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Researchers Identify World's First Known Omnivorous Shark Species

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Are all sharks carnivorous? A team of researchers found that bonnethead sharks also incorporate sea grass into their diets, suggesting that they may be the world’s first known omnivorous sharks.

Seagrass In Shark Diet

Since 2007, bonnethead sharks have been observed to consume seagrass ever since ecologist Dana Bethea recorded the creatures’ inclination toward the diet. However, for years, it was not quite clear if this was a deliberate feeding or merely an accidental one in quest of the bonnetheads’ typical food choice of crustaceans, clams, small fish, and octopuses.

To determine if the seagrass consumption is deliberate or merely accidental, researchers of a new study published in Proceedings of the Royal Society B gathered five bonnethead sharks in a laboratory setting and fed them with a special diet consisting of 10 percent squid and 90 percent seagrass with a unique carbon isotope signature.

The bonnetheads’ stomachs are actually identical to the stomachs of other shark species’ stomachs in that they are specialized for meat-based diets, so researchers needed to determine if the bonnetheads actually digested the seagrass they consumed.

Accidental Or Deliberate?

Within three weeks with the specialized diet, the five bonnethead sharks all gained weight, and testing revealed the presence of the unique isotope in the sharks’ blood and liver. This suggests that the sharks actually digested the sea grass and absorbed its nutrients.

Further, the researchers found that the sharks had digestive enzymes that break down plant-based food. Carnivores such as sharks usually have low levels of such enzymes that deal with fibers and carbohydrates, but the bonnetheads had significant levels of the enzymes.

The evidence suggests that bonnethead sharks deliberately consume sea grass for its nutritional value and not merely accidentally in their quest for meaty food. In fact, researchers suggest that seagrass comprises up to 60 percent of bonnethead sharks’ diet. This makes the bonnethead sharks the first shark species that may be considered as omnivorous.

As such, researchers believe that it is now important to look at the bonnethead sharks’ role in seagrass meadows all around the world. Such marine ecosystems are home to many species, ang it helps filter water and absorb excess carbon dioxide in the atmosphere.

Bonnethead Sharks

It is quite obvious from looking at the bonnethead shark that it is a relative of the hammerhead shark. In the hammerhead family, however, bonnetheads are considered the second to the smallest member, growing up to a maximum length of 59 inches.

Such creatures can typically be found in tropical and subtropical waters and often thrive in shallow bays with mud or sand bottoms and coral reefs. Although they are often at the top of local food chains, some larger sharks such as tiger sharks and lemon sharks prey on bonnethead sharks.

Bonnethead sharks are not considered a threatened species.

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