A type of Mexican fish heads every spring to the Gulf of California to spawn—and their "reproductive orgies," as the AFP puts it, are so loud they can damage hearing in other marine life. A pair of studies from the same researchers, one published in June in the Scientific Reports journal and one posted just this month in the Biology Letters journal, says that the sound of an individual Gulf corvina issuing a pulsating mating call sounds like a "really loud machine gun." And when hundreds of thousands of them get together to do the deed, "the collective chorus sounds like a crowd cheering at a stadium or perhaps a really loud beehive," says study co-author Timothy Rowell. This commotion-filled copulation isn't just the "loudest sound ever recorded for a fish species," Rowell says. When this happens, it's "among the loudest wildlife events found on planet Earth."
The researchers gathered data in March and April 2014, when about 1.5 million corvinas converged in the Colorado River Delta to procreate. Different tools were used to measure fish location, density, and loudness. What scientists found was a racket so loud (listen to clips at Gizmodo) it can cause hearing loss in dolphins, seals, and sea lions, even deafening them—though, oddly, sea lions and dolphins were found feeding nearby. The noise the spawning fish make doesn't help themselves, either: Fishermen are able to track exactly where they're located from the sound and scoop them out of the water. Gizmodo notes this ends up as a harvest that's "hugely disruptive" to the species, leaving them "vulnerable" to extinction due to overfishing. The researchers say the sex sounds came about as part of the evolutionary process, allowing the fish to communicate above the surrounding din. (Maybe they should go spawn in Sweden.)