Marine biologists have gotten a grisly treat courtesy of remotely operated vehicles surveying the seafloor off Angola for the oil and gas industry: For the first time, the carcasses of large fish—a whale shark and three mobulid rays—and the feeding frenzy they create have been filmed. The researchers note that previous studies on the fate of vertebrate remains below 600 feet "have been restricted to either small porpoise and dolphin carcasses or large whale carcasses," the latter known as "whale falls." Lead author Dr. Nick Higgs explains to the BBC the sudden richness of the evidence—four carcasses across an area roughly a half-square-mile when none had been seen before—by the fact that there is a large amount of sea-life activity in the waters above the seabed, which has been surveyed more "intensively" than most areas because of its industrial uses.
Large carcasses are interesting, the scientists write in the journal Plos One, because otherwise the main food source in depths beyond where sunlight penetrates is "marine snow" consisting of millimeter-long "dead plankton and fecal pellets." These dead large sea creatures could make up 4% of the food available in these environments (this one was three-quarters-of-a-mile below the surface). Four fish species were identified among the remains, including eel pouts, which prey on other fish that come to scavenge. But the "zombie worms" known to flock to whale bones were absent. "The ecosystem does seem different to whale falls," says Higgs.