Cookiecutter shark
Encyclopedia
The cookiecutter shark (Isistius brasiliensis), also called the cigar shark, is a species
of small dogfish shark
in the family
Dalatiidae
. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from as deep as 3.7 km (2.3 mi). It migrates vertically
up to 3 km (1.9 mi) every day, approaching the surface at dusk and descending with the dawn. Reaching only 42–56 cm (16.5–22 in) in length, the cookiecutter shark has a long, cylindrical body with a short, blunt snout, large eyes, two tiny spineless dorsal fin
s, and a large caudal fin. It is dark brown in color, with light-emitting photophore
s covering its underside except for a dark "collar" around its throat and gill slit
s.
The name "cookiecutter shark" refers to its feeding habit of gouging round plugs, like a cookie cutter
, out of larger animals. Marks made by cookiecutter sharks have been found on a wide variety of marine mammal
s and fish
es, as well as on submarine
s, undersea cables, and even human bodies. It also consumes whole smaller prey such as squid
. Cookiecutter sharks have adaptation
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
lips and specialized pharynx
and neatly excises a chunk of flesh using its bandsaw-like set of lower teeth. This species has been known to travel in school
s.
Though rarely encountered because of its oceanic habitat
, a handful of documented attacks on humans
were apparently caused by cookiecutter sharks. Nevertheless, this diminutive shark is not regarded as highly dangerous. The International Union for Conservation of Nature (IUCN) has listed the cookiecutter shark under Least Concern
, as it is widely distributed, has no commercial value, and is not particularly susceptible to fisheries.
s Jean René Constant Quoy
and Joseph Paul Gaimard
originally described the cookiecutter shark during the 1817–1820 exploratory voyage of the corvette
Uranie, giving it the name Scymnus brasiliensis because the type specimen 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
's 13-volume report on the voyage. In 1865, American ichthyologist Theodore Nicholas Gill coined the new genus Isistius for this species, after Isis
, the Egyptian goddess of light.
One of the earliest accounts of the wounds left by the cookiecutter shark on various animals is in ancient Samoa
n legend, which held that atu (skipjack tuna
) entering Palauli 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
s, bacteria
, and invertebrate
parasites. In 1971, Everet Jones of the U.S. Bureau of Commercial Fisheries (a predecessor of the National Marine Fisheries Service
) discovered the cigar shark, as it was then generally known, was responsible. Shark expert Stewart Springer
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.
oceanic basin
s, the cookiecutter shark is most common between the latitude
s of 20°N
and 20°S
, where the surface water temperature is 18–26 °C (64.4–78.8 F). In the Atlantic, it has been reported from 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 occurs from Fiji
north to the Hawaiian Islands
, and east to the Galápagos
, Easter
, and Guadalupe Island
s. Fresh wounds observed on marine mammal
s suggest this shark may range as far as California
in favorable, warm years.
Based on catch records, the cookiecutter shark appears to conduct a diel vertical migration
of up to 3 km (1.9 mi) each way. It spends the day at a depth of 1–3.7 km (0.621372736649807–2.3 mi), and at night it rises into the upper water column, usually remaining below 85 m (278.9 ft), but on rare occasions venturing to the surface. This species may be more tolerant of low dissolved oxygen levels than sharks in the related genera Euprotomicrus and Squaliolus
. 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 sexual segregation.
s have a very short flap of skin in front. The large, oval, green eyes are placed forward on the head, though not such that there is extensive binocular vision
. Behind the eyes are large spiracle
s, 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. There are 30–37 tooth rows in the upper jaw and 25–31 tooth rows 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. 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
s are small.
