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Fish Spawning Aggregations: an illusion of plenty

This article is brought to you by the International League of Conservation Photographers (iLCP). Read our other articles on the National Geographic Voices blog featuring the work of our iLCP Fellow Photographers all around the world. 

Text by iLCP Fellow Jaime Rojo, and photos by iLCP Fellow Octavio Aburto, as part of their Natural Numbers initiative. 

Spawning aggregations are a behavior shared by many species across the globe, often including 95% of the population of one single fish. Grunts in a mangrove forest, Baja California, Mexico.
Spawning aggregations are a behavior shared by many species across the globe, often including 95% of the population of one single fish.
Grunts in a mangrove forest, Baja California, Mexico.

Spawning aggregations are massive gatherings of fish for breeding, a behavior shared by many species across the globe in many different habitats. They are predictable because they usually happen at the same place and at the same time each year, and humans have taken advantage of this to harvest large numbers of fish with minimal effort. Spawning aggregations support some of the most productive fisheries: from multibillion-dollar industries to subsistence cultures, but according to Brad Erisman, Professor of Marine Science from the University of Austin at Texas “management attention for spawning aggregations is not equivalent to their importance. Despite their contribution to global fisheries production, ecosystem health, and food security, few aggregations are managed and protected in the right way. Among those that have been studied, more than half are declining and roughly 10% have disappeared. Fortunately, there is growing evidence that when aggregations are managed and/or protected, they can recover to benefit both fisheries and ecosystems.”

In the upper Gulf of California, in Mexico, a large marine fish known as Gulf Corvina offers an insight into the importance of this behavior. During a single fishing season, up to 2 million corvinas can be caught in just 25 days of labor A truckload of corvinas in Santa Clara, Upper Gulf of California.
In the upper Gulf of California, in Mexico, a large marine fish known as Gulf Corvina offers an insight into the importance of this behavior. During a single fishing season, up to 2 million corvinas can be caught in just 25 days of labor
A truckload of corvinas in Santa Clara, Upper Gulf of California.
Fisherman in the Upper Gulf of California.
Fisherman in the Upper Gulf of California.

In the upper Gulf of California, in Mexico, a large marine fish known as Gulf Corvina offers an insight into the importance of this behavior. Every year, just before the spring tides, corvinas migrate to spawn in the shallow estuary of the Colorado River Delta and during a brief period of time, the whole population concentrates in an area that is less than 1% of its entire home range. During a single fishing  season, up to 2 million corvinas can be caught in just 25 days of labor, flooding the market, dropping the prices and forcing local communities to fish more and more in an attempt to make a profit. By the time the market shuts down, several tons of corvine that have already been caught end up in landfills wasting not only the fish, but also the eggs that would replenish the stock.

Fishermen loading corvinas for the market, Santa Clara. Baja California, Mexico.
Fishermen loading corvinas for the market, Santa Clara. Baja California, Mexico.
Bigeye Trevally
Bigeye Trevally aggregation (Caranx sexfasciatus).

“This vicious circle repeats over and over triggered by and illusion of plenty” explains Octavio Aburto, a professor from Scripps Institution of Oceanography in San Diego, “We are still unable to accurately estimate the real abundance of a fish stock and fishers go on for several years, harvesting the same amount, confident that the stock is stable because there is no decline in the catch. But often, they are surpassing the capacity of the population to recover and one year, suddenly, they harvest the last sizeable catch and the fishery collapses”.

Bigeye trevallys (Caranx sexfasciatus). Cabo Pulmo National Park, Mexico.
Bigeye trevallys (Caranx sexfasciatus). Cabo Pulmo National Park, Mexico.

Spawning aggregations are a critical step in the life cycle of many fish species. A small investment in the management and protection of spawning aggregations, the mechanism that sustains the replenishment of the fisheries, can offer disproportionately large benefits to both ecosystem and local communities. If aggregations are part of our natural capital, eggs and juveniles are the interests…is it a wise economic decision to live of our capital?

The communications initiative Natural Numbers presents Spawning Aggregations, the fifth video of this popular web series that combines sound science, photography and creative graphics to present the value of the natural capital and the conflicts of its exploitation, with the goal of transforming the audience into an environmentally engaged citizenship.

To find out more visit http://www.thenaturalnumbers.org

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