MODELING THE EFFECTS OF DESTRUCTIVE FISHING PRACTICES ON TROPICAL CORAL REEFS

A literature review of the use of underwater explosives indicated that the largest lethal zone for swimbladder fishes is located near the surface of the water. Mortality in this zone is due to rupture of the swimbladder from negative pressure induced by cavitation of the near-surface water volume from a subsurface explosion. Observational studies of blast fishing in the Philippines indicated that valuable pelagic species rather than typical coral reef species were the primary targets. Empirical data on the extent of various destructive fishing practices (blast fishing, anchor damage, and use of poisons), as well as coral regrowth estimates, provided inputs to a nomographic model of the reef ecosystem. The model provided time graphs of fish diversity and the amount of coral regrowth under various conditions. The results of the simulation model studies indicated that the sum of all current destructive practices was sufficient to continue loss of diversity and loss of live coral cover for about 25 yr before any recovery was expected. On the other hand a reduction in the rate of destructive fishing to about 30% of the current level would permit continuing slow recovery of both diversity and live coral cover. Available observational information suggests that this might best be accomplished by attempting to eliminate the use of poisons (such as cyanide) in reef areas and reducing anchor damage in addition to reducing blast fishing in coral areas. The probable effects of the latter may have been overemphasized in the past.