When Gulf corvina mate, they are not shy about making noise. Each year the species’ entire population gathers off the coast of Mexico to spawn. Like so many crickets, cicadas and frogs, male corvina produce a thumping love song that likely acts as an audible come-hither signal for females. The resulting din turns out to be the loudest fish noise ever recorded, andrivaling some whalesone of the loudest naturally produced sounds in the ocean, according to research published this week in Biology Letters.
At first, we thought our equipment was broken, says study co-author Brad Erisman, a fisheries ecologist at the University of Texas at Austin. No one anticipated fish would be this loud.
Erisman and his colleagues traveled to the Colorado River Delta, where the river empties into the Sea of Cortez. It is here and only here that Gulf corvina come to spawn, likely because the delta’s extreme 25-foot tides help to flush their fertilized eggs out to sea. The researchers were originally interested in quantifying the number of fish that congregate there annually, but that is not as simple as looking down and counting them; the chocolate milk-colored water is much too murky. Instead they used soundmeasured with an echosounder (a sonar unit) and a hydrophone (underwater microphone)to reveal there were as many as 1.5 million fish in the aggregation, distributed over a 17-mile stretch of river channel, during one peak spawning day. The total population is likely much higher, they say, but this snapshot provides a starting point for future work.
Next Erisman’s team turned its attention to the sound itself. While thousands of fish species produce sounds, the Gulf corvina’s is the loudest ever measured, the group found. At 179 to 190 decibels, the corvinas’ aggregate mating call is louder than the equivalent of standing next to the stage at a rock concert. The noise is so loud, in fact, that it may harm the hearing of other marine animals caught up in the action, the researchers write.
“This paper is solid and the findings are convincing,” says Stephen Simpson, a marine biologist and fish ecologist at the University of Exeter, who was not involved in the research. He adds that the fact that the Gulf corvina gathers in a single estuary to breed each year “makes the species highly vulnerable to overfishing, but also easy to manage by avoiding targeting it during the spawning season.”
Indeed, despite their record-breaking clamor, the fish are probably much quieter than they once were. At least two million corvina are fished per year, and over the past five years, their average body size has steadily decreased, as has the area their mating aggregation covers.
Lots of fishes are heavily exploited and endangered because of this amazing behavior where they come together to spawn, which makes them extremely vulnerable, Erisman says. In the age of gill nets and trawls, the evolutionary advantages of group spawning, in other words, can paradoxically imperil the species’ survival.
2017 Scientific American, a Division of Nature America, Inc.