Cookie-cutter Shark
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The cookiecutter shark (''Isistius brasiliensis''), also called the cigar shark, is a
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of small squaliform shark in the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Dalatiidae The Dalatiidae are the family of kitefin sharks of the order Squaliformes (the term "kitefin shark" also refers specifically to the species '' Dalatias licha''). Members of this family are small, under long, and are found worldwide. They have c ...
. This shark lives in warm, oceanic waters worldwide, particularly near islands, and has been recorded as deep as . It migrates vertically up to every day, approaching the surface at dusk and descending with the dawn. Reaching only in length, the cookiecutter shark has a long, cylindrical body with a short, blunt snout, large eyes, two tiny spineless
dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...
s, and a large
caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...
. It is dark brown, with light-emitting
photophore A photophore is a specialized anatomical structure found in a variety of organisms that emits light through the process of boluminescence. This light may be produced endogenously by the organism itself (symbiotic) or generated through a mut ...
s covering its underside except for a dark "collar" around its throat and
gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In c ...
s. The name "cookiecutter shark" refers to its feeding method of gouging round plugs, as if cut out with a
cookie cutter A cookie cutter in North American English, also known as a biscuit cutter outside North America, is a tool to cut out cookie/biscuit dough in a particular shape. They are often used for seasonal occasions when well-known decorative shapes are ...
, out of larger animals. Marks made by cookiecutter sharks have been found on a wide variety of
marine mammal Marine mammals are mammals that rely on marine ecosystems for their existence. They include animals such as cetaceans, pinnipeds, sirenians, sea otters and polar bears. They are an informal group, unified only by their reliance on marine enviro ...
s and fishes, and on
submarine A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or infor ...
s,
undersea cable Submarine cable is any electrical cable that is laid on the seabed, although the term is often extended to encompass cables laid on the bottom of large freshwater bodies of water. Examples include: *Submarine communications cable A submarine ...
s, and human bodies. It also consumes whole smaller prey, such as
squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...
. Cookiecutter sharks have
adaptation In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the p ...
s for hovering in the water column, and likely rely on stealth and subterfuge to capture more active prey. Its dark collar seems to mimic the silhouette of a small fish, while the rest of its body blends into the downwelling light via its ventral photophores. When a would-be predator approaches the lure, the shark attaches itself using its
suctorial Suctorial pertains to the adaptation for sucking or suction, as possessed by marine parasites such as the Cookiecutter shark, specifically in a specialised lip organ enabling attachment to the host. Suctorial organs of a different form are possesse ...
lips and specialized
pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...
and neatly excises a chunk of the flesh using its
bandsaw A bandsaw (also written band saw) is a power saw with a long, sharp blade consisting of a continuous band of toothed metal stretched between two or more wheels to cut material. They are used principally in woodworking, metalworking, and lum ...
-like set of lower teeth. This species has been known to travel in
school A school is the educational institution (and, in the case of in-person learning, the Educational architecture, building) designed to provide learning environments for the teaching of students, usually under the direction of teachers. Most co ...
s. Though rarely encountered because of its oceanic
habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
, a handful of documented attacks on humans were apparently caused by cookiecutter sharks. Nevertheless, this diminutive shark is not regarded as dangerous to humans. The
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...
has listed the cookiecutter shark under
least concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...
, as it is widely distributed, has no commercial value, and is not particularly susceptible to
fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life or, more commonly, the site where such enterprise takes place ( a.k.a., fishing grounds). Commercial fisheries include wild fisheries and fish farm ...
.


