The cookiecutter shark (Isistius brasiliensis) is a member of the “sleeper shark” family, Dalatiidae. This group in turn belongs to Order Squaliformes, the dogfish sharks. Physically it looks like a typical dogfish, with a long thin body, a short cone-shaped snout, and no anal fin. The skin is greyish brown, with a darker brown area around the throat and gills, and a lighter belly.
The cookiecutter shark is named after the cookie-shaped wounds that it leaves on the bodies of its prey. This small fish is also known as the cigar shark because of its body shape. It lives in the deep-waters of warmer areas worldwide. Adult males can grow up to 42 cm (16.5″) long, and females grow a little larger, up to 56 cm (22″) in total length.
Cookiecutter Shark Facts
Okay, check this out. These little sharks are crazy cool, in many ways:
Relative to its body size, the cookiecutter has the largest teeth of all sharks. It uses them to take round chunks out of larger marine creatures – their trademark bites can be seen on large fish and whales of the deep ocean. In fact, this shark is such a motivated hunter that it will try to eat the sonar domes of submarines (hmm, I bet rubber doesn’t taste as good as tuna).
When the teeth of this critter are shed, they are sometimes swallowed and digested. This is thought to aid in strengthening the skeleton with calcium (remember that all shark’s skeletons are made of cartilage ) – a process known as calcification. Having a fortified skeleton might be helpful for the deep diving this species does. The cookiecutter shark also has an oily liver that is larger compared the liver of similar sharks, which might also aid them in swimming to greater depths.
The genus name Isistius is in honor of the Egyptian goddess of light, Isis. Why might that be, you ask? The entire lower surface of the body (except for the darker throat) isbioluminescent, being able to emit a greenish glow. It 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”.
Habitat and Range
The cookiecutter is a wide-ranging pelagic shark that lives in the temperate and tropical waters of the Atlantic and Pacific Oceans, around the globe.
It is often found close to islands: this could be because there is a higher concentration of prey, for better mating opportunities, or because areas around islands provide ideal nursery habitat. All of these possibilities have been suggested but no evidence is available to distinguish among them.
These fish are typically found in deep water below 3,281 feet (1000 m) in the daytime, but have been recorded to depths of 3.7 km (2.3 mi).
At night, cookiecutter sharks move closer to the surface to feed, but they still stay at least 90 m (300 ft) deep. The feeding method is very curious: although this species is rather small, 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.
This shark’s mouth is unmistakable: the small teeth in the upper jaw are erect, and the teeth in the lower jaw are large and triangular.
The light emitted from the shark’s belly attracts larger fish. The dark patch of the throat, against the glow of the underside, is thought to appear like a small fish when viewed from deeper waters. This draws in the larger prey that are looking for a meal.
Then, just prior to reaching the cookiecutter, the larger fish is surprised by the shark. (Pretty ingenious and brave of the little guy, huh?) The shark attaches to the prey using its strong, sucking lips, and then the efficient teeth go to work, almost like a can-opener. Targets commonly include 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.
Aside from the feeding method, little is known about these sharks’ biology. They are believed to be mostly solitary, interacting with other members of the species mainly to mate. (However one report suggested that “schools” of these sharks would be very attractive to large prey items, for the bioluminescence would make them look like a school of tiny fish).
Other species that feed on the cookiecutter include sharks and other larger fish.
Male cookiecutters reach maturity at about 36 cm (14″) and females mature at roughly 40 cm (16″). This species is ovoviviparous, giving birth to pups that develop inside egg cases within the mother. Each litter contains 6-12 live young that are born after 12-22 months. They are fully developed at birth, already able to hunt.
Humans and Conservation
Fishers only occasionally trap cookiecutter sharks, because they are so small. This usually happens at night, when the sharks move toward the surface to feed and are thus more likely to be netted. The species targets larger, sought after fish as prey, but this does not have much of an economic effect on fisheries.
Cookiecutter sharks are not considered dangerous to people because they reside in deep-water habitat. However, the first documented bite of a human – a long-distance ocean swimmer – was reported recently (Honebrink et al. 2011). The authors suggest that people entering deep waters at night, in the range of this shark, should be aware.
The conservation status of this species, according to the IUCN Red List, is “Least Concern”.
There is little worry because of its wide distribution, deep-water habitat (making it harder to catch accidentally), and lack of interest to fisheries.
Written By: by Kara Lefevre
Berger M & G (2000). What do sharks eat for dinner? Questions and answers about sharks. Scholastic Inc., NY.
Honebrink R, Buch R, Galpin P & Burgess G (2011). First documented attack on a live human by a Cookiecutter Shark (Squaliformes, Dalatiidae: Isistius sp.). Pacific Science 65: 365-374.
Milius S (1998). Glow-in-the-dark shark has killer smudge. Science News 154 (5): 70.
Stevens J (2003). Isistius brasiliensis. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2.
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