Cookiecutter_shark

Cookiecutter shark

The cookiecutter shark, Isistius brasiliensis, also known as the cigar shark or luminous shark, is a small rarely-seen dogfish shark.

Anatomy and morphology

Cookiecutters are a small about 50 cm (20 in) shark with a cigar shaped body. It has large eyes with green pupils, and prominent 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 cookiecutter 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 cookiecutter 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

Cookiecutter 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 "cookiecutter" 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 cookiecutter shark. However, cookiecutter sharks made damaging cuts on the neoprene boots of AN/BQR-19 hydrophone arrays until fiberglass covers were installed to protect the arrays located on a retractable mast in the sail of some United States submarines. There was an incident in which a cookiecutter 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.