Cookie-cutter shark
2008/9 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and Fish
| Cookie-cutter shark | ||||||||||||||||||
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 Drawing by Dr Tony Ayling
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Least Concern
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| Isistius brasiliensis ( Quoy & Gaimard, 1824) |
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 Range of cookie-cutter shark (in blue)
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The cookie-cutter shark, Isistius brasiliensis, also known as the cigar shark or luminous shark, is a small rarely-seen dogfish shark.
Anatomy and morphology
Cookie-cutters are a small about 50 cm (20 in )shark with a cigar shaped body. It has large eyes with green pupils, and prominent triangular teeth used for feeding on the lower jaw. The upper jaw of the shark consists of small teeth. In addition to the sharp teeth, the cookie-cutter shark bears rather fleshy lips. The creature has 2 small dorsal fins located toward the tail. The underside of the shark is bioluminescent, glowing a pale blue-green that matches the background light from the ocean's surface that serves as camouflage to creatures beneath it. However, a small non-luminescent patch appears black, deceiving the shark's prey, smaller predatory fish (like tuna), into thinking the shark is an even smaller fish. When the predatory fish tries to strike at the shark, the shark strikes back, earning itself another meal. This is the only known instance whereby a bioluminescent lure is created by the absence of luminescence (contrast with anglerfish).
Distribution
Worldwide in deep water. The cookie-cutter shark has been found at depths of about 1,000 m (3,300 ft).
Ecology and life history
Feeding ecology
It derived its name from its habit of removing small circular chunks of flesh from cetaceans and large fish. It is hypothesized that the shark seizes its much larger prey with its jaws, then rotates its body to achieve a highly symmetrical cut. They are considered parasites.
Life history
Cookie-cutter sharks reproduce through aplacental viviparity in the same way as great white sharks. Little else is known about their reproduction.
Etymology and taxonomic history
Its name comes from its feeding style in which almost perfectly circular "cookie-cutter" shaped plugs are removed from the skin of marine mammals and larger fish and sharks.
Interaction with humans
There has been little interaction between humans and the cookie-cutter shark. However, there was an incident in which a cookie-cutter shark took a bite out of the rubber sonar dome of a US Navy submarine, causing damage to the housing, and forcing the submarine out of service until the rubber could be replaced. Though this is not considered a "true" interaction, cookie-cutters' distinct marks can be seen on some fish in some supermarkets if you look closely.