Kitefin shark
Encyclopedia
The kitefin shark or seal shark (Dalatias licha) is a species
of dogfish shark
in the family Dalatiidae
, and the only species
in its genus
. It is found sporadically around the world, usually close to the sea floor at depths of 200–600 m (656.2–1,968.5 ft). With a sizable oil-filled liver
to maintain neutral buoyancy
, this shark is able to cruise slowly through the water while expending little energy. The kitefin shark has a slender body with a very short, blunt snout, large eyes, and thick lips. Its teeth are highly differentiated between the upper and lower jaws, with the upper teeth small and narrow and the lower teeth large, triangular, and serrated. Its typical length is 1–1.4 m (3.3–4.6 ft).
Armed with large teeth and a strong bite, the kitefin shark is a powerful, solitary predator that takes many different types of prey, ranging from bony fishes, sharks and rays, to cephalopod
s, crustacean
s, polychaete worms, siphonophores, and possibly carrion
. It also takes bites out of animals larger than itself, similar to its smaller relative, the cookiecutter shark
(Isistius brasiliensis). This shark is aplacental viviparous and gives birth to 10–14 young. The kitefin shark is fished commercially
for its meat, skin, and liver oil, primarily by Portugal
and Japan
. A fishery targeting this species existed off the Azores
from the 1970s to the 1990s, but collapsed due to overfishing
and falling liver oil prices; the rapid depletion of the Azores stock is often cited as an example of the susceptibility of deep-sea sharks to human exploitation. The low reproductive rate of this species renders it susceptible to overfishing
and, coupled with known population declines, has led it to be assessed as Near Threatened
by the International Union for Conservation of Nature (IUCN).
Pierre Joseph Bonnaterre
, in his 1788 Tableau encyclopédique et méthodique des trois regnes de la nature; the type specimen from "Le cap Breton" has since been lost. This species was later placed in its own genus, Dalatias, which came from the synonymy
of Constantine Rafinesque
's 1810 Dalatias sparophagus with S. licha. However, some authorities dispute this on the grounds that D. sparophagus is a nomen dubium
, and prefer to use the next available genus name Scymnorhinus. The genus name Dalatias is derived from the Greek dalos or dalou, meaning "torch". The specific epithet licha comes from la liche, the French name for this shark. Additional common name
s used for the kitefin shark include black shark and darkie Charlie.
), with which they share several dentition
al, skeletal
, and muscular
similarities. Dalatias and Isistius are believed to have evolutionarily diverged
shortly after the transition between the Cretaceous and Tertiary
periods (65.5 Ma), as part of a larger adaptive radiation
of dogfish sharks from the deep sea into relatively shallower habitats.
The oldest fossil
teeth that definitively belong to the kitefin shark date to the Middle Eocene epoch, such as those recovered from Bortonian-stage deposits (43.0–37.0 Ma) in New Zealand
. Dalatias fossil teeth dating to various ages have also been discovered in Europe
, the former USSR
, Japan, and western India
. The fossil material now recognized as belonging to this species were historically described under a multitude of different names.
in tropical and warm-temperature waters, consisting of a number of widely separated populations with likely little interchange between them. This shark has not been reported from the eastern Pacific and northern Indian Oceans. In the northern Atlantic, it occurs in the Georges Bank
and the northern Gulf of Mexico
, and from the North Sea
to Cameroon
, including around the British Isles
, in the western and central Mediterranean Sea
, and off Madeira
and the Azores
. In the Indian Ocean, it is found off South Africa
and Mozambique
. In the Pacific, it occurs off Japan, Java
, Australia
and New Zealand
, and the Hawaiian Islands
. There is a single record of this species in the southern Atlantic, from off southern Brazil
.
