The ecosystem approach to managing fisheries: achieving conservation objectives for predators of fished species
Managing fisheries to achieve ecosystem objectives is in its infancy. A general approach is proposed for maintaining ecological relationships and providing for the recovery of depleted populations in food webs supporting fisheries. This paper addresses the following general questions for applying the ecosystem approach to managing fisheries: (i) how might fisheries impact incidentally on an ecosystem, (ii) what should be the conservation objectives for predators of fished species, and (iii) what approaches could be considered for achieving the conservation objectives? The approach proposed here takes account of uncertainties in knowledge of the structure of ecosystems. Estimates of predator production arising from the consumption of fished species (encapsulated in proposed indices P and W) may provide useful indicators for management purposes because they integrate across a range of 'ecosystem' effects and, as formulated here, can also be related directly to the effects of fishing. These features are currently unavailable in ecosystem approaches to managing fisheries, which do not weight input data for assessments, such as per-capita breeding success, according to the relative influence of fished species on those estimates. The paper describes the steps required to establish management procedures based on these indices.