Reefs threatened by overfishing

Modeling the threat from overfishing

Overfishing of coral reefs is widespread in Southeast Asia. Overfishing typically results in shifts in fish size, abundance, and species composition. RRSEA developed an indicator that evaluates the pressure on coral reefs fisheries from local populations within 10 square kilometers of the coast and evaluates overfishing pressure out to 20 square kilometers offshore. This indicator does not address remote offshore fishing. It was adjusted to include an estimate of management effectiveness.

Overfishing results

Overfishing is the most pervasive of the threats evaluated. The RRSEA project estimates that across the region, 64 percent of coral reefs are at risk (medium threat or higher) from overfishing, with about 20 percent at high risk. Most countries have 50 percent or more of their reefs classified as threatened by overfishing. Cambodia, Japan, and the Philippines have even higher pressure from overfishing, with over 70 percent of their reefs threatened and over 35 percent classified as high risk.

Threat description

More than 80 percent of the populations of Indonesia, Malaysia, the Philippines, Taiwan, and Singapore reside within 50 square kilometers of the coast.[1] Many of these people have come to rely on the coastal zone not only for their food but also for their livelihoods. However, coastal resources have increasingly been exploited beyond their sustainable limits as populations in the region have skyrocketed. Much of this growth is occurring among people living at subsistence levels. For example, small-scale operations contribute about 95 percent of total marine fisheries production in Indonesia.[2] Although the population explosion has put unprecedented pressures on coastal resources and jeopardized food security throughout the region, regional population increase is not solely responsible for the increasing pressure on coastal fish resources. The demand in wealthy Southeast Asian countries for marine aquarium fish, live reef food fish, pelagics, and bottomfish has further fueled regionwide exploitation of certain species.

Overfishing is a complex problem with varied impacts on coastal communities, the economy, and coastal ecosystems. If effectively managed, fisheries can provide a renewable source of food and livelihoods, but in Southeast Asia, many fish species are currently overexploited. Coral reefs are capable of supporting low levels of fishing sustainably, especially when the fishing is done with nondestructive gear and effort is spread among several species of carnivorous fishes. Fishing effort on any given species should not cause it to decline or make it vulnerable to natural fluctuations in survival rate. However, widespread poverty and the generally open-access nature of coral reef fisheries in the region can cause people to enter or remain in reef fisheries until the average fisher makes no net profit owing to high effort and low catch. If stock levels are low enough, fishers may shift from high-valued fish to less valuable species.[3] Overfishing can also cause the mix of fish species to change radically and total fish abundance to drop by an order of magnitude. Moreover, because fish play an integral role in the balance of the coral reef ecosystem, their removal makes reefs less resilient to natural and anthropogenic disturbances. Without the normal suite of fish and invertebrates, corals are more likely to be replaced by algae that prevent coral settlement and growth.

When overfishing is caused by large-scale commercial operations, government regulations and enforcement may be the key to reducing the problem. However, where coral reefs are adjacent to crowded coastlines, effective fisheries management is crucial. Key elements in improving compliance with fishing regulations include the development of alternative livelihoods, the implementation of small fishing reserves, and the involvement of fishers in resource decisionmaking. (See Management of coastal resources).

For more information on overfishing, see:

• Subsurface reefs and trawling
• Threats to reefs: Overfishing of target species