The pectoral fins are short and roughly trapezoidal in shape. Two spineless dorsal fin
s 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. The caudal fin is broad, with the lower lobe almost as large as the upper, which has a prominent ventral notch. The dermal denticles 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 there is a dark "collar" that 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
s densely cover the entire underside, except for the collar, and produce a vivid green glow. The maximum recorded length for this species is 42 cm (16.5 in) for males and 56 cm (22 in) for females.
from marine mammals and large fish, the cookiecutter shark is considered a facultative
ectoparasite, as it also wholly ingests smaller prey. It has a wide gape and a very strong bite, by virtue of heavily calcified
cranial and labial
cartilages. With small fins and weak muscles, this ambush predator
spends much of its time hovering in the water column. To maintain neutral buoyancy
, its liver
, which can comprise some 35% of its weight, is rich in low-density lipid
s. As this species has higher skeletal density than Euprotomicrus or Squaliolus, its body cavity
and liver are proportionately much larger, and the oil content is much higher. Its large caudal fin allows for 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 14 cm (5.5 in) long has been calculated to have shed 15 sets of lower teeth by the time it is 50 cm (19.7 in) long, totaling 435–465 teeth. This represents a significant investment of resources and is probably why the old sets of teeth are swallowed, so that the shark can recycle the calcium
content. Unlike other sharks, the retina
of the cookiecutter shark has ganglion cell
s 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
, which may increase the effectiveness of its lure (see below), as well as discourage counterattacks by much larger predators.
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 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.
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 cetaceans (including porpoise
s, dolphin
s, pilot whale
s, beaked whale
s, sperm whale
s, and baleen whale
s), pinniped
s (including fur seal
s, leopard seal
s, and elephant seal
s), dugong
s, sharks (including blue shark
s, goblin shark
s, and megamouth shark
s), deepwater stingray
s, and bony fishes (including billfish
es, tuna
s, dolphinfishes, jacks
, escolar
s, opah
s, and pomfret
s). The cookiecutter shark also regularly hunts and eats entire squid
with a mantle
length of 15–30 cm (5.9–11.8 in), comparable in size to the shark itself, as well as bristlemouths, copepod
s, and other prey of more modest dimensions.
Parasitic attacks by the cookiecutter shark leave a round "crater wound", averaging 5 cm (2 in) across and 7 cm (2.8 in) deep. The prevalence of these attacks can be high; off Hawaii, nearly every adult spinner dolphin
bears scars from this species. Diseased or otherwise weakened animals appear to be more susceptible; in the western Atlantic, there are records of emaciated beached
melon-headed whale
s with dozens to hundreds of recent and healing cookiecutter shark wounds, while such wounds are rare on nonemaciated 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
for its parasitic lifestyle. The shark first secures itself to the body surface of its prey by closing its spiracle
s and retracting its basihyal (tongue
) to create negative pressure; its suctorial lips ensure a tight seal. It then bites, using its narrow upper teeth as anchors while its lower teeth slices 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. This shark's ability to create strong suction into its mouth is likely also of utility in capturing smaller prey such as squid.
s being sustained by yolk until birth. Females have two functional uterus
es and give birth to litters of six to 12 pups. There is a record of a female carrying 9 embryos 12.4–13.7 cm (4.9–5.4 in) long; though they were close to the birth size, they still had well-developed yolk sac
s, 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
. Newborn cookiecutter sharks measure 14–15 cm (5.5–5.9 in) long. Males attain sexual maturity
at a length of 36 cm (14.2 in), and females at a length of 39 cm (15.4 in).
s; in one notable case, a school of fierce, 30 cm (11.8 in) long fish with blunt snouts attacked an underwater photographer on an open ocean dive. Similar reports have come from shipwreck
survivors, of suffering small, clean, deep bites during nighttime. In March 2009, Maui
resident Mike Spalding was bitten by a cookiecutter shark while swimming across Alenuihaha Channel. There are at least two records of bodies recovered from the water with post-mortem cookiecutter shark bites.
During the 1970s, several U.S. Navy submarine
s were forced back to base for repairs 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 thirty 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.
