New acoustic techniques that measure fish populations could potentially be used to help endangered species like the totoaba – and in turn the even rarer vaquita porpoise, which is on the brink of extinction.
(From News Deeply / by Matthew O. Berger) — If you’re over the right patch of water in the northern Gulf of California in Mexico at the right time of year, you might hear a low rumbling noise coming from the sea below. If you had a fishing net to drop over the side of your boat in the direction of the rumbling, you’d be able to fill it in one go with Gulf corvina, silvery croaker-like fish that congregate together in a noisy, rollicking spawning orgy.
“Most of the sound reflects off the surface of the water and remains underwater, but if there’s enough noise it can escape the water,” said Timothy Rowell, a graduate student at Scripps Institution of Oceanography in California, who has been studying corvina. “The rumbling noise can make you have to raise your voice, and the hull of the boat can act as a sort of speaker, amplifying the noise.”
The International Union for Conservation of Nature lists gulf corvina as vulnerable and threatened by overfishing, but few reliable population data for the fish are available. Rowell has been working with a team of researchers to find a way to nail down those population figures.
Before coming to the Gulf of California, Rowell had been studying the behavior and abundance of grouper in the Caribbean by tracking and measuring the sounds they make. It occurred to the researcher that similar acoustic techniques might be especially useful in studying the loud mating call of the Gulf corvina.
That insight has now led to acoustic methods that allow the researchers to estimate the number of Gulf corvina in a spawning aggregation just by listening. The findings, published in the journal Nature, highlight recent advances in the use of acoustics to study fisheries. They also raise the potential of using similar techniques to study other fragile, data-deficient fisheries, including one of the Gulf corvina’s neighbors, the politically controversial and critically endangered totoaba, whose bladder is a highly sought-after and highly paid-for delicacy in China.
In turn, illegal nets set for totoaba often ensnare the even more critically endangered vaquita porpoise, which is now on the brink of extinction, with just a few of these marine mammals surviving in the Gulf of California.
There are two broad ways in which researchers can use sound to find out what’s happening in the oceans: active, which involves sending out sound waves and studying how they bounce back, and passive, which involves listening. As scientists learn more about how noisy certain species of fish are and how to measure that noise, the latter is becoming increasingly useful.
Read the full story here: https://www.newsdeeply.com/oceans/articles/2017/06/27/scientists-are-listening-to-fish-to-figure-out-how-to-save-them?utm_campaign=b6c378ec79-EMAIL_CAMPAIGN_2017_06_29&utm_medium=email&utm_source=Oceans+Deeply&utm_term=0_dfde037196-b6c378ec79-117758789