Fish Spawning Aggregations: A Reef Resilience Toolkit Module

Importance of FSAs

Fish spawning aggregations are important from ecological, social, and economic perspectives, among others. The precise value of an FSA to the local ecosystem is difficult to define in monetary terms, although there are various economic valuation methods that can quantify the ecosystem value of a resource to humans. Despite the lack of empirical data for FSA worth, their importance to local or regional population persistence and fisheries maintenance cannot be underestimated.

FSAs are important in a number of ways such as:

• Sources of larvae
• Sources of food for other reef-associated and pelagic organisms
• Sources of income to local economies

Sources of Larvae

FSAs are likely the only source of larvae for many species, and therefore, FSA protection is critical for population persistence. While long-distance larval dispersal is possible, a greater number of studies suggest local retention of larvae1, such that the persistence of local populations may be closely linked to the persistence of local FSAs.

It is helpful to consider spawning aggregations from a banking perspective. The FSA acts as a bank, with fish in the FSA acting as the capital, and the eggs and larvae derived from it, the interest. The greater the capital, the greater the interest. The interest, in turn, supplies greater capital, with ever-greater interest. When FSAs are fished down, both the capital and interest are reduced. A lost or depleted FSA has little capital and little interest. Continued fishing on an FSA is the equivalent of bankruptcy. Alternatively, when FSAs are allowed to be maintained, or increase in abundance, the potential for increased interest is high. Similarly, MPAs may be thought of as banks with capital and interest protected and, when enforced, allowed to grow to provide resource wealth to the surrounding reef and fishing community.

Sources of Food

There is evidence that a number of species exploit FSAs as a food source. For example, in the Central Pacific, bluefin trevally, (Caranx melampygus) and blue smalltooth jobfish(Aphareus furca)have been observed feeding on spawning fishes, while the planktivorous black triggerfish (Melichthys niger)and pinktail triggerfish (M. vidua)were seen feeding on recently released gametes. In Belize, whale sharks (Rhincodon typus) have been observed to form seasonal aggregations around an important spawning aggregation site, to feed on fish spawn2 and several smaller fish species fed on eggs, including yellowtail snapper (Ocyurus chrysurus), Atlantic spadefish (Chaetopidterus faber) and rainbow runner (Elagatis bipinnulata)3.

Protecting spawning populations ultimately helps to ensure the livelihood of fishers into the future. Photo © S. Wear/TNC

Sources of Income to Local Economies

FSAs have historically been an important source of income to local economies, and full-scale industries have developed around them4. Many coastal communities are highly dependent on marine resources, and the disappearance of FSAs may affect local food security5. These aggregations may also act as safety valves during times of social or economic hardships, or disturbances of local economies6.

While FSAs have historically been fished in some areas to provide subsistence and income to communities, any level of fishing pressure on FSAs is potentially detrimental. The ecological value of a protected FSA is, over the long term, greater than the economic value gained through direct exploitation of spawning fishes. In other words, an FSA that is fully conserved and protected is more valuable, because it may ensure the continued replenishment of local fish stocks; whereas the extraction of fish from an FSA may provide short-term economic benefits, while being detrimental to the entire fishery in future years.

Fishes sold in the global ornamental fish trade may be targeted in FSAs. While most freshwater species are now cultivated in captivity, the majority of marine species are collected from the wild. The past decades have seen growth in the marine ornamental fish trade industry, with most of these species being collected from tropical coral reefs7. Therefore, FSAs of ornamental species should also receive protection.

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