The harm inflicted by cookiecutter sharks on fishing net
s and economically important species may have a minor negative effect on commercial fisheries. The shark itself is too small to be of value, and is only infrequently taken, as bycatch
, on pelagic longlines and in midwater trawls and plankton
nets. The lack of significant population threats, coupled with a worldwide distribution, has led the IUCN to assess the cookiecutter shark as of Least Concern
.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of small dogfish shark
Squaliformes
Squaliformes is an order of sharks that includes about 97 species in seven families.Members of the order have two dorsal fins, which usually possess spines, no anal fin or nictitating membrane, and five gill slits. In most other respects, however, they are quite variable in form and size...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Dalatiidae
Dalatiidae
Dalatiidae is a family of sharks in the order Squaliformes, commonly known as kitefin sharks . Members of this family are small, under long, and are found worldwide. They have cigar-shaped bodies with narrow heads and rounded snouts...
. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from as deep as 3.7 km (2.3 mi). It migrates vertically
Diel vertical migration
Diel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone...
up to 3 km (1.9 mi) every day, approaching the surface at dusk and descending with the dawn. Reaching only 42–56 cm (16.5–22 in) in length, the cookiecutter shark has a long, cylindrical body with a short, blunt snout, large eyes, two tiny spineless dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s, and a large caudal fin. It is dark brown in color, with light-emitting photophore
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...
s covering its underside except for a dark "collar" around its throat and gill slit
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, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s.
The name "cookiecutter shark" refers to its feeding habit of gouging round plugs, like a cookie cutter
Cookie cutter
A cookie cutter in American English and biscuit cutter in Commonwealth English 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 desired, or for large batches of cookies where simplicity and uniformity...
, out of larger animals. Marks made by cookiecutter sharks have been found on a wide variety of marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es, as well as on submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s, undersea cables, and even human bodies. It also consumes whole smaller prey such as squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
. Cookiecutter sharks have adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
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
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....
lips and specialized pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
and neatly excises a chunk of flesh using its bandsaw-like set of lower teeth. This species has been known to travel in school
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
s.
Though rarely encountered because of its oceanic habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
, a handful of documented attacks on humans
Shark attack
A shark attack is an attack on a human by a shark. Every year around 60 shark attacks are reported worldwide, although death is quite unusual. Despite the relative rarity of shark attacks, the fear of sharks is a common phenomenon, having been fueled by the occasional instances of serial attacks,...
were apparently caused by cookiecutter sharks. Nevertheless, this diminutive shark is not regarded as highly dangerous. The International Union for Conservation of Nature (IUCN) has listed the cookiecutter shark under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
, as it is widely distributed, has no commercial value, and is not particularly susceptible to fisheries.
Taxonomy
French naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
s Jean René Constant Quoy
Jean René Constant Quoy
Jean René Constant Quoy was a French zoologist.Along with Joseph Paul Gaimard he served as naturalist aboard La Coquille under Louis Isidore Duperrey during its circumnavigation of the globe , and the Astrolabe under the command of Jules Dumont d'Urville...
and Joseph Paul Gaimard
Joseph Paul Gaimard
Joseph Paul Gaimard was a French naval surgeon and naturalist.Along with Jean René Constant Quoy he served as naturalist on the ships L'Uranie under Louis de Freycinet 1817-1820, and L'Astrolabe under Jules Dumont d'Urville 1826-1829...
originally described the cookiecutter shark during the 1817–1820 exploratory voyage of the corvette
Corvette
A corvette is a small, maneuverable, lightly armed warship, originally smaller than a frigate and larger than a coastal patrol craft or fast attack craft , although many recent designs resemble frigates in size and role...
Uranie, giving it the name Scymnus brasiliensis because the type specimen was caught off Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
. 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 de Freycinet
Louis Claude de Saulces de Freycinet was a French navigator. He circumnavigated the earth, and was one of the first to produce a comprehensive map of the coastline of Australia.-Biography:...
's 13-volume report on the voyage. In 1865, American ichthyologist Theodore Nicholas Gill coined the new genus Isistius for this species, after Isis
Isis
Isis or in original more likely Aset is a goddess in Ancient Egyptian religious beliefs, whose worship spread throughout the Greco-Roman world. She was worshipped as the ideal mother and wife as well as the matron of nature and magic...
, the Egyptian goddess of light.
