Research shows that hammerhead sharks “hold their breath” in deeper, cooler waters

Scalloped hammerhead sharks can dive to depths of more than 2,600 feet (800 meters) to hunt for squid and other food.

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Gerard Sorey / Getty Images

Scalloped hammerhead sharks can dive to depths of more than 2,600 feet (800 meters) to hunt for squid and other food.

Gerard Sorey / Getty Images

Sharks are among the best swimmers on the planet, but new research suggests that even they sometimes “hold their breath” while diving deep into the water.

The reason is that sharks are thermogenic or cold-blooded, and their body temperature basically corresponds to the water in which they swim. In order to dive deeply, it must conserve body heat, and the best way to do this is to close the gill slits tightly.

It all makes sense, but the idea of ​​a fish holding its breath underwater “still shocks and baffles me,” she says. Mark RoyerResearcher at the University of Hawaii at Manoa and the Hawaii Institute of Marine Biology, which led the study.

We don’t need a bigger boat

Royer set out to study the diving habits of a species of shark called the scalloped hammerhead. They are known to swim in the coast waters with warmer temperatures, but previous studies have shown that they can also dive to more than 2,600 feet (800 meters) below the surface. At those frigid depths, the water temperature drops to 41 degrees Fahrenheit (5 degrees Celsius).

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It would be a shock to anyone’s system, Royer says: “Imagine you’re on a warm sunny beach, and then you jump out of the warm water and immediately plunge into an ice bath.”

But for these sharks, the drop in temperature is a matter of life and death. Since the shark cannot generate its own body heat, it begins to freeze even deeper. that it Muscles, eyes and brain become sluggish. If it’s too cold, he can’t swim. And if they stop swimming, the water will not move through their gills. You can’t breathe. It’s basically drowning.

Some other large fish have specialized anatomy that allows them to stay warmer at great depths, Royer says, but the scalloped hammerheads do not. This raised an obvious question: “How could warm coastal tropical species descend to such deep depths and survive?”

To find out, Royer and his colleagues went to Near their lab where hammerheads swim. They used a small boat, “because we want to be able to lean back and get as close as possible.” They caught the fish briefly and attached an electronic sensor beam to each shark’s fin.

This is basically the same as Fitbit mode On the shark,” he says. Fitbit shark She will release herself from the fin after several weeks under water.

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Deep dive

When Royer and his colleagues analyzed the data later, they were astounded by what they found: Sharks dive, spend only a few minutes at depth (perhaps catching squid), “then shoot upwards at 80 degrees.” Angle and shoot towards the surface.”

The really wild thing is that their body temperature doesn’t drop. He remains stationary until they begin to return from the depths. Royer soon realized what was going on: “They were closing their gill slits and preventing water from flowing through their gills that would cool their bodies,” he says.

The sharks then reopen their gills once they get close to the surface. the Finding It was published Thursday in the journal Sciences.

This behavior is seen in marine mammals (and humans, of course), but unlike animals with lungs, sharks do not return to the surface to breathe. Instead, they simply go to a depth where it is warm enough for them to feel comfortable and open their nostrils again.

Scalloped hammerheads may not be the only ones doing this. “This strategy could be widespread,” he writes. Mark Mikan And Adrian GleesTwo Australian marine scientists unaffiliated with the study, V Companion commentary on the new search.

The work, they write, is another example of how new electronic tags and sensors help explain “the extraordinary persistence of these animals across 400 million years of changing ocean environments.”

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