Hammerhead sharks 'hold their breath' in deeper, colder waters, research shows

https://www.npr.org/2023/05/11/ [login to see] /hammerhead-sharks-hold-breath-study
Sharks are among the best swimmers on the planet, but new research suggests that even they sometimes "hold their breath" while diving deep underwater.

The reason is that sharks are ectothermic, or cold-blooded, and their body temperature essentially matches the waters they swim in. To do deep dives, they must conserve body heat, and the best way to do that is to tightly close their gill slits.

It all makes sense, but the idea of a fish holding its breath underwater "still shocks and baffles me," says Mark Royer, a researcher at the University of Hawaii at Manoa and the Hawaii Institute of Marine Biology, who led the study.