THE IMPORTANCE OF 'COVER' IN THE LIFE HISTORIES OF DEMERSAL AND BENTHIC MARINE RESOURCES: A NEGLECTED ISSUE IN FISHERIES ASSESSMENT AND MANAGEMENT

摘要

Postplanktonic stages of motile demersal marine macrofauna often settle in complex habitats that protect small organisms, and later stages may depend on geographically limited topographical features. Most benthic habitats are structurally simple, and human activity can further reduce complexity. Many demersal organisms change habitats with size and age, but the stage-specific risk of death remains approximately the same, because as stage duration increases, predation risk per unit time declines. Stock replenishment is threatened by degradation of the habitats of successive life stages. Migrations must often risk predation by crossing seascapes where cover connectivity is limited. Natural recruitment bottlenecks may nullify spawning success and can be exacerbated by habitat destruction. Motile marine organisms are subject to lower natural mortality while "under cover" than while "in the open" during foraging or migration. Loss of cover therefore increases mortality, reduces foraging success, and affects other life-history activities. A habitat's carrying capacity may therefore be limited by the capacity of the stage-specific habitat with the lowest carrying capacity and not by gamete production, adult food supply, or adult habitat. Remediation of limited areas of critical habitat could therefore increase production but cannot coexist with trawl gear designed to fish on rough bottom.