Taxonomy

French
naturalist Natural history is a domain of inquiry involving organisms, including animals, fungi, and plants, in their natural environment, leaning more towards observational than experimental methods of study. A person who studies natural history is cal ...
s
Jean René Constant Quoy Jean René Constant Quoy (10 November 1790 in Maillé, Vendée, Maillé – 4 July 1869 in Rochefort, Charente-Maritime, Rochefort) was a French naval surgeon, zoologist and anatomist. In 1806, he began his medical studies at the school of naval ...
and
Joseph Paul Gaimard Joseph Paul Gaimard (31 January 1793 – 10 December 1858) was a French naval surgeon and naturalist. Biography Gaimard was born at Saint-Zacharie on January 31, 1793. He studied medicine at the naval medical school in Toulon, subsequen ...
originally described the cookiecutter shark during the 1817–1820 exploratory voyage of the
corvette A corvette is a small warship. It is traditionally the smallest class of vessel considered to be a proper (or " rated") warship. The warship class above the corvette is that of the frigate, while the class below was historically that of the sloo ...
''Uranie'' under
Louis de Freycinet Louis Claude de Saulces de Freycinet (7 August 1779 – 18 August 1841) was a French Navy officer. He circumnavigated the Earth, and in 1811 published the first map to show a full outline of the coastline of Australia. Biography He was born at M ...
, giving it the name ''Scymnus brasiliensis'' because the
type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...
was caught off Brazil. In 1824, their account was published as part of ''Voyage autour du monde...sur les corvettes de S.M. l'Uranie et la Physicienne'',
Louis de Freycinet Louis Claude de Saulces de Freycinet (7 August 1779 – 18 August 1841) was a French Navy officer. He circumnavigated the Earth, and in 1811 published the first map to show a full outline of the coastline of Australia. Biography He was born at M ...
's 13 volume report on the voyage. In 1865, American
ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 35,800 species of fish had been described as of March 2 ...
Theodore Nicholas Gill Theodore Nicholas Gill (March 21, 1837 – September 25, 1914) was an American ichthyologist, mammalogist, malacologist, and librarian. Career Born and educated in New York City under private tutors, Gill early showed interest in natural histor ...
coined the new genus ''Isistius'' for this species, after
Isis Isis was a major goddess in ancient Egyptian religion whose worship spread throughout the Greco-Roman world. Isis was first mentioned in the Old Kingdom () as one of the main characters of the Osiris myth, in which she resurrects her sla ...
, the
Egyptian god Ancient Egyptian deities are the gods and goddesses worshipped in ancient Egypt. The beliefs and rituals surrounding these gods formed the core of ancient Egyptian religion, which emerged sometime in prehistory. Deities represented natural for ...
dess of light.Bester, C
Biological Profiles: Cookiecutter Shark
. Florida Museum of Natural History Ichthyology Department. Retrieved on January 26, 2010.
One of the earliest accounts of the wounds left by the cookiecutter shark on various animals is in ancient Samoan legend, which held that ''atu'' (
skipjack tuna The skipjack tuna (''Katsuwonus pelamis'') is a perciform fish in the tuna family, Scombridae, and is the only member of the genus ''Katsuwonus''. It is also known as katsuo, arctic bonito, mushmouth, oceanic bonito, striped tuna or victor fish. ...
) entering
Palauli Palauli is a district and village of Samoa, with a population (2016 Census) of 9,300. It consists of two sections on the southern side of Savai'i. The capital is Vailoa which is also referred to as Vailoa i Palauli (Vailoa in Palauli district). ...
Bay would leave behind pieces of their flesh as a sacrifice to Tautunu, the community chief. In later centuries, various other explanations for the wounds were advanced, including
lamprey Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...
s, bacteria, and
invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...
s. In 1971, Everet Jones of the U.S. Bureau of Commercial Fisheries (a predecessor of the
National Marine Fisheries Service The National Marine Fisheries Service (NMFS), informally known as NOAA Fisheries, is a United States federal agency within the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) that is responsible for the ste ...
) discovered the cigar shark, as the cookiecutter shark was then generally known, was responsible. Shark expert
Stewart Springer Stewart Springer (5 June 190623 August 1991) was an American ichthyologist and herpetologist. He was an expert on shark behavior, classification (taxonomy), and population distribution. More than 35 species of sharks, skates, rays, and other cr ...
thus popularized the name "cookiecutter shark" for this species (though he originally called them "demon whale-biters"). Other common names used for this shark include luminous shark, smalltooth cookiecutter shark, and smooth cookiecutter shark.


