Small shark with fascinating features, the Cookiecutter shark (Isistius brasiliensis) is a deepwater dwelling shark from the family Dalatiidae. This Shark got its name from the way it feeds. That is by creating a deep round hole on larger animals as it bites out a chunk of flesh. The injury appears as if cut out with a “cookie-cutter”.
The cookiecutter shark grows just between 16 to 22 inches (42 to 56 cm ) in length. It is a species of small squaliform shark habiting the warm waters of the oceans around the world. These are waters usually close to islands. And, cookiecutter sharks occur as deep as 2.3 miles (3.7 km) below the ocean surface. However, they do a vertical migration of up to 1.9 miles (3 km) each day to get to the water surface usually at dusk and descending back at dawn.
There are records of attacks on humans from this shark species, but very few. A wide variety of marine fish and mammals have cut from the cookiecutter shark. Even more, inanimate objects are not safe from marks made by this shark. As such, submarines and undersea cables also get cut marks from the cookiecutter shark.
Species Variations
There are two species with the common name cookiecutter shark, thus, there is the smalltooth cookiecutter shark also known as the smooth cookiecutter shark or more commonly just cookiecutter shark. And on the other hand, there is the largetooth cookiecutter shark.
The major difference between the two species is that the largetooth cookiecutter shark has much larger lower teeth than its counterpart. This is only noticeable with the sharks’ mouth wide open. They are the same size with roughly similar appearance when their mouth is not open, except, of course for the dark collar around the gills of the cookiecutter shark.
Naming and Scientific Classification of Cookiecutter Sharks
Both the cookiecutter shark and the largetooth cookiecutter shark are from the genus Isistius. This name is after an Egyptian goddess Isis who was the goddess of throne, nature, magic, mothers, children, and of heavenly lights which were the main reason cookiecutter sharks got their name from her. Of course, these sharks are bioluminescent. As such, they have light-emitting cells known as photophores densely covering their entire underside. This makes the cookiecutter shark able to produce a bright green glow at night on its own, hence the name.
The scientific name of the cookiecutter shark is Isistius brasiliensis. This shark got the second part of its species name from its common appearance around Brazil. Another common name of the cookiecutter shark is Cigar shark.
While the largetooth cookiecutter shark is known scientifically as Isistius plutodus. This shark got the second part of its species name from two Greek words plutos meaning “great” and odous meaning “teeth”
Where to Find Cookiecutter Sharks
The cookiecutter shark has a wide distribution throughout the oceans around the world. This shark inhabits the tropical and warm-temperate ocean basins. They occur as far north as Japan and far south as New Zealand. Usually, they occur near islands perhaps, it could be due to reproductive purposes or maybe because they hold a congregation of large prey animals.
In the Atlantic region, there are reports of this shark species in southern Brazil and off the Bahamas in the west. Also, reports of this shark extend to Cape Verde, southern Angola, Guinea to Sierra Leone, and South Africa in the east, and in the south, the Ascension Island.
In the indo-pacific region, the cookiecutter shark has been caught from Mauritius to New Guinea, Australia, and New Zealand. This region also includes the Lord Howe Island, Tasmania, and off Japan.
In the central and eastern pacific, this shark occurs from north Fiji to the Hawaiian Islands and the Galapagos, Easter, and Guadalupe islands towards the east. There are further suggestions that this shark might range as far as California during warm years due to fresh cuts observed on marine mammals.
The largetooth cookiecutter shark is rarer than the smooth cookiecutter shark. In fact, there are reports of only ten individuals to have been caught which extends off the coasts of southern United States, North Africa, Brazil, Australia, and Japan.
How to Identify the Cookiecutter Shark
The cookiecutter shark has a small body in the shape of a cigar with a short conical snout accompanied by peculiar lips adapted for sucking. It has nostrils towards the front with a short flap of skin. The eyes of this Shark are large, oval and green located towards the front of the head, though not in a way they can get much of the binocular vision. After the eyes, on the upper surface of the head comes the shark’s large spiracles. This shark has five pairs of small gill slits.
Dentition
The upper jaw of the cookiecutter shark has about 30 to 37 teeth, while the lower jaw has 25 to 31 larger teeth. Teeth in the upper jaws differ greatly from that of the lower jaw. Thus, the upper jaw has smaller, narrow, and erect teeth and the lower jaw has larger triangular teeth interlocking at the base making the whole set appear like the cutting edge of a saw. This allows the entire teeth row to move when one tooth is touched.
