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Hammerhead sharks found to hold their breath on deep water hunts to stay warm:

Scalloped hammerhead sharks hold their breath to keep their bodies warm during deep dives into cold water where they hunt prey such as deep sea squids. This discovery, published in Science by University of Hawai'i at Mānoa researchers, provides important new insights into the physiology and ecology of a species that serves as an important link between the deep and shallow water habitats.

"This was a complete surprise," said Mark Royer, lead author and researcher with the Shark Research Group at the Hawai'i Institute of Marine Biology (HIMB) in the UH Mānoa School of Ocean and Earth Science and Technology. "It was unexpected for sharks to hold their breath to hunt like a diving marine mammal. It is an extraordinary behavior from an incredible animal."

Shark gills are natural radiators that would rapidly cool the blood, muscles, and organs if scalloped hammerhead sharks did not close their gill slits during deep dives into cold water. These sharks are warm water animals but feed at depths where seawater temperatures are similar to those found in Kodiak Alaska (around 5ºC/ 40ºF), yet they need to keep their bodies warm in order to hunt effectively.

"Although it is obvious that air-breathing marine mammals hold their breath while diving, we did not expect to see sharks exhibiting similar behavior," said Royer. "This previously unobserved behavior reveals that scalloped hammerhead sharks have feeding strategies that are broadly similar to those of some marine mammals, like pilot whales. Both have evolved to exploit deep dwelling prey and do so by holding their breath to access these physically challenging environments for short periods."

[...] "This discovery fundamentally advances our understanding of how scalloped hammerhead sharks are able to dive to great depths and withstand frigid temperatures in order to capture prey," said Royer. "It also demonstrates the delicate physiological balance that scalloped hammerhead sharks must strike in order to forage successfully."

[...] "This extraordinary physiological feat that allows scalloped hammerhead sharks to expand their ecological niche into the deep sea could very well make them vulnerable to additional human impacts."

Journal Reference:
Mark Royer et al., "Breath holding" as a thermoregulation strategy in the scalloped hammerhead, Science (2023). DOI: 10.1126/science.add4445.

Original Submission