Wildlife Spotlight: Cookie Cutter Shark (Isistius brasiliensus)

By Michael Morris
Published: March 2007

Cookie cutter shark's razor sharp teeth.

Imagine you are a seal or a dolphin. You are swimming in the ocean depths when you spot a glowing something near the sea bottom. You’ve been looking and listening for prey and here it is. You dive down near the creature which is less than two feet long, a slow swimmer, and a perfect meal.

Then it hits you, literally, and bores a doubloon size hole in your flesh. You’ve just had an encounter with the cookie cutter shark.

These strange creatures troll the sea bottom during the day, are murky brown in color with a blunt snout, and thus are hard to identify by their intended predators. The glow is the result of a bioluminescent patch on its ventral side (like the luminescent lure of an angler fish). However, one dark collar around its throat makes the shark appear smaller and it is this bit of illusion that seems to trick its victims.

Cookie cutter sharks are cigar-shaped and like dogfish sharks (family relatives), lack anal fins. They have a row of bottom teeth that look like the serrated strip on a box of aluminum foil, only much sharper. When they attack (whales, seals, tuna, dolphins and even the occasional submarine) the lips lock on to the victim like a suction cup. The top set of teeth is planted, and then they swivel and with their bottom row of razor sharp teeth remove an oval shaped bite of flesh.

Of late, seals that inhabit the Farallones Marine Sanctuary have been observed with the bite marks of these ravenous predators.  "It's not unusual for pinnipeds to come into the Marine Mammal Center with bites from cookie cutter sharks,” says Doreen Gurrola of the Marine Mammal Center.  “It's sad to see their flesh cut away by these voracious creatures, but it's rarely deadly.  Go take a look at the sea lions at Fisherman’s Wharf and you will see the telltale scars caused by these strange sharks."

Although cookie cutter sharks are found worldwide in deep water, the sharks do tend to congregate around islands. Scientists are unsure if this is the result of a larger array of prey or if it might be related to breeding habits.

Humans have little to fear from cookie cutter sharks because they are such deep swimmers. Strangely though, as mentioned above, there are reports of the creature attacking the rubber sonar domes of submarines. One such incident caused damage to the housing to an extent that the submarine had to go to port for repairs.