One of the earliest accounts of the wounds left by the cookiecutter shark on various animals is in ancient Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
n legend, which held that atu (skipjack tuna
Skipjack tuna
The skipjack tuna, Katsuwonus pelamis, is a medium-sized perciform fish in the tuna family, Scombridae. It is otherwise known as the aku, arctic bonito, mushmouth, oceanic bonito, striped tuna, or victor fish...
) entering Palauli Bay
Palauli
Palauli is a district and village of Samoa, with a population of 8,984. It consists of two sections on the southern side of Savai'i...
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
Lamprey
Lampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...
s, bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, and invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
parasites. In 1971, Everet Jones of the U.S. Bureau of Commercial Fisheries (a predecessor of the National Marine Fisheries Service
National Marine Fisheries Service
The National Marine Fisheries Service is a United States federal agency. A division of the National Oceanic and Atmospheric Administration and the Department of Commerce, NMFS is responsible for the stewardship and management of the nation's living marine resources and their habitat within the...
) discovered the cigar shark, as it was then generally known, was responsible. Shark expert Stewart Springer
Stewart Springer
Stewart Springer, was a world renowned expert on shark behavior, classification , and distribution of shark populations. There are more than 35 species of sharks, skates, rays, and other animals either classified originally by him or named after him.-Education:Springer was a field naturalist,...
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.
Distribution and habitat
Inhabiting all of the world's major tropical and warm-temperateTemperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
oceanic basin
Oceanic basin
Hydrologically, an oceanic basin may be anywhere on Earth that is covered by seawater, but geologically ocean basins are large geologic basins that are below sea level...
s, the cookiecutter shark is most common between the latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s of 20°N
20th parallel north
The 20th parallel north is a circle of latitude that is 20 degrees north of the Earth's equatorial plane. It crosses Africa, Asia, the Indian Ocean, the Pacific Ocean, North America, the Caribbean and the Atlantic Ocean....
and 20°S
20th parallel south
The 20th parallel south is a circle of latitude that is 20 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, Africa, the Indian Ocean, Australasia, the Pacific Ocean and South America....
, where the surface water temperature is 18–26 °C (64.4–78.8 F). In the Atlantic, it has been reported from off the Bahamas and southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
in the west, Cape Verde
Cape Verde
The Republic of Cape Verde is an island country, spanning an archipelago of 10 islands located in the central Atlantic Ocean, 570 kilometres off the coast of Western Africa...
, Guinea
Guinea
Guinea , officially the Republic of Guinea , is a country in West Africa. Formerly known as French Guinea , it is today sometimes called Guinea-Conakry to distinguish it from its neighbour Guinea-Bissau. Guinea is divided into eight administrative regions and subdivided into thirty-three prefectures...
to Sierra Leone
Sierra Leone
Sierra Leone , officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea to the north and east, Liberia to the southeast, and the Atlantic Ocean to the west and southwest. Sierra Leone covers a total area of and has an estimated population between 5.4 and 6.4...
, southern Angola
Angola
Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...
, and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
in the east, and Ascension Island
Ascension Island
Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around from the coast of Africa and from the coast of South America, which is roughly midway between the horn of South America and Africa...
in the south. In the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
region, it has been caught from Mauritius
Mauritius
Mauritius , officially the Republic of Mauritius is an island nation off the southeast coast of the African continent in the southwest Indian Ocean, about east of Madagascar...
to New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, including Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
and Lord Howe Island
Lord Howe Island
Lord Howe Island is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, directly east of mainland Port Macquarie, and about from Norfolk Island. The island is about 11 km long and between 2.8 km and 0.6 km wide with an area of...
, as well as off Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. In the central and eastern Pacific, it occurs from Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
north to the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
, and east to the Galápagos
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
, Easter
Easter Island
Easter Island is a Polynesian island in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian triangle. A special territory of Chile that was annexed in 1888, Easter Island is famous for its 887 extant monumental statues, called moai, created by the early Rapanui people...
, and Guadalupe Island
Guadalupe Island
Guadalupe Island, or Isla Guadalupe is a volcanic island located 241 kilometers off the west coast of Mexico's Baja California peninsula and some 400 kilometers southwest of the city of Ensenada in Baja California state, in the Pacific Ocean...
s. Fresh wounds observed on marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s suggest this shark may range as far as California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
in favorable, warm years.
