cookiecutter shark or cigar shark

Taxonomy:

Phylum– Chordata

Class– Chondrichthyles

Subclass– Elasmobranchii

Order– Squaliformes

Common Name– Dogfish Sharks

Family– Dalatiidae

Common Name– Kitefin Sharks

Genus– Isistius

Species– brasiliensis

Status: IUCN Red List LEAST CONCERN

Average Size and Length: Mature male Cookiecutter sharks are between 1-1.2 feet in length on average. The maximum male is greater than 1.3 feet. Females range from 1.2-1.4 feet with a maximum greater than 1.6 feet.

Current Rare Mythical Sightings: The name “Cookiecutter shark” refers to its feeding habit of extracting round plugs out of larger animals, just like you would imagine using a cookie cutter. Marks made by Cookiecutter sharks have been found on a wide variety of marine mammals and fishes, as well as undersea cables, rubber sonar domes on nuclear submarines, and even human bodies!

Teeth and Jaw: The mouth is short, forming a nearly transverse line, and is surrounded by enlarged, fleshy, suctorial lips. About 30–37 tooth rows are in the upper jaw and 25–31 tooth rows are in the lower jaw, increasing with body size. The upper and lower teeth are extremely different; the upper teeth are small, narrow, and upright, tapering to a single, smooth-edged cusp. They are hook-like. The lower teeth are also smooth-edged, but much larger, triangular, broader, and knife-like, with their bases interlocking to form a single saw-like cutting edge. The jaws of a Cookiecutter shark make an unmistakable mark. There are other sharks in this family that behave similar.

The Cookiecutter shark regularly replaces its teeth like other sharks but sheds its lower teeth in entire rows rather than one at a time. A Cookiecutter shark 5.5 inches long has been calculated to have shed 15 sets of lower teeth by the time it is 20 inches long, totaling 435–465 teeth. They swallow the old sets to recycle the calcium content. (Strasburg, D.W. (March 30, 1963). “The Diet and Dentition of Isistius brasiliensis, with Remarks on Tooth Replacement in Other Sharks“.)

It has a wide gape and a very strong bite, by virtue of heavily calcified cranial and labial cartilages.

Head: The Cookiecutter shark has a short, bulbously rounded snout. The nostrils have a very short flap of skin in front. The large, oval, green eyes are placed forward on the head. Behind the eyes are large spiracles, positioned on the upper surface of the head.

Unlike other sharks, the retina of the Cookiecutter shark has retinal ganglion cells concentrated in a concentric area rather than in a horizontal streak across the visual field; this may help to focus on prey in front of the shark. (Bozzano, A.; S.P. Collin (April 2000). “Retinal ganglion cell topography in elasmobranchs“. Brain Behavior and Evolution.)

Denticles: The dermal denticles on the Cookiecutter shark or Cigar shark are squarish and flattened, with a slight central concavity and raised corners.

Tail: The caudal fin of the Cookiecutter shark is broad and paddle-shaped, with the lower lobe almost as large as the upper, which has a prominent ventral notch. It is symmetrical.

Demographic, Distribution, Habitat, Environment and Range: Inhabiting all of the world’s major tropical and warm-temperate oceanic basins, the Cookiecutter shark is most common between the latitudes of 20°N and 20°S, where the surface water temperature is 64–79 °F). It is epipelagic to bathypelagic. Only caught at night, frequently near islands (perhaps for reproductive purposes or because they hold congregations of large prey animals).

In the Atlantic, it has been reported off the Bahamas and southern Brazil in the west, Cape Verde, Guinea to Sierra Leone, southern Angola, and South Africa in the east, and Ascension Island in the south. In the Indo-Pacific region, it has been caught from Mauritius to New Guinea, Australia, and New Zealand, including Tasmania and Lord Howe Island, as well as off Japan. In the central and eastern Pacific, it can be found from Fiji north to the Hawaiian Islands, and east to the Galápagos, Easter, and Guadalupe Islands. Fresh wounds observed on marine mammals suggest that the Cookiecutter shark may range as far as California in warm years. In the northeastern Atlantic, most adults are found between 11°N and 16°N, with the smallest and largest individuals being found in lower and higher latitudes.

