By James Miller
Geographic Range
Pelagic: The cookie-cutter shark is found in seas as far north as Japan and south to Southern Australia. It is a deep-water fish, and wide-ranging, often found near islands.
Biogeographic Regions:
atlantic ocean 
(native ); pacific ocean (native ).
Habitat
Cookie-cutter sharks are wide-ranging creatures, found in tropical oceanic climates all across the world. They tend to be found closer to islands, but they have been caught in open sea, as well.
Physical Description
The cookie-cutter shark is a typical member of the dogfish order; it has no anal fin, a thin, cigar shaped body, and short snout. It has suctorial lips, small upper teeth, and large, triangular cusped lower teeth in 25 to 32 rows. Coloration is medium grey to grey-brown, with a dark collar marking its throat. Females are larger than males, reaching perhaps 20 inches at full size. (Compagno 1984)
Some key physical features:
bilateral symmetry .
Reproduction
Reproduction of the cookie-cutter shark is accomplished through internal fertilization. The male has instead two 'claspers' (pterygopodes), located on his underside in the rear. Fertilization is accomplished by his insertion of one of his claspers into the female's cloaca. Like other small sharks, this shark is oviparous, and the female coats her eggs in a horny casing before attaching them to rocks and seaweed. Hatching can take place after 12 to 22 months. When the young emerge, they are fully developed and capable of hunting for themselves. Males mature at approximately 14 inches and grow to a size of 16 inches, while females mature at 16 inches and reach up to 20 inches (Stoakely 1997).
Behavior
Cookie-cutter sharks are essentially a solitary species, coming together only to mate. They follow a diel cycle of movement, coming closer to the surface at night, when they are more likely to be caught in fishing nets. Even during the night, however, they stay at least 300 feet below the surface. It is unknown exactly how deep they swim during the day, but their depth is thought to exceed two miles. They are often found near islands, but it is uncertain whether this is because of a greater concentration of prey or in order to mate. The oily liver of this species (the super-equivalent to a swim bladder in bony fishes) is larger than that of most similar sharks, and it is thought to allow them to swim to greater depths. Their skeleton, though still cartilaginous, is calcified, perhaps to aid in their deep water forays for food. This species is known to attack submarines, evidently mistaking them for prey. (Compagno 1984)
Key behaviors:
natatorial ; motile .
Food Habits
Like many sharks, the cookie-cutter shark is a carnivore. It attaches itself to its prey with its strong sucking mouth, and then twists about, using its sharp lower teeth to slice out a plug of flesh, which can sometimes be twice as deep as its diameter. It then uses its hook-like upper teeth to hold the plug, while the lower teeth scoop the plug out. Detaching, it swims away to enjoy its meal. It preys on deep water organisms, including crustaceans, squid, large bony fishes, cetaceans, and even large sharks. It is bioluminescent, able to emit a greenish light from its belly. It may use this light to attract the attention of potential victims (Compagno 1984, Roesch 1997).
Economic Importance for Humans: Negative
They have a potential negative impact on fisheries, as they prey on commercially important fish, but damage is slight. The attacks on submarines are considered at most a nuisance. Because of its small size, and deep water habitat, this species is of little or no danger to swimmers and divers.
Other Comments
The cookie-cutter shark often swallows and digests its teeth, which is thought to aid in calcification of the skeleton. Shark copulation is still very much a mystery and has never been observed in the wild (Compagno 1984, Stoakely 1997)
Contributors
James Miller (author), University of Michigan.
