Seahorses are known for making little “click” sounds while they’re feeding, but a group of Austrian and Brazilian researchers have discovered a completely new, never before heard type of seahorse vocalization, which they describe as a “growl.”
While it has been known since at least the late 1800s that seahorses could make sounds, studies investigating the functions of those sounds have been rare. To begin to address that dearth of research, scientist T. P. R. Oliveira rounded up a group of longsnout seahorses, Hippocampus reidi, a species which is found along the eastern coast of the Americas from Cape Hatteras to Brazil, and in the Gulf of Mexico.
Then, having equipped an aquarium tank with a hydrophone, the researchers took audio recordings of seahorses in three different situations: feeding, courtship, and stress. Feeding and courtship are straightforward enough. To induce a stressful situation, the researchers simply handled the seahorses. Oliveira explains that a researcher held onto each seahorse’s body at a distance of two centimeters from the hydrophone. “Although handling has a level of artificiality,” write the researchers, “it does provoke fish to produce sounds as if they were captured by a predator. Seahorses are frequently grabbed and held by predators such as frogfish before being swallowed.”
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