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Big catches at spawning sites wipe out fish

Every year nearly the entire population of Gulf corvina fish migrate to a single spot to spawn. During a period of less than a month, fishers in Mexico can catch more than 2 million corvinas—but the practice severely depletes the population and egg supplies at the time and in future years. (Credit: Octavio Aburto-Oropeza, University of California, San Diego)

Hundreds of fish species in more than 50 countries across the globe migrate to specific locations to breed in large numbers for only a few days or weeks each year. And with them come lots of fishers.

These events are known as fish spawning aggregations, and only a fraction of known seasonal breeding areas and events are protected or monitored. As a result, countries around the world may soon see a massive loss of fish species, which could challenge areas that depend on fishing for their economy.

Overfishing has already led to severe declines in fish populations and the fisheries that depend on them, warns Brad Erisman, assistant professor in the marine science department at the University of Texas at Austin, who says better management of fish spawning aggregations would not only benefit marine life, but people as well.

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“Spawning aggregations are crucial to human livelihoods, food security, and the health of our oceans, but overfishing in the midst of these events has a big impact, too often preventing future generations of fish from thriving,” he says. “More than half of all spawning aggregations that have been monitored are in decline, and 1 in 10 has disappeared altogether. Managing and protecting these brief, important events would benefit fisheries and ecosystems alike in the long run.”

According to a new study, published in the journal Fish and Fisheries, only about half of spawning aggregations have been assessed, and only about one-third have any sort of protection or monitoring in place to prevent overfishing.

There are at least 300 fish species that predictably gather to breed en masse in specific spots each year. For example, Gulf corvina typically range over large parts of the ocean, but nearly the whole population migrates to a single spot where during the rest of the year only about 1 percent of the total population can be found. During a period of less than a month, fishers in Mexico can catch more than 2 million corvinas, severely depleting the population and egg supplies in future years.

Similarly groupers are also at risk, with nearly 12 percent of grouper species in danger of extinction, scientists say.

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“Spawning aggregations leave fish vulnerable at a really important time in their life cycle,” Erisman says. “Protecting these breeding aggregations—the same way we already do for many seabirds, sea turtles, and whales—would prevent mass disruption both in the environment and in the economies that are dependent on the survival of these species.”

New advances in affordable technologies and knowing when and where these aggregations occur make it easier to effectively monitor spawning aggregations and related fishing, the researchers say. That sort of monitoring would inform appropriate limits, such as partial-day bans on fishing or whole-season limits to where and when fishing takes place, for a given area and its species that spawn there. The result would be more sustainable, productive, and profitable fisheries over time.

Researches from Texas A&M University, the Ecological Research Associates, Old Dominion University, the National Oceanic and Atmospheric Administration, the University of California, San Diego, and the University of the Virgin Islands are coauthors of the study.

The National Science Foundation, the Walton Family Foundation, and the David and Lucile Packard Foundation funded the work.

Source: University of Texas at Austin