The fish had swallowed a shark whole, as the busy predators darted about to grab morsels from the 250-lb. (110 kilograms) carcass of a swordfish.
"Oh my god — I'm going to remember this my whole life," one of the researchers says in footage of the feeding frenzy. [In Photos: Great White Sharks Attack]
A remotely operated vehicle called the Deep Discoverer captured the video. The scientists operating the vehicle were conducting research for the National Oceanic and Atmospheric Administration (NOAA) aboard the ship Okeanos Explorer. This was the Deep Discoverer's seventh dive on an expedition called Windows to the Deep.
The scientists were operating the Deep Discoverer 1,476 feet (450 meters) below the surface of the Atlantic Ocean, searching for a World War II shipwreck. They directed the rover up a small incline, expecting to find the boat but instead discovered the swarm of small sharks, called dogfish. The predators had likely sensed this swordfish "food fall" from a long distance and had traveled for the feast, Peter J. Auster of Mystic Aquarium and the University of Connecticut, wrote in the team's mission log.
When the wreckfish, a type of grouper, meandered in front of the camera with a shark tail protruding from its mouth, the scientists came to a clear conclusion: The guest had been watching the feeding frenzy the entire time, stealthily hiding behind the rover itself.
Though surprising, this isn't the first time a fish has been caught on camera swallowing a shark. Last year, people fishing off the coast of Florida caught footage of a 500-lb. (227 kg) goliath grouper darting up to the water's surface and nabbing a 4-foot-long (1.2 m) shark, Fox News reported at the time.
One shark expert said this behavior is run-of-the-mill, "fish-eat-fish" ocean life.
"It might be unusual to see it, but it's not entirely unusual [for it to happen], no," Daniel Abel, a marine biologist at Coastal Carolina University, told Live Science. "A big grouper is going to eat anything smaller than itself."
The law of the ocean food chain is a brutal one, Abel said: Anything smaller than yourself is fair game for predators like sharks and groupers. Large groupers are known predators of sharks like dogfish, Abel said. And aside from humans, sharks are their own greatest predators, he added.
The unlucky dogfish caught on camera didn't fall victim to a fellow shark, but it did just happen to be smaller than the hungry grouper watching it — and too busy chowing down to notice.
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- Images: Sharks & Whales from Above
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Originally published on Live Science.