Cookiecutter Shark 

The cookiecutter shark (Isistius brasiliensis) lives worldwide and prefers warmer waters near islands. The shark is known for its ability to migrate up from around 2 miles below the ocean’s surface daily.

Known for their distinctive feeding strategy, these sharks take perfectly round ‘bites’ out of much larger animals, leaving behind what looks like the work of a cookiecutter. It’s classified as a facultative ectoparasite and usually works as an ambush predator. 

Join us as we explore the fascinating world of the cookiecutter shark, from its bioluminescent belly to its fearless nature.

Appearance 

The shark has a small size, It can only reach around 22 inches, or 56 centimeters when fully grown. Its body is long and cylindrical. It has a small head with large eyes and a blunt nose. The shark’s body features two small dorsal fins and one large caudal fin. The name “cigar shark” comes from the shape of its body. 

The shark is darkly colored with photophores or spots that emit light, on its underside. It also features a dark band around its throat. The shark also has suctorial lips and a pharynx to cut circular pieces of flesh out of its prey.

The eyes are located toward the front of the head, but far enough back that the shark lacks much of a binocular field of vision. Their skeleton, is cartilaginous and calcified, perhaps to aid in their deep water search for food.

The pelvic fins are larger than the dorsal fins; the pectoral fins are subquadrate in shape. The caudal fin is large with a long ventral lobe. However, the anal fin is absent in this species.

Its teeth have been compared to a bandsaw in the way that they cut through materials. The shark has somewhere from 30-37 erect teeth in the upper jaw and 25-31 rows in the lower jaw. The number varies depending on the size of the animal. 

It attaches itself to its host, turns its body in a circle, and removes a plug of flesh, leaving symmetrical crater wounds or cookie-shaped wounds.

This shark’s luminescence is the strongest of any known shark. Some reports suggest that it can last as long as three hours after the shark has been removed from the water. 

Habitat

The cookiecutter shark lives in Earth’s major tropical or warm ocean basins and near islands. This small fish spends most of its life in the deep water zone. It is common within the Atlantic, around Brazil, Sierra Leone, southern Angola, South Africa, Guinea, and more. It has also been captured around Tasmania, New Zealand, and Australia. The shark might also be found around the Hawaiian Islands and eat in the Galápagos.

The shark engages in what is known as a diel vertical migration of around 1.9 miles or 3 kilometers every day. The shark spends the day at around .5-2.3 miles in depth, then rises up to around 270 feet at night. Sometimes, it’s even been spotted at the surface. 

It travels in schools of other cookiecutter sharks. 

Diet 

The cookiecutter shark gets its common name from its feeding strategy of biting off small circular chunks out of much larger sharks, bony fish, marine mammals, and even human beings.

All ocean animals are at threat from this shark.

This includes megamouth sharks, beaked whales, blue fin tuna, sperm whales, leopard seals, stingrays, tunas, cetaceans, and more. It’s been known to bite undersea cables and even submarines. The shark also eats prey whole, like squid and crustaceans.

It’s believed that these shark hunt stealthily, likely creeping up on prey rather than actively pursuing them. Scientists believe that the dark collar around its neck evolved as a way to mimic the shape of other fish. The shark attaches itself to predators that approach, thinking they’re about to capture a smaller fish.

Like other sharks, it regularly replaces its teeth. But, unlike other sharks, it sheds entire rows of teeth at a time rather than one tooth at a time. It swallows these old sets of teeth in what scientists believe is an effort to increase their calcium content. 

Reproduction

They reproduce through ovoviviparity. Once the pups are fully developed, the mother gives birth to them. They are born as miniature versions of adults, fully capable of fending for themselves.

Males mature at approximately 14 inches (35.6 cm) in length and the females are mature at 16 inches (40.6 cm) in length. The gestation period of these small sharks is unknown, but it’s likely to be around 12 to 22 months, similar to other shark species.

One fascinating aspect of cookiecutter shark reproduction is that the females have a bioluminescent patch on their underside which may play a role in attracting mates.

Threats 

The cookiecutter shark lives deep within the ocean, making it uncommon for human beings to come into contact with the marine animal. This means that it’s also rarely at risk from fisheries.

Despite this, it is sometimes caught within nets meant for other fish as bycatch. This is most common at night when the shark completes its migration towards the surface. Currently, the IUCN lists the shark as “Least Concern,” the lowest level on their conservation status scale. 

5 More Interesting Facts About the Cookiecutter Shark 

1. It is considered harmless to people due to its deep-water habitat as well as its small size.
2. The shark’s luminescence is the strongest of any known shark.
3. It sheds entire rows of teeth at a time rather than one tooth at a time and swallows its old teeth. 
4. This shark’s feeding habits also classify it as a parasite because it harms its prey without killing it.
5.  The bites of cookiecutter sharks can cause significant damage to larger fish and marine mammals.

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