Bonnethead shark swimming in ocean in natural habitat

Photo by: FtLaudGirl


Sharks Eat Plants, Too!

By: Sarah Agnone

Shark scientists recently dispelled a longstanding belief about shark diets. As the ultimate predator, it’s long been assumed sharks only eat meat. However, a recent study of the Bonnethead Shark (Sphyrna tiburo) revealed that some sharks have an appetite for plants.

Bonnetheads, an extremely common species of Hammerhead, are “flexitarians” -- meaning they’re able to switch between meat and plant-based nutrition.



Photo by: Tom Brakefield

Tom Brakefield

For the past decade, researchers have observed the species eating sea grass, which took up over 62 percent of the sharks’ stomach content. It was assumed this consumption was incidental as they searched for crabs, fish, and other small animals living within the seagrass. But to determine if bonnethead’s were truly omnivorous, they needed to know if the seagrass provided actual nutritional value.

The research team collected five bonnethead sharks, as well as samples of seagrass to grow in their lab. The seagrass was modified with an easily traceable carbon isotope added to the water. When consumed, traces of the grass would be could be tracked throughout the shark’s digestion system.



Bonnethead shark swimming in ocean in natural habitat

Photo by: FtLaudGirl


First, the sharks were fed a diet of 10 percent squid and 90 percent seagrass for three weeks. All of the sharks gained weight, but to confirm their hypothesis that the seagrass provided sustenance, the team then conducted blood tests. The blood tests would determine how much of the seagrass was digested versus excreted.

The chemical tracer was found throughout the sharks’ bloodstream and liver tissue, indicating nutritional absorption of over half the seagrass’s organic content. Furthermore, the bonnethead’s enzymes indicated omnivorous digestion. While carnivores have low levels of fiber digesting enzymes, bonnetheads were found to have high levels of enzymes capable of breaking down the seagrass.

Omnivorous shark diets have immense implications for seagrass habitats. This new finding restructures scientific assumptions about local food chains and how to best preserve the seagrass that serves as a home to significant populations of the world’s sea creatures.

Next Up

Swimming with Sharks

One research foundation is working to change public perception of sharks by taking people swimming with them – without a cage.

Endangered Sharks of the World

Our world's oceans are continually challeged by pollution, overfishing, and climate change. This affects sharks just as much as it affects humans--if not more so. Read on to learn about some endangered sharks that need our help.

New Pocket Shark Discovery

A new Pocket Shark has been discovered and it's insanely cute! Here's what you need to know...

A 300 Million Year Old Shark Skull Was Discovered Inside Kentucky Cave

Paleontologists have now found and identified the fossilized remains of around 150 individual sharks from between 15 and 20 different species buried in the limestone layers of the cave.

Shark Flings Itself Out of Water to Avoid Becoming Orca’s Snack

A sevengill shark flings itself out of the water and onto rocks to avoid becoming an orca's meal.

What Caused the Death of Great White Found With Sea Turtle Stuck In Mouth?

Shark scientist Dr. Neil Hammerschlag debunks news of Great White dying from choking on a sea turtle.

What Happens When a Great White Can’t Breach?

Fun fact on great whites who never get airborne.

New Canadian Law is Great News for Mako Sharks

Canada has become the first North Atlantic country to put a longstanding recommendation from conservation scientists to protect Mako sharks into law.

There’s a Lot You Don’t Know About Sharks

SHARK WEEK starts August 9th, only on Discovery. But in the meantime, here are some fin-tastic facts you probably didn’t know about sharks.

Twin Red Panda Cubs Born at Chester Zoo

In June, twin red pandas were born at England’s Chester Zoo as part of its endangered species breeding program, and they are as adorable as ever! After nine weeks in their nest boxes, these cubs passed their health checkup, which is great news in the animal world as there are less than 10,000 in the wild.
Related To: