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Bonnethead shark (Sphyrna tiburo) Seaquarium du Grau du Roi, France © Getty Images

First ever omnivorous sharks identified

Published: 07th November, 2018 at 09:01
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Bonnethead sharks get the nutrition they require through a diet of vegetation and meat.

We’re going to need a bigger salad cart. Researchers at the University of California have found that bonnethead sharks, smaller cousins of the more famous hammerheads, supplement their diet of crabs, shrimp and squid with mouthfuls of seagrass. It is the first time sharks have ever been confirmed to be omnivorous, they say.


Traces of seagrass have often been found in the guts of bonnethead sharks but it was assumed that they were consuming it unintentionally rather than seeking it out. To test this the team grew seagrass in water laced with powdered sodium bicarbonate. As the seagrass grew it absorbed a distinctive form of carbon into its structure that the team were able to detect the presence of in the sharks livers, plasma and red blood cells.

They then fed five captive sharks a diet consisting of 90 per cent of the modified seagrass and ten per cent squid for three weeks. All of the sharks gained weight during this time. The resulting analysis of the sharks revealed that not only were the sharks deliberately consuming the seagrass but that they were also able to break it down and absorb nutrients from it. It turns out that bonnetheads have special enzymes in their stomach acids that allow them to breakdown the cellulose found in the plant material. They were able to digest 45 per cent of the organic matter found in the seagrass putting them on a par with juvenile green sea turtles.

Why have hammerhead sharks evolved their distinctive heads? © iStock


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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Science Focus Podcast.


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