Night shark
Encyclopedia
The night shark is a species
of requiem shark
, family
Carcharhinidae, found in the temperate
and tropical waters of the Atlantic Ocean
. An inhabitant of the outer continental shelf
and upper continental slope, this shark most commonly occurs at depths of 50–600 m (164–1,968.5 ft) and conducts a diel vertical migration
, spending the day in deeper water and moving into shallower waters at night. Off northeastern Brazil
, large numbers congregate around seamount
s of varying depth. A slender, streamlined species, the night shark typically reaches a length of 2 m (6.6 ft). It can be identified by its long pointed snout and large green eyes (when alive), and is dark grayish blue or brown above and white below.
Night sharks are quick, nocturnally active, schooling
predators that feed mainly on small bony fishes and squid
. Reproduction is viviparous as with the other members of its family; females mate
during the summer and give birth to litters of usually 12–18 pups after a gestation period
of a year. This deepwater species is not known to pose a danger to humans. It is caught incidentally by commercial
tuna
and swordfish
longline fisheries in the western Atlantic, and also by a targeted longline fishery operating off northeastern Brazil. The night shark is highly valued for its fins
, and additionally as a source of meat, liver oil
, and fishmeal. However, most sharks caught off northeastern Brazil have been found to contain unsafe concentrations of mercury
.
Because of its low reproductive rate and historically documented declines in areas such as the Caribbean
, the night shark has been assessed as Vulnerable
by the International Union for Conservation of Nature (IUCN) and the American Fisheries Society (AFS), and listed as a "Species of Concern" by the U.S. National Marine Fisheries Service
(NMFS). A population assessment has indicated that this species is secure in the waters off the United States, but this may not be true elsewhere.
zoologist Felipe Poey
in 1868, as part of a series of papers entitled Repertorio fisico-natural de la isla de Cuba. He based his description on a single set of jaws and gave it the name Hypoprion signatus. In 1973, Leonard Compagno
synonymized
the genus
Hypoprion with Carcharhinus. No type specimen has been designated for this species. Its common name
comes from the fact that it is mostly captured at night.
and upper continental slopes of the Atlantic Ocean, from the U.S. state
of Massachusetts
to Argentina
in the west, including the Gulf of Mexico
and the Caribbean Sea
, and from Senegal
to northern Namibia
in the east. In United States
waters, it is relatively common off North Carolina
and Florida
(particularly the Florida Straits) and rarer elsewhere. There are questionable reports of this species off the Pacific coast of Panama
.
The night shark is a deepwater species that has been reported from as far down as 2 km (1.2 mi), though it occasionally ventures to within 26 m (85.3 ft) of the surface. Off the southeastern United States, it is usually caught at a depth range of 50–600 m (164–1,968.5 ft). Off northeastern Brazil
, the night shark is most commonly found near the summits of seamount
s ranging from 38 m (124.7 ft) to 370 m (1,213.9 ft) deep. Off West Africa
, it occurs at depths of 90–285 m (295.3–935 ft), where the temperature is 11–16° C (52–61° F), the salinity
is 36 ppt, and the dissolved oxygen level is 1.81 ml/l. Annual variation in Cuban catch rates may indicate a seasonal migration
.
s and a nictitating membrane
(protective third eyelid
). The mouth lacks conspicuous furrows at the corners and usually bears 15 tooth rows on either side of both jaws, plus 1–2 upper and 1 lower symphysial (jaw midline) tooth rows. Each upper tooth has a smooth to serrated edge, a narrow cusp becoming more oblique towards the corner of the mouth, and 2–5 coarse serrations at the base of the trailing margin. The number and size of serrations on the leading margin of the tooth cusp increase relative to those on the trailing margin as the animal grows older. The lower teeth are upright and smooth-edged. The five pairs of gill slit
s are rather short.
