Whale Sharks are well-known for their characteristic large mouths, shy demeanors, and iconic spots. Many know that these large sharks eat krill, but marine scientists in Australia just discovered that these sharks also eat plants, making them the largest omnivore on the planet.
Whalesharks: Largest Omnivore on the Planet
Whale sharks are filter feeders. For so long, they have been observed at Western Australia's Ningaloo Reef to eat krill. But researchers that analyzed the fish biopsy samples discovered that the large shark ate a lot of plant material.
Dr. Mark Meekan, the first author of the Australian Institute of Marine Science study, says that the findings cause researchers to rethink everything they initially believed about what the whale sharks ate, including what they do in open waters.
The study published in the journal Ecology, titled "The world's largest omnivore is a fish," reports that whale sharks that reach 18 meters in length are the largest omnivores on the planet.
Meekan explains that all the large animals have always been herbivorous on land. In the sea, however, researchers believed that the animals that grew larger such as whales and the whale shark were feeding a step up the food chain on shrimp-like animals and even small fishes, reports TeleSurHD.
He adds that perhaps the evolution system on land isn't as different from water as researchers previously believed.
Understanding Whale Shark Diet
To uncover what the whale shark diet comprises, researchers gathered samples of possible food sources at the Australian reefs, from plankton to large seaweed. Then, researchers compared the amino and fatty acids in the plankton and plant samples to those in the whale sharks.
Dr. Meekan says that the whale shark tissue contained Sargassum compounds, a brown seaweed common at the reefs that break off the reef and float to the ocean's surface.
He says that they believe that over the whale sharks' evolutionary time, the fish evolved the ability to digest some plant material that's going into their guts. Hence, the vision the team has of whale sharks coming to the reef for the sole purpose of feasting on the krill is not the full story. In fact, whale sharks also go to the reefs to eat a fair amount of algae.
Dr. Andy Revill, an organic biogeochemist at CSIRO Oceans and Atmosphere, analyzed the whale shark tissue samples using compound-specific isotope analysis. He explains that the technology allowed the team to study what animals used for energy and growth, and not just what their diet consisted of, reports PhysOrg.
He adds that whale sharks, which swing through the mouth with open mounts, will ingest various materials. However, it is hard to tell how much of the materials are being used by the animal and how much just gets dumped back into the ocean.
Whale sharks are endangered and can live up to 70 years in the wild. These large fish have been reported to grow up to 32.8 feet and weigh 20.6 tons. With the decrease in their population, understanding their diet will help researchers identify further threats to the species.
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