Why some hammerhead sharks seem to ‘hold their breath’ during dives
Even fish sometimes hold their breath in cold, dark, deep water. Scalloped hammerhead sharks living near Hawaii spend their days basking in warm surface waters. But at night, these fish hunt for squid and other prey in the cold ocean depths hundreds of meters below the surface. The sharks may hold on to body heat in the frigid waters by suppressing the use of their gills while diving, essentially “holding their breath” for around an hour at a time, researchers report in the May 12 Science. Whales and other deep-diving mammals are known to hold their breath (SN: 9/23/20). But this is the first time the behavior has been spotted in diving fish, says Mark Royer, a shark physiology and behavior researcher at the University of Hawaii at Manoa in Honolulu. Sharks and other fish are ectotherms, meaning that their body temperature is largely controlled by the warmth of the water around them....