Los Angeles: Scientists say they have identified the first known omnivorous shark species, with 60 percent of its diet consisting of seagrass.
The finding, published in the journal Proceedings of the Royal Society B, overturns the idea that all sharks are exclusive meat-eaters.
Researchers from the University of California, Irvine in the US found that bonnethead sharks happily graze upon seagrass, in addition to eating bony fish, crabs, snails and shrimp.
Omnivores feed on a variety of food of both plant and animal origin.
The bonnethead shark is abundant in the shallow waters of the Western Atlantic, and the Gulf of Mexico, 'The Guardian' reported.
Though small by shark standards, adult females the larger of the sexes can still reach an impressive five feet long.
The researchers analysed the sharks' dietary habits after reading reports of the fish chomping on seagrass, the flowering marine plant that forms subsea meadows in some coastal waters. They retrieved seagrass from Florida Bay and hauled it back to the lab where they re-planted it.
As the seagrass took root, the researchers added sodium bicarbonate powder made with a specific carbon isotope to the water. This was taken up by the seagrass, giving it a distinctive chemical signature.
The researchers, including those from Florida International University in the US, next caught five bonnethead sharks and brought them to the lab. They were fed on a three-week diet of the seagrass and squid.
The scientists ran a series of tests on the sharks. These showed that they successfully digested the seagrass with enzymes that broke down components of the plants, such as starch and cellulose.
Lacking the kind of teeth best suited for mastication, the shark may rely on strong stomach acids to weaken the plants' cells so the enzymes can have their digestive effects, researchers said.