4 Rare Undersea Boneyards Discovered

whale shark carcass — Fish feed on the fleshy head of a decomposing whale shark. (Image credit: PLOS ONE, doi:10.1371/journal.pone.0096016.g002)

In a chance discovery, scientists found the first images of a dead whale shark and three dead rays on the bottom of the Atlantic Ocean.

Marine creatures naturally fall to the seafloor when they die, and their bodies can provide an important source of nutrients for bottom-dwellers, such as crabs. However, the sunken carcasses of even large animals like whales are rarely observed. Only nine vertebrate carcasses (or carcasses from animals with a backbone) have been documented over the course of five decades of deep-sea photography.

A shows the what's left of a whale shark off the coast of Angola. B, C and D show the bodies of mobulid rays found nearby. (Image credit: PLOS ONE, doi:10.1371/journal.pone.0096016.g002)

At nearly three-quarters of a mile (1,210 meters) below the surface, all that was left of the whale shark (Rhincodon typus) was its fleshy head, pectoral fins and part of its spine, the scientists reported online May 7 in the journal PLOS ONE. The three rays, which likely belonged to the genus Mobula, were similarly reduced to their skeletons and little flesh. Scavengers — mostly eel-like fish known as zoarcids — were spotted feeding and roosting on the carcasses.

Previous studies have shown that so-called "whale falls" host complex ecosystems and support a diverse array of life from sharks and eels to bone-eating zombie worms and bacteria. Rare footage of these boneyards has even led to the discovery of new species, such as sea snails, worms, sea anemones and tiny crustaceans.

But the four new "fish falls" off the coast of Angola were not teeming with as much life as is typically found around a whale fall, the scientists said. Compared with marine mammals, elasmobranchs (a family that includes sharks, rays and skates) decompose more quickly and aren't as nutrient-rich.

"Their flesh is primarily muscular and lacks the fatty blubber layer carried by whales," wrote the researchers, led by Nicholas Higgs of Plymouth University in the United Kingdom. Whale bones can survive on the seafloor for decades, but fish skeletons lack the minerals and lipid-rich bone marrow that marine mammals have, which may cause them to degrade in a matter of weeks or months, the scientists said.

The authors of the study speculate that fish falls are primarily important sources of food for scavengers. But the fact that the four carcasses in this study were found within a relatively small area of about 0.5 square miles (1.48 square km) suggests dead whale sharks and rays might be quite common seafloor sights.

Follow Megan Gannon on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Megan has been writing for Live Science and Space.com since 2012. Her interests range from archaeology to space exploration, and she has a bachelor's degree in English and art history from New York University. Megan spent two years as a reporter on the national desk at NewsCore. She has watched dinosaur auctions, witnessed rocket launches, licked ancient pottery sherds in Cyprus and flown in zero gravity. Follow her on Twitter and Google+.