Description

The cookiecutter shark has an elongated, cigar-shaped body with a short, bulbously rounded snout. The
nostril A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...
s have a very short flap of skin in front. The large, oval, green eyes are placed forward on the head, though not so that
binocular vision Binocular vision is seeing with two eyes. The Field_of_view, field of view that can be surveyed with two eyes is greater than with one eye. To the extent that the visual fields of the two eyes overlap, #Depth, binocular depth can be perceived. Th ...
is extensive. Behind the eyes are large spiracles, positioned on the upper surface of the head. The mouth is short, forming a nearly transverse line, and is surrounded by enlarged, fleshy, suctorial lips. The upper jaw has 30–37 rows of teeth, and the lower jaw has 25–31, 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. The lower teeth are also smooth-edged, but much larger, broader, and knife-like, with their bases interlocking to form a single saw-like cutting edge. The five pairs of
gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In c ...
s are small. The
pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...
s are short and roughly trapezoidal in shape. Two spineless
dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...
s are placed far back on the body, the first originating just ahead of the
pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...
s 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 Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...
is absent. The
caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...
is broad, with the lower lobe almost as large as the upper, which has a prominent ventral notch. The
dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...
s are squarish and flattened, with a slight central concavity and raised corners. The cookiecutter shark is chocolate brown in color, becoming subtly lighter below, and a dark "collar" wraps around the gill region. The fins have translucent margins, except for the caudal fin, which has a darker margin. Complex, light-producing organs called
photophore A photophore is a specialized anatomical structure found in a variety of organisms that emits light through the process of boluminescence. This light may be produced endogenously by the organism itself (symbiotic) or generated through a mut ...
s densely cover the entire underside, except for the collar, and produce a vivid green glow. The maximum recorded length for this species is for males and for females. Cookiecutter shark head.jpg, The cookiecutter shark has a short, rounded head with large, anteriorly placed eyes and a transverse mouth. Isistius brasiliensis SI.jpg, Head Isistius brasiliensis jaws.jpg, Jaws Isistius brasiliensis lower teeth.jpg, Lower teeth Isistius brasiliensis upper teeth.jpg, Upper teeth Cookiecutter shark skull.png, Jaw diagram


