HARVEST REFUGIA IN MARINE INVERTEBRATE FISHERIES - MODELS AND APPLICATIONS TO THE RED-SEA URCHIN, STRONGYLOCENTROTUS-FRANCISCANUS

Benthic marine invertebrates with planktonic larvae may exhibit Allee effects in reproduction or recruitment. Hydrodynamic considerations an d experimental evidence suggest that species broadcasting gametes suff er greatly reduced fertilization efficiencies as densities decline. Th ere is also evidence for some species, including the red sea urchin, t hat post-dispersal recruitment success declines at low densities of ad ults, if adults provide shelter from predators or other sources of mor tality. Species displaying strong Allee effects may be susceptible to catastrophic population collapses with slight increases in mortality d ue to harvesting or natural causes. A simple two patch logistic model suggests that the establishment of a harvest refuge is necessary to pr event collapses and maintain sustainable catches at high levels of har vesting effort. A more detailed, age structured model based on the bio logy of the red sea urchin, Strongylocentrotus franciscanus produces s imilar results. Effects of harvesting strategies are sensitive to Alle e effects caused by both fertilization efficiency and the disruption o f adult spine canopies. Theoretical requirements for the size and spac ing of marine reserves depends upon the dispersal abilities of the tar get species. Multiple reserves, spaced more closely than the average l arval dispersal distance, appear to be an effective and conservative s trategy for maintaining healthy populations and sustainable levels of harvest.