Feasts are rare on the barren landscape of the ocean depths. So researchers couldn't believe their luck when they stumbled on a feeding frenzy of deep-sea sharks chowing down on a fallen swordfish off the US coast earlier this year.

But they never imagined they would also capture footage of one of those sharks becoming the prey for another deep-sea creature.

With their rover hovering nearby, a late arrival took advantage of the submersible's shadow. Nobody might blame a wary fish for holding back while ravenous sharks feed, but this heavyweight had plans to turn one of the diners into its dinner.

A video posted by the US National Oceanic and Atmospheric Administration (NOAA) shows the aftermath of the ambush by a hungry wreckfish. You can watch it for yourself in the clip below, with shark lunch being served at around 1:42.

The action took place at a depth of about 450 metres (roughly 1,480 ft) near a rise in the sea floor 130 kilometres (80 miles) off the coast of South Carolina.

While scouting for the wreck of the oil tanker SS Bloody Marsh, NOAA's remotely operated vehicle Deep Discoverer chanced upon the remains of a 2.5 metre (8 ft) long swordfish being chewed on by nearly a dozen deep-sea sharks.

"The cause of the death of this majestic animal is unclear, perhaps owing to age, disease, or some other injury," says marine scientist Peter J. Auster from the University of Connecticut.

"There was no visible hook or trail of fishing line suggesting this was a lost catch. However, any type of injury would have been masked by the massive damage caused by hundreds of shark bites."

The sharks were two species of slow-moving, deep-sea dogfish commonly referred to as sleeper sharks. Two of the larger individuals were likely to be roughskin dogfish (Centroscymnus owstonii).

Others belonged to a relatively newly discovered animal: Genie's dogfish (Squalus clarkae), named in honour of Mote Marine Laboratory founder Eugenie 'Shark Lady' Clark, which was determined to be a distinct species only last year.

Both of the sleeper shark species are commonly found at these kinds of depths, sluggishly cruising about until some morsel happens by. Or, as in this case, happens to rain down like manna from heaven somewhere in the area.

Sniffing out food on the currents, or perhaps detecting the vibrations of earlier arrivals, it's believed they would have journeyed from some distance just to fill up on the food drop.

Whatever attracted the scavengers, it wasn't long before what looks to be a solitary deep water Atlantic wreckfish (Polyprion americanus) also homed in on the scene for an easy meal.

These massive fish are also referred to as stone bass and bass gropers. They can exceed 2 metres (about 7 feet) in length, and usually hang out around deep water caves and shipwrecks.

Whether it came for the daily special but stayed for the party isn't clear. But as the feast continued, the wreckfish emerged from the glare of the Deep Discover's lights to wrap its lips around one of the sharks.

"This rare and startling event leaves us with more questions than answers, but such is the nature of scientific exploration," says Auster.

A version of this story was first published in July 2019.