Based on catch records, the cookiecutter shark appears to conduct a diel vertical migration
Diel vertical migration
Diel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone...
of up to 3 km (1.9 mi) each way. It spends the day at a depth of 1–3.7 km (0.621372736649807–2.3 mi), and at night it rises into the upper water column, usually remaining below 85 m (278.9 ft), but on rare occasions venturing to the surface. This species may be more tolerant of low dissolved oxygen levels than sharks in the related genera Euprotomicrus and Squaliolus
Squaliolus
Squaliolus is a genus of deep-sea dogfish sharks in the family Dalatiidae.-Species:* Squaliolus aliae Teng, 1959 * Squaliolus laticaudus H. M. Smith & Radcliffe, 1912...
. 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 sexual segregation.
Description
The cookiecutter shark has an elongated, cigar-shaped body with a short, bulbously rounded snout. The nostrilNostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s have a very short flap of skin in front. The large, oval, green eyes are placed forward on the head, though not such that there is extensive binocular vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
. Behind the eyes are large spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s, 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. There are 30–37 tooth rows in the upper jaw and 25–31 tooth rows 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. 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 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, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are small.
The pectoral fins are short and roughly trapezoidal in shape. Two spineless dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s 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. The caudal fin is broad, with the lower lobe almost as large as the upper, which has a prominent ventral notch. The dermal denticles 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 there is a dark "collar" that 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
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...
s densely cover the entire underside, except for the collar, and produce a vivid green glow. The maximum recorded length for this species is 42 cm (16.5 in) for males and 56 cm (22 in) for females.
Biology and ecology
Best known for biting neat round chunks of tissueTissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
from marine mammals and large fish, the cookiecutter shark is considered a facultative
Facultative
Facultative means "optional" or "discretionary" , used mainly in biology in phrases such as:* Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production...
ectoparasite, as it also wholly ingests smaller prey. It has a wide gape and a very strong bite, by virtue of heavily calcified
Calcification
Calcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...
cranial and labial
Lip
Lips are a visible body part at the mouth of humans and many animals. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech...
cartilages. With small fins and weak muscles, this ambush predator
Ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...
spends much of its time hovering in the water column. To maintain neutral buoyancy
Neutral buoyancy
Neutral buoyancy is a condition in which a physical body's mass equals the mass it displaces in a surrounding medium. This offsets the force of gravity that would otherwise cause the object to sink...
, its liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, which can comprise some 35% of its weight, is rich in low-density lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
s. As this species has higher skeletal density than Euprotomicrus or Squaliolus, its body cavity
Body cavity
By the broadest definition, a body cavity is any fluid-filled space in a multicellular organism. However, the term usually refers to the space located between an animal’s outer covering and the outer lining of the gut cavity, where internal organs develop...
and liver are proportionately much larger, and the oil content is much higher. Its large caudal fin allows for 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 14 cm (5.5 in) long has been calculated to have shed 15 sets of lower teeth by the time it is 50 cm (19.7 in) long, totaling 435–465 teeth. This represents a significant investment of resources and is probably why the old sets of teeth are swallowed, so that the shark can recycle the calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
content. Unlike other sharks, the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
of the cookiecutter shark has ganglion cell
Ganglion cell
A retinal ganglion cell is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells...
s 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
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
, which may increase the effectiveness of its lure (see below), as well as discourage counterattacks 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 serve to disrupt its silhouette from below by matching the downwelling light, a strategy known as "counterillumination", that is common 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 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 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.
