When millions of the silvery Gulf Corvina fish get together to spawn it can get as deafening as an 80’s rock concert.
A research team led by scientists from Scripps Institution of Oceanography at the University of California San Diego and The University of Texas at Austin have discovered a way to use the incredibly loud, distinctive sounds produced by the fish when they gather to spawn to protect them from overfishing.
The team developed an inexpensive method to estimate how many fish are in a spawning aggregation, based on 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.
The researchers developed the method specifically for the Gulf Corvina, a popular fish in Mexico’s Gulf of California, but it can be adapted to any fish that make courtship sounds, such as cod, groupers, croakers, and totoaba—a species exclusive to the Gulf of California, considered endangered, and actively poached for its high value in the illegal trafficking of swim bladders.
“Overharvesting 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,” said Scripps graduate student Timothy Rowell, lead author of the study published June 13 in the journal Scientific Reports. “Developments in the field of fish bioacoustics, as presented in our study, may provide us with improved ‘acoustic’ access to these exciting spawning events and a better understanding of what fish are doing below the surface and how many of them are doing it to set sustainable harvest levels.”
Each spring, the entire adult population of Gulf Corvina—more than two 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 loud enough to damage eardrums if it were on land.
“It's louder than a rock concert,” said study coauthor Brad Erisman from The University of Texas at Austin. “It’s louder than standing less than a meter from a chainsaw.”
All that noise is dangerous to the fish, too, since it leads fishermen right to the Corvina spawning aggregations. During about 20 nights each spring, they can harvest more than a million fish with minimal effort. Because the entire species spawns in one place, they are extremely vulnerable.
Until now, it’s been difficult to monitor the population, but there is anecdotal evidence that illegal fishing is on the rise and that the fish being caught are getting smaller over time, both signs that they might be overfished.
According to the UN Food and Agricultural Organization about a third of the world’s fish stocks are being overfished, meaning they’re being harvested faster than they can reproduce. Species that spawn seasonally in large groups are especially vulnerable because it’s easy for fishermen to locate and pluck them from the water, often before they’ve seeded the next generation.
The new acoustic method for monitoring spawning populations could help ensure that Corvina fishing is sustainable in the long run.
“The fishermen are by no means the enemy here,” said Erisman. “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.”
One way to accurately measure the number of fish in a spawning aggregation is to use echosounders, a sonar system that sends out high frequency sounds and, based on the sounds reflected back, estimates the density and numbers of fish. But echosounder data collection is expensive and time intensive, plus it’s complicated to analyze the results.
The scientists found a way to achieve the accuracy of echosounders in a simpler, less expensive way. They went out to sea on days when the Corvina were spawning and simultaneously collected both echosounder data and sound intensities of fish calls using hydrophones. They discovered that during peak spawning times, there was a linear relationship between the two kinds of data. Now, going forward, scientists can measure sound intensities alone and use a simple mathematical equation to estimate the density and numbers of fish in real time.
“Ideally, this method could be replicated in other areas where fisheries can’t be assessed with visual methods, such as lagoons or river deltas. Fishermen can be trained to use hydrophones, so the communities that harvest these resources can be involved in data collection and management,” said Octavio Aburto-Oropeza, assistant professor at the Scripps Center for Marine Biodiversity and Conservation and a senior author of the study.
The researchers 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. 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 different groups that have a stake in the fishery and the environment together to try to work it out,” said Erisman. “And it's nice that science is playing a role in that.”
Rowell, Aburto, and Erisman’s co-authors are David Demer and John Hyde from the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center; 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.
Hear the spawning sounds of the Gulf Corvina at “Can Sound Save a Fish?”
--Adapted from The University of Texas at Austin news release
Related Video: spawning sounds of the Gulf Corvina