May 12. (EUROPE PRESS) –
Scalloped hammerheads hold their breath to keep their bodies warm during deep dives in cold water where they hunt for prey like deep sea squid.
This discovery, published in Science by researchers at the University of Hawai’i at Manoa, provides important new insights into the physiology and ecology of a species that serves as an important link between deep- and shallow-water habitats.
“It was a complete surprise,” he said. it’s a statement Mark Royer, lead author and a researcher with the Shark Research Group at the Hawaii Institute of Marine Biology (HIMB) in the UH Manoa School of Earth and Ocean Sciences and Technology. “It was unexpected that sharks would hold their breath to hunt like a diving marine mammal. It’s extraordinary behavior from an incredible animal.”
Shark gills are natural radiators that would rapidly cool blood, muscles, and organs if scalloped hammerheads did not close their gill slits during deep dives in cold water. These sharks are warm water animals but they feed in depths where seawater temperatures are around 5ºC, and they need to keep their bodies warm in order to hunt effectively.
“Although it is obvious that air-breathing marine mammals hold their breath while diving, we did not expect to see sharks exhibiting similar behavior,” Royer said. “This previously unobserved behavior reveals that scalloped hammerheads have feeding strategies that are very similar to those of some marine mammals, such as pilot whales. Both have evolved to exploit deep-dwelling prey.” And they do it by holding their breath to access these physically challenging environments for short periods.”
The research team discovered this unexpected phenomenon by outfitting deep-diving scalloped hammerheads with devices that simultaneously measure muscle temperature, depth, body orientation and activity levels.
They saw that their muscles stayed warm during their dive in deep, cold water, but suddenly cooled down as the sharks neared the surface towards the end of each dive. Computer models suggested that hammerheads must avoid losing heat from their gills. to keep their bodies warm during these deep cold water dives.
In addition, a video of a scalloped hammerhead shark swimming along the seafloor at a depth of 1,044 meters showed its gills tightly closed, while similar images of surface waters show these sharks swimming with their gills open. A sudden cooldown in muscle temperature as scalloped hammerheads near the surface at the end of each dive suggests that they opened their gills to resume breathing while still in relatively cold water.
“Holding your breath keeps scalloped hammerheads warm, but it also cuts off their oxygen supply,” Royer said. “So although these sharks hold their breath for an average of 17 minutes, they only spend an average of four minutes on the bottom of their dives at extreme depths before quickly returning to warmer, well-oxygenated surface waters where breathing resumes.” .
“This discovery fundamentally advances our understanding of how scalloped hammerheads can dive to great depths and endure freezing temperatures to capture prey,” Royer said. “It also demonstrates the delicate physiological balance that scalloped hammerheads must achieve to feed successfully.”