The pectoral fins are less than a fifth as long as the total body length and taper towards a somewhat rounded tip. The first dorsal fin
is relatively small, triangular, and pointed, originating over the free rear tips of the pectoral fins. The second dorsal fin is much smaller than the first and originates over or slightly ahead of the anal fin. There is a ridge running between the dorsal fins. The dermal denticles are not tightly packed and overlap each other minimally. Each denticle is diamond-shaped with horizontal ridges leading to marginal teeth, the number increasing from 3 in juveniles to 5–7 in adults. The coloration is grayish blue or brown above and whitish below, without fin markings. There is a faint band on each side and sometimes small black spots scattered over the back. This species usually grows to 2 m (6.6 ft) long, but has been recorded reaching a length and weight of 2.8 m (9.2 ft) and 76.7 kg (169.1 lb) respectively.
, mackerel
, butterfish, sea basses
, and flyingfish
. Squid
and shrimp
are also sometimes taken. Most feeding activity occurs at night, hence its common name
, with peaks at dawn and dusk. Catch records indicate that this species is usually found in schools
and conducts a diel vertical migration
, spending the day at a depth of 275–366 m (902.2–1,200.8 ft) and moving up to shallower than 183 m (600.4 ft) at night. Ovulating
and gravid females are rarely ever caught, suggesting that during this period they may stop feeding or segregate themselves from others of their species. Potential predators of the night shark include larger sharks. Known parasites include the copepod
s Kroyeria caseyi, which attach to the gills, Pandarus bicolor and P. smithii, which infest the skin, and the tapeworms Heteronybelinia yamagutii, H. nipponica and Progrillotia dollfusi, which are found in the spiral valve
intestine
. Another parasite is an undescribed isopod similar to Aega webbii. The common remora
(Remora remora) may be found attached to this species.
Like other members of its family, the night shark is viviparous: once the developing embryo
s exhaust their supply of yolk, the depleted yolk sac
is converted into a placenta
l connection through which the mother delivers nourishment. Adult females have a single functional ovary
(on the right) and two functional uterus
es, which are divided into separate compartments for each embryo. Within the uterus the embryos lie lengthwise with their heads pointing the same direction as their mother. Most information known about the night shark's life history comes from the subpopulation off northeastern Brazil, and may not hold true in other parts of the species range. Northeastern Brazilian sharks mate
throughout the summer, with the males biting at the female's body and fins as a prelude to copulation.
After a year-long gestation period
, females give birth to 4–18 (usually 12 or more) pups. Embryos at varying stages of development have been found in both February and June, suggesting that the parturition takes place over a span of several months. An important nursery area is believed to exist at the continental shelf break at 34°S
latitude
, near the southern extreme of this species' range. The newborn young measure 50–72 cm (19.7–28.3 in) long, and add around 25 cm (9.8 in) or 38% of their body length in their first year. This fast rate of growth serves to shorten the period immediately after birth when the small pups are most vulnerable to predators, a strategy similar to that employed by the silky shark
(C. falciformis). By the time the sharks reach adulthood, the growth rate slows to a more modest 8.6 cm (3.4 in) per year. There is no difference in growth rate between sexes. Males mature sexually at a length of 1.8–1.9 m (5.9–6.2 ft), corresponding to an age of 8 years, and females at a length of 2–2.1 m (6.6–6.9 ft), corresponding to an age of 10 years. The oldest known individuals are 17 years old; based on growth curves the maximum lifespan has been estimated at 28 years for males and 30 years for females.
, and is also utilized as a source of meat, liver oil
, and fishmeal. Traditionally it has comprised a part of the bycatch
of pelagic longline fisheries targeting swordfish
(Xiphius gladius) and tuna
in the western Atlantic. Since 1991, it has also been the focus of a longline fishery operating over seamounts off northeastern Brazil, where large numbers of sharks congregate and are easily captured. Some 90% of the seamount shark and ray catch in this area now consists of night sharks; of those approximately 89% are juveniles. However, a study has found that night sharks from off northeastern Brazil accumulate high levels of mercury
within their bodies, likely from their piscivorous diet. Some 92% of sharks examined contained mercury levels higher than that allowed for marketed carnivorous fish set by the Brazilian legislature, and the average mercury concentration was 1.742 mg/kg. Therefore, eating only 0.1 kg (0.220462262184878 lb) of night shark meat per day could result in the ingestion of several times the daily mercury content judged safe by the World Health Organization
.
