Scalloped hammerhead sharks stop their physique temperature dropping on deep-water dives by closing their gills
Deron Verbeck
Scalloped hammerheads seem to carry their breath after they dive into chilly, deep water. By shuttering their blood-rich gills, they could preserve heat whereas looking prey, successfully sidestepping their very own cold-blooded biology.
Researchers already knew that scalloped hammerheads (Sphyrna lewini) made repeated, transient, plunging nighttime dives, says Mark Royer on the University of Hawaiʻi at Mānoa. The dramatic descents could also be for looking, because the beaks of squid from the visited depths have turned up within the sharks’ stomachs.
But it wasn’t clear how the tropical hammerheads managed to tolerate the frigid temperatures in such deep water, generally round 5°C. Other fishes, equivalent to nice white sharks and tunas, have circulatory techniques that recycle warmth produced by their flexing muscle groups, letting the energetic predators keep heat in chilly water. Hammerheads don’t, says Royer. He and his colleagues caught scalloped hammerheads in Kāneʻohe Bay, Hawaiʻi, briefly secured them in opposition to the aspect of the boat and connected packages of devices to the bottom of every shark’s dorsal fin. These devices measured water and muscle temperature, and the shark’s tail beating and acceleration in all instructions. After a couple of weeks of gathering information on three sharks, the packages dislodged and floated to the floor for the workforce’s retrieval.
The researchers discovered that, when diving, hammerheads abruptly rocket in direction of the underside at an 80-degree angle, furiously beating their tails.
“You should expect to see their body temperature drop right away,” says Royer. “But that’s not what’s happening.”
Instead, their physique temperature holds excessive above ambient temperatures all through the several-minutes-long plunge to about 800 metres. The sharks then zoom in direction of the floor. Only then does their physique temperature lastly drop.
Sharks lose some warmth to cooler environment by means of their physique wall, however the researchers suspected these puzzling outcomes needed to do with the sharks’ gills. Sharks breathe by absorbing oxygen dissolved in water by means of blood vessels of their gills, which means they’re part of the physique the place plenty of blood is uncovered to chilly water.
“The greatest rate of heat loss for any gill-breathing animal is through the gills,” says Royer. “It’s basically like having a giant radiator strapped to your head.”
If the sharks have been respiration closely throughout their demanding dives, their physique temperature ought to have quickly plummeted. The researchers suspected the diving hammerheads averted this by clamping down their gill slits.
Indeed, video footage of scalloped hammerheads swimming a kilometre down has proven their gill slits tightly closed.
José Emilio Trujillo on the University of Otago in New Zealand wonders how the hammerheads handle to be so athletic with so little oxygen. Diving mammals have variations for coping with very low oxygen of their tissues, he provides, so maybe hammerheads do too.
The breath holding speculation is attention-grabbing and worthy of additional investigation, says Phillip Morrison at Vancouver Island University in Canada. However, he isn’t satisfied it’s the “sole mechanism” with out extra analysis, equivalent to analyses of physique temperature below completely different ranges of gill warmth loss.
“If [the researchers] are correct, I think that this is one of the coolest physiological traits among sharks,” says Morrison.
Other shark species can also use this freediving technique. Royer factors out that oceanic whitetip sharks (Carcharhinus longimanus) make related repeated, steep dives.
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Source: www.newscientist.com