Distribution and habitat

Inhabiting all of the world's major tropical and warm-
temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...
oceanic basin In hydrology, an oceanic basin (or ocean basin) is anywhere on Earth that is covered by seawater. Geologically, most of the ocean basins are large Structural basin, geologic basins that are below sea level. Most commonly the ocea ...
s, the cookiecutter shark is most common between the
latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...
s of 20°N and 20°S, where the surface water temperature is . In the
Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...
, it has been reported off the
Bahama The Bahamas, officially the Commonwealth of The Bahamas, is an archipelagic and island country within the Lucayan Archipelago of the Atlantic Ocean. It contains 97 per cent of the archipelago's land area and 88 per cent of its population. It ...
s and southern Brazil in the west,
Cape Verde Cape Verde or Cabo Verde, officially the Republic of Cabo Verde, is an island country and archipelagic state of West Africa in the central Atlantic Ocean, consisting of ten volcanic islands with a combined land area of about . These islands ...
,
Guinea Guinea, officially the Republic of Guinea, is a coastal country in West Africa. It borders the Atlantic Ocean to the west, Guinea-Bissau to the northwest, Senegal to the north, Mali to the northeast, Côte d'Ivoire to the southeast, and Sier ...
to
Sierra Leone Sierra Leone, officially the Republic of Sierra Leone, is a country on the southwest coast of West Africa. It is bordered to the southeast by Liberia and by Guinea to the north. Sierra Leone's land area is . It has a tropical climate and envi ...
, southern
Angola Angola, officially the Republic of Angola, is a country on the west-Central Africa, central coast of Southern Africa. It is the second-largest Portuguese-speaking world, Portuguese-speaking (Lusophone) country in both total area and List of c ...
, and South Africa in the east, and
Ascension Island Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the Atlantic Ocean, South Atlantic Ocean. It is about from the coast of Africa and from the coast of South America. It is governed as part of the British Overs ...
in the south. In the
Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...
region, it has been caught from
Mauritius Mauritius, officially the Republic of Mauritius, is an island country in the Indian Ocean, about off the southeastern coast of East Africa, east of Madagascar. It includes the main island (also called Mauritius), as well as Rodrigues, Ag ...
to
New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...
, Australia, and New Zealand, including
Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...
and
Lord Howe Island Lord Howe Island (; formerly Lord Howe's Island) is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, part of the Australian state of New South Wales. It lies directly east of mainland Port ...
, as well as off Japan. In the central and eastern Pacific, it occurs from
Fiji Fiji, officially the Republic of Fiji, is an island country in Melanesia, part of Oceania in the South Pacific Ocean. It lies about north-northeast of New Zealand. Fiji consists of an archipelago of more than 330 islands—of which about ...
north to the
Hawaiian Islands The Hawaiian Islands () are an archipelago of eight major volcanic islands, several atolls, and numerous smaller islets in the Pacific Ocean, North Pacific Ocean, extending some from the Hawaii (island), island of Hawaii in the south to nort ...
, and east to the Galápagos,
Easter Easter, also called Pascha ( Aramaic: פַּסְחָא , ''paskha''; Greek: πάσχα, ''páskha'') or Resurrection Sunday, is a Christian festival and cultural holiday commemorating the resurrection of Jesus from the dead, described in t ...
, and
Guadalupe Island Guadalupe Island () is a volcanic island located off the western coast of Mexico's Baja California peninsula and about southwest of the city of Ensenada in the state of Baja California, in the Pacific Ocean. The various volcanoes are extinc ...
s. Fresh wounds observed on
marine mammal Marine mammals are mammals that rely on marine ecosystems for their existence. They include animals such as cetaceans, pinnipeds, sirenians, sea otters and polar bears. They are an informal group, unified only by their reliance on marine enviro ...
s suggest this shark may range as far as California in warm years. Based on catch records, the cookiecutter shark appears to conduct a
diel vertical migration Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The adjective "diel" ( IPA: , ) comes from , and refers to a 24-hour ...
up to each way. It spends the day at a depth of , and at night it rises into the upper
water column The (oceanic) water column is a concept used in oceanography to describe the physical (temperature, salinity, light penetration) and chemical ( pH, dissolved oxygen, nutrient salts) characteristics of seawater at different depths for a defined ...
, usually remaining below , but on rare occasions venturing to the surface. This species may be more tolerant of low
dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can ...
levels than sharks in the related genera ''
Euprotomicrus The pygmy shark (''Euprotomicrus bispinatus''), the second-smallest of all the shark species after the dwarf lanternshark, is a squaliform shark of the family Dalatiidae, the only member of the genus Genus (; : genera ) is a taxonomic ran ...
'' and ''
Squaliolus ''Squaliolus'' is a genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV cla ...
''. It is frequently found near islands, perhaps for reproductive purposes or because they hold congregations of large prey animals. 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, respectively. There is no evidence of sex segregation.


