Stock complexity in fisheries management: a perspective of emerging issuesrelated to population sub-units

The common approaches to evaluation and management of marine finfish stocks assume discrete populations. While it has long been recognized that this a ssumption is complicated to some degree by migrations and mixing between ma nagement units, there has been little attention paid recently to the comple xity of spawning components within management units. Several marine finfish species appear to have more complex stock structure than is recognized, an d in many cases, management units contain stock complexes or metapopulation s with several spawning components rather than single discrete populations. Unfortunately, these spawning components are typically difficult to define from traditional fisheries data, or to discriminate by conventional stock identification techniques. Failure to recognize or to account for this comp lex stock structure in management, however, may lead to erosion of spawning components, with unknown ecological consequences. The management of comple x fish stocks, at appropriate scales, so as to preserve stock complexity, t herefore, remains a major challenge. Maintenance of the full diversity of s pawning locations and times is an important aspect of topical discussions o f biodiversity and marine protected areas. Consequently, the importance of stock identification will increase as a result of a new emphasis on managem ent which takes into account stock complexity within areas traditionally as sumed to contain a single stock. This new emphasis on stock complexity is n ecessary if management is to comply with a "precautionary approach" to fish eries management. (C) 1999 Elsevier Science B.V. All rights reserved.