Hammerhead sharks employ a unique “breath-holding” technique to regulate their body temperature while hunting in deep, cold waters, according to a recent study. This previously unobserved strategy resembles thermoregulation methods used by marine mammals and may be prevalent in other deep-diving sharks and fish. Researchers used remote biologgers implanted in adult scalloped hammerhead sharks to collect data on depth, water temperature, and internal body temperature during dives that can reach over 800 meters, where temperatures drop to around 4 degrees Celsius. They discovered that these sharks maintain elevated body temperatures—up to 20 degrees Celsius higher than the surrounding water—by closing their mouths and/or gill slits to limit the flow of cold water across their gills. This technique minimizes heat loss during deep dives, with significant heat loss occurring only upon their ascent toward warmer waters as they reopen their gill slits. The researchers suggest that breath-holding thermoregulation may not only be a feature of hammerhead sharks but potentially widespread among epipelagic and teleost fishes. Further investigation is necessary to explore the prevalence of this fascinating thermoregulation strategy among other marine species.