Feeding
Porpoise
Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...
s, dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
s, pilot whale
Pilot whale
Pilot whales are cetaceans belonging to the genus Globicephala. There are two extant species, the long-finned pilot whale and the short-finned pilot whale . The two are not readily distinguished at sea and analysis of the skulls is the best way to tell the difference between them...
s, beaked whale
Beaked whale
Beaked whales are 21 species of toothed whales, members of the family Ziphiidae, are notable for their elongated beaks. Beaked whales are one of the world's most extreme divers. They can dive for long periods—20 to 30 minutes is common, and 85 minute dives have been recorded—and to...
s, sperm whale
Sperm Whale
The sperm whale, Physeter macrocephalus, is a marine mammal species, order Cetacea, a toothed whale having the largest brain of any animal. The name comes from the milky-white waxy substance, spermaceti, found in the animal's head. The sperm whale is the only living member of genus Physeter...
s, and baleen whale
Baleen whale
The Baleen whales, also called whalebone whales or great whales, form the Mysticeti, one of two suborders of the Cetacea . Baleen whales are characterized by having baleen plates for filtering food from water, rather than having teeth. This distinguishes them from the other suborder of cetaceans,...
s), pinniped
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...
s (including fur seal
Fur seal
Fur seals are any of nine species of pinnipeds in the Otariidae family. One species, the northern fur seal inhabits the North Pacific, while seven species in the Arctocephalus genus are found primarily in the Southern hemisphere...
s, leopard seal
Leopard Seal
The leopard seal , also referred to as the sea leopard, is the second largest species of seal in the Antarctic...
s, and elephant seal
Elephant seal
Elephant seals are large, oceangoing seals in the genus Mirounga. There are two species: the northern elephant seal and the southern elephant seal . Both were hunted to the brink of extinction by the end of the 19th century, but numbers have since recovered...
s), dugong
Dugong
The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...
s, sharks (including blue shark
Blue shark
The blue shark is a species of requiem shark, family Carcharhinidae, that inhabits deep waters in the world's temperate and tropical oceans. Preferring cooler waters, blue sharks migrate long distances, for example from New England to South America. Although generally lethargic, they can move very...
s, goblin shark
Goblin shark
The goblin shark, Mitsukurina owstoni, is a deep-sea shark, the sole living species in the family Mitsukurinidae. The most distinctive characteristic of the goblin shark is the unusual shape of its head. It has a long, trowel-shaped, beak-like rostrum or snout, much longer than other sharks' snouts...
s, and megamouth shark
Megamouth shark
The megamouth shark, Megachasma pelagios, is an extremely rare species of deepwater shark. Since its discovery in 1976, only a few megamouth sharks have been seen, with 53 specimens known to have been caught or sighted as of 2011, including three recordings on film...
s), deepwater stingray
Deepwater stingray
The deepwater stingray or giant stingaree 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 slope at depths of . This species reaches in length and in width...
s, and bony fishes (including billfish
Billfish
The term billfish is applied to a number of different large, predatory fish characterised by their large size and their long, sword-like bill. Billfish include the sailfish and marlin, which make up the family Istiophoridae, and the swordfish, sole member of the family Xiphiidae...
es, tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
s, dolphinfishes, jacks
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
, escolar
Escolar
The escolar, Lepidocybium flavobrunneum, a species of fish in the family Gempylidae, is found in deep tropical and temperate waters around the world...
s, opah
Opah
Opah are large, colorful, deep-bodied pelagic Lampriform fish comprising the small family Lampridae . There are only two living species in a single genus: Lampris...
s, and pomfret
Pomfret
Pomfret are perciform fishes belonging to the family Bramidae.They are found in the Atlantic, Indian, and Pacific Oceans, and the largest species, the Atlantic pomfret, Brama brama, grows up to long....
s). The cookiecutter shark also regularly hunts and eats entire squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
with a mantle
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
length of 15–30 cm (5.9–11.8 in), comparable in size to the shark itself, as well as bristlemouths, copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s, and other prey of more modest dimensions.
