The cookie that bit back
Thinking of Sharks, your mind instantly springs to the more well known ones such as the Great white shark (Carcharodon carcharias), Tiger shark (Galeocerdo cuvier) and Scalloped Hammerhead shark (Sphyrna lewini). You do not think straight away of a small half a meter shark known as the Cookie Cutter (Isistius brasiliensis). Aptly named for the cylindrical bite marks it leaves upon its prey. Adult males can grow up to 42 cm (16.5 inches) long, and females grow a little larger, up to 56 cm (22 inches) in total length. The genus name Isistius is in honor of the Egyptian goddess of light, Isis, this homage to the Egyptian goddess is due to the entire lower surface of the body except its throat is bioluminescent, being able to emit a greenish glow. the entirety of the shark is covered in tiny light-producing organs called photophores. These are thought to attract the attention of potential prey, giving this fish yet another of its common names: “luminous shark”.
The cookie cutter although small, is a wide ranging pelagic shark living temperate to tropical waters and climates of the Atlantic and Pacific Oceans. It is often found close to islands as there are suggestions of a higher chance of mating, prey abundance and nursery habitats. However these suggestions as to why the Cookie Cutter is found off the coast of islands is lacking evidence so remain unresolved and open to discovery through field work.
They are typically found in depths of 1000 meters but have been recorded at depths of 3500 meters.
Relative to its body size, the cookie cutter has the largest teeth of all sharks. It uses them to take round chunks out of larger marine creatures. At night the cookie cutter moves closer to the surface to around 90 meters in depth, it uses the unique teeth in its round mouth to take cookie-sized bites from the flesh of larger marine creatures, like dolphins. The bites are not fatal.
The bioluminescent capability the shark has is a tactic to lure larger fish. As the light that is emitted against the dark colour of its throat, makes it appear to be a smaller fish drawing in the larger prey from the cookie cutter to strike. The shark to remain attached to the prey uses its lips to act as a vacuum and the teeth then begin to carve out the distinct cookie shaped hole of flesh. Prey that is common for this shark are large fish such as marlin, tuna, other sharks and stingrays, and marine mammals including seals and whales. The diet can also include whole squid and crustaceans.
Reproduction and Breeding
Male cookiecutters reach maturity at about 36 cm (14 inches) and females mature at roughly 40 cm (16 inches). This species of shark is ovoviviparous, giving birth to pups that develop inside egg cases within the mother. Female Cookie cutter sharks have two functioning uteruses. After a gestation period of 12-22 months 6-12 pups are born from each litter. They are born fully developed and are able to hunt straight away.