Threatened Species: How World's Largest Fish Diets on Tiniest Marine Life

As pandas have proven, if you're big and you eat small or low-protein food, you have to move slo-owly. Or at least, researchers from Texas A&M University, the Australian Institute of Marine Science and the University of Texas Marine Science Institute say that whale sharks--the largest fish on the planet at up to 75,000 pounds--depend for nutrients on tiny krill and plankton, and dive and swim in a way that requires little energy. The team's research was recently published in the journal Frontiers of Marine Science.

These researchers learned about the whales, which can weigh as much as 18 U.S. cars, by attaching video and data recorders to two of them near Western Australia's Ningaloo Reef, which is the world's second-largest coral reef behind the Great Barrier Reef, according to a release.

They studied the sharks' movements and feeding behavior. In order to dive sometimes as far as 1,500 feet into water that is cold at that depth, the great fish have patterns of minimalist swimming at a fixed, low-power pace. Sometimes they glide at depth, and dive in an assymmetrical way, said the team, noted the release.

It's likely that the whale sharks are increasing their food-finding efficiency by as much as 32 percent by using these low-energy methods, say the researchers.
"Conservation of heat and energy while they are diving for food in cold waters appears to be the key for survival for these large creatures," Davis added in a release.

Whale sharks, by the way, are docile and toothless, and use a filtration system to catch plankton and krill while letting up to 1,500 gallons of water pour through their gills. The International Union for the Conservation of Nature (IUCN) considers them vulnerable, said the release.

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