Whale sharks are the largest shark species in the world, and now scientists have discovered that the giant sharks are even more wondrous eating machines than previously thought. In addition to gobbling huge bites of krill — tiny shrimp-like crustaceans — whale sharks also swallow huge portions of seaweed, allowing the water giants to officially dethrone Kodiak bears (Ursus arctos middendorffic) as the world’s largest omnivores.
Researchers made the discovery by analyzing whale shark (Rhincodon typus) 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 an average length of about 12 meters, according to the National Ocean Service. Until now, scientists thought the gentle giants were primarily filter feeders, their cavernous mouths wide open to swallow about 21,200 cubic feet (600 cubic meters) of water every hour. Then, by forcing the water out through their gills, the sharks are left with bites of plankton, shrimp, small fish and crustaceans to swallow.
But the new discovery, published July 19 in the journal Ecology, has given scientists important new information to chew on.
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“This makes us rethink everything we thought we knew about what whale sharks eat” and questions other aspects of the sharks’ behavior “in the open ocean,” lead researcher Mark Meekan, a fish biologist at the Australian Institute of Marine sciences in Queensland, said in a statement.
Meekan said the discovery contradicts the common assumption that large terrestrial animals are typically herbivores, but those that live in the sea occupy a different place in the food chain, feeding on small shrimp and fish.
“It turns out that the evolution system on land and in the water may not be that different after all,” Meekan said.
For their study, the scientists collected the sharks’ possible food sources — ranging from small crustaceans and plankton to large clumps of seaweed — and then chemically analyzed the samples to reveal their amino acids and fatty acids. After cross-referencing these acids with those found in whale shark skin samples, the researchers identified high concentrations of sargassum — a type of brown seaweed made up of thousands of microscopic algae — in the sharks’ diet.
The scientists think this omnivorous diet may be the result of the sharks evolving to digest accidentally ingested seaweed, saving them the energy costs of spitting it out again.
“We think that over the course of evolution, whale sharks have evolved the ability to digest some of this sargassum that ends up in their guts,” Meekan said. “So the vision we have of whale sharks coming to Ningaloo to feast on these little krill is only half the story. They eat quite a bit of algae there too.”
Having a wider range of food sources may sound like good news for whale sharks, as it could help them withstand potential upheavals in their marine ecosystems due to climate change. But the scientists said it’s more complicated than that. According to the study, the sharks’ tendency to swallow most of what is swept into their mouths may make them much more likely to swallow large amounts of plastic in the ocean.
“Whale sharks can pass some plastic through the gut,” but by ingesting small or large pieces of plastic, the sharks can throw up their meals, reduce their gut capacity and interfere with digestion, the researchers wrote.
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Originally published on Live Science.