This shark shed it’s lower teeth all at once, unlike most other sharks that shed theirs’ one at a time. Surprisingly, the cookiecutter shark would swallow its teeth as it sheds them. They do this probably to recycle the calcium content.
Fins
The cookiecutter shark has two spineless dorsal fins closely positioned to each other at the far end of the shark’s body. While the two dorsal fins may appear to be of the same size, the second one is slightly later than the first. On the opposite side of this shark in between the first and second dorsal fins is the pelvic fin which is larger than the dorsal fins.
There are the pectoral fins short and with roughly the shape of a trapezoid. This shark does not have an anal fin. And, the caudal fin is broad with a pronounced ventral notch. The lower lobe of the caudal fin is almost as large as the upper lobe.
Skin and Coloration
Roughly square-shaped dermal denticles with slight depressions in the middle, raised at the corners cover the body of this shark. The cookiecutter shark is dark-brown in color which is most prominent at the backside and lighter toward the underside. Also, the entire underside of this shark except for the gill area covered by a dark-brown collar has a dense concentration of “photophores”.
Where the photophores are complex light-emitting organs that produce a clear green glow. Except for the caudal fin with a darker margin, the other fins have translucent margins.
Growth Size and Maturity
The female cookiecutter shark tends to grow larger than the males with a maximum recorded length of 22 inches (56 cm). While the males grow to a maximum length of 16.5 inches (42 cm). Though, the males mature at a length of about 14 inches (35.5 cm), while the females mature when they are about 16 inches (40.6 cm) in length.
Typical Behavior of a Cookiecutter Shark
The cookiecutter shark is a conditional ectoparasite popular for creating neat round holes on the bodies of marine mammals and larger fish through biting. And on the other hand, it can equally swallow smaller prey as a whole.
The fins of this shark are small and weak, thus they mostly hover around the water waiting to ambush its prey. It has a wide gape and a very strong bite. This shark can get a quick burst of speed from its large caudal fin enabling it to catch up with faster prey that comes in range.
An observed 5.5 inches (14 cm) long cookiecutter shark shed as much as 15 sets of the lower teeth by the time it is 20 inches (50.8 cm) in length. All totaling about 435 – 465 teeth with this shark ingesting the teeth as it sheds them.
Cookiecutter sharks tend to travel in schools which may make their luring behavior more efficient and helps to discourage attacks from larger predators.
Feeding Behavior and Diet
The cookiecutter shark is a parasitic feeder leaving a round cookie-cutter injury on the body of its host while biting out a chunk of flesh. This shark can lure its prey with the light produced by the photophores. And, when larger fish approaches this shark, it launches an unexpected attack on the fish. Moreover, it has mouthparts adapted for such attacks.
Thus, the cookiecutter shark first secures itself to the body of its prey with the suctorial lips ensuring a tight seal. Then, it uses the upper pointed teeth to anchor on the body while the very sharp serrated lower teeth slices into its prey. To complete the circular cut, the shark then twists and rotates its body. Afterward, this shark leaves its prey with a perfectly round cut hole as if made by a cookie-cutter.
The prey of the cookiecutter shark includes almost all medium and large-sized animals sharing the same oceanic habitat with it. As a result, bite marks of the cookiecutter shark have been identified on a wide variety of sea animals, for example, cetaceans, pinnipeds, dugong sharks, stingrays, and bony fishes. Other food materials for the cookiecutter shark is the squid which the shark can swallow as a whole, copepods, bristlemouths, crustaceans, and other moderately sized prey.
Mating and Reproduction Behavior
The cookiecutter shark is an ovoviviparous species, as such, they give birth to live pups after developing the embryos in a yolk sac within the uterus of the mother. Thus, the developing embryos are being sustained by yolk until birth.
The female cookiecutter shark has two functional uteri and gives birth to litters ranging from 6 – 12 pups. The gestation period of this shark species is not known, however, there are speculations that it has a long gestation period. This suggestion came from a record of female cookiecutter shark carrying 9 embryos about 4.9 to 5.2 inches (12.4 to 13.7 cm) in length almost the birth size. But, the yolk sac is still well-developed, meaning there is a slow rate of yolk absorption, thus a long gestation period. There was a noticeable brown pigmentation on the embryos, but no dark collar nor differentiated teeth
At birth, the pups of this shark measure about 5.5 to 5.9 inches (14 to 15 cm) in length. Just a little is known about the mating process of the cookiecutter shark. There is a belief that this species may be using oceanic islands as nursery habitats.
