September 6, 2018 | David F. Coppedge

Sharks Can Digest Vegetables: Scientists Flabbergasted

An apex carnivore of the sea not only eats seagrass, but can digest it just fine.

Notice the surprise of the scientific community that a bonnet shark has been observed grazing on seagrass. They checked its stomach, and found that it is digesting the seagrass and gaining nutritional benefit from it.

‘Vegetarian’ shark discovery: First omnivorous species of sea predator stuns scientists (Fox News).

Surprised scientists have identified the seagrass-munching bonnethead as the first omnivorous shark species…

We were absolutely surprised to find that the bonnethead sharks were taking an omnivorous digestive strategy,” Samantha Leigh, a doctoral candidate at the University of California, Irvine and the study’s lead author, told Fox News….

In their paper, the researchers explain that the sharks are doing a decent job of digesting the seagrass. “We have always thought of sharks as strict carnivores, but the bonnethead is throwing a wrench into that idea by digesting a fair amount of the seagrass that they consume,” Leigh told Fox News.

‘Carnivore’ sharks have a stomach for greens: study ( The find is ‘Truly remarkable,’ this article begins. It says that seagrass may compose about 62% of the shark’s diet.

Leigh described the results as “surprising“.

“Bonnetheads have a digestive system that is very similar to other closely-related species that are definitely strictly carnivorous, so the fact that they are acting like omnivores is truly remarkable!” she said.

The world’s first flexitarian shark grazes like a cow (Nature News).

Bonnethead shark (Smithsonian, public domain)

Sharks are notorious carnivores, but one small hammerhead shark also feels the need to eat its greens….

Samantha Leigh at the University of California, Irvine, and her colleagues fed five captive bonnetheads on seagrass grown in water containing carbon-13, an uncommon form of carbon. After several weeks on this regimen, the sharks’ blood contained high levels of carbon-13, which must have come from the seagrass in their diet. The team also found that the creatures’ guts host enzymes capable of breaking down cellulose and other carbohydrates found in grasses.

This makes the bonnethead the first omnivorous shark ever recorded. Because they are both predators and grazers, bonnetheads play an important part in seagrass ecosystems, the authors say.

We’ve discovered a shark that eats plants as a side dish to shellfish (New Scientist). More surprises reported by Yvaine Ye:

Biologists had previously noticed that bonnetheads consume copious amounts of seagrass in addition to crustaceans and other shellfish. But because the bonnethead’s digestive system looks almost identical to other meat-eating sharks – and so seems to be best suited to deal with a high protein diet – scientists always assumed the seagrass ingestion was accidental….

The bonnethead shark has a gut that looks carnivorous, but is acting omnivorous,” Leigh says. “This means we need to re-classify what it means to have an ‘omnivorous’ digestive morphology. Also, as omnivores, it’s likely that the bonnethead play a role in stabilising food web dynamics and transporting nutrients throughout the seagrass meadows.”

The reports call this the ‘first’ case of an omnivorous shark, but it may not be the last.

Great White (Illustra Media)

Score one for Biblical creationists, who have insisted that animals were vegetarian before the curse. In a world we know that is rife with carnivory, especially in the ocean, I admit I always found that claim a bit difficult to swallow. “What vegetables did great white sharks eat?”, I wondered. Well, here’s a shark eating seagrass and enjoying it! Maybe big teeth do not always imply meat-eating. This bonnet shark probably goes after a field of seagrass like a lawnmower. Nature News says it grazes like a cow.

One example does not make the case for creationism, of course. Even the most ardent creationists who believe animals were vegetarian have to draw a line somewhere. Anteaters count as “vegetarian” only if ants are not really “animals” in the classification. And what about the great whales that scoop up tons of krill and planktonic animals with every gulp? Also, since the bonnet shark does eat shellfish and squid, creation scientists would need to demonstrate that it could survive on vegetable matter exclusively.

The take-home lesson from this story is the surprise effect. Who was surprised? Not creationists, but secular scientists who had assumed that ocean carnivores never eat their greens.






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