Not all carnivorous sharks. Bonnethead shark (Sphyrna tiburo) was also happy to eat seaweed. They can even survive just by relying on seaweed.
Scientists at the Society for Integrative and Comparative Biology meeting in early January said the shark could digest well the seaweed it eats. That means besides meat, seaweed is also an important food for Bonnethead sharks.
Bonnethead sharks are the only omnivorous sharks in the world.
The Bonnethead shark is the smallest shark present in a hammerhead shark family, with a body length of about 91 centimeters. Their digestive tract looks very similar to other sharks.
"Until ten years ago, we thought they were carnivores like other sharks," said Samantha Leigh, an ecology student and evolutionary biologist at the University of California, Irvine, who led the study.
The views of scientists changed in 2007, when they examined the contents in the belly of the Bonnethead sharks in the Gulf of Mexico. It turns out the fish's half-belly is a plant, and this is very strange for carnivorous sharks.
To find out more about the shark's digestion, Leigh and his colleagues captured 5 Bonnethead sharks from the Florida Keys and fed a largely grown diet for almost 3 weeks.
"I make food for them by making the seaweed spheres and filling them with a little squid. And the sharks want to eat it, "Leigh said.
Although their diet consists of 90 percent of seaweed, the shark can still gain weight during the experiment. And when he saw his shit, Leigh was surprised that they could digest the seaweed.
The researchers also found an enzyme used to digest seaweed. The blood sample of the fish contains nutrients found in seaweed.
Bonnethead sharks do not seem to be predators that can regulate the fish and crab populations that fall prey to them. Finding out what role these sharks play in the seagrass ecosystem can help researchers to know how to preserve it.
"It's important to know what they eat and how they digest it to save their environment," Leigh said.