The Essence of the Bioluminescence
The green luminescence of the cookiecutter shark originating from the photophores is the strongest of any known shark. In fact, it persists for three hours after the death of the shark. This shark engages in counter-illumination which is a strategy that allows bioluminescent organisms to hide their figure in the light. Therefore, the cookiecutter shark’s ventrally positioned photophores help to disrupt its figure from below as it matches the light shining downward.
The individual photophores are very small and set around the denticles that they cannot be seen with the naked eyes. This means that the bioluminescence of the cookiecutter shark evolved so much to deceive even animals with high visual acuity and at close range.
The darker collar of this shark that is non-luminescent tends to taper at both sides of the throat, hence researchers suggest it serves as a lure by mimicking the figure of a small fish from below. More so, when in school, the appeal of the lure would definitely increase. Although these are mere hypotheses, if the collar happens to function in such a way, then the cookiecutter shark would be the only known case of bioluminescence in which light absence attracts prey, while the photophores serve to prevent detection by predators.
The vertical migration of the cookiecutter shark may serve to preserve the effectiveness of its disguise at various times of the day and weather conditions This is because the bioluminescence of this shark can only match a limited range of light intensities.
Interaction with Humans
Due to its preferred off-shore and deepwater habitat, the cookiecutter shark rarely encounters humans. Thus, it is safe to say that this shark species is harmless to humans considering also their small size. However, there have been few records of unprovoked attacks on humans by this shark.
Cookiecutter sharks have no economic value and only sometimes taken as bycatch. In fact, this shark appears to be more of a nuisance to commercial fisheries than of value. This shark cause damages on fishing nets and inflicts injury on species of more economic value, although these may only create a minor negative effect.
There are reports of cookiecutter sharks attack on submarines causing damages that forced them back to base. More so, this shark causes damage to oceanographic equipment and telecommunication cables.
Threats and Conservation
There is no significant threat to the population of cookiecutter sharks. Also, this shark has a worldwide distribution. All these are factors that led to the IUCN assessment of this species as Least Concern (LC).
Amazing Cookiecutter Shark Facts at a Glance
1. The Cookiecutter Shark is a Cinematic Star
This shark species played a supporting role in the 2011 horror film Shark Night 3D.
2. Largest Teeth of All Sharks
Even as small as cookiecutter sharks are they have very large teeth. Interestingly, their teeth are the largest of all shark species including the dreaded teeth of the great white shark.
3. Liver Constitute 35% of Overall Shark Weight
The cookiecutter shark has a large liver comprising about 35% of the shark’s weight. This liver is rich in a low-density lipid that accounts for the overall buoyancy of the shark.
4. Cookiecutter Sharks Glows
The whole of the ventral side (underside) except for the collar region is covered with tiny light-emitting organs known as photophores. These produce a vivid green glow through the process of bioluminescence.
5. They Swallow Their Teeth After Shedding
This shark species lose all of its lower teeth at once and even swallows them, probably in an attempt to recycle the calcium content.
6. Isistius is a name After an Egyptian Goddess
The genus name of the cookiecutter shark Isistius is after an Egyptian goddess of heavenly lights Isis. Certainly, this follows the bioluminescence characteristics of this.
7. They are Schooling Sharks
Cookiecutter sharks travel in schools. Probably as a result of this behavior, they efficiently lure their prey and defend themselves again predators.
8. Cookiecutter Sharks are Parasitic
This implies that the cookiecutter shark feeds off larger sea animals without having to kill them, thus, they only bite off a chunk of flesh.
9. They are Among the Smallest Sharks
Cookiecutter sharks do not grow large and are among the smallest sharks known, but this does not hinder its “mischievious” activities.
10. Their Glow Persist Even After Death
Reports have it that the light emitted by the cookiecutter shark persists after the shark dies for up to 3 hours.
Final Thoughts
The Cookiecutter shark (Isistius brasiliensis) is a shark of small size, but, its activities in the marine world speak louder of it. From attacking almost all the sea animals inhabiting the same water with to attacking inanimate objects. This shark is a good example of “small but mighty”.
The population of this shark lacks any pronounced threat, hence the Least Concern status in the IUCN Red List. However, there is still a need to monitor their population just in case.
Further Reading
- “Cookiecutter Shark”, Wikipedia (edited 17 January 2020), Wikipedia. Online here
- “Isistius brasiliensis (Cookiecutter Shark)”, IUCN Red List of threatened species. Online here
- “Largetooth Cookiecutter Shark”, Wikipedia (edited 26 December 2019), Wikipedia. Online here
- “10 Interesting Facts About Cookiecutter Shark”, ipfactly. Online here
- “13 Amazing Facts About Cookiecutter Shark”, Sharksider. Online here