Contemporary management issues confronting fisheries science

Stock collapses have occurred worldwide. The most frequently cited cause is over-fishing, suggesting that fisheries management has been ineffective in controlling exploitation rates. The progression of a fishery from an over- exploited to a collapsed state involves impairment of the reproductive capa city of the target species, i.e. recruitment over-fishing. In many cases, t his occurs by reduction of the spawning stock biomass (SSB) through the sys tematic elimination of spawning components within a stock complex. While op erational definitions of minimum levels of SSB have been developed, they ha ve seldom been applied and never adopted in a Canadian groundfish managemen t context. The answer to the question of how much is enough to perpetuate a stock under exploitation has been illusive. Serebryakov [J. Cons. Int. Exp lor. Mer, 47 (1990) 267] has advocated definition of critical levels of SSB based on survival rates (R/SSB). We review his method and discuss the util ity of the approach. An alternative approach to the problem of estimating m inimum SSB is through a fundamental revision of the traditional stock and r ecruitment relationship. Explicit theoretical SSB thresholds below which re production/recruitment is severely impaired based upon density-dependent ma ting success (or Allee effects) is considered a superior approach to the qu estion of how much is enough because of its ecological grounding. However, the successful application of this approach will require re-definition of t he space/time scales of the management unit. Finally, support is growing fo r the establishment of closed areas or "no-take zones" as an alternative ap proach to managing the problems of fishing a stock complex by enabling subp opulations to escape fishing. While the expected benefits of areas protecte d from fishing are numerous, clear demonstrations of benefits of such areas in marine temperate ecosystems are lacking. In fact, unintended negative c onsequences may result from such actions. (C) 2001 Elsevier Science B.V. Al l rights reserved.