An offshore, deepwater species, the kitefin shark is most common at a depth of 200–600 m (656.2–1,968.5 ft), but has been captured from the surface to as deep as 1800 m (5,905.5 ft). Off the Azores
this shark segregates by sex, with females most common around a depth of 230 m (754.6 ft) and males most common around 412–448 m (1,351.7–1,469.8 ft). The kitefin shark inhabits the outer continental shelves and upper continental slopes, and is also found around oceanic islands and seamount
s. It is the only member of its family that tends to be found close to the sea floor as opposed to in the middle of the water column, though on occasion it has been captured well above the bottom.
The kitefin shark has a moderately elongated body with a very short, rounded snout. The eyes and spiracle
s are large. The lips are thick with pleats or fringes, though are not modified to be suctorial
. There are 16–21 tooth rows in the upper jaw and 17–20 tooth rows in the lower jaw. The upper teeth are small and spike-shaped, curving slightly towards the corners of the mouth. The lower teeth are very large, knife-shaped, and serrated, with their bases interlocking to form a continuous cutting surface.
The first dorsal fin
is slightly smaller and shorter-based than the second, and neither has spines. The first dorsal fin originates behind the free rear tip of the pectoral fins, while the second originates above the middle of the pelvic fin bases. The pectoral fins are short and rounded. The caudal fin has a prominent upper lobe with a well-developed notch near the tip, and a barely present lower lobe. The form and arrangement of the fins is similar to the Portuguese dogfish
(Centroscymnus coelolepis), from which this species can be distinguished by the lack of fin spines. The dermal denticles are small and flat, with a single horizontal ridge ending in a point.
The coloration is a uniform dark brown or gray, sometimes with faint black spots on the back. The fins have white or translucent margins, and the tip of the caudal fin is black. An 90 cm (3 ft) long kitefin shark with partial albinism
, lacking pigment
on 59% of its body, was caught in the Gulf of Genoa
in 2003. Unlike in a previous case of an albino Portuguese dogfish, the abnormal coloration of this individual had not diminished its ability to capture prey. Most kitefin sharks are 1–1.4 m (3.3–4.6 ft) long and weigh 8 kg (17.6 lb); the maximum reported length is 1.6 m (5.2 ft), possibly 1.8 m (5.9 ft).
filled with squalene
, a lipid
less dense than water, allowing it to maintain neutral buoyancy and hover above the bottom with little effort. Studies off the coast of North Africa
and in the Gulf of Genoa have found males outnumbering females by 2:1 and 5:1 respectively; this imbalanced sex ratio
has not been observed off South Africa and may reflect sampling bias. The kitefin shark is preyed upon by larger fishes and sharks, as well as by sperm whale
s (Physeter macrocephalus). Parasite data on this species is limited; an examination of two sharks caught off Ireland
found three nematode
s in the stomach
lumen
. One could be identified as Anisakis simplex L3, while another may have been a larva
l Raphidascaris.
A powerful and versatile deepwater predator, the short, robust jaws of the kitefin shark give it an enormously strong bite. It feeds mainly on bony fishes (including deepwater smelts, viperfish
es, scaly dragonfish
es, barracudina
s, greeneye
s, lanternfish
es, bristlemouths, cod and other gadids
, grenadier
s, deepwater scorpionfish
es, bonito
, snake mackerels, deepwater cardinalfish
es, and sea toad
s), but also takes a wide variety of other animals, including skates, smaller sharks (Galeus
, Squalus, Etmopterus
and Centrophorus
), squid
and octopus
, crustaceans (amphipods, isopods, shrimp
and lobster
s), polychaete worms, and siphonophores. Like the related cookiecutter shark, the kitefin shark is also capable of excising chunks of flesh from animals larger than itself, including other sharks and whale
s. The presence of fast-swimming fishes in its diet suggests the kitefin shark may scavenge, or have some other means of capturing faster prey. In the Mediterranean, bony fishes are the most important food year-round, with the second-most important prey being sharks in the winter and spring, crustaceans in the summer, and cephalopods in the fall. Captured males are more likely to have full stomachs than females for unknown reasons.
