Night Shark
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The night shark (''Carcharhinus signatus'') is a
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
requiem shark Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas (sometimes of brackish or fresh water) and include such species as the bull shark, lemon shark, blac ...
, in the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Carcharhinidae, found in the temperate and tropical waters of the Atlantic Ocean. An inhabitant of the outer
continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...
and upper
continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margi ...
, this shark most commonly occurs at depths of and conducts a
diel vertical migration Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The adjective "diel" ( IPA: , ) comes from , and refers to a 24-hour ...
, spending the day in deeper water and moving into shallower waters at night. Off northeastern Brazil, large numbers congregate around
seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...
s of varying depths. A slender, streamlined species, the night shark typically reaches a length of . 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,
nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...
ly active,
schooling A school is the educational institution (and, in the case of in-person learning, the building) designed to provide learning environments for the teaching of students, usually under the direction of teachers. Most countries have systems of fo ...
predators that feed mainly on small
bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...
es and
squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...
. Reproduction is
viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...
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 In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once i ...
of a year. This deepwater species is not known to pose a danger to humans. It is caught incidentally by
commercial Commercial may refer to: * (adjective for) commerce, a system of voluntary exchange of products and services ** (adjective for) trade, the trading of something of economic value such as goods, services, information or money * a dose of advertising ...
tuna A tuna (: tunas or tuna) is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae ( mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bul ...
and
swordfish The swordfish (''Xiphias gladius''), also known as the broadbill in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are the sole member of the Family (biology), family Xiphiidae. They ...
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 A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foil (fluid mechanics), foils that produce lift (force), lift or thrust, or provide the ability to steer or stabilize motion while travelin ...
, and additionally as a source of meat, liver oil, and
fishmeal Fish meal (sometimes spelled fishmeal) is a commercial product made from whole wild-caught fish, bycatch, and fish by-products to feed farm animals, such as pigs, poultry, and farmed fish.R. D. Miles and F. A. Chapman.FA122: The Benefits of Fish ...
. 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 Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...
, the night shark has been assessed as vulnerable by the American Fisheries Society. 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 Cuban
zoologist Zoology ( , ) is the scientific study of animals. Its studies include the structure, embryology, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. Zoology is one ...
Felipe Poey Felipe Poey (May 26, 1799 – January 28, 1891) was a Cuban zoologist. Biography Poey was born in Havana, the son of French and Spanish parents. He spent several years (1804 to 1807) of his life in Pau, Pyrénées-Atlantiques, Pau then studied ...
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 Joseph Victor Compagno (1943-2024) was 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 Agri ...
synonymized the
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
''Hypoprion'' with ''Carcharhinus''. No
type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...
has been designated for this species. Its
common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...
is because it is mostly captured at night.


Distribution and habitat

The distribution of the night shark extends along the outer continental shelves and upper continental slopes of the Atlantic Ocean, from the
U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its so ...
of
Massachusetts Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...
to
Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
in the west, including the
Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...
and the
Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...
, and from
Senegal Senegal, officially the Republic of Senegal, is the westernmost country in West Africa, situated on the Atlantic Ocean coastline. It borders Mauritania to Mauritania–Senegal border, the north, Mali to Mali–Senegal border, the east, Guinea t ...
to northern
Namibia Namibia, officially the Republic of Namibia, is a country on the west coast of Southern Africa. Its borders include the Atlantic Ocean to the west, Angola and Zambia to the north, Botswana to the east and South Africa to the south; in the no ...
in the east. In United States waters, it is relatively common off
North Carolina North Carolina ( ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, South Carolina to the south, Georgia (U.S. stat ...
and
Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...
(particularly the
Florida Straits The Straits of Florida, Florida Straits, or Florida Strait () is a strait located south-southeast of the North American mainland, generally accepted to be between the Gulf of Mexico and the Atlantic Ocean, and between the Florida Keys (U.S.) ...
) and rarer elsewhere. There are questionable reports of this species off the Pacific coast of
Panama Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...
. The night shark is a deepwater species that has been reported from as far down as , though it occasionally ventures to within of the surface. Off the southeastern United States, it is usually caught at a depth range of . Off northeastern
Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
, the night shark is most commonly found near the summits of
seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...
s ranging from deep. Off
West Africa West Africa, also known as Western Africa, is the westernmost region of Africa. The United Nations geoscheme for Africa#Western Africa, United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Gha ...
, it occurs at depths of , where the temperature is , the
salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...
is 36 ppt, and the
dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can ...
level is 1.81 mL/L. Annual variation in Cuban catch rates may indicate a seasonal
migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
.