Based on catch records, the Cookiecutter shark or Cigar shark appears to conduct a diel vertical migration up to 1.9 miles each way. It spends the day at a depth of 0.62–2.70 miles, and at night it rises into the upper water column, usually remaining below 279 feet, but on rare occasions venturing to the surface. They may be more tolerant of low dissolved oxygen levels than sharks.

Diet: The Cookiecutter shark bites well-ordered, round chunks of tissue from large marine mammals and fish. It also swallows smaller prey whole, like squid.

The Cookiecutter shark or Cigar shark eats every type of medium- to large-sized oceanic animal that shares its habitat. Bite scars have been found on cetaceans (including porpoises, dolphins, Beaked whales, Sperm whales and Baleen whales), pinnipeds (including Fur seals, Leopard seals and Elephant seals), dugongs, sharks (including Blue sharks, Goblin sharks, Basking sharks, Great White sharks, Megamouth sharks and Smalltooth Sand Tiger sharks), stingrays (including deepwater stingrays, pelagic stingrays and sixgill stingrays), and bony fishes (including Billfishes, Tunas, Dolphinfishes, Jacks, Escolars, Opahs, and Pomfrets). The Cookiecutter shark also regularly hunts and eats entire squid with a mantle length of 5.9–11.8 inches, comparable in size to the shark itself, as well as bristlemouths, copepods, and other prey.

Parasitic attacks by the Cookiecutter shark leave a round “crater wound”, averaging 2.0 inches across and 2.8 inches deep. The occurrence of these attacks can be high, leaving large mammals with dozens of bite wounds and scars.

Ram-Suction Index: As we have discussed, both. Its caudal fin allows them to burst speed to ram prey, then followed by suction. The Cookiecutter shark creates strong suction into its mouth.

The Cookiecutter shark exhibits a number of specializations to its mouth and pharynx for its parasitic lifestyle. The shark first secures itself to the body surface of its prey by closing its spiracles and retracting its basihyal (tongue) to create pressure lower than that of the surroundings; its suctorial lips ensure a tight seal. It then bites, using its narrow upper teeth as anchors while its razor-sharp lower teeth slice into the prey. Finally, the shark twists and rotates its body to complete a circular cut, quite possibly aided by the initial forward momentum and subsequent struggles of its prey. The action of the lower teeth may also be assisted by back-and-forth vibrations of the jaw, a mechanism similar to that of an electric carving knife.

Aesthetic Identification: The Cookiecutter shark has an elongated, cigar-shaped body with 5 pairs of small gill slits. The Cookiecutter shark or Cigar shark is medium to dark grey-brown or chocolate brown in color, becoming subtly lighter below, and a dark “collar” wraps around the gill region. The pectoral fins are short and roughly trapezoidal in shape. Two spineless dorsal fins are placed far back on the body, the first originating just ahead of the pelvic fins and the second located just behind. The second dorsal fin is slightly larger than the first, and the pelvic fins are larger than either. The anal fin is absent. he fins have translucent margins, except for the caudal fin, which has a darker margin. Complex, bioluminescent, light-producing organs called photophores densely cover the entire underside, except for the collar, and yield an intense green glow.

Biology and Reproduction: The Cookiecutter shark is scientifically considered a facultative ectoparasite. It has very small fins and weak muscles, and therefore has a liver to compensate and allow it to hover in the water column. To maintain neutral buoyancy, its liver, which can comprise some 35% of its weight, is rich in low-density lipids. The body cavity is also larger. It also has a higher skeletal density.

