Discoveries

May 25, 2023

Deep Dive

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Sharks are fast swimmers and fearsome predators – but even they struggle at great depths, a new study shows.

Marine researchers discovered that a species of hammerhead sharks “hold their breath” while taking deep dives underwater, NPR reported.

For their paper, lead author Mark Royer and his colleagues set out to study the diving habits of scalloped hammerheads, a species known for swimming in warm coastal waters and able to dive to depths of more than 2,600 feet below the surface.

They attached an electronic sensor package to each shark’s fin and later analyzed the data from the deep dives.

The researchers explained that sharks are cold-blooded creatures and their body temperatures match the waters they swim in. However, the temperatures can drop to 41 degrees Fahrenheit at great depths, which can cause the apex predators to become colder, more sluggish, and struggle to swim.

If it doesn’t swim, water doesn’t move across the gills and the creature drowns.

Royer’s team found that scalloped hammerheads have developed a trick to survive deep dives: They close their gill slits before a dive – i.e. they hold their breath – which prevents cold water from flowing across them and also prevents drops in their body temperature.

The sharks only reopen their gills once they get closer to the surface, where the water is warmer and it is comfortable for them to do so, Royer noted.

The study also surprised other marine scientists, who suggested that the hammerheads’ strategy could be more widespread.

They added that the findings shed further light on “the extraordinary persistence of these animals across 400 million years of changing ocean environments.”

This story originally appeared in the May 25, 2023 newsletter, Inch By Inch.