Squid with a side of seagrass? UC Irvine scientists find first known omnivorous shark

A bonnethead shark swims at the Aquarium of the Pacific in Long Beach.
(Joe Klamar / AFP/Getty Images)

Ruining the reputation of sharks as bloodthirsty predators, California researchers said they have found a shark that enjoys a side of seagrass with its prey.

Bonnethead sharks not only eat grass while chomping fish and squid — they also digest the plant and gain nutrition from it, scientists at UC Irvine announced Wednesday.

It turns out bonnetheads have high levels of enzymes that break down fiber and carbohydrates, compared with the low amount carnivores typically have. That makes the bonnethead the first known omnivorous shark, researchers said.

The findings were published in the journal Proceedings of the Royal Society B.


Laboratory video posted online shows a small bonnethead devouring a meal of 90% seagrass and 10% squid. It was previously believed that bonnetheads were unintentionally consuming the grass in shallow areas where the species lives along some coastlines in the U.S. and Central and South America.

The smallest of the 10 hammerhead species, bonnetheads are typically about 2 to 3 feet long.

Samantha Leigh, who headed the four-year study at UC Irvine’s School of Biological Sciences, said she hopes the discovery will help protect seagrass ecosystems that are at risk from climate change.

“The fact a highly abundant kind of shark feeds on the grasses is yet another indication of why we need to preserve this vegetation,” she said.


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