The Veg: first omnivorous shark species is identified - it takes salad with its seafood

It is one of the most radical rebrandings in history: contrary to their bloodthirsty image, some sharks are not irrepressible meat eaters, but are happy to munch on vegetation too.

According to US researchers, one of the most common sharks in the world, a relative of the hammerhead which patrols the shores of the Americas, is the first variety of shark to be outed as a bona fide omnivore.

The bonnethead shark is abundant in the shallow waters of the eastern Pacific, the Western Atlantic, and the Gulf of Mexico, where they feed on crab, shrimp, snails and bony fish. Though small by shark standards, adult females – the larger of the sexes – can still reach an impressive 1.5 metres long.

Scientists at the University of California in Irvine, and Florida International University in Miami, decided to investigate 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.

“It has been assumed by most that this consumption was incidental and that it provided no nutritional value,” said Samantha Leigh, a researcher on the team. “I wanted to see how much of this seagrass diet the sharks could digest, because what an animal consumes is not necessarily the same as what it digests and retains nutrients from.”

To see whether the sharks are truly flexitarian, the scientists retrieved sea grass 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.