Scientists have discovered that dramatic-looking sharks hold their breath for about 17 minutes to keep warm during hunting dives in cold water.
Scallop Hammerhead (Sfirna Lewini) are found in warm near-surface waters around the world, especially along coastlines, and can reach up to about 12 feet in length. But these sharks venture into deep, cold water to hunt. This is potentially problematic because scallop hammerheads, like most sharks, are cold-blooded and their body temperature matches that of the surrounding environment. “If they get cold when they get into cold water, they can’t hunt as effectively,” says Mark Royer, a shark biologist at the Hawaii Institute of Marine Biology. “To be an effective hunter, it’s important to keep yourself as warm as possible.”
Fish such as bluefin tuna, great white shark (Carcharodon Carcharias) and swordfish have special muscles and blood vessels that can keep their brains, eyes and swimming muscles warm even in cold water, but not the scalloped hammerhead shark. However, Royer and colleagues analyzed 106 deep dives made by six scalloped hammerhead sharks and found that sensors that recorded the temperature of the shark’s muscles, orientation, depth of dive and surrounding environment showed that these sharks were It was found to be miraculously warm during these voyages. ambient water temperature.
“We looked at temperature data. [and] We quickly realized that these sharks were doing something very interesting and very different compared to other fish,” says Royer. “It’s clearly not simple thermal inertia that these sharks rely on to maintain their body temperature during deep dives. There’s something more complicated.”
Researchers found that sharks swooped down to feed for a few minutes in deep water, then returned to the surface at breakneck speed. On average, Royer said he kept warm for 17 minutes before the animals slowed down. The team’s findings were announced on May 11, chemistry.
Researchers believe the mystery lies in the shark’s gills. These organs act as lungs and draw oxygen from sea water. However, the gills have the disadvantage that a large amount of water passes through them. “The gills are like giant radiators strapped to the head,” Royer says. “When sharks and fish enter cold water, they lose heat very quickly through their gills because of the large surface area of their gills.”
While the researchers weren’t able to directly monitor the shark’s gills, Royer says he hopes to equip the sharks with pectoral fin cameras aimed at the gills in the future. But for now, scientists think sharks close their gills during their daring dives, essentially holding their breath. (Royer points out that other researchers have footage of one hammerhead shark diving with its gills closed.)
“This is definitely something that, to my knowledge, has not been proposed for external heat. [cold-blooded] Ashley Shuter, a marine biologist at Sacred Heart University who specializes in fish, said he specializes in fish and wasn’t involved in the new study.
Royer said scalloped hammerhead sharks may not be unique in adopting this technique for deep diving. whitetip shark (Medicahinus longimanus) They don’t dive as often as scallop hammerheads, but they’re still known for their dramatic dives, he says. And scientists know that these sharks also lack specialized muscles and blood vessels that keep fish warm. Still, the scalloped hammerhead’s breath-holding technique appears to be an unusual approach to brave cold water. “This is incredible and unexpected behavior in a remarkable species,” says Royer.