The International Union for Conservation of Nature (IUCN) has assessed the night shark globally as Vulnerable
, citing its slow reproductive rate and historical declines under fishing pressure. It has also been listed as Vulnerable by the American Fisheries Society (AFS). This species was once a significant part of the Cuban artisanal
shark fishery, comprising 60–75% of the catch from 1937 to 1941, before its numbers dropped substantially in the 1970s. Similarly, the proportion of night sharks in the shark catch of the southeastern U.S. pelagic longline fishery fell from 26.1% from 1981 to 1983 to 0.3–3.3% in 1993 and 1994; a comparable decline was observed in catches by south Florida marlin
tournaments since the 1970s. Currently, the intense Brazilian targeted fishery is of particular concern, although fishing pressure on the night shark may be relaxing as the fishery is beginning to shift towards swordfish and bigeye tuna
(Thunnus obesus). No fishery information on the night shark is available for the eastern Atlantic, leading to an IUCN assessment of Data Deficient
for that region.
In 1997, the U.S. National Oceanographic and Atmospheric Administration (NOAA) National Marine Fisheries Service
(NMFS) listed the night shark as a "Species of Concern", meaning that it merits conservation concern but there is insufficient evidence for listing on the Endangered Species Act
(ESA). In 1999, the NMFS Fishery Management Plan (FMP) of the Atlantic tunas, swordfish, and sharks was revised to prohibit the retention of 19 species, including the night shark. The prohibition of this species was upheld by Amendment 1 of the FMP, added in 2003. Night sharks suffer high bycatch mortality on longlines, and prohibited or not some are kept by fishers because of their value and the difficulty of identifying disembodied parts to species. Nevertheless, a 2003–2008 NMFS population assessment concluded that night shark population in United States waters has stabilized (perhaps even increasing) and no longer merits categorization as a "Species of Concern", though recommended that the prohibition on retention be maintained as a precautionary measure. This species should also benefit from the imposition of time/area closures in the Florida Straits and on the Charleston Bump. Off Brazil and elsewhere, fishing continues largely unmanaged. IUCN members have urged that Brazil improve catch monitoring and enforcement of existing regulations, declare some critical habitat off-limits, and implement the Brazilian National Plan of Action for Sharks (NPOA-Sharks) under the FAO International Plan of Action for the Conservation and Management of Sharks (IPOA-Sharks).
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 requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
, 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...
Carcharhinidae, found in the temperate
Temperate
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...
and tropical waters of the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
. An inhabitant of the outer continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
and upper continental slope, this shark most commonly occurs at depths of 50–600 m (164–1,968.5 ft) and conducts 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...
, spending the day in deeper water and moving into shallower waters at night. Off northeastern 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...
, large numbers congregate around 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 of varying depth. A slender, streamlined species, the night shark typically reaches a length of 2 m (6.6 ft). It can be identified by its long pointed snout and large green eyes (when alive), and is dark grayish blue or brown above and white below.
Night sharks are quick, nocturnally active, schooling
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...
predators that feed mainly on small bony fishes and 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...
. Reproduction is viviparous as with the other members of its family; females mate
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
during the summer and give birth to litters of usually 12–18 pups after a 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 a year. This deepwater species is not known to pose a danger to humans. It is caught incidentally by commercial
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...
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...
and swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
longline fisheries in the western Atlantic, and also by a targeted longline fishery operating off northeastern Brazil. The night shark is highly valued for its fins
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
, and additionally as a source of meat, liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
, and fishmeal. However, most sharks caught off northeastern Brazil have been found to contain unsafe concentrations of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
.
