Whale sharks are the largest shark species in the world, and now scientists have discovered that giant sharks are even more prodigious eating machines than previously thought. In addition to taking huge mouthfuls of krill (tiny shrimp-like crustaceans), whale sharks also swallow large amounts of algae, allowing the aquatic giants to officially dethrone Kodiak bears (Ursus arctos middendorffi) as the largest omnivores Of the world.
The researchers made the discovery by analyzing whale shark (Rhincodon typus) skin samples collected near Western Australia’s Ningaloo Reef. These huge sharks are the largest fish in the sea, weighing up to 40 tons (36 metric tons) and averaging about 12 meters (40 feet) in length, according to the National Oceanic Service. Until now, scientists thought the gentle giants were primarily filter feeders, with cavernous mouths open to drink in roughly 21,200 cubic feet (600 cubic meters) of water every hour. Then, by straining the water through the gills, the sharks are left with mouthfuls of plankton, shrimp, tiny fish and crustaceans to swallow.
But the new discovery, published on 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 shark behavior “in the open ocean,” study lead author Mark Meekan, a fish biologist at the ‘Australian Institute of Marine Sciences in Queensland, he said in a statement.
Meekan said the discovery contradicts the common assumption that large land creatures are usually herbivores, but those living in the sea occupy a different niche in the food chain, feeding on small shrimp and fish.
“It turns out that maybe the evolutionary system on land and in water isn’t so different after all,” Meekan said.
For their study, the scientists collected the sharks’ potential food sources, ranging from small crustaceans and plankton to large clumps of algae, and then chemically analyzed the samples to reveal their amino acids and fatty acids. After cross-referencing these acids with those found in skin samples taken from whale sharks, the researchers identified high concentrations of sargassum, a type of brown algae made up of thousands of microscopic algae, in the sharks’ diet.
Scientists think this omnivorous diet could be the result of sharks evolving to digest accidentally swallowed algae, saving them the energy cost of spitting it back out.
“We think that over evolutionary time, whale sharks have developed the ability to digest some of this sargassum that gets into their guts,” Meekan said. “So the view we have of whale sharks coming to Ningaloo just to feast on this little krill is only half the story. In fact, they’re also eating a fair amount of algae.”
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’s possible that the propensity of sharks to swallow most of what they swallow in their mouths makes them much more likely to swallow large amounts of plastics that end up in the ocean.
“Whale sharks can pass some plastics through their gut,” but ingesting small or large pieces of plastic could cause sharks to regurgitate their meals and could reduce their gut capacity and interfere with digestion, they wrote. the investigators.
Originally published in Live Science.