If the Brothers Grimm ever wrote a fairy tale about sharks, it would feature the cookiecutter shark. The cookiecutter shark (Isistius brasiliensis) is seemingly small and unmenacing, with large dark eyes and a pleasant russet brown body color. However, the cookiecutter is equipped with an impressive set of curved jaws and protruding lips–perfect for using a little suction to grip onto unsuspecting pelagic fish before slicing out a near-perfect circle of flesh.
As if that wasn’t enough to make them great fairy tale villains, these sharks may even lure unsuspecting victims close to their mouths with the temptation of a tasty treat. Like many other mesopelagic organisms, cookiecutter sharks have bioluminescent organs on their ventral (bottom) surface. This is actually a form of camouflage, since the light emitted by the organs replaces the light blocked and absorbed by the fish’s body, helping to eliminate a conspicuous silhouette for predators to cue in on. However, the cookiecutter is unusual in that it possesses a dark, non-luminescent band under the neck region. If the rest of the fish is successfully camouflaged, it is hypothesized that this band would then appear to be easy pickings. The unsuspecting “predator” approaches the cookie cutter lure, only to become a snack themselves!
Of course, what we all want to know is whether or not these sharks are seeking to make cut-outs of our own doughy flesh. I was surprised to find a documented report of a cookiecutter bite on a live human, but it is also true that the circumstances were not typical. The swimmer was on a long open water swim at night with a spotlight from a boat. The cookiecutter was most likely attracted to the light and/or the other bioluminescent organisms attracted to the light.
Honebrink, R, R Buch, P Galpin, GH Burgess. 2011. First documented attack on a live human by a Cookiecutter Shark (Squalifornes, Dalatiidae: Isistius sp.). Pacific Science 65:365-374.
Widder, E. 1998. A predatory use of counterillumination by the squaloid shark, Isistius brasiliensis. Environmental Biology of Fishes 53:267-273.