Parasitic attacks by the cookiecutter shark leave a round "crater wound", averaging 5 cm (2 in) across and 7 cm (2.8 in) deep. The prevalence of these attacks can be high; off Hawaii, nearly every adult spinner dolphin
Spinner Dolphin
The Spinner Dolphin is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which they spin longitudinally along their axis as they leap through the air.-Taxonomy:...
bears scars from this species. Diseased or otherwise weakened animals appear to be more susceptible; in the western Atlantic, there are records of emaciated beached
Beached whale
A beached whale is a whale that has stranded itself on land, usually on a beach. Beached whales often die due to dehydration, the body collapsing under its own weight, or drowning when high tide covers the blowhole.-Species:...
melon-headed whale
Melon-headed Whale
The melon-headed whale is a cetacean of the oceanic dolphin family . It is closely related to the pygmy killer whale and pilot whale, and collectively these dolphin species are known by the common name blackfish. It is also related to the false killer whale...
s with dozens to hundreds of recent and healing cookiecutter shark wounds, while such wounds are rare on nonemaciated 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
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
for its parasitic lifestyle. The shark first secures itself to the body surface of its prey by closing its spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s and retracting its basihyal (tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
) to create negative pressure; its suctorial lips ensure a tight seal. It then bites, using its narrow upper teeth as anchors while its lower teeth slices 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. This shark's ability to create strong suction into its mouth is likely also of utility in capturing smaller prey such as squid.
Life history
Like other dogfish sharks, the cookiecutter shark is aplacental viviparous, with the developing embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s being sustained by yolk until birth. Females have two functional uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
es and give birth to litters of six to 12 pups. There is a record of a female carrying 9 embryos 12.4–13.7 cm (4.9–5.4 in) long; though they were close to the birth size, they still had well-developed yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
s, suggesting a slow rate of yolk absorption and a long gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
. The embryos had developed brown pigmentation, but not the dark collar or differentiated dentition
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...
. Newborn cookiecutter sharks measure 14–15 cm (5.5–5.9 in) long. Males attain sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at a length of 36 cm (14.2 in), and females at a length of 39 cm (15.4 in).
Human interactions
Favoring offshore waters and thus seldom encountered by humans, the cookiecutter shark is not considered very dangerous because of its small size. However, it has been implicated in a few attackShark attack
A shark attack is an attack on a human by a shark. Every year around 60 shark attacks are reported worldwide, although death is quite unusual. Despite the relative rarity of shark attacks, the fear of sharks is a common phenomenon, having been fueled by the occasional instances of serial attacks,...
s; in one notable case, a school of fierce, 30 cm (11.8 in) long fish with blunt snouts attacked an underwater photographer on an open ocean dive. Similar reports have come from shipwreck
Shipwreck
A shipwreck is what remains of a ship that has wrecked, either sunk or beached. Whatever the cause, a sunken ship or a wrecked ship is a physical example of the event: this explains why the two concepts are often overlapping in English....
survivors, of suffering small, clean, deep bites during nighttime. In March 2009, Maui
Maui
The island of Maui is the second-largest of the Hawaiian Islands at and is the 17th largest island in the United States. Maui is part of the state of Hawaii and is the largest of Maui County's four islands, bigger than Lānai, Kahoolawe, and Molokai. In 2010, Maui had a population of 144,444,...
resident Mike Spalding was bitten by a cookiecutter shark while swimming across Alenuihaha Channel. There are at least two records of bodies recovered from the water with post-mortem cookiecutter shark bites.
During the 1970s, several U.S. Navy submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s were forced back to base for repairs by cookiecutter shark bites to the neoprene
Neoprene
Neoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene in general has good chemical stability, and maintains flexibility over a wide temperature range...
boots of their AN/BQR-19 sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
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
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
covers around the domes. In the 1980s, some thirty 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.
The harm inflicted by cookiecutter sharks on fishing net
Fishing net
A fishing net or fishnet is a net that is used for fishing. Fishing nets are meshes usually formed by knotting a relatively thin thread. Modern nets are usually made of artificial polyamides like nylon, although nets of organic polyamides such as wool or silk thread were common until recently and...
s and economically important species may have a minor negative effect on commercial fisheries. The shark itself is too small to be of value, and is only infrequently taken, as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
, on pelagic longlines and in midwater trawls and plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
nets. The lack of significant population threats, coupled with a worldwide distribution, has led the IUCN to assess the cookiecutter shark as of Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
.