Reproduction in the kitefin shark is aplacental viviparous, with the embryo
s hatching inside the uterus
and being sustained to term by yolk. Adult females have two functional ovaries
and two functional uteruses; the uterus is not divided into compartments. In the Mediterranean, breeding occurs throughout the year with peaks in spring and fall; females may have a year of rest in between pregnancies. The litter size is 10–16, increasing with female size. The young are born at a length of 30–45 cm (11.8–17.7 in), varying by geographic location, after a possible gestation period
of two years. The males mature sexually at a length of 77–121 cm (2.5–4 ft), and the females at a length of 117–159 cm (3.8–5.2 ft). There is no relationship between an individual's size at birth, size at maturity, and maximum size.
The kitefin shark inhabits depths too great for it to be a danger to humans. Its upper teeth have been found lodged in underwater fiberoptic cables. This species has a long history of human exploitation: the meat is consumed in the eastern Atlantic and Japan, and the offal
processed into fishmeal. The liver oil is utilized in Portugal, Japan, and South Africa. The skin is made into a type of shagreen
useful in the making of furniture and jewelry, and is also favored for the manufacture of "boroso", a Spanish polished leather
. This shark has no commercial value in the western Atlantic.
The continuing expansion of commercial fisheries into the deep sea has raised concerns about the vulnerability of this and other deepwater shark species to overfishing
, as these sharks have slow growth and reproductive rates. This is exemplified by the rapid stock depletion and collapse of the Azores kitefin shark fishery. This targeted fishery began in the early 1970s for the production of liver oil. In the early 1980s, the fishing fleet was enlarged with the addition of industrial vessels equipped with demersal gillnets, resulting in a fishery peak in 1984 of 937 tons landed. After 1991, kitefin shark catches declined precipitously to under 15 tons annually which, along with a drop in the global price of liver oil, led to the fishery becoming unprofitable by the end of the decade. A population assessment has suggested that the northwestern Atlantic stock had fallen to 50% of the pre-exploitation biomass.
Fisheries operating off Portugal and Japan are responsible for most commercial landings of the kitefin shark, generally as bycatch
in bottom trawls and on hook-and-line. Portugal reported a kitefin shark bycatch of 282 tons in 2000 and 119 tons in 2003. In other areas of the northeastern Atlantic this shark is rare and reported catches are likely confounded by misidentifications of other species; some are caught by mixed-species gillnet
fisheries operating in deep water west of the British Isles, where surveys suggest that kitefin shark numbers may have declined by 94% since the 1970s. In the Mediterranean, this shark is caught incidentally by bottom trawl and gillnet fisheries. Although it is generally discarded alive, many are unable to return to deep water and do not survive. In the Southern Hemisphere, catches by the Australian South East Trawl Fishery are increasing following the relaxation of regulations regarding seafood mercury
content; this species is not included under Australian fishery quota
s. New Zealand kitefin shark catches peaked from 1986 to 1997. The International Union for Conservation of Nature (IUCN) has assessed the kitefin shark as Near Threatened
worldwide, and as Vulnerable
in the northeastern Atlantic in light of documented population declines.
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 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 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...
, and the only species
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
in its genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
. It is found sporadically around the world, usually close to the sea floor at depths of 200–600 m (656.2–1,968.5 ft). With a sizable oil-filled 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...
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...
, this shark is able to cruise slowly through the water while expending little energy. The kitefin shark has a slender body with a very short, blunt snout, large eyes, and thick lips. Its teeth are highly differentiated between the upper and lower jaws, with the upper teeth small and narrow and the lower teeth large, triangular, and serrated. Its typical length is 1–1.4 m (3.3–4.6 ft).
Armed with large teeth and a strong bite, the kitefin shark is a powerful, solitary predator that takes many different types of prey, ranging from bony fishes, sharks and rays, to cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, polychaete worms, siphonophores, and possibly carrion
Carrion
Carrion refers to the carcass of a dead animal. Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters include vultures, hawks, eagles, hyenas, Virginia Opossum, Tasmanian Devils, coyotes, Komodo dragons, and burying beetles...