Because of its low reproductive rate and historically documented declines in areas such as the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
, the night shark has been assessed 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:...
by the International Union for Conservation of Nature (IUCN) and the American Fisheries Society (AFS), and listed as a "Species of Concern" by the U.S. 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...
(NMFS). A population assessment has indicated that this species is secure in the waters off the United States, but this may not be true elsewhere.
Taxonomy
The first scientific description of the night shark was published by CubanCubans
Cubans or Cuban people are the inhabitants or citizens of Cuba. Cuba is a multi-ethnic nation, home to people of different ethnic and national backgrounds...
zoologist Felipe Poey
Felipe Poey
-Biography:Poey was born in Havana, the son of French and Spanish parents. He spent several years of his life in Pau then studied law in Madrid. He became a lawyer in Spain but was forced to leave due to his liberal ideas, returning to Cuba in 1823. He began to concentrate on the study of the...
in 1868, as part of a series of papers entitled Repertorio fisico-natural de la isla de Cuba. He based his description on a single set of jaws and gave it the name Hypoprion signatus. In 1973, Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...
synonymized
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...
the 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...
Hypoprion with Carcharhinus. No type specimen has been designated for this species. Its 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...
comes from the fact that it is mostly captured at night.
Distribution and habitat
The distribution of the night shark extends along the outer continental shelvesContinental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
and upper continental slopes of the Atlantic Ocean, from the U.S. state
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
of Massachusetts
Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
to Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
in the west, including the 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 the Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
, and from Senegal
Senegal
Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...
to northern Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
in the east. In United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
waters, it is relatively common off North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
and Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
(particularly the Florida Straits) and rarer elsewhere. There are questionable reports of this species off the Pacific coast of Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
.
The night shark is a deepwater species that has been reported from as far down as 2 km (1.2 mi), though it occasionally ventures to within 26 m (85.3 ft) of the surface. Off the southeastern United States, it is usually caught at a depth range of 50–600 m (164–1,968.5 ft). Off northeastern 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...
, the night shark is most commonly found near the summits of 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 ranging from 38 m (124.7 ft) to 370 m (1,213.9 ft) deep. Off West Africa
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
, it occurs at depths of 90–285 m (295.3–935 ft), where the temperature is 11–16° C (52–61° F), the salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
is 36 ppt, and the dissolved oxygen level is 1.81 ml/l. Annual variation in Cuban catch rates may indicate a seasonal migration
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
.
Description
The night shark has a slender build with an elongated, pointed snout. The nares are flanked by moderately developed flaps of skin. The eyes are large, circular, and green in life, with irregularly shaped pupilPupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
s and a nictitating membrane
Nictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
(protective third eyelid
Eyelid
An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
). The mouth lacks conspicuous furrows at the corners and usually bears 15 tooth rows on either side of both jaws, plus 1–2 upper and 1 lower symphysial (jaw midline) tooth rows. Each upper tooth has a smooth to serrated edge, a narrow cusp becoming more oblique towards the corner of the mouth, and 2–5 coarse serrations at the base of the trailing margin. The number and size of serrations on the leading margin of the tooth cusp increase relative to those on the trailing margin as the animal grows older. The lower teeth are upright and smooth-edged. 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 rather short.
The pectoral fins are less than a fifth as long as the total body length and taper towards a somewhat rounded tip. 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 relatively small, triangular, and pointed, originating over the free rear tips of the pectoral fins. The second dorsal fin is much smaller than the first and originates over or slightly ahead of the anal fin. There is a ridge running between the dorsal fins. The dermal denticles are not tightly packed and overlap each other minimally. Each denticle is diamond-shaped with horizontal ridges leading to marginal teeth, the number increasing from 3 in juveniles to 5–7 in adults. The coloration is grayish blue or brown above and whitish below, without fin markings. There is a faint band on each side and sometimes small black spots scattered over the back. This species usually grows to 2 m (6.6 ft) long, but has been recorded reaching a length and weight of 2.8 m (9.2 ft) and 76.7 kg (169.1 lb) respectively.
