Cookiecutter Shark (Isistius brasiliensis)

Today’s blog entry is a nasty little creature. I first came across them back when I did my post on Oceanic Dolphins, and found a picture of a dolphin with a circular wound on its side. That kind of cut is specific to today’s animal, the cookiecutter shark.

Cookiecutter sharks are members of the dogfish family, and live all over the world. They tend to stay in the warmer areas of the world, not venturing into the frigid Arctic or Antarctic regions. Cookiecutter sharks are mostly deep-water animals, that spend the day at depths of up to 3.7km. At night they travel closer to the surface, but still stays below 85m  for the most part.

The defining feature of the cookiecutter shark is its feeding method. Cookiecutter sharks have specially designed jaws, lips and teeth that help it perform its namesake bite. Cookiecutters latch onto big prey with its loose lips, and sucks its tongue into its throat while closing openings behind its eyes to create suction. Once the shark has latched on, it uses its upper teeth to anchor itself. These teeth are thin and narrow, while the shark’s lower teeth are broader and linked at the bottom to form a saw-like edge. After the top teeth have gripped the poor shark’s victim, the cookiecutter wiggles around until its bottom teeth saw a hole in the animal. It’s pretty nasty stuff. Except for the shark, who swims away with a chunk of meat and a tasty meal.

The fearsome bottom teeth of a cookiecutter shark. They regrow their bottom teeth all at once, and swallow each old set to reuse the calcium.

The fearsome bottom teeth of a cookiecutter shark. They regrow their bottom teeth all at once, and swallow each old set to reuse the calcium.

Cookiecutter sharks are fairly small, growing at most to 50cm. They attack all kinds of animals, including other sharks, whales, big fish, and even submarines. In order to attack such dangerous prey, the cookiecutter shark has to be very sneaky. Luckily for the shark, it has some neat adaptations that help it with this. One is its ability to hover in the water; this helps the shark stay still to avoid detection. It can hover mainly due to its large liver, which is filled with tons of oils that increase the shark’s buoyancy. The other adaptation is the cookiecutter’s bioluminescent photophores that line its belly. These help the shark blend into the water, by imitating the light shining through the water. To further confuse other animals, the cookiecutter shark has a dark collar right behind its gills. From below, this contrasts with the shark’s photophores and the incoming light to look like a small fish. Any predator that comes looking for an easy meal gets a bit of a surprise when they’re met by a cookiecutter shark.

A classic cookiecutter bite. Pretty nasty looking, isn't it?

A classic cookiecutter bite. Pretty nasty looking, isn’t it?

Cookiecutter sharks are nasty animals – some whales that have beached on shore reportedly have hundreds of cookiecutter bites on them. Although I don’t think what cookiecutters do is very friendly, it is quite ingenuous, and I can’t begrudge any animal a good meal.

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3 thoughts on “Cookiecutter Shark (Isistius brasiliensis)

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