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How can a cookie be a cigar? When it’s a parasite! Meet the cookie cutter shark

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Round scars on the flank of a stranded female Gray's beaked whale (Mesoplodon grayi), probably from cookie-cutter shark bites. Photo credit: Avenue.
Round scars on the flank of a stranded female Gray’s beaked whale (Mesoplodon grayi), probably from cookie-cutter shark bites. Photo credit: Avenue.

By Taylor Rudow

When most people hear the word shark, the cookie cutter shark is not the image that comes to mind. With brown skin, large green eyes, and a body that only grows to be 20 inches long, the cookie cutter shark hardly is the image most people have in mind when discussing sharks. In fact, the long, brown shape of the shark is why it also called the cigar shark.

What it lacks in size, the cookie cutter shark (Isistius brasiliensis) makes up for with its unusual teeth that allow the animal to carve a biscuit-sized, circular wound in its victims.  Photo credit: NOAA.
What it lacks in size, the cookie cutter shark (Isistius brasiliensis) makes up for with its unusual teeth that allow the animal to carve a biscuit-sized, circular wound in its victims. Photo credit: NOAA.

While the cookie cutter shark’s appearance is almost comical, its parasitic lifestyle is anything but funny.

A parasite is an organism which feeds off another organism without killing it. The cookie cutter shark (Isistius brasiliensis) is believed to be the only shark that can be classified as a parasite.

Cookie cutter sharks spend their days in deep equatorial waters, usually resting about 3,000 feet below the surface. However, at night these vertical migrators swim toward shallower water to hunt. When the cookie cutter shark finds its prey, it suctions on to the skin using its strong suctorial lips. Once suctioned, its top row of triangular teeth work like a fork to anchor the shark to its meal while its lower teeth work like a screwdriver spinning into the flesh. Through a combination of jaw movements and violent body twisting, the cookie cutter shark is able to remove an almost-perfectly round bite. The bite of a cookie cutter shark can be up to 4 inches in diameter and up to 3 inches deep, making one wonder if a more appropriate name for the shark would be the “ice cream scoop” shark. The bites may be large, but they are not fatal to the host; in fact, whales have been spotted with dozens of scars from past cookie cutter shark encounters.

While tales of the cookie cutter’s bite dissuade the romantic notion of a moonlit swim, the chances of a human getting bitten are extremely low. In fact, the first reported case of a cookie cutter shark attack occurred in 2009 in Hawaii when Mike Spaulding was bitten while attempting a night swim across the channel. Spaulding now boasts an impressive calf scar, but the cookie cutter shark’s bite was hardly life threatening.

Global distribution of the cookie cutter shark (Isistius brasiliensis). Photo credit: Florida Museum of Natural History.
Global distribution of the cookie cutter shark (Isistius brasiliensis). Photo credit: Florida Museum of Natural History.

A human is far from the largest prey cookie cutter sharks have been known to attack. Whales, dolphins, and even great white sharks have been found with cookie cutter wounds, sometimes many of them.

The cookie cutter shark hunts at night with the help of photophores. Bioluminescent photophores are light-emitting organs found along the entirety of the shark’s bottom, with the exception of the neck. It is believed that the green glow makes the shark appear to be a small fish ideal to prey upon. Would-be predators attack the shark, realizing only too late that they were wrong and instead of being the predator, they have now become the next prey for the cookie cutter shark.

Adding to the unusualness of this species, a cookie cutter shark’s bioluminescent photophores have been reported to continue glowing green for three hours after death.

SOURCES:

“14 Facts About the Cookiecutter Shark”

“Cookiecutter Shark”

“Cookiecutter Sharks, Isistius brasiliensis

“Cookie Cutter Shark”

“Deep Sea: The Twilight Zone and Beyond: The Cookiecutter Shark”

“What Bit This Great White Shark? A Cookie-Cutter”

 
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