Bonnethead Shark's Plants-Plus-Prey Diet Makes It Unique

The Bonnethead shark's plants-plus-prey diet may ruin the reputation of bloodthirsty predators, but California researchers said it definitely enjoys a side of seagrass with its fish and squid.

Bonnethead sharks not only eat grass while chomping fish — they also digest the plant and gain nutrition from it, scientists at the University of California, 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.

Laboratory video posted online shows a small bonnethead devouring a meal of 90 percent seagrass and 10 percent squid.

It was previously believed that bonnetheads unintentionally consumed the grass in shallow areas where the species lives along some coastlines in the U.S., Central and South America.

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

Samantha Leigh, who headed the four-year study at UCI'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.

Dr. Sandy Trautwein of the Aquarium of the Pacific in Long Beach called the findings "unique, but not surprising, given bonnetheads' niche in tropical ecosystems."

She said she hopes the study "opens up the door for additional research" about seagrass communities and sharks in general.