Published: Sun, September 09, 2018
Sci-tech | By Patricia Wade

First known omnivorous shark species identified

First known omnivorous shark species identified

They also provide a home and nurseries for thousands of fish and invertebrates that make up the lion's share of the bonnethead diet.

The bonnethead shark has entered the history books after scientists proclaimed it to be the first known omnivorous shark - consuming, digesting and assimilating large quantities of seagrass as well as small fish and molluscs.

"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", she added.

The downside for humans is that bonnethead sharks look a little bit like hammerheads, so if you're splashing around there may not be time to distinguish one from the other. Being able to digest plants as well means the bonnethead shark's stomach has different digestive biochemistry.

The scientists then ran a series of tests on the sharks.

"Understanding how the consumption and digestion habits of bonnethead sharks impacts seagrass ecosystems is important as these omnivores may stabilize food web dynamics and even play a role in nutrient redistribution and transport", the study reads.

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Samantha Leigh, who headed the four-year study at UCI's School of Biological Sciences, said she hopes the discovery will help protect seagrass ecosystems that are at risk from climate change.

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.

In order to see if the sharks were actually seeking out the seagrass as food - rather than scooping it up accidentally when eating bottom-dwelling crabs or snails - the researchers fed captive sharks a mostly vegetarian diet coated with special isotopes to create a unique carbon signature. It was generally thought that they fed mainly on crustaceans and mollusks.

In a new study published by researchers at the University of California-Irvine and Florida International University, the bonnethead shark, which dwells in seagrass meadows off the Atlantic and Gulf of Mexico coasts, was found to be not exclusively carnivorous, as previously thought - it's been sighted having a good nom on that seagrass on multiple occasions.

We may know sharks as bloodthirsty predators but scientists have discovered one of the most common species is actually an omnivore. "This has implications for fragile and crucial seagrass meadow habitat management", said Leigh.

The team said: "Remarkably, the bonnethead's digestibility of organic matter is comparable to juvenile green sea turtles (Chelonia mydas)".

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