Like many fish, male Gulf corvina emit a thrum of seductive calls to attract females during breeding periods. But as Ben Guarino reports for the Washington Post, a new study has shown that the collective chorus of Gulf corvina is exceptionally loud—so loud, in fact, that it can damage the hearing of aquatic mammals.
The Gulf corvina is a species of croaker (so named for their signature sound) that dwells in the waters of the Gulf of California and the Colorado River delta. Every year between February and June, adults Gulf Corvina migrate to a 12-mile stretch of the Colorado River delta, where they breed in murky waters. As many as 1.5 million Gulf corvina converge during peak spawning time—a breeding behavior that scientists call “spawning aggregation.”
When they are feeling amorous, Gulf corvina burst into a thunderous cacophony of rapid sound pulses. And in 2014, two marine biologists—Timothy Rowell of the Scripps Institution of Oceanography in California and Brad E. Erisman, a fisheries scientist at the University of Texas at Austin—set out to measure the Gulf corvina’s courtship call.
Rowell and Erisman relied on a sonar unit and underwater microphone to gather the data, but even without the equipment, they could tell that the Gulf corvina’s call was very powerful. “When you arrive at the channels of the delta, you can hear it in the air even while the engine is running on the boat,” Rowell tells Guarino. In an interview with the Agence France Presse, he compares the sound to “a crowd cheering at a stadium or perhaps a really loud beehive.”
According to the duo’s findings, published recently in the journal Biology Letters, the Gulf corvina’s chorus reached a crescendo of 202 decibels, and individual calls were as loud as 177 decibels. That is, according to researchers, the loudest sound by a fish species ever recorded. Of all marine animals, only whales are known to be louder. The frequencies of sound emitted by Gulf corvina were strong enough to damage the hearing of sea lions and dolphins—which surprisingly did not stop the animals from feeding in the area, Rowell and Erisman note in their study.
Gulf corvina are able to produce such a powerful noise because their swim bladder, a gas-filled organ in the abdomen, is surrounded by “sonic muscles,” Rowell tells Guarino of the Post. The muscles drum against the bladder when the fish contract their abdomens, resulting in the beehive-like sound heard by researchers.
But the Gulf corvina’s enthusiastic courtship ritual comes at a cost. Because the critters are so loud, the fish are easy to target and catch. According to Scientific American, at least two million Gulf corvina are fished every year and the their body size is shrinking—a sign of overfishing. The International Union for Conservation of Nature lists the Gulf corvina as a “vulnerable” species.
Rowell tells the AFP that he hopes the Gulf corvina’s tremendous mating calls will garner “increased appreciation and conservation” for the very vocal fish.