The inherent green bioluminescence of the Cookiecutter shark is the strongest known of any shark and has been reported to persist for three hours after it has been taken out of water. The ventrally positioned photophores are used as a method of counter illumination. They disrupt its silhouette from below by matching the downwelling light. This is a common trait among bioluminescent organisms of the mesopelagic zone. The individual photophores are set around the denticles and are small enough that they cannot be discerned by the naked eye, suggesting they have evolved to fool animals with high visual acuity and/or at close distances.

Set apart from the glowing underside, the darker, nonluminescent collar tapers at both sides of the throat, and has been hypothesized to serve as a lure by mimicking the silhouette of a small fish from below. The appeal of the lure would be multiplied in a shoal of sharks. If the collar does function in this way, the Cookiecutter shark would be the only known case of bioluminescence in which the absence of light attracts prey, while its photophores serve to prevent premature detection by incoming would-be predators. As the shark can only match a limited range of light intensities, its vertical movements likely serve to preserve the effectiveness of its disguise across various times of day and weather conditions. (Widder, E.A. (November 1998). “A predatory use of counterillumination by the squaloid shark, Isistius brasiliensis“. Environmental Biology of Fishes).

The Cookiecutter shark is more than likely ovoviviparous. Litter size is usually 6-7 pups, but some suggest up to 12. Newborn Cookiecutter sharks measure 5.5–5.9 inches long. Males attain sexual maturity at a length of 14 inches and females at a length of 15 inches.

A case has been recorded of a female carrying 9 embryos 4.9–5.4 inches long; though they were close to the birth size, they still had well-developed yolk sacs, suggesting a slow rate of yolk absorption and a long gestation period. The embryos had developed brown pigmentation, but not the dark collar or differentiated dentition.

Behavioral Traits, Sensing and Intelligence: As mentioned above; unlike other sharks, the retina of the Cookiecutter shark has retinal ganglion cells concentrated in a concentric area rather than in a horizontal streak across the visual field; this may help to focus on prey in front of the shark.

The Cookiecutter shark travels in shoals and behaves much like a parasite (facultative ectoparasite). Travelling in shoals is though to help the effectiveness of their lure. The Cookiecutter shark is considered an ambush predator.

There is no evidence of gender segregation.

Speed: It is a fat shark, therefore a very poor, and slow swimmer so it hovers in the water column instead. The large caudal fin allows for a quick burst of speed to catch larger, faster prey that come in range.

Cookiecutter Shark Future and Conservation: It is widely distributed, has no commercial value, and is not particularly susceptible to fisheries. They are taken as bycatch infrequently. The harm inflicted by cookiecutter sharks on fishing nets and economically important species may have a minor negative effect on commercial fisheries.

Cookiecutter Shark Recorded Attacks on Humans: The Cookiecutter shark is rarely encountered because of its oceanic habitat, but there are a handful of documented attacks on humans were apparently caused by Cookiecutter sharks. However, it is not regarded as highly dangerous to humans.

In March 2009, Maui resident Mike Spalding was bitten by a Cookiecutter shark while swimming across Alenuihaha Channel. Similar reports have come from an under-water photographer on an open-ocean dive, and from shipwreck survivors, of suffering small, clean, deep bites during night time. There are several records of bodies recovered from the water with post-mortem Cookiecutter shark bites.

During the 1970s, several U.S. Navy submarines were forced back to base to repair damage caused by Cookiecutter shark bites to the neoprene boots of their AN/BQR-19 sonar domes, which caused the sound-transmitting oil inside to leak and impaired navigation. An unknown enemy weapon was initially feared, before this shark was identified as the culprit, and the problem was solved by installing fiberglass covers around the domes. In the 1980s, some 30 U.S. Navy submarines were damaged by Cookiecutter shark bites, mostly to the rubber-sheathed electric cable leading to the sounding probe used to ensure safety when surfacing in shipping zones. Again, the solution was to apply a fiberglass coating. Oceanographic equipment and telecommunications cables have also been damaged by this species. (Martin, R.A. Attacked by a Dogfish. ReefQuest Centre for Shark Research.).