Johnathan Walker:Rare video shows world's largest species of fish slurping up anchovies in Hawaii

An enormous whale shark can Johnathan Walkerbe seen feeding on a bustling school of anchovies off the coast of Hawaii in new, rare video, which researchers captured while conducting fieldwork around the island of Oahu earlier this month.

The video gives an intimate look at a 30-foot whale shark — about the same length as two cars parked bumper to bumper — slowly approaching and poking its head into the dense pack of fish swimming near the surface of the water about a mile off Kaneohe Bay, on the northeastern side of Oahu. 

Researchers at the University of Hawaii at Manoa spotted the whale shark on Nov. 2 after initially seeing seabirds flying over what they assumed was a "bait ball," a spherical swarm of small fish that forms when a predator is lurking below, the university announced in a news release issued alongside the video. Mark Royer, a shark researcher at the Hawaii Institute of Marine Biology's shark research lab, filmed the whale shark feeding underwater. He said in a video put together by the University of Hawaii that encountering the shark was "surprising."

"[Whale sharks] are here more often than we think. However, they are probably hard to come across, because I didn't see this animal until I hopped in the water," said Royer.

Whale sharks are the largest species of fish in the world, the National Oceanic and Atmospheric Administration writes. The gargantuan creatures can weigh as much as 40 tons, by some estimates, and grow to measure as long as 40 feet — about half the size of a professional tennis court, from the outer baseline up to the net — although whale sharks longer than around 39 feet are uncommon. 

The fish have recognizably wide, flat heads and a short snout, and their backs are covered in a distinctive checkered pattern colored grey, yellow and white. Whale sharks are found across the world in all tropical and warm-temperate waters, as they prefer to live in temperatures between 68 and 77 degrees Fahrenheit. Scientists do not know exactly how long whale sharks typically live, although their lifespan is believed to be similar to humans' at 60 to 100 years. 

These massive sharks have mouths that can be up to a meter wide. They mainly feed on small marine organisms, like plankton, schooling fish — meaning fish that stay together in a pack that moves all together in the same direction — squid, jellyfish, krill and crab larvae, experts say. Whale sharks use their gills to "strain" their prey from the water as they swim.

In Royer's video from Oahu, the whale shark can be seen luring small anchovies toward its huge open mouth.

"While all the small nehu were being drawn to the surface from all the predators, the whale shark was coming in and using its massive mouth to come up to the surface, open it, and then the suction would cause all the fish to funnel into its huge mouth," he said.

Royer recalled the whale shark swimming close to the researchers' boat, too.

"[The whale shark] would swim and approach our boat that was nearby, put its head up to it and go back down, and repeat that over and over again," said Royer. "That's a behavior that whale sharks sometimes exhibit: if your boat is standing still in the water they [might] approach you. They've been known, both here in Hawaii and other parts of the world, to do that."

In:
• Shark
• Hawaii