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Great white shark with suspected cookie-cutter shark scars. Credit: Gerardo del Villar/Pacific Science

What Bit This Great White Shark? A Cookie-Cutter

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Great white shark with suspected cookie-cutter shark scars. Credit: G. del Villar/Pacific Science.

Every year, between August and December, great white sharks arrive at the western coast of Mexico, and people jump into the ocean to see them. Operators chum the waters to lure in the sharks, while divers enter in floating steel cages.

On 25 August 2010, one of these divers, Gerardo del Villar, saw a great white shark off Guadalupe Island with two odd wounds on its head. One was a crescent-shaped scar. The other was a round crater, still open and bloody. Both were just behind the corner of the young male’s fearsome mouth. Del Villar took photos of the animal and sent them to a team of scientists, including Yannis Papastamatiou from the Florida Museum of Natural History.

He had seen wounds like these before. “A wound from a hook should leave more of a hole and would not be as smooth,” he says.  Instead, Papastamatiou thinks that they were the bite-marks of another shark, just a sixth of the size—a cookie-cutter. “I dont know of any other animal that leaves a bite like that.”

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Cookie-cutter shark, by the NOAA Observer Project

There are three species of cookie-cutter sharks, but only one that’s known to swim off Mexico – Isistius brasiliensis. It looks like a demonic cigar. It’s a small cat-sized animal with chocolate-coloured skin, a rounded snout, and large green eyes. Beneath the bizarre head, its lower jaw contains what looks like a saw—a row of huge, serrated teeth, all connected at their bases.

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Cookie-cutter shark lower teeth, byKarsten Hartel, NOAA

When the cookie-cutter finds a victim, it latches on with its large fleshy lips and bites down with its saw blade. With twisting motions, it scoops out a chunk of flesh, leaving behind circular craters exactly like those that del Villar saw on the great white. These are serious injuries—the biggest craters ever recorded were 5 centimetres wide and 7 centimetres deep. (These chunks are conical, so the cookie-cutter metaphor isn’t quite right; “Ice cream scoop shark” or “watermelon baller shark” are more accurate, if less catchy.)

Shark want cookie

Papastamatiou cautions that we can’t be sure of what happened, but here are some plausible guesses. Cookie-cutters spend the daytime at depths of up to 3,500 metres, where no great whites venture. But they rise to the surface at night, and one of them may have encountered our poor shark during such an excursion.

Cookie-cutters glow. Their entire undersides give off a vivid, green light, except for a dark collar around their throats. Some scientists have suggested that they use this light to turn themselves into bait. The glow matches moonlight and starlight beaming down from above, rendering the sharks invisible to any predators looking up from below. That is, except for the dark collar, which resembles the silhouette of a fish. The predator comes in for a closer look, and the cookie-cutter attacks.

This is all speculation – no one has ever seen a cookie-cutter attack. We only have the scars to go on. But the luring hypothesis could explain why the great white was bitten near its mouth, rather than some less dangerous body part like a tail or underside. Maybe it tried to make a meal of the cookie-cutter and became a meal instead.

If this actually happened, it was probably a rare event. Divers off Guadalupe Island have amassed the largest catalogue of white shark photos, and many individuals have been seen year after year. None of these other individuals had similar wounds. The fact that the youngster had two might mean that the cookie-cutter launched an unsuccessful strike, leaving the crescent-shaped wound, before finally getting a proper mouthful.

Cookie-cutters vs. everything

French naturalists discovered the cookie-cutter in the early 19th century, but no one connected this bizarre creature to the weird craters found on large fish until the 1970s. For years, these wounds were a mystery. People wondered if they were caused by other predators, parasitic lice, lampreys with their round toothy suckers, or even bacterial infections.

The first breakthrough came in 1963, when a man called Donald Strasburg noticed that the cookie-cutter shark would shed its saw-like lower teeth as a single unit. By contrast, other sharks replace their teeth one at a time. In 1971, Everet Jones discovered small conical plugs of flesh in the stomachs of these sharks. He also noticed that their mobile tongues and large lips allow them to form a vacuum on a smooth surface. It became clear that this tiny animal was wounding some of the ocean’s mightiest residents.

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Cookie-cutter shark bites on a Gray's beaked whale, by Avenue

The cookie-cutter has a distinguished track record of turning the tables on top predators. Its list of victims includes: killer whales; at least 48 other species of whale or dolphin; many types of shark; fur, leopard and elephant seals; dugongs; stingrays; and big bony fish like tuna and swordfish. (It’s a risky strategy that occasionally fails–one whole cookie-cutter was found in the stomach of a large tuna.)

Humans are fair game too. In 2004, a Japanese team found the shark’s distinctive circular scars have been found on the corpse of a 60-year-old woman who had likely drowned herself beforehand.  And in 2009, a cookie-cutter bit a man who was attempting the 30-mile swim between Hawaii and Maui at night. The shark carved a chunk out of his chest and calf. (Update: Al Dove interviewed the poor guy!)

The fearless cookie-cutters have even disabled the most dangerous ocean creature of all—the nuclear submarine. They attacked exposed soft areas including electrical cables and rubber sonar domes. In several cases, the attacks effectively blinded the subs, forcing them back to base for repairs. They later returned, fitted with fibreglass coverings.

Yet more bonus material: Here’s a recent video showing a dolphin with a nasty cookie-cutter injury. Hat-tip to Justin Gregg
Justin Gregg

Bonus: Here, from shark scientist David Shiffman, is some sage advice on how to avoid being bitten by a cookie-cutter shark:

@edyong209 Don’t swim at night, over a deep sea trench, while being lit from above by boat-based floodlights.

— David Shiffman (@WhySharksMatter) January 23, 2013

Reference: Hoyos-Padilla, Papastamatiou, O’Sullivan & Lowe. 2013. Observation of an Attack by a Cookiecutter Shark (Isistius brasiliensis) on a White Shark (Carcharodon carcharias). Pacific Science http://dx.doi.org/10.2984/67.1.10

Hat-tip to Douglas Main for alerting me to this story.