Meet the First Known Omnivorous Shark

Bonnetheads munch on seagrass, and new study finds it's not just incidental
By Arden Dier,  Newser Staff
Posted Sep 5, 2018 6:15 PM CDT
Meet the Shark That Likes Grass More Than Meat
File photo of a bonnethead shark.   (Getty Images / wrangel)

Jaws would've been a lot less scary had Steven Spielberg replaced his great white villain with a bonnethead shark. It's "the first known omnivorous species of shark," says researcher Samantha Leigh, co-author of a new study that describes the hammerhead relative as a lover of seagrass. Indeed, up to 60% of the bonnethead shark's diet is seagrass found in coastal waters around the Americas, with the rest made up of bony fish, crabs, snails, and shrimp, reports the Guardian. Researchers were previously aware of bonnethead sharks munching on the marine plant but "it has been assumed by most that this consumption was incidental and that it provided no nutritional value," says Leigh. Through a series of tests, scientists proved that wasn't the case.

They captured five bonnetheads, which can reach up to five feet long, and put them on a three-week diet of squid as well as seagrass the researchers had given a distinctive chemical signature. Using enzymes to break down starch and cellulose—strong stomach acids might also be at play—the sharks digested more than half of the organic material in the grass, meaning they were better at digesting plant material than pandas, per Mashable, or "on a par with young green sea turtles," per the Guardian. A carbon isotope added to the seagrass was also found in the sharks' blood and liver tissue, indicating the plant does serve a nutritional purpose for the sharks. The "ecological implications" of 4.9 million bonnethead sharks munching on seagrass are not yet fully understood. (There was once a shark twice the size of a great white.)

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