Machine Guns Underwater
Imagine you are on a fishing trip on the Colorado River Delta where the river flows into the Sea of Cortez by Baja California. You spot a section of water that seems to be churned up and muddy, almost muddy like someone was mixing cocoa powder to make hot chocolate. You get a bit closer, and all of a sudden you instinctively duck under the nearest deck chair. It sounds like someone is firing a machine gun at you. But the sound does not stop and only keeps getting louder. Finally, you gather the courage to peak out and ask the boat’s captains, biologists Erisman and Rowell, what might be going on.
Erisman and Rowell probably are picking themselves up from the floor after a hard laugh. In a recently published paper in Biology Letters (2017) they report the cacophony produced by more than a million Gulf Corvina that convene in this region every year to spawn. The male calls out for a mating partner by beating specialized muscles on their air bladders. And when there are a million of these fish singing their love song in unison, underwater sound levels can reach between 170 and 190 dB (re: 1 µPa), second in amplitude to only some whale songs.
You can hear the song of the Gulf Corvina and an interview with the authors of the paper. A sound worth saving: acoustic characteristics of a massive fish spawning aggregation
Erisman BE, Rowell TJ. (2017) A sound worth saving: acoustic characteristics of a massive fish spawning aggregation. Bio Lett December 20.