Biology and ecology
Fast and energetic, the night shark feeds primarily on small, active bony fishes such as mulletMullet (fish)
The mullets or grey mullets are a family and order of ray-finned fish found worldwide in coastal temperate and tropical waters, and in some species in fresh water. Mullets have served as an important source of food in Mediterranean Europe since Roman times...
, mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
, butterfish, sea basses
Serranidae
Serranidae is a large family of fishes, belonging to the order Perciformes. The family contains about 450 species of serranids in 64 genera, including the sea basses and the groupers...
, and flyingfish
Flyingfish
Exocoetidae, is a family of marine fish in the order Beloniformes of class Actinopterygii. Fish of this family are known as flying fish. There are about 64 species grouped in seven to nine genera.- Etymology :...
. 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 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...
are also sometimes taken. Most feeding activity occurs at night, hence its 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...
, with peaks at dawn and dusk. Catch records indicate that this species is usually found 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...
and conducts 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...
, spending the day at a depth of 275–366 m (902.2–1,200.8 ft) and moving up to shallower than 183 m (600.4 ft) at night. Ovulating
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
and gravid females are rarely ever caught, suggesting that during this period they may stop feeding or segregate themselves from others of their species. Potential predators of the night shark include larger sharks. Known parasites include the 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 Kroyeria caseyi, which attach to the gills, Pandarus bicolor and P. smithii, which infest the skin, and the tapeworms Heteronybelinia yamagutii, H. nipponica and Progrillotia dollfusi, which are found in the spiral valve
Spiral valve
A spiral valve is the lower portion of the intestine of some sharks, rays, skates and bichirs. A modification of the ileum, the spiral valve is internally twisted or coiled to increase the surface area of the intestine, to increase nutrient absorption....
intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
. Another parasite is an undescribed isopod similar to Aega webbii. The common remora
Common remora
The common remora, Remora remora, is a pelagic marine fish belonging to family Echeneidae. Remora remora is different from other remoras in the family Echeneidae by the modification of its dorsal fin...
(Remora remora) may be found attached to this species.
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 exhaust their supply of yolk, the depleted 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...
is converted into a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection through which the mother delivers nourishment. Adult females have a single functional ovary
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...
(on the right) and 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, which are divided into separate compartments for each embryo. Within the uterus the embryos lie lengthwise with their heads pointing the same direction as their mother. Most information known about the night shark's life history comes from the subpopulation off northeastern Brazil, and may not hold true in other parts of the species range. Northeastern Brazilian sharks mate
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
throughout the summer, with the males biting at the female's body and fins as a prelude to copulation.
After a year-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:...
, females give birth to 4–18 (usually 12 or more) pups. Embryos at varying stages of development have been found in both February and June, suggesting that the parturition takes place over a span of several months. An important nursery area is believed to exist at the continental shelf break at 34°S
34th parallel south
The 34th parallel south is a circle of latitude that is 34 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, Africa, the Indian Ocean, Australasia, the Pacific Ocean and South America....
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...
, near the southern extreme of this species' range. The newborn young measure 50–72 cm (19.7–28.3 in) long, and add around 25 cm (9.8 in) or 38% of their body length in their first year. This fast rate of growth serves to shorten the period immediately after birth when the small pups are most vulnerable to predators, a strategy similar to that employed by the silky shark
Silky shark
The silky shark is a species of requiem shark, family Carcharhinidae, named for the smooth texture of its skin. It is one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge...
(C. falciformis). By the time the sharks reach adulthood, the growth rate slows to a more modest 8.6 cm (3.4 in) per year. There is no difference in growth rate between sexes. Males mature sexually at a length of 1.8–1.9 m (5.9–6.2 ft), corresponding to an age of 8 years, and females at a length of 2–2.1 m (6.6–6.9 ft), corresponding to an age of 10 years. The oldest known individuals are 17 years old; based on growth curves the maximum lifespan has been estimated at 28 years for males and 30 years for females.
