Cookiecutter shark - Isistius brasiliensis
WHAT TO LOOK FOR
A small cigar-shaped shark with a very short bulbous snout. The shark has suctorial lips, its dorsal fins are set far back, and it has a large, nearly symmetrical paddle-shaped caudal fin with a long ventral lobe.
Medium grey or grey-brown with light-edged fins and a prominent dark collar mark around its throat. Luminous organs cover its lower surface except for the fins and collar, which glow bright green.
Males mature at a length of 1 to 1.2 ft [31 to 37 cm], while females mature at 1.2 to 1.4 ft [38 to44 cm]. The maximum length for males is more than 1.3 ft [39 cm], and for females it is greater than 1.6 ft [50 cm].
The shark has large, triangular lower teeth in 25-31 rows.
The shark is a wide-ranging tropical oceanic shark, epipelagic to bathypelagic. It can range from the surface to more than 11482.9 ft [3500 m] deep, but usually range from 278.9 to 11482.9 ft [85-3500 m]. These sharks are often found near islands, which are possibly their pupping grounds or where concentrations of prey are located.
Atlantic, southern Indian and Pacific Oceans.
General – The shark has a large, oil-filled liver, body cavity, and small fins which suggest a neutral buoyancy (or may compensate for highly calcified skeleton). Its lower teeth are swallowed as they are replaced in rows (perhaps to recycle calcium).
Prey – Feeds on deepwater fish, squid, and crustaceans.
Reproduction – Presumably ovoviviparous, with about 6-7 pups per litter.
Cookiecutter sharks are poor swimmers, and generally only caught at night. They probably migrate vertically from deep water [2000-3000 m] to midwater or surface at night. They are an ectoparasite on large fish and cetaceans, which are possibly lured to the shark by its bioluminescent light organs. Its thick lips and modified pharynx are used to attach itself to the prey, then razor-sharp lower teeth bite into the skin and twisting movements cut out a plug of flesh. Once cut out, the shark pulls free, holding the plug of tissue by its hook-like upper teeth and leaving behind a crater wound. Reported to have attacked rubber sonar domes on nuclear submarines and there is a case (GSAF 2009.03.17) in which a long-distance swimmer was bitten by a Cookiecutter shark. Can be active and bite when caught.
These sharks are too small to be taken by most fishers.