Sharks are infamous as meat eaters who often prey on sea creatures and sometimes humans. However, a new study has found that there is a species of shark that can survive on a vegetarian diet.

Meet the bonnethead shark, a member of the hammerhead shark genus Sphyrna in the family Sphyrnidae. A study, led by Samantha Leigh, a doctoral candidate at the University of California, Irvine, found that these sharks are able to survive on a diet of seagrass, a plant that grows on the ocean floor.

The study was based on a research conducted 10-years ago, which examined the sharks' stomach contents. It found that more than half of the materials found inside bonnethead sharks' stomach was seagrass.

This research, which failed to explain if the sharks were actually consuming grass and extracting nutrients from it, or just accidentally swallowing it underwater, inspired Leigh to investigate the ability of bonnetheads to digest plants.​

“We captured several individuals and brought them into the laboratory at Florida International University, where they were fed a diet of 90% seagrass for several weeks,” scientists involved in the study said. “The seagrass had been labeled with stable isotope carbon-13, so when the sharks consumed it, we could test for a signature of carbon-13 in the sharks’ tissues and see if nutrients from the seagrass were actually taken up into the body.”

“We also collected the shark’s feces, to see how much of the seagrass nutrients (such as carbohydrates, proteins, etc) was simply excreted undigested,” the study said. “Further, we looked at digestive enzymes in the intestines of the bonnetheads, to see if they even have any ability to break down plant material.”

“A purely carnivorous animal should have no mechanism to digest plants, but if the bonnethead sharks eat seagrass regularly, they should have enzymes for this purpose,” the scientists addded.

Blood tests confirmed the sharks were digesting the plants and extracting nutrients from it, and not just excreting it as waste. Results from this research were reported at the Society of Integrative and Comparative Biology annual meeting last week.

Found in New England, the Gulf of Mexico, Brazil, southern California and Ecuador, these sharks are more common in the inshore waters of the Carolinas and Georgia in summer, and off Florida and in the Gulf of Mexico in spring, summer, and fall.

Bonnethead sharks are on an average 2-3 feet long, with a maximum size of about 5 feet.

The team also found that the sharks had the digestive enzyme b-glucosidase in their guts, which breaks down cellulose material found in plants such as seagrass.

The study also found that bonnetheads did not face any difficulty surviving on a 90 percent vegetarian diet.

“We observed no negative health effects, and the sharks even gained weight during the study,” the researchers noted. “While in the wild bonnethead sharks would likely eat less than 90% seagrass, the ability to thrive on such a high plant diet is further support for their ability to obtain nutrients from seagrass.

“Adaptations for omnivory may allow the bonnetheads to be generalists as opposed to strictly predators, giving them flexibility to consume both plants and protein,” Leigh said. “We always think of sharks as these apex predators, but here is this shark that is not really acting like an apex predator at all… but more like an omnivore.”

However, further study may be required to determine whether the sharks intentionally consumed grass or if they ingest the plants accidentally and later adapted a digestive mechanism.

“A greater concern is what may happen to bonnethead sharks if these seagrass meadows, which are currently threatened, are destroyed,” the authors said. “While bonnetheads are not currently endangered, this research indicates seagrass is an important part of their diet, in addition to their habitat.”