Hammerhead sharks pinch their gills for warmth during deep dives

A school of scalloped hammerhead sharks off Hawai?i Island

Scalloped hammerhead sharks shut their gills throughout deep water dives, stopping their physique temperature from falling.

Deron Verbeck

Scalloped hammerheads appear to carry their breath as they dive into chilly, deep water. By closing their blood-rich gills, they will keep heat whereas searching their prey and successfully escape their very own cold-blooded biology.

Researchers discovered that scalloped hammerheads (sphyrna lewini) made repeated, brief, deep evening dives, he says. Mark Royer on the College of Hawaii at Mānoa. Dramatic descents might be for searching, as squid beaks from visited depths present up in sharks’ stomachs.

However it wasn’t clear how tropical hammerheads may tolerate chilly temperatures in such deep waters, normally round 5°C. Different fish, equivalent to nice white sharks and tuna, have circulatory techniques that recycle the warmth produced by their flexing muscle tissue, permitting energetic predators to remain heat in chilly water. Hammerheads do not, Royer says. He and his colleagues caught scalloped hammerheads in Hawaii’s Kāneʻohe Bay, mounted them briefly on the aspect of the boat, and hooked up software packs to the bottom of every shark’s dorsal fin. These devices measured water and muscle temperature, and the shark’s tail kick and acceleration in all instructions. After a number of weeks of amassing knowledge on the three sharks, the packages displaced and surfaced for the staff to retrieve.

The researchers found that whereas they have been diving, the hammerheads all of a sudden shot towards the underside at an 80-degree angle and furiously beat their tails.

“It’s best to count on physique temperatures to drop instantly,” says Royer. “However that is not what it’s.”

As a substitute, their physique temperature stays above ambient temperatures all through the dive, which takes a number of minutes to about 800 meters. The sharks then transfer nearer to the floor. Solely then does their physique temperature lastly drop.

Sharks lose some warmth by their physique partitions to chill the setting, however the researchers suspected these stunning outcomes have been associated to the sharks’ gills. Sharks breathe by absorbing dissolved oxygen within the water by blood vessels of their gills, which means they’re a part of the physique the place quite a lot of blood is uncovered to chilly water.

“The most important price of warmth loss for any animal that breathes gills is thru the gills,” says Royer. “Principally, it is like having an enormous radiator strapped to your head.”

If sharks have been respiratory deeply throughout their onerous dive, their physique temperature must drop quickly. The researchers suspected that diving hammerheads averted this by pinching their gill slits.

Certainly, video footage of scalloped hammerheads swimming a kilometer down confirmed that their gill slits have been tightly closed.

José Emilio Trujillo A researcher on the College of Otago in New Zealand wonders how hammerheads might be so athletic with so little oxygen. Diving mammals have diversifications to cope with the very low oxygen of their tissues, he provides, and possibly hammerheads do too.

Breath-hold speculation is attention-grabbing and price additional investigation, says Phillip Morrison on the College of Vancouver Island in Canada. Nonetheless, he was not satisfied that this was the “solely mechanism” with out additional investigation, equivalent to analyzes of physique temperature beneath totally different ranges of gill warmth loss.

“If [the researchers] If true, I feel this is likely one of the coolest physiological traits amongst sharks,” says Morrison.

Different shark species may use this freediving technique. Royer, oceanic whitefin sharks (carcharhinus longimanus) make comparable repeated, steep dives.


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