. It also takes bites out of animals larger than itself, similar to its smaller relative, the cookiecutter shark
Cookiecutter shark
The cookiecutter shark , 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 . It migrates vertically up to every day, approaching the...
(Isistius brasiliensis). This shark is aplacental viviparous and gives birth to 10–14 young. The kitefin shark is fished commercially
Commercial fishing
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 pursue fish far into the ocean under adverse conditions...
for its meat, skin, and liver oil, primarily by Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
and 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...
. A fishery targeting this species existed off the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
from the 1970s to the 1990s, but collapsed due to overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
and falling liver oil prices; the rapid depletion of the Azores stock is often cited as an example of the susceptibility of deep-sea sharks to human exploitation. The low reproductive rate of this species renders it susceptible to overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
and, coupled with known population declines, has led it to be assessed as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
by the International Union for Conservation of Nature (IUCN).
Taxonomy
The kitefin shark was originally described as Squalus licha by French naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Pierre Joseph Bonnaterre
Pierre Joseph Bonnaterre
Abbé Pierre Joseph Bonnaterre was a French naturalist who contributed sections on cetaceans, mammals, birds, reptiles, amphibians, and insects to the Tableau encyclopédique et méthodique...
, in his 1788 Tableau encyclopédique et méthodique des trois regnes de la nature; the type specimen from "Le cap Breton" has since been lost. This species was later placed in its own genus, Dalatias, which came from the synonymy
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of Constantine Rafinesque
Constantine Samuel Rafinesque-Schmaltz
Constantine Samuel Rafinesque-Schmaltz, as he is known in Europe, was a nineteenth-century polymath who made notable contributions to botany, zoology, the study of prehistoric earthworks in North America and Mesoamerican ancient linguistics.Rafinesque was eccentric, and is often portrayed as an...
's 1810 Dalatias sparophagus with S. licha. However, some authorities dispute this on the grounds that D. sparophagus is a nomen dubium
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
, and prefer to use the next available genus name Scymnorhinus. The genus name Dalatias is derived from the Greek dalos or dalou, meaning "torch". The specific epithet licha comes from la liche, the French name for this shark. Additional common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s used for the kitefin shark include black shark and darkie Charlie.
Phylogeny and evolution
Cladistic studies have consistently found that the closest relatives of the kitefin shark are the cookiecutter sharks (IsistiusIsistius
Isistius is a genus of dogfish sharks in the family Dalatiidae. They are commonly known as cookiecutter sharks. Members of the genus are known for their unusual behaviour and dentition.-Species:...
), with which they share several 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...
al, skeletal
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
, and muscular
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
similarities. Dalatias and Isistius are believed to have evolutionarily diverged
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
shortly after the transition between the Cretaceous and Tertiary
K–T boundary
The K–T boundary is a geological signature, usually a thin band, dated to 65.5 ± 0.3 Ma ago. K is the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period...
periods (65.5 Ma), as part of a larger adaptive radiation
Adaptive radiation
In evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...
of dogfish sharks from the deep sea into relatively shallower habitats.
The oldest fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
teeth that definitively belong to the kitefin shark date to the Middle Eocene epoch, such as those recovered from Bortonian-stage deposits (43.0–37.0 Ma) in 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...
. Dalatias fossil teeth dating to various ages have also been discovered in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, the former USSR
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
, Japan, and western India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. The fossil material now recognized as belonging to this species were historically described under a multitude of different names.
Distribution and habitat
The kitefin shark has an almost circumglobal rangeRange (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
in tropical and warm-temperature waters, consisting of a number of widely separated populations with likely little interchange between them. This shark has not been reported from the eastern Pacific and northern Indian Oceans. In the northern Atlantic, it occurs in the Georges Bank
Georges Bank
Georges Bank is a large elevated area of the sea floor which separates the Gulf of Maine from the Atlantic Ocean and is situated between Cape Cod, Massachusetts and Cape Sable Island, Nova Scotia ....
and the northern Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
, and from the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
to Cameroon
Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...
