A Gruesome Feeding Frenzy in the Atlantic Ocean

When Michalove returned to the whale again last week—this time with one of the shark biologists he works with, Greg Skomal of Massachusetts Marine Fisheries—even less of the whale remained. The calorie-rich blubber was mostly gone. Occasionally, Skomal told me, a feeding shark would puncture the abdominal cavity of the whale, which released a burst of gas trapped inside. The carcass already smelled bad, but the gas was “probably the worst smell of my life,” he said.

Sharks have an exceptional ability to smell underwater, but what is foul to humans is apparently not to sharks. “They’ll still feed on remains even if they’re pretty nasty,” says John Chisholm, a shark scientist at the New England Aquarium who has worked with both Skomal and Michalove. He’s seen photos where only blobs of blubber remained of a dead whale; even then, a great white was hanging around.

A dead whale can mean many things, but fundamentally, it is fat, flesh, and bone decomposing very slowly into nothing. All whales eventually sink; on the floor of the deep ocean, they can become “whale falls,” where ocean life dramatically blooms. But some whales briefly float—or sink and then refloat—buoyed by blubber and gas that microbes release inside the decomposing gut. Much of what we know about which whale species float or sink immediately after death comes from the old observations of whalers.

Right whales, like the one that Michalove observed, do tend to float because of their normally ample stores of fat. In fact, intact whale falls of this species are rare, says Michael Moore, a marine biologist at Woods Hole Oceanographic Institution. Right whales don’t usually sink in one piece. “It’s basically going to disintegrate in situ, and bones and other heavy things will end up hitting the bottom, but randomly,” he told me. “You’re just going to get bits raining down as they fall out of the animal.”

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The whale’s floating body also forms a chum slick on the surface—a trail of blood, oil, and chunks of fat and flesh that might stretch for miles across the water. Oil, after all, is what made whales so valuable during the heyday of commercial whaling, and it leaks out when blubber begins to break down. (“The oil slick was so thick, you could almost walk on it,” said Michalove of the whale he saw.) This chum slick is what attracts sharks from afar. Seabirds are drawn to it too. The layer of whale oil actually calms the waters under it; when using a plane to locate a dead whale in the ocean, pilots look for this strip of unusually calm water.

A floating right whale can also become bloated with gas released from decomposition. Without a pressure valve—such as a shark bite—the gas inside builds and builds. The innards liquefy. Eventually, the gas and liquids find a path of least resistance, which is usually the whale’s mouth. “You get this hugely ballooned-out whale, which can become a bomb,” Moore said, “with the guts, the viscera, the lungs, and eventually the bones all departing the carcass.” If the whale is pregnant, “it has been known for the fetus to be launched, like a rocket, through the mouth,” he added. A colleague witnessed this exact event, Moore confirmed, while responding to a report of a dead right whale. The deaths of North Atlantic right whales are tracked especially closely because they are critically endangered, with fewer than 400 left in the world.