Whale sharks are the largest species of shark in the world, and scientists have now found that giant sharks are more fascinating eating machines than previously thought. In addition to eating massive amounts of krill – tiny shrimp-like crustaceans – whale sharks also ingest huge amounts of seaweed, enabling the aquatic giants to officially get rid of kodiak bears (Middendorf bears) as the largest carnivores in the world.
Researchers made the discovery by analyzing the whale shark (Rincodon type) Skin samples collected near the Ningaloo Reef in Western Australia. These giant sharks are the largest fish in the sea, weighing up to 40 tons (36 metric tons) and growing to about 40 feet (12 meters) on average, according to the National Ocean Service. Until now, scientists believed the gentle giants were primarily filter feeders, opening their cavernous mouths wide to swallow approximately 21,200 cubic feet (600 cubic metres) of water every hour. Then, by filtering the water through the gills, the sharks are left full of plankton, shrimp, small fish and crustaceans to swallow.
But the new discovery was published on July 19 in the journal Ecology Give scientists new and important information to chew on.
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“It prompts us to rethink everything we thought we knew about what sharks eat” and raises questions about other aspects of shark behavior “in the open ocean,” said lead study author Mark Meekan, a fish biologist at the Australian Institute of Marine Science in Queensland, He said in a statement.
Mikan said the finding contradicts the common assumption that large land organisms are usually herbivores, but that those in the sea occupy a different place in the food chain, feeding on shrimp and small fish.
“It turns out that maybe the evolution system on land and in water isn’t that different after all,” Mikan said.
For their study, the scientists collected the sharks’ potential food sources – from small crustaceans and plankton to large clumps of seaweed – and then chemically analyzed the samples for amino and fatty acids. After cross-referencing these acids with those in skin samples taken from whale sharks, the researchers identified high concentrations of sargassum – a type of brown seaweed made up of thousands of microscopic algae – in the sharks’ diet.
Scientists believe this diet could be the result of sharks evolving to digest accidentally ingested seaweed, saving them the energy cost of spitting it out again.
“We think that over evolutionary time, whale sharks have evolved the ability to digest some of this sargassum entering their guts,” Mikan said. “So the vision we have of whale sharks coming to Ningaloo just to eat these little krill food is only half the story. They actually eat a fair amount of algae too.”
Having a wider range of food sources may seem like good news for whale sharks, as it could help them withstand potential disruptions to their marine ecosystems caused by climate change. But scientists said it’s more complicated than that. According to the study, it is possible that sharks’ tendency to swallow most of what falls into their mouths may make them more likely to ingest copious amounts of ocean-borne plastic.
“Whale sharks can pass some plastic through the gut,” the researchers wrote, “but eating small or large pieces of plastic can cause sharks to vomit their meals, reduce their digestive capacity and hinder digestion.”
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Originally published on Live Science.
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