, including around the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
, in the western and central Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, and off Madeira
Madeira
Madeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
and the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
. In the Indian Ocean, it is found off 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...
and Mozambique
Mozambique
Mozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest...
. In the Pacific, it occurs off Japan, Java
Java
Java is an island of Indonesia. With a population of 135 million , it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java...
, 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...
, and 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...
. There is a single record of this species in the southern Atlantic, from off 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...
.
An offshore, deepwater species, the kitefin shark is most common at a depth of 200–600 m (656.2–1,968.5 ft), but has been captured from the surface to as deep as 1800 m (5,905.5 ft). Off the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
this shark segregates by sex, with females most common around a depth of 230 m (754.6 ft) and males most common around 412–448 m (1,351.7–1,469.8 ft). The kitefin shark inhabits the outer continental shelves and upper continental slopes, and is also found around oceanic islands and seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
s. It is the only member of its family that tends to be found close to the sea floor as opposed to in the middle of the water column, though on occasion it has been captured well above the bottom.
Description
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 are large. The lips are thick with pleats or fringes, though are not modified to be 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....
. There are 16–21 tooth rows in the upper jaw and 17–20 tooth rows in the lower jaw. The upper teeth are small and spike-shaped, curving slightly towards the corners of the mouth. The lower teeth are very large, knife-shaped, and serrated, with their bases interlocking to form a continuous cutting surface.
The first 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...
is slightly smaller and shorter-based than the second, and neither has spines. The first dorsal fin originates behind the free rear tip of the pectoral fins, while the second originates above the middle of the pelvic fin bases. The pectoral fins are short and rounded. The caudal fin has a prominent upper lobe with a well-developed notch near the tip, and a barely present lower lobe. The form and arrangement of the fins is similar to the Portuguese dogfish
Portuguese dogfish
The Portuguese dogfish or Portuguese shark is a species of sleeper shark, family Somniosidae. This globally distributed species has been reported down to a depth of , making it the deepest-living shark known. It inhabits lower continental slopes and abyssal plains, usually staying near the bottom...
(Centroscymnus coelolepis), from which this species can be distinguished by the lack of fin spines. The dermal denticles are small and flat, with a single horizontal ridge ending in a point.
The coloration is a uniform dark brown or gray, sometimes with faint black spots on the back. The fins have white or translucent margins, and the tip of the caudal fin is black. An 90 cm (3 ft) long kitefin shark with partial albinism
Albinism
Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin...
, lacking pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
on 59% of its body, was caught in the Gulf of Genoa
Gulf of Genoa
The Gulf of Genoa is the northernmost part of the Ligurian Sea. The width of the gulf is about 125 km, from the city of Imperia in the west to La Spezia in the east. The largest city on the its coast is Genoa, which has an important port....
in 2003. Unlike in a previous case of an albino Portuguese dogfish, the abnormal coloration of this individual had not diminished its ability to capture prey. Most kitefin sharks are 1–1.4 m (3.3–4.6 ft) long and weigh 8 kg (17.6 lb); the maximum reported length is 1.6 m (5.2 ft), possibly 1.8 m (5.9 ft).
Biology and ecology
Relatively common where it occurs, kitefin sharks are usually solitary in nature but may form small groups. It is a slow swimmer with a large liverLiver
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...
filled with squalene
Squalene
Squalene is a natural organic compound originally obtained for commercial purposes primarily from shark liver oil, though plant sources are used as well, including amaranth seed, rice bran, wheat germ, and olives. All plants and animals produce squalene, including humans...
, a 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...
less dense than water, allowing it to maintain neutral buoyancy and hover above the bottom with little effort. Studies off the coast of North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...
and in the Gulf of Genoa have found males outnumbering females by 2:1 and 5:1 respectively; this imbalanced sex ratio
Sex ratio
Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms....
has not been observed off South Africa and may reflect sampling bias. The kitefin shark is preyed upon by larger fishes and sharks, as well as by 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 (Physeter macrocephalus). Parasite data on this species is limited; an examination of two sharks caught off Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
found three nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s in the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
lumen
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
. One could be identified as Anisakis simplex L3, while another may have been a larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l Raphidascaris.
