These Fish Have Sex So Loudly It Might Make Dolphins Go Deaf

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Every year in the Gulf of California, millions of frisky fish gather to have what is probably the loudest orgy in the animal kingdom. In fact, the cacophony is so loud researchers believe that what Gulf corvina get up to between the waves could easily cause marine mammals, like dolphins and sea lions, to go deaf.

Unlike us, fish reproduce by spawning – the females release large numbers of unfertilized eggs into the water, while the males release millions of sperm to fertilize them.

In the case of the Gulf corvina, the male fish also let out a mating call that according to researchers, sounds pretty much like a “really loud machine gun”. “These spawning events are among the loudest wildlife events found on planet Earth,” study co-author Timothy Rowell told The Guardian. Not bad for a fish.

The sound levels produced are enough to make marine mammals temporarily, if not permanently, deaf. The findings are published in the journal Biology Letters

Every spring, the world’s entire population of Gulf corvina travels to the Colorado River Delta, at the top of the Gulf of California, where they amass in millions and occupy just 1 percent of their normal range.

The fish are large, growing to about a meter (3.3 feet) and weighing up to 12 kilograms (26 pounds).

The males call to attract females, but in doing so they also attract another, unwanted surprise. The pulsing sound reverberates off the bottom of small boats, drawing in fishermen. About 500 nets get lowered into the water, silencing the unlucky fish that get trapped inside. Each net can catch around 2 tonnes of fish.  

According to the International Union for Conservation of Nature (IUCN), the Gulf corvina is currently “vulnerable” to extinction. But the fish being caught are getting smaller and smaller, a worrying sign that they are being fished faster than they can reproduce and recover.

However, Rowell, along with colleague Brad Erisman, believes that the raucous sounds that attract the fishers could also be used for good, by aiding conservationists. In 2014 they reported that they had developed an effective way of monitoring populations by eavesdropping on the calls.

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"Over-harvesting from the aggregation site could result in the functional extinction of the species in the ecosystem, which would have negative effects on the local economy and cause the fishery to collapse," Rowell said in a statement. "This is why sustainable harvest levels need to be set.”

About a third of fish in our oceans are overfished, meanwhile they have all sorts of other threats like plastic bottles and toxic pollution to contend with. Listening in to the sounds produced by the Gulf corvina might just help scientists ensure it is fished sustainably, allowing its bizarre chorus to continue for many years to come.

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