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The Cookiecutter Shark (Isistius brasiliensis) is a small, slow-swimming shark. The cookiecutter is
also known as the cigar shark (due to its color and shape), the luminous shark (because it emits a green glow from its belly),
and the Brazilian shark. It is a large-eyed predator that lives in deep tropical ocean waters worldwide, at depths of about
3500 m.
Anatomy: This brown shark grows to be about 20 inches (50 cm) long and has a blunt snout. The dorsal fin is small
and closer to its tail than on most sharks. The large eyes have green pupils. It is harmless to humans and is rarely even
seen by divers. The belly of the cookiecutter shark has a small patch of bioluminescence on it. This patch is thought to lure
fish to it in the dark, deep ocean environment. Hungry fish think the cookiecutter is a smaller fish than it is (because the
patch is smaller than the cookiecutter and that is all they can see in the dark); the cookiecutter can then ambush and bite
the surprised "hunter." The cookiecutter reproduces via aplacental viviparity, but little else is known about its reproduction.
Teeth and Diet: The cookie-cutter shark eats by taking round (cookiecutter-shaped) bites out of its victims with
its long teeth and powerful jaws, mostly attacking large fish and whales (including dolphins). In an attack, the cookiecutter
shark's lips attach to its victim like a suction cup (creating a vacuum). It then uses saw-like teeth that swivel and take
an oval-shaped bite of flesh. The teeth in the lower jaws are large, prominent, and triangular; the teeth in the upper jaws
are smaller.
Classification: Kingdom Animalia, Phylum Chordata, Class Chondrichthyes, Order Squaliformes, Family Squalidae (dogfish sharks), Genus Isistius, Species brasiliensis.
By James Miller
Species: Isistius brasiliensis
Geographic Range
Pelagic: The cookie-cutter shark is found in seas as far north as Japan and south to Southern Australia. It is a deep-water
fish, and wide-ranging, often found near islands.
Habitat
Cookie-cutter sharks are wide-ranging creatures, found in tropical oceanic climates all across the world. They tend to
be found closer to islands, but they have been caught in open sea, as well.
Physical Description
The cookie-cutter shark is a typical member of the dogfish order; it has no anal fin, a thin, cigar shaped body, and short
snout. It has suctorial lips, small upper teeth, and large, triangular cusped lower teeth in 25 to 32 rows. Coloration is
medium grey to grey-brown, with a dark collar marking its throat. Females are larger than males, reaching perhaps 20 inches
at full size. (Compagno 1984)
Reproduction
Reproduction of the cookie-cutter shark is accomplished through internal fertilization. The male has instead two 'claspers'
(pterygopodes), located on his underside in the rear. Fertilization is accomplished by his insertion of one of his claspers
into the female's cloaca. Like other small sharks, this shark is oviparous, and the female coats her eggs in a horny casing
before attaching them to rocks and seaweed. Hatching can take place after 12 to 22 months. When the young emerge, they are
fully developed and capable of hunting for themselves. Males mature at approximately 14 inches and grow to a size of 16 inches,
while females mature at 16 inches and reach up to 20 inches (Stoakely 1997).
Behavior
Cookie-cutter sharks are essentially a solitary species, coming together only to mate. They follow a diel cycle of movement,
coming closer to the surface at night, when they are more likely to be caught in fishing nets. Even during the night, however,
they stay at least 300 feet below the surface. It is unknown exactly how deep they swim during the day, but their depth is
thought to exceed two miles. They are often found near islands, but it is uncertain whether this is because of a greater concentration
of prey or in order to mate. The oily liver of this species (the super-equivalent to a swim bladder in bony fishes) is larger
than that of most similar sharks, and it is thought to allow them to swim to greater depths. Their skeleton, though still
cartilaginous, is calcified, perhaps to aid in their deep water forays for food. This species is known to attack submarines,
evidently mistaking them for prey. (Compagno 1984)
Food Habits
Like many sharks, the cookie-cutter shark is a carnivore. It attaches itself to its prey with its strong sucking mouth,
and then twists about, using its sharp lower teeth to slice out a plug of flesh, which can sometimes be twice as deep as its
diameter. It then uses its hook-like upper teeth to hold the plug, while the lower teeth scoop the plug out. Detaching, it
swims away to enjoy its meal. It preys on deep water organisms, including crustaceans, squid, large bony fishes, cetaceans,
and even large sharks. It is bioluminescent, able to emit a greenish light from its belly. It may use this light to attract
the attention of potential victims (Compagno 1984, Roesch 1997).
Economic Importance for Humans: Negative
They have a potential negative impact on fisheries, as they prey on commercially important fish, but damage is slight.
The attacks on submarines are considered at most a nuisance. Because of its small size, and deep water habitat, this species
is of little or no danger to swimmers and divers.
Other Comments
The first sharks emerged in the early Jurassic, and centuries of evolution have changed them little, other than small improvements
in feeding and swimming apparati. The cookie-cutter shark often swallows and digests its teeth, which is thought to aid in
calcification of the skeleton. Shark copulation is still very much a mystery and has never been observed in the wild (Compagno
1984, Stoakely 1997)
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