A powerful and versatile deepwater predator, the short, robust jaws of the kitefin shark give it an enormously strong bite. It feeds mainly on bony fishes (including deepwater smelts, viperfish
Viperfish
A viperfish is a saltwater fish in the genus Chauliodus, with long, needle-like teeth and hinged lower jaws. They grow to lengths of 30 to 60 cm . Viperfish stay near lower depths in the daytime and shallow at night. Viperfish mainly stay in tropical and temperate waters...
es, scaly dragonfish
Stomiidae
Stomiidae is a family of deep-sea ray-finned fish, including the barbeled dragonfishes, stareaters and loosejaws.Stomiids are generally elongated fish with black or near-black bodies, but they are highly variable in form, and are sometimes grouped into multiple different families as a result. The...
es, barracudina
Barracudina
Barracudinas are about 50 species of marine fishes of the family Paralepididae, found almost worldwide in deep waters.They are elongated, slender fish with large eyes, and a pointed snout containing fang-like teeth...
s, greeneye
Greeneye
Greeneyes are deep-sea aulopiform marine fishes in the small family Chlorophthalmidae. Thought to have a circumglobal distribution in tropical and temperate waters, the family contains just 18 species in two genera...
s, lanternfish
Lanternfish
Cooper Lanternfishes are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. They are aptly named after their conspicuous use of bioluminescence...
es, bristlemouths, cod and other gadids
Gadidae
Gadidae is a family of marine fish, included in the order Gadiformes. It includes the cod, haddock, whiting, and pollock.Most species of gadid are found in temperate waters of the northern hemisphere, although there are some exceptions. They are generally medium sized fish, and are distinguished...
, grenadier
Rattail
Grenadiers or rattails are generally large, brown to black gadiform marine fish of the family Macrouridae...
s, deepwater scorpionfish
Setarchidae
Setarchidae is a small family of scorpionfishes.Not all classifications recognise this family; Nelson and ITIS include it in the family Scorpaenidae....
es, bonito
Bonito
Bonito is a name given to various species of medium-sized, predatory fish in the Scombridae family. First, bonito most commonly refers to species in the genus Sarda, including the Atlantic bonito and the Pacific bonito ; second, in Japanese cuisine, bonito refers to the skipjack tuna , which, in...
, snake mackerels, deepwater cardinalfish
Deepwater cardinalfish
Deepwater cardinalfishes are perciform fishes in the family Epigonidae.They are small fishes: the largest species, Epigonus telescopes, reaches 75 cm in length, and most species grow to no more than 20 cm or so....
es, and sea toad
Sea toad
Coffinfish are a family, Chaunacidae, of deep-sea anglerfishes.They are bottom-dwelling fishes found on the continental slopes of the Atlantic, Indian and Pacific Oceans, at depths of up to ....
s), but also takes a wide variety of other animals, including skates, smaller sharks (Galeus
Galeus
Galeus is a genus of catshark, family Scyliorhinidae, commonly known as sawtail catsharks in reference to a distinctive saw-toothed crest of enlarged dermal denticles found along the upper edges of their caudal fins. They are found in the Atlantic, the western and central Pacific, and the Gulf of...
, Squalus, Etmopterus
Etmopterus
Etmopterus, commonly known as lantern sharks, is a diverse genus of dogfish sharks in the family Etmopteridae. This genus has 35 described species.-Species:* Etmopterus baxteri...
and Centrophorus
Centrophorus
Centrophorus is a genus of squaliform sharks. They are deep-water sharks found in temperate and tropical oceans throughout the world. They are characterized by grey or brown bodies, large green eyes, and spines on both dorsal fins...
