University of Texas Marine Science Institute Uses Fish Mating Sounds To Stem Over-Fishing

AUSTIN, TX — Marine scientists at the University of Texas Marine Science Institute have found a way to use the implausibly loud yet distinctive sound of spawning fish as a means to protect them from commercial over-fishing, officials said.

By some estimates, roughly one-third of the world’s fish stocks are being over-fished, meaning they’re being harvested faster than they can reproduce, officials explained. Fish species that spawn seasonally in large groups are especially vulnerable, easy for fishers to locate and plucked from the water often before they’ve seeded the next generation, according to researchers.

A team led by marine scientists from The University of Texas Marine Science Institute (UTMSI) in Port Aransas, Texas, and the Scripps Institution of Oceanography at the University of California San Diego have discovered a way to use the incredibly loud, distinctive sounds that fish make when they gather to spawn—not to catch them but to protect them, officials said.

It's the males that make the sounds, emitted via muscles around their swim bladders, that give them away to fishermen. The noise, if taking place on earth, would be deafening—described as louder than a rock concert or equivalent to standing in near proximity to a chainsaw. Millions of love-struck male fish emit the sounds in attracting mates but the noise yields a dead giveaway for fishermen. In a matter of minutes, fishermen can drop a net and fill it with up to two tons of fish—hapless male ones distracted while in the throes of seeking mates to keep their lineage going.

The team developed an inexpensive yet accurate method for estimating how many fish are in a spawning aggregation, based on their mating calls. Accurate data on when and where fish spawn, as well as how many there are, would help fisheries managers design effective management practices and monitor the ongoing health of a fishery, scientists said.

“It can be extremely challenging to get a complete picture of fish spawning events because they can happen over very short to very long times and are often in difficult environments such as murky water,” says Brad Erisman, assistant professor at UTMSI and senior author of a study published June 13 in the journal Scientific Reports. “Our work opens an acoustic window into these exciting spawning events.”

The paper’s lead author is Timothy Rowell, a graduate student of Octavio Aburto-Oropeza’s at Scripps.

While the researchers developed the method specifically for the Gulf corvina, a popular fish in Mexico’s Gulf of California, it can be adapted to any fish that make courtship sounds such as cod, groupers and croakers, including the endangered totoaba, a species that is also endemic to the Gulf of California, marine specialists detailed.

Scientists expound on what they found in the Gulf of California as prototypical of the applications of the research: Each spring, the entire adult population of Gulf corvina—more than 2 million fish—migrates to a small area at the northern tip of the Gulf of California. When the males start calling to attract mates, the sound is deafening. Using underwater microphones called hydrophones, Rowell discovered that these fish can make sounds up to 192 decibels—enough to damage your eardrums if it were on land.

“It's louder than a rock concert,” Erisman noted. “It’s louder than standing less than a meter from a chain saw.”

Hear the spawning sounds of the Gulf Corvina and learn more about the research from: “Can Sound Save a Fish?”

But all that noise is dangerous to the fish, as it leads fishermen directly to the corvina spawning aggregations in what amounts to a mother lode, yielding a harvest of more than a million fish with minimal effort over the course of 20 nights each spring. As if the fish decibels didn't put them in enough jeopardy, their mass gathering in a single spot makes them even more vulnerable.

It's really like the gulf equivalent of catching fish in a barrel.

Until now, it's been difficult to monitor the population, yet anecdotal evidence suggests illegal fishing is on the rise and that the fish being caught are getting smaller over time, both signs that they might be over-fished, scientists said.

“Over-harvesting from the aggregation site could result in the functional extinction of the species in the ecosystem, which would have negative effects on the local economy and cause the fishery to collapse,” Rowell said. “This is why sustainable harvest levels need to be set. At the moment we do not know what these levels are.”

Rowell and Erisman’s new acoustic method for monitoring spawning populations could help ensure that corvina fishing is sustainable in the long run: "The fishers are by no means the enemy here,” Erisman said. “They're actually the ones who have provided us with all the information and access to the resource, and they're the ones most interested in sustainability.”

Erisman and Rowell are part of an international research group, the Gulf of California Marine Program, that has created an interactive online tool called dataMARES where anyone can study how corvina populations are changing, officials explained. And those who fish, fisheries managers and conservationists can now do a better job of keeping corvina populations sustainable.

“The idea is we try to bring all the stakeholders, different groups that have a vested interest in the fishery and the environment, together to try to work it out,” Erisman said. “And it's nice that science is playing a role in that.”

Erisman and Rowell’s co-authors are David Demer and John Hyde of the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center; Octavio Aburto-Oropeza of the Scripps Institution of Oceanography; and Juan José Cota-Nieto from Centro para la Biodiversidad Marina y Conservación A.C.

The project was funded in part by grants from the National Oceanic and Atmospheric Administration, the Walton Family Foundation and the David and Lucile Packard Foundation.

>>> Illustration by Jenna Luecke, courtesy of University of Texas Marine Science Institute