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Sharks literally puke their guts out — here's why

Sharks literally puke their guts out — here's why


‘I just saw a huge plume of feathers explode on the back of the boat’

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On November 13th, 2010, marine biologist Austin Gallagher was out on a boat in the Florida Keys, when he and his team pulled an 8-foot-long tiger shark on board to tag it with a satellite tracker. Gallagher was straddling the shark to take measurements, when all of a sudden, “I just saw a huge plume of feathers explode on the back of the boat,” he says.

The shark had just puked a bunch of 8- to 9-inch-long feathers. Gallagher couldn’t believe his luck. He’d heard of sharks vomiting when they’re in high-stress situations, but he’d never seen one before. “Oh my god, this finally happened to me,” Gallagher recalls thinking. “I probably had a huge smile on my face.”

See, when sharks are stressed out, they barf — and not just food. Sometimes they puke out their entire stomachs. That happened to a 6-foot-long blue shark that beached in Provincetown, Massachusetts, a couple years ago, for example — and this is what it looked like.

A beached blue shark regurgitated its stomach about two years ago in Provincetown, Massachusetts.
A beached blue shark regurgitated its stomach about two years ago in Provincetown, Massachusetts.
Photo by Center for Coastal Studies / Facebook

Why? Why do sharks do this? Well, some sharks — like tiger sharks — are voracious eaters that pretty much gobble down whatever they find, including things that aren’t very digestible, like bird feathers, turtles shells, or other bones. If a shark finds itself in a high-stress situation — hooked up to fishing gear, for instance, or stranded on a beach — its instinct reaction is to get rid of that foreign, hard-to-digest food right away.

It might be easier to escape on an empty stomach, says Neil Hammerschlag, a shark researcher at the University of Miami. (Snakes, for instance, are also pukers — they’re known for regurgitating big meals if put under sudden stress after eating.) It’s just a stress response, says Gregory Skomal, a senior scientist at Massachusetts Marine Fisheries, just like a pregnant shark tangled in fishing nets might abort its fetus.

Puked up: huge lobster claws, king crabs, feathers, and the beak of a sea turtle

Being lifted up on a boat and held down while someone’s taking measurements isn’t exactly your regular, laid-back swim in the ocean — it’s pretty stressful. So it’s not exactly unusual for biologists like Gallagher to encounter shark barf; in fact, he says he’s observed puke from a dozen to two dozen tiger sharks. One in the Bahamas hocked up “amazing stuff,” including huge lobster claws, king crabs, feathers, and the beak of a sea turtle. “That all came out of one tiger shark,” he says.

But why do sharks barf out their entire stomachs? (This has a scientific name, by the way, and it’s called stomach or gastric eversion.) Apparently, it’s just a way for the sharks to cleanse their stomachs. “It’s basically rinsing it out,” Skomal says. A 2005 paper describing such behavior in a Caribbean reef shark seems to confirm that, saying that sharks do this to remove “indigestible food particles, parasites or mucus.”

In fact, rays — which are closely related to sharks — are also known for hurling their stomachs to rinse them out, to remove “noxious material,” according to a 2000 study published in Nature. Don’t worry, both rays and sharks survive the procedure. In the case of the Caribbean reef shark described in the 2005 paper, the animal retracted its stomach back into its body in less than a second and seemed to be doing just fine. You can see it in this video, by the way:

Some sharks are not as lucky, however. Gallagher says he’s experienced some sharks throwing up their stomach while he was taking measurements. In those cases, he’s helped put the stomachs back into the animals using long objects like pliers, for instance. (Gallagher confirmed he would never do that using his own arm.)

Hammerschlag says he once experienced something even wilder: he was swimming in False Bay, South Africa, when he saw a white shark spew a seal it’d just eaten after being approached by a larger white shark from behind. Maybe the smaller shark was startled? Maybe it didn’t want to get into a fight with the larger shark? In any case, it decided to retch up the seal and then swim away. The larger shark then ate the seal.

“It’s pretty extraordinary, it’s nature in the raw,” Hammerschlag says. “It’s like watching the most amazing documentary, instead you’re kind of living it.”

Bird feathers regurgitated by a tiger shark in 2010.
Bird feathers regurgitated by a tiger shark in 2010.
Photo by Austin Gallagher

White sharks have also been observed puking to make room for more food. This reminds me of the ancient Romans, who were (wrongly) thought to use vomitoriums to barf after a lavish meal so they could eat more. The white sharks — as described in a 2013 paper published in PLoS One by both Hammerschlag and Gallagher — were feasting on baleen whale carcasses off the coast of South Africa: they “would routinely regurgitate large chunks of whale blubber only to immediately return to the carcass and feed once again,” the study says.

The sharks’ motivation wasn’t gluttony, however. Instead, they were probably using the complex sensory structure inside their mouths to assess the quality of the food — if the whale part they’ve just eaten doesn’t meet their standards, they’ll disgorge it in favor of eating a better chunk of meat, says Hammerschlag. That’s pretty rad.

Unfortunately, this type of behavior is rarely spotted, and so it’s hard to confirm exactly why it happens. That’s why Gallagher was so excited when he first experienced the tiger shark puke the bird feathers. (“I guess I’m the shark vomit guy!” Gallagher says.)

“These really unique instances ... provide us insights into the secret lives of these animals,” he says. “I kind of felt honored that I’d finally been able to see something like that.”

Update June 20th 9:15AM ET: This article was originally published on June 2, 2017 and has been updated to include video.