), 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...
and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
, crustaceans (amphipods, isopods, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
and lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s), polychaete worms, and siphonophores. Like the related cookiecutter shark, the kitefin shark is also capable of excising chunks of flesh from animals larger than itself, including other sharks and whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s. The presence of fast-swimming fishes in its diet suggests the kitefin shark may scavenge, or have some other means of capturing faster prey. In the Mediterranean, bony fishes are the most important food year-round, with the second-most important prey being sharks in the winter and spring, crustaceans in the summer, and cephalopods in the fall. Captured males are more likely to have full stomachs than females for unknown reasons.
Reproduction in the kitefin shark is aplacental viviparous, with the embryo
Embryo
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 hatching inside the 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...
and being sustained to term by yolk. Adult females have two functional ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
and two functional uteruses; the uterus is not divided into compartments. In the Mediterranean, breeding occurs throughout the year with peaks in spring and fall; females may have a year of rest in between pregnancies. The litter size is 10–16, increasing with female size. The young are born at a length of 30–45 cm (11.8–17.7 in), varying by geographic location, after a possible 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:...
of two years. The males mature sexually at a length of 77–121 cm (2.5–4 ft), and the females at a length of 117–159 cm (3.8–5.2 ft). There is no relationship between an individual's size at birth, size at maturity, and maximum size.
Human interactions
Offal
Offal , also called, especially in the United States, variety meats or organ meats, refers to the internal organs and entrails of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but includes most internal organs other than...
processed into fishmeal. The liver oil is utilized in Portugal, Japan, and South Africa. The skin is made into a type of shagreen
Shagreen
Shagreen is a type of leather or rawhide consisting of rough untanned skin, formerly made from a horse's back or that of an onager . Shagreen is now commonly made of the skins of sharks and rays....
useful in the making of furniture and jewelry, and is also favored for the manufacture of "boroso", a Spanish polished leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
. This shark has no commercial value in the western Atlantic.
The continuing expansion of commercial fisheries into the deep sea has raised concerns about the vulnerability of this and other deepwater shark species to overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
, as these sharks have slow growth and reproductive rates. This is exemplified by the rapid stock depletion and collapse of the Azores kitefin shark fishery. This targeted fishery began in the early 1970s for the production of liver oil. In the early 1980s, the fishing fleet was enlarged with the addition of industrial vessels equipped with demersal gillnets, resulting in a fishery peak in 1984 of 937 tons landed. After 1991, kitefin shark catches declined precipitously to under 15 tons annually which, along with a drop in the global price of liver oil, led to the fishery becoming unprofitable by the end of the decade. A population assessment has suggested that the northwestern Atlantic stock had fallen to 50% of the pre-exploitation biomass.
Fisheries operating off Portugal and Japan are responsible for most commercial landings of the kitefin shark, generally 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...
in bottom trawls and on hook-and-line. Portugal reported a kitefin shark bycatch of 282 tons in 2000 and 119 tons in 2003. In other areas of the northeastern Atlantic this shark is rare and reported catches are likely confounded by misidentifications of other species; some are caught by mixed-species gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
fisheries operating in deep water west of the British Isles, where surveys suggest that kitefin shark numbers may have declined by 94% since the 1970s. In the Mediterranean, this shark is caught incidentally by bottom trawl and gillnet fisheries. Although it is generally discarded alive, many are unable to return to deep water and do not survive. In the Southern Hemisphere, catches by the Australian South East Trawl Fishery are increasing following the relaxation of regulations regarding seafood mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
content; this species is not included under Australian fishery quota
Individual fishing quota
Individual fishing quotas also known as "individual transferable quotas" are one kind of catch share, a means by which many governments regulate fishing. The regulator sets a species-specific total allowable catch , typically by weight and for a given time period. A dedicated portion of the TAC,...
s. New Zealand kitefin shark catches peaked from 1986 to 1997. The International Union for Conservation of Nature (IUCN) has assessed the kitefin shark as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
worldwide, and as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
in the northeastern Atlantic in light of documented population declines.