Biology and ecology

Best known for biting neat round chunks of tissue from marine mammals and large fish, the cookiecutter shark is considered a
facultative Facultative means "optional" or "discretionary" (antonym ''obligate''), used mainly in biology in phrases such as: * Facultative (FAC), facultative wetland (FACW), or facultative upland (FACU): wetland indicator statuses for plants * Facultative ...
ectoparasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...
, as it also wholly ingests smaller prey. It has a wide gape and a very strong bite, by virtue of heavily
calcified Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...
cranial Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Thi ...
and labial cartilages. With small fins and weak muscles, this
ambush predator Ambush predators or sit-and-wait predators are carnivorous animals that capture their prey via stealth, luring or by (typically instinctive) strategies utilizing an element of surprise. Unlike pursuit predators, who chase to capture prey u ...
spends much of its time hovering in the water column. Its
liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...
, which can comprise some 35% of its weight, is rich in low-density
lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...
s, which enables it to maintain
neutral buoyancy Neutral buoyancy occurs when an object's average density is equal to the density of the fluid in which it is immersed, resulting in the buoyant force balancing the force of gravity that would otherwise cause the object to sink (if the body's de ...
. This species has higher skeletal density than ''Euprotomicrus'' or ''Squaliolus'', and its
body cavity A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human body cavities are the ventral body cavity, a ...
and liver are proportionately much larger, with much higher oil content. Its large caudal fin allows it to make a quick burst of speed to catch larger, faster prey that come in range. 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 has been calculated to have shed 15 sets of lower teeth, totaling 435–465 teeth, from when it was long to when it reached , a significant investment of resources. The shark swallows its old sets of teeth, enabling it to recycle the
calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
content. Unlike other sharks, the
retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...
of the cookiecutter shark has
ganglion cells Introduction In neurophysiology, a ganglion cell is a cell found in a ganglion (a cluster of neurons in the peripheral nervous system). Depending on their location and function, ganglion cells can be categorized into several major groups: * ...
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. This shark has been known to travel in
schools A school is the educational institution (and, in the case of in-person learning, the building) designed to provide learning environments for the teaching of students, usually under the direction of teachers. Most countries have systems of ...
, which may increase the effectiveness of its lure (see below), and discourage attacks by much larger predators.


Bioluminescence

The intrinsic green luminescence 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 A photophore is a specialized anatomical structure found in a variety of organisms that emits light through the process of Bioluminescence, boluminescence. This light may be produced endogenously by the organism itself (symbiotic) or generat ...
serve to disrupt its silhouette from below by matching the downwelling light, a strategy known as
counter-illumination Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength. Marine animals of ...
, that is common among bioluminescent organisms of the
mesopelagic zone The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...
. 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 school 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 inhibit detection by predators. Milius, S. (August 1, 1998).
Glow-in-the-dark shark has killer smudge
'. ''Science News.'' Retrieved on December 15, 2014.
As the shark can only match a limited range of light intensities, it has been suggested that its vertical movements might serve to preserve the effectiveness of its disguise across various times of day and weather conditions.