Human interactions
Because of its deepwater habitat, the night shark is not known to pose a danger to humans. This species is prized for its large fins, which are exported for use in shark fin soupShark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
, and is also utilized as a source of meat, liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
, and fishmeal. Traditionally it has comprised a part of the 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...
of pelagic longline fisheries targeting swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
(Xiphius gladius) and 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...
in the western Atlantic. Since 1991, it has also been the focus of a longline fishery operating over seamounts off northeastern Brazil, where large numbers of sharks congregate and are easily captured. Some 90% of the seamount shark and ray catch in this area now consists of night sharks; of those approximately 89% are juveniles. However, a study has found that night sharks from off northeastern Brazil accumulate high levels of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
within their bodies, likely from their piscivorous diet. Some 92% of sharks examined contained mercury levels higher than that allowed for marketed carnivorous fish set by the Brazilian legislature, and the average mercury concentration was 1.742 mg/kg. Therefore, eating only 0.1 kg (0.220462262184878 lb) of night shark meat per day could result in the ingestion of several times the daily mercury content judged safe by the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
.
The International Union for Conservation of Nature (IUCN) has assessed the night shark globally 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:...
, citing its slow reproductive rate and historical declines under fishing pressure. It has also been listed as Vulnerable by the American Fisheries Society (AFS). This species was once a significant part of the Cuban artisanal
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
shark fishery, comprising 60–75% of the catch from 1937 to 1941, before its numbers dropped substantially in the 1970s. Similarly, the proportion of night sharks in the shark catch of the southeastern U.S. pelagic longline fishery fell from 26.1% from 1981 to 1983 to 0.3–3.3% in 1993 and 1994; a comparable decline was observed in catches by south Florida marlin
Marlin
Marlin, family Istiophoridae, are fish with an elongated body, a spear-like snout or bill, and a long rigid dorsal fin, which extends forward to form a crest. Its common name is thought to derive from its resemblance to a sailor's marlinspike...
tournaments since the 1970s. Currently, the intense Brazilian targeted fishery is of particular concern, although fishing pressure on the night shark may be relaxing as the fishery is beginning to shift towards swordfish and bigeye tuna
Bigeye tuna
The bigeye tuna, Thunnus obesus, is an important food fish and prized recreational game fish. It is a true tuna of the genus Thunnus, belonging to the wider mackerel family Scombridae....
(Thunnus obesus). No fishery information on the night shark is available for the eastern Atlantic, leading to an IUCN assessment of Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
for that region.
In 1997, the U.S. National Oceanographic and Atmospheric Administration (NOAA) 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...
(NMFS) listed the night shark as a "Species of Concern", meaning that it merits conservation concern but there is insufficient evidence for listing on the Endangered Species Act
Endangered Species Act
The Endangered Species Act of 1973 is one of the dozens of United States environmental laws passed in the 1970s. Signed into law by President Richard Nixon on December 28, 1973, it was designed to protect critically imperiled species from extinction as a "consequence of economic growth and...
(ESA). In 1999, the NMFS Fishery Management Plan (FMP) of the Atlantic tunas, swordfish, and sharks was revised to prohibit the retention of 19 species, including the night shark. The prohibition of this species was upheld by Amendment 1 of the FMP, added in 2003. Night sharks suffer high bycatch mortality on longlines, and prohibited or not some are kept by fishers because of their value and the difficulty of identifying disembodied parts to species. Nevertheless, a 2003–2008 NMFS population assessment concluded that night shark population in United States waters has stabilized (perhaps even increasing) and no longer merits categorization as a "Species of Concern", though recommended that the prohibition on retention be maintained as a precautionary measure. This species should also benefit from the imposition of time/area closures in the Florida Straits and on the Charleston Bump. Off Brazil and elsewhere, fishing continues largely unmanaged. IUCN members have urged that Brazil improve catch monitoring and enforcement of existing regulations, declare some critical habitat off-limits, and implement the Brazilian National Plan of Action for Sharks (NPOA-Sharks) under the FAO International Plan of Action for the Conservation and Management of Sharks (IPOA-Sharks).