The underbelly of a hammerhead shark is illuminated with other sea-life swimming above them silhouetted.

Do sharks hold their breath underwater? This species might.

The “completely unexpected” behavior reported in scalloped hammerhead sharks raises questions about how widespread it may be among other species.

By holding their breath, scalloped hammerhead sharks may be able to regulate their body temperature when diving thousands of feet below ​surface waters.

Photograph By GREG LECOEUR

Scalloped hammerhead sharks may be holding their breath when they dive deep into frigid waters. The revelation, published today in Science, suggests that this strategy may allow the warm-water dwellers to regulate their temperature while they hunt.  

This technique is “completely unexpected,” says Mark Royer, a shark biologist at the University of Hawaii who led the research. “This kind of behavior has never been observed in any kind of deep-diving fish,” he says, and it now raises questions about how widespread breath-holding may be among other species. 

These critically endangered hammerhead sharks typically rely on forward movement to force water across their gills, which enables them to extract needed oxygen to breathe. Yet when the predators swim half a

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