Feeding

Virtually every type of medium- to large-sized oceanic animal sharing the habitat of the cookiecutter shark is open to attack; bite scars have been found on
cetacean Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...
s (including
porpoise Porpoises () are small Oceanic dolphin, dolphin-like cetaceans classified under the family Phocoenidae. Although similar in appearance to dolphins, they are more closely related to narwhals and Beluga whale, belugas than to the Oceanic dolphi ...
s,
orca The orca (''Orcinus orca''), or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. The only extant species in the genus '' Orcinus'', it is recognizable by its black-and-white-patterned body. A cosmopol ...
s, dolphins,
beaked whale Beaked whales (systematic name Ziphiidae) are a Family (biology), family of cetaceans noted as being one of the least-known groups of mammals because of their deep-sea habitat, reclusive behavior and apparent low abundance. Only three or four of ...
s,
sperm whale The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the Genus (biology), genus ''Physeter'' and one of three extant species in the s ...
s and
baleen whale Baleen whales (), also known as whalebone whales, are marine mammals of the order (biology), parvorder Mysticeti in the infraorder Cetacea (whales, dolphins and porpoises), which use baleen plates (or "whalebone") in their mouths to sieve plankt ...
s),
pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant taxon, extant families Odobenidae (whose onl ...
s (including
fur seal Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family Otariidae. They are much more closely related to sea lions than Earless seal, true seals, and share with them external ears (Pinna (anatomy ...
s,
leopard seal The leopard seal (''Hydrurga leptonyx''), also referred to as the sea leopard, is the second largest species of seal in the Antarctic (after the southern elephant seal). It is a top order predator, feeding on a wide range of prey including cep ...
s and
elephant seal Elephant seals or sea elephants are very large, oceangoing earless seals in the genus ''Mirounga''. Both species, the northern elephant seal (''M. angustirostris'') and the southern elephant seal (''M. leonina''), were hunted to the brink of ...
s),
dugong The dugong (; ''Dugong dugon'') is a marine mammal. It is one of four living species of the order Sirenia, which also includes three species of manatees. It is the only living representative of the once-diverse family Dugongidae; its closest ...
s, larger sharks (including
blue shark The blue shark (''Prionace glauca''), also known as the great blue shark, is a species of requiem shark, in the family Carcharhinidae and the only member of its genus which inhabits deep waters in the world's temperate and tropical oceans. Ave ...
s,
goblin shark The goblin shark (''Mitsukurina owstoni'') is a rare species of deep-sea shark. Sometimes called a "living fossil", it is the only extant representative of the family Mitsukurinidae, a lineage some 125 million years old. This pink-skinned ani ...
s,
basking shark The basking shark (''Cetorhinus maximus'') is the second-largest living shark and fish, after the whale shark. It is one of three Planktivore, plankton-eating shark species, along with the whale shark and megamouth shark. Typically, basking sh ...
s,
great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocea ...
s,
megamouth shark The megamouth shark (''Megachasma pelagios'') is a species of deepwater shark. Rarely seen by Human, humans, it measures around long and is the smallest of the three extant taxon, extant filter-feeding sharks alongside the much larger whale sha ...
s and
smalltooth sand tiger The smalltooth sand tiger or bumpytail ragged-tooth (''Odontaspis ferox'') is a species of Lamniformes, mackerel shark in the family (biology), family Sand shark, Odontaspididae, with a patchy but worldwide distribution in tropical and warm tempe ...
sharks),
stingray Stingrays are a group of sea Batoidea, rays, a type of cartilaginous fish. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae (deepwate ...
s (including
deepwater stingray The deepwater stingray or giant stingaree (''Plesiobatis daviesi'') is a species of stingray and the sole member of the family Plesiobatidae. It is widely distributed in the Indo-Pacific, typically over fine sediments on the upper continental sl ...
s,
pelagic stingray The pelagic stingray (''Pteroplatytrygon violacea'') is a species of stingray in the family Dasyatidae, and the sole member of its genus. It is characterized by the wedge-like shape of its pectoral fin disc, which is much wider than long, as wel ...
s and sixgill stingrays), and
bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...
es (including
billfish The billfish are a group (Xiphioidea) of saltwater fish, saltwater predatory fish characterised by prominent pointed beak, bills (rostrum (anatomy), rostra), and by their large size; some are longer than . Extant billfish include sailfish and m ...
es,
tuna A tuna (: tunas or tuna) is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae ( mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bul ...
s,
dolphinfish ''Coryphaena'' is a genus of marine ray-finned fishes known as the dolphinfishes, and is currently the only known genus in the family Coryphaenidae. The generic name is from Greek κορυφή (''koryphē'', "crown, top") and -αινα (-''aina ...
es, jacks,
escolar The escolar, ''Lepidocybium flavobrunneum'', a species of fish in the family Gempylidae, is found in deep (200–885 metres, or 656–2,904 ft) tropical and temperate waters around the world. It is also known as snake mackerel, ' ( ...
s,
opah The opah, also commonly known as moonfish, sunfish (not to be confused with Molidae), cowfish, kingfish, and redfin ocean pan are large, colorful, deep-bodied Pelagic zone, pelagic lampriform Fish, fishes comprising the genus ''Lampris'', of ...
s, and
pomfret Pomfrets are scombriform fish belonging to the family Bramidae. The family currently includes 20 species across seven genera. Several species are important food sources for humans, especially ''Brama brama'' in South Asia. The earlier form of ...
s).Martin, R.A
Deep Sea: Cookiecutter Shark
ReefQuest Centre for Shark Research. Retrieved on January 26, 2010.
Martin, R.A

