimichthys polyactis) du large de la cote de Chine, nous avons simule une population de poissons comprenant trois sous-populations qui se melangent a des niveaux intermediaires, ce qui est considere la << veritable >> structure spatiale de la population dans notre etude. Nous avons suppose trois scenarios de structure spatiale de la population dans l'evaluation et la gestion de cette peche simulee, (i) une metapopulation qui a la meme structure que la population << veritable >>, (ii) trois sous-populations independantes, ce qui neglige les echanges entre les sous-populations et (iii) une population unitaire qui ignore completement la structure spatiale de la population. Nous avons utilise des methodes semblables pour evaluer et gerer chacune de ces populations hypothetiques de poissons. Nous avons determine une periode de gestion de 10 ans avec deux niveaux de recolte (c.-a-d. le rendement maximum durable (MSY) et [f.sub.0,1]). L'evaluation et la gestion de la metapopulation comme plusieurs populations independantes pourraient mener a une forte probabilite de surexploitation. La gestion de la metapopulation comme une population unitaire pourrait provoquer des depletions locales. L'utilisation de MSY comme cible de gestion peut entrainer des risques, s'il existe une metapopulation; l' utilisation d' une mortalite due a la peche inferieure a [f.sub.0,1] comme cible de gestion semble donc plus desirable. [Traduit par la Redaction]
Introduction A metapopulation is defined as a group of subpopulations in which local subpopulation dynamics are driven in part by dispersal from other subpopulations in the group (Hanski 1999). Many [...]