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