ReefQuest Centre for Shark Research. Retrieved on January 26, 2010.
The cookiecutter shark also regularly hunts and eats entire
squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...
with a mantle length of , comparable in size to the shark itself, as well as
bristlemouth The Gonostomatidae are a family of mesopelagic marine fish, commonly named bristlemouths, lightfishes, or anglemouths. It is a relatively small family, containing only eight known genera and 32 species. However, bristlemouths make up for their l ...
s,
copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...
s, and other smaller prey. Parasitic attacks by the cookiecutter shark leave a round "crater wound", averaging across and deep. The prevalence of these attacks can be high: off Hawaii, nearly every adult
spinner dolphin The spinner dolphin (''Stenella longirostris'') is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a ...
bears scars from this species. Diseased or otherwise weakened animals appear to be more susceptible, and in the western Atlantic observations have been made of emaciated beached
melon-headed whale The melon-headed whale (''Peponocephala electra''), also known less commonly as the electra dolphin, little killer whale, or many-toothed blackfish, is a toothed whale of the oceanic dolphin family (Delphinidae). The common name is derived from t ...
s with dozens to 100's of recent and healing cookiecutter shark wounds, while such wounds are rare on non-emaciated beached whales. The impact of parasitism on prey species, in terms of resources diverted from growth or reproduction, is uncertain. The cookiecutter shark exhibits a number of specializations to its mouth and
pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...
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 The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...
) 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 akin to that of an electric carving knife.Martin, R.A
Attacked by a Dogfish
ReefQuest Centre for Shark Research. Retrieved on January 26, 2010.
This shark's ability to create strong suction into its mouth probably also helps in capturing smaller prey such as squid.


Life history

Like other dogfish sharks, the cookiecutter shark is
aplacental viviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that rema ...
, with the developing
embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...
s being sustained by
yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...
until birth. Females have two functional
uteri The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic and fetal development of one or more fertilized eggs until bir ...
and give birth to litters of 6 to 12 pups. A case has been recorded of a female carrying 9 embryos long; though they were close to the birth size, they still had well-developed
yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...
s, suggesting a slow rate of yolk absorption and a long
gestation period In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once i ...
. The embryos had developed brown pigmentation, but not the dark collar or differentiated
dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...
. Newborn cookiecutter sharks are long. Males attain
sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans, it is related to both puberty and adulthood. ''Puberty'' is the biological process of sexual maturation, while ''adulthood'', the condition of being socially recognized ...
at a length of , and females at a length of .


