Tropical Hammerhead Sharks can dive into frigid depths to find food, say scientists in a recent study of shark behaviour documented in The New York Times on 11 May 2023.
The Scalloped Hammerhead Shark (Sphyrna lewini) is an elasmobranch ectotherm fish in the Sphyrnidae family with a cartilaginous skeleton. It is also known as the Bronze Hammerhead, the Kidney-Headed Hammerhead, or the Southern Hammerhead. It likes warm ocean water, such as the tropical waters of Hawaii.
Research scientists have found that the tropical Hammerhead Shark can dive more than 790 metres (2,600 feet) from the warm ocean surface to frigid depths multiple times a night to hunt for fish and squid.
Mark Royer, a shark biologist at the University of Hawaii at Manoa, studied the Scalloped Hammerhead Shark. He attached sensor tags near the dorsal (back) fins of six Hammerhead Sharks near Hawaii. The sensor tags emitted satellite signals which Mark Royer examined after the tags detached from the sharks – they were designed to fall of the sharks after several weeks.
He found that the Scalloped Hammerhead Sharks stay warm even in the frigid depths by closing their gills – holding their breath. This strategy for regulating an ectotherm fish’s temperature has never been observed before.
The sensor tags, similar to Fitbits, collected data on depth and body temperature. They detected that the sharks lost only a little body heat when they started to dive down, and then their bodies quickly returned to the same warm-water surface-level temperatures even when they kept diving further down. Even when the water temperature was as cold as 4C (39F), the sharks had a body temperature of about 24C (75F) during the hour-long dives.
Mark Royer and his research team published the finding in the Science journal in May 2023. Using a mathematical model, the team found that the sharks were conserving body heat. Holding their breath meant that the sharks were stopping the flow of water over their gills, and their ability to take in oxygen as they swam more than a kilometre (3,000 feet) below the surface.
Next, Dr. Royer wants to attach video cameras to the Hammerhead Sharks to confirm the results and to learn more. He is planning to study the metabolism of the Hammerhead Sharks to better understand the recovery period between dives each night.
The Scalloped Hammerhead Shark has a hammer-shaped head, called a cephalofoil. Its nostrils and eyes are located on the sides of the hammer part of its head, and not in front. This allows a full circle of vision. It can see above it, below it, and all around it. It has gill slits on the side of its body. It grows to 200-350 centimetres (79-138 inches) in length.
The Scalloped Hammerhead Shark is found in the tropical waters of the Indian Ocean, Pacific Ocean, and Atlantic Ocean along coastlines and continental shelves. It eats fish (mainly sardines, mackerel, and herring), squid, octopus, stingrays, and crustaceans, such as crabs, lobsters, and shrimp. It stalks its prey at the bottom of the ocean.
The Scalloped Hammerhead Shark is usually solitary at night. During the day, it usually swims in schools of about 100 individuals.
Location of photographs: Aquarium de Paris-Cinéaqua, France
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM