Bonnethead: First known Omnivorous Shark

Gwen Vasquez
September 9, 2018

Researchers say that makes the bonnethead the first known omnivorous shark.

- About 4.9 million alone in the Atlantic and Gulf of Mexico coastal waters of the United States of America -combined with their eating habits suggest that we need to re-evaluate the role that bonnetheads play in seagrass meadows.

The researchers wrote in their paper: "We provide conclusive evidence that bonnethead sharks, animals previously thought to be exclusively carnivorous, can assimilate nutrients from seagrass".

Experts from the University of California-Irvine and Florida International University in Miami chose to investigate the bonnethead sharks' dietary habits after reading reports of them munching on seagrass, reports Xinhua news agency.

They planted seagrass collected from Florida Bay in the tanks and gave the plants an easily identifiable chemical signature by adding sodium bicarbonate powder made with a specific carbon isotope to the water.

For the objective of this study, the seagrass was grown in special conditions that involved water sprinkled with sodium bicarbonate powder.

The researchers then fed the bonnetheads a diet made up of 90% seagrass and 10% squid.

The Guardian reported that up to 60% of the bonnethead shark's diet is seagrass.

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'I wanted to see how much of this seagrass diet the sharks could digest, because what an animal consumes is not necessarily the same as what it digests and retains nutrients from'.

Initially, researchers knew of bonnethead sharks eating up the marine plant but "it has been assumed by most that this consumption was incidental and that it provided no nutritional value", says Leigh.

Their experiment showed that, unlike other known carnivores which can't digest plants efficiently, these sharks have highly acidic stomachs.

"As green sea turtles mature, they become nearly entirely herbivorous, and their digestibility of seagrass increases".

According to Leigh, this discovery has come as a big surprise.

The team argues that these sharks are thriving on seagrass.

The sharks' blood and liver tissue are tested and a carbon isotope added to the seagrass was also found indicating the plant does serve a nutritional goal for the sharks.

One more mystery remains to be solved, namely finding out when the bonnetheads first took up the habit of chomping down on plants.

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