Human interactions

Favoring offshore waters and thus seldom encountered by humans, the cookiecutter shark is not considered dangerous because of its small size. However, it has been implicated in a few attacks on humans; in one case, a school of 30-cm (12 in) long fish with blunt snouts attacked an underwater photographer on an open-ocean dive. Similar reports have come from
shipwreck A shipwreck is the wreckage of a ship that is located either beached on land or sunken to the bottom of a body of water. It results from the event of ''shipwrecking'', which may be intentional or unintentional. There were approximately thre ...
survivors, of suffering small, clean, deep bites during the night. In March 2009,
Maui Maui (; Hawaiian language, Hawaiian: ) is the second largest island in the Hawaiian archipelago, at 727.2 square miles (1,883 km2). It is the List of islands of the United States by area, 17th-largest in the United States. Maui is one of ...
resident Mike Spalding was bitten by a cookiecutter shark while swimming across Alenuihaha Channel. Swimmer Eric Schall was bitten by a cookiecutter shark on March 31, 2019 while crossing the Kaiwi Channel, and suffered a large laceration to his stomach. A second cookiecutter attack occurred in the same spot three weeks later: Isaiah Mojica was attempting the channel swim on April 6, 2019 as part of the
Oceans Seven The Oceans Seven is a marathon swimming challenge consisting of seven open water channel swims. It was devised in 2008 as the swimming equivalent of the Seven Summits mountaineering challenge. It comprises the North Channel, the Cook Strait, th ...
challenge when he was bitten on the left shoulder. A third person attempting to complete the swim was bitten in nearly the same area of the channel: Adherbal Treidler de Oliveira was attempting the swim on July 29, 2019, when he was bitten on the stomach and on the left thigh. Two of the three swimmers were using electrical shark deterrents, but they did not deter the sharks. In 2017, a seven-year-old boy, Jack Tolley, was bitten in the leg while wading in Alma Bay in North Queensland with his family. The shark caused a 7.3 cm wound that was nearly down to the bone. On February 9, 2022, a deep-water swimmer off
Kailua-Kona Kailua-Kona is an unincorporated community and census-designated place (CDP) in Hawaii County, Hawaii, United States. It is most commonly referred to simply as Kona (a name it shares with the district to which it belongs), but also as Kona To ...
,
Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
was bitten on the right foot and calf. In March 2023, Andy Walberer was attacked by two cookiecutter sharks while swimming the Molokai channel. He was able to grab and throw both sharks before serious injury was inflicted. There are several records of human bodies recovered from the water with post-mortem cookiecutter shark bites. During the 1970s, several
U.S. Navy The United States Navy (USN) is the maritime service branch of the United States Department of Defense. It is the world's most powerful navy with the largest displacement, at 4.5 million tons in 2021. It has the world's largest aircraft ...
submarine A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or infor ...
s were forced back to base to repair damage caused by cookiecutter shark bites to the
neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion Rub ...
boots of their AN/BQR-19
sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances ( ranging), communicate with or detect objects o ...
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; the problem was solved by installing
fiberglass Fiberglass (American English) or fibreglass (English in the Commonwealth of Nations, Commonwealth English) is a common type of fibre-reinforced plastic, fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened i ...
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 Oceanography (), also known as oceanology, sea science, ocean science, and marine science, is the scientific study of the ocean, including its physics, chemistry, biology, and geology. It is an Earth science, which covers a wide range of top ...
equipment and telecommunications cables have also been damaged by this species. The harm inflicted by cookiecutter sharks on
fishing net A fishing net or fish net is a net (device), net used for fishing. Fishing nets work by serving as an improvised fish trap, and some are indeed rigged as traps (e.g. #Fyke nets, fyke nets). They are usually wide open when deployed (e.g. by cast ...
s and economically important species may have a minor detrimental effect on
commercial fisheries Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often p ...
. The shark itself is too small to be of value, and is only infrequently taken, as
bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...
, on pelagic longlines and in midwater trawls and
plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
nets. The lack of significant population threats, coupled with a worldwide distribution, has led the
IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...
to assess the cookiecutter shark as of
least concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...
. In June 2018 the
New Zealand Department of Conservation The Department of Conservation (DOC; Māori language, Māori: ''Te Papa Atawhai'') is the public service department of New Zealand charged with the conservation of New Zealand's natural and historical heritage. An advisory body, the New Zealand ...
classified the cookiecutter shark as "Not Threatened" with the qualifier "Secure Overseas" under the
New Zealand Threat Classification System The New Zealand Threat Classification System is used by the Department of Conservation to assess conservation priorities of species in New Zealand. The system was developed because the IUCN Red List, a similar conservation status system, had s ...
.


References

{{Good article Isistius Bioluminescent sharks Parasitic vertebrates Fish described in 1824