Fish Spawning Aggregations: A Reef Resilience Toolkit Module

Destructive Fishing Methods

Because spawning aggregations are so important and so vulnerable, one might believe that all types of fishing pressure on FSAs are equally destructive. However, some forms of fishing are particularly destructive, especially those that not only extract fish with the intention of making large, short-term profits, using little effort, but also damage the habitat in the process. Such types of destructive fishing include the following practices:

Blast fishing physically destoys reef habitat and kills fish indiscriminately. Photo © Jos Pet

• Blast fishing and chemical use, including cyanide and Derris root extract
• Night spearfishing
• Overfishing outside aggregations
• Ghost fishing, for example, by traps or nets

Blast Fishing and Cyanide Use

Destructive fishing techniques, such as cyanide or dynamite, have the effect of killing all reef life, including corals and other invertebrates, as well as unmarketable species, for short-term profits. While cyanide use is typically equated with the international live reef fish trade, targeting spawning aggregations and aquarium fishes, dynamite use is often for subsistence, or for local small-scale commercial fisheries. One study reports that the reef-degrading capacity of the cyanide fishery, for food on Indonesian coral reefs, amounts to a loss of live coral cover of approximately 0.05 square meters per 100 square meters of reef per year1.

Reefs that have been fished with destructive methods may take many years to recover, and be left largely devoid of life, and unsuitable for FSA formation, fishing, or ecotourism activities. After the reef habitat has been destroyed, fishers typically move on to another location, increasing the damage and the pressure on remaining fishes, spawning aggregations and reefs. Fishing using these techniques is for short-term gain, and depletes natural resources that could otherwise provide steady long-term income for an entire community or region.

Night Spearfishing

Many FSA-forming species are inactive at night, and become easy targets for fishing. Spearfishing is widely known to be a destructive fishing technique, and has catalyzed overfishing in many parts of the world2. The practice is being increasingly banned from a number of areas, although it is widely used in many parts of the Indo-Pacific.

Overfishing Migration Corridors

Ghost fishing trammel net off Wales. Tangled gadoid probably lured the shag into the net. Photo © Blaise Bullimore/CCW/JNCC UK

Recent evidence suggests that a number of aggregating species use common reproductive migratory corridors to travel to and from FSA sites3. There is also evidence that some individuals travel together in groups along these corridors4. When these groups are targeted, the effect not only extracts schools of fish from the population, but also removes the reproductively active members of the population before they have a chance to reproduce. Both adult and juvenile populations require adequate protection from fishing outside spawning areas, and times, to produce and maintain FSAs.

Ghost Fishing

Ghost fishing refers to the loss of fishes by discarded or lost gear. Lost or damaged lines, nets, and traps continue to inflict fishing mortality long after they are no longer in use. This is clearly wasteful, as the catch is simply lost and produces no human benefit.