The cookiecutter shark is one of the most interesting sharks in the ocean, and it never grows bigger than 18-20 inches (~50 cm). It gets its common name from its feeding strategy of biting off small chunks of much larger animals (see more below). This species is small and lives much of its life in the deep water column (mesopelagic). It is therefore difficult to study, so there is little known about exactly where it lives, but it has been collected or observed in many places around the world, most significantly in tropical to temperate latitudes.
The cookiecutter shark is a parasite, meaning it feeds off larger animals, without killing them. It uses its sharp, pointed upper teeth to latch on the skin of a much larger shark, bony fish, or marine mammal and its thick, strong, triangular lower teeth to scoop out a mouth-sized chunk of flesh (or blubber). Several species – including bluefin tuna, great white sharks, spinner dolphins, and other large predators – have been observed with one or more scars caused by these sharks. Like all sharks, cookiecutter sharks lose several sets of teeth throughout their lifetimes. This process ensures that they always have sharp, healthy teeth capable of feeding by their preferred strategy. Unlike other species, though, cookiecutter sharks apparently purposely swallow the teeth that they lose. Some scientists believe that to be a result of them living in the nutrient-poor deep water column. By swallowing the relatively large teeth, they may be able to recycle the calcium and other materials important in tooth development.
These sharks are covered with light organs, likely used for either communication or camouflage. Cookiecutter sharks feed closer to the surface at night and in deeper water during the day, so they are almost always in the dark.
Though this species lives in the open ocean, there has been one confirmed case where an individual bit a person. The circumstances that led to that incident, however, are extreme. The person was a distance athlete, swimming a very long distance between islands in Hawaii, at night, surrounded by boats with lights that attracted prey. That swimmer was bitten on the calf, leaving a gruesome scar but otherwise not causing permanent damage.
The cookiecutter shark is not fished commercially, and is only rarely captured accidentally in fisheries targeting other species. Based on a recent analysis, scientists believe the cookiecutter shark to be a species of least concern.