Hammerhead Sharks: Masters of Breath Holding in Deep Waters
Scalloped hammerhead sharks have been found to close their gills while diving to conserve body heat and remain active for hunting in deep, cold waters. They have neither the size nor the specialized heat-exchange systems of other fish that can conserve body heat. Researchers found that the sharks would dive several times into deep water at temperatures of 5–11 °C and remain there for 5–7 minutes at a time before surfacing. The sharks are effectively ‘holding their breath’ to keep their core temperature stable by not opening their gills or mouth during the dive.