Hammerhead Sharks Utilize Breath-Holding Technique to Stay Warm While Diving into Frigid Waters

A new study suggests that hammerhead sharks hold their breath to maintain their body temperature while hunting in deep, cold waters. Previously unobserved and unexpected behaviour, which has broad similarities to those used by marine mammals, may be widespread among other deep-diving sharks and fishes. Scalloped hammerhead sharks, for example, dive to depths exceeding 800 metres to search for prey, but by reducing convective heat loss at their gills, they are able to maintain both muscle and heart temperature, potentially preserving cardiac function during deep dives. The researchers measured the sharks’ depth, ambient water temperature, activity rates, body movements and internal body temperature using state-of-the-art implants. While the study suggests the sharks maintain their body heat by effectively holding their breath while diving, further research is needed to confirm the thermoregulation strategy.

Like most fishes, sharks are fully ectothermic (cold-blooded), and their body temperatures are largely regulated by their immediate environment. For large predatory fish like hammerhead sharks, this can be a challenge since they need certain body temperatures to function yet venture into colder, deeper waters to find prey. However, the researchers suggest that the strategy of holding their breath to maintain body heat could be widespread among other epipelagic and teleost fishes.