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From the College of Natural Sciences
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Fish Spawning and Illusions of Plenty

Fish Spawning and Illusions of Plenty

Overfishing causes serious damage in marine ecosystems, but few people understand the natural phenomenon that precedes humans removing too many fish from the oceans. Brad Erisman, an assistant professor in the Marine Science Department, is helping to put a spotlight on the science.

In a new video, for which Erisman was a producer, the phenomenon, known as spawning aggregations, is explained as events where fish gather in massive numbers to breed. Spawning aggregations are predictable, usually happening at the same place and time every year. Humans, whether they are connected to multibillion-dollar industries or subsistence cultures, have long taken advantage of spawning aggregations to harvest large numbers of fish with minimal effort.

Erisman and fellow scientists worked with a team of videographers to produce English- and Spanish-language versions of the newest episode of Natural Numbers, which explores ecological issues, including how better fisheries management is crucial to address declining fish populations. Erisman co-created the storyboard and script and worked with the project from initial fund-raising through completion so that it could reach a broad audience.

"Despite their contribution to global fisheries production, ecosystem health and food security, few spawning aggregations are managed and protected in the right way," Erisman says. "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."

The team behind the video obtained footage from locations such as Palau, Australia, Baja California, the Gulf of Mexico, and the Caribbean to illustrate the beauty and importance of spawning aggregations.

"This is probably one of the most complex stories that we have had to tell in the series," said Jaime Rojo, co-founder of Natural Numbers "Some science topics are difficult to communicate to a broader audience, and the team did a great effort to summarize a huge volume of information into such a short video. It is a pleasure to work with scientists that understand the importance of outreach and public awareness."

The video uses a fish known as Gulf Corvina in the upper Gulf of California, in Mexico, as an example. Corvinas migrate every year 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 fish that have already been caught end up in landfills wasting not only the corvinas, but also the eggs that would replenish the stock.

Watch the video to learn more about exploitation of spawning aggregations and measures that communities can take to help prevent it.

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Friday, 03 February 2023

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