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
pupil The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black becau ...
s and a
nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. Most ...
(protective third
eyelid An eyelid ( ) is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. "Palpebral ...
). The mouth lacks conspicuous furrows at the corners and usually bears 15 tooth rows on either side of both jaws, plusone to two upper and one 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 two to five coarse serrations at the base of the trailing margin.Barzan, K
Biological Profiles: Night Shark
Florida Museum of Natural History Ichthyology Department. Retrieved on September 14, 2009.
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 slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In c ...
s are rather short. The
pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...
s are less than a fifth as long as the total body length and taper towards a somewhat rounded tip. The first
dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...
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 Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...
. A ridge runs between the dorsal fins. The
dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...
s are not tightly packed and overlap each other minimally. Each denticle is diamond-shaped with horizontal ridges leading to marginal teeth, the number increasing from three in juveniles to five to seven in adults. The coloration is grayish blue or brown above and whitish below, without fin markings. A faint band occurs on each side and sometimes small black spots are scattered over the back. This species usually grows to long, but has been recorded reaching a length and weight of and , respectively. Carcharhinus signatus drawing.jpg, Drawing of a night shark and its tooth Carcharhinus signatus eye nefsc.jpg, The eyes of the night shark are bright green in life Carcharhinus signatus jaws.jpg, Jaws Carcharhinus signatus upper teeth.jpg, Upper teeth Carcharhinus signatus lower teeth.jpg, Lower teeth


Biology and ecology

Fast and energetic, the night shark feeds primarily on small, active
bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...
es such as mullet,
mackerel Mackerel is a common name applied to a number of different species of pelagic fish, mostly from the family Scombridae. They are found in both temperate and tropical seas, mostly living along the coast or offshore in the oceanic environment. ...
, butterfish, sea basses, and flyingfish.
Squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...
and
shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...
are also sometimes taken. Most feeding activity occurs at night, hence its
common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...
, with peaks at dawn and dusk. Catch records indicate that this species is usually found in
schools A school is the educational institution (and, in the case of in-person learning, the building) designed to provide learning environments for the teaching of students, usually under the direction of teachers. Most countries have systems of ...
and conducts a
diel vertical migration Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The adjective "diel" ( IPA: , ) comes from , and refers to a 24-hour ...
, spending the day at a depth of and moving up to shallower than at night.
Ovulating Ovulation is an important part of the menstrual cycle in female vertebrates where the egg cells are released from the ovaries as part of the ovarian cycle. In female humans ovulation typically occurs near the midpoint in the menstrual cycle and af ...
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
parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...
s include the
copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...
s ''Kroyeria caseyi'', which attach to the gills, ''Pandarus bicolor'' and ''P. smithii'', which infest the skin, and the
tapeworm Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass being Cestodaria). Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Ce ...
s ''Heteronybelinia yamagutii'', ''H. nipponica'' and ''Progrillotia dollfusi'', which are found in the spiral valve
intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...
. Another parasite is an undescribed
isopod Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...
similar to ''Aega webbii''. The
common remora The common remora (''Remora remora'') is a pelagic marine fish belonging to the family Echeneidae. The dorsal fin, which has 22 to 26 soft rays, acts as a suction cup, creating a vacuum to allow the fish to attach to larger marine animals, such ...
(''Remora remora'') may be found attached to this species. Like other members of its family, the night shark is
viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...
; once the developing
embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...
s exhaust their supply of
yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...
, the depleted
yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...
is converted into a
placenta The placenta (: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas, and waste exchange between ...
l connection through which the mother delivers nourishment. Adult females have a single functional
ovary The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/ oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are end ...
(on the right) and two functional
uteri The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic and fetal development of one or more fertilized eggs until bir ...
, 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 Mate may refer to: Science * Mate, one of a pair of animals involved in: ** Mate choice, intersexual selection *** Mate choice in humans ** Mating * Multi-antimicrobial extrusion protein, or MATE, an efflux transporter family of proteins Pers ...
throughout the summer, with the male biting at the female's body and fins as a prelude to
copulation Sexual intercourse (also coitus or copulation) is a sexual activity typically involving the insertion of the erect male penis inside the female vagina and followed by thrusting motions for sexual pleasure, reproduction, or both.Sexual inte ...
. After a year-long
gestation period In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once i ...
, females give birth to four to 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 In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...
, near the southern extreme of this species' range. The newborn young measure long, and add around 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 The silky shark (''Carcharhinus falciformis''), also known by numerous names such as blackspot shark, gray whaler shark, olive shark, ridgeback shark, sickle shark, sickle-shaped shark and sickle silk shark, is a species of requiem shark, in the ...
(''C. falciformis''). By the time the sharks reach adulthood, their growth rate slows to a more modest per year. No difference is seen in growth rate between sexes. Males mature sexually at a length of , corresponding to an age of 8 years, and females at a length of , corresponding to an age of 10 years. The oldest known individuals are 17 years old; based on growth curves, their
maximum lifespan Maximum life span (or, for humans, maximum reported age at death) is a measure of the maximum amount of time one or more members of a population have been observed to survive between birth and death. The term can also denote an estimate of the m ...
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 soup Shark's fin soup is a soup or stewed dish served in parts of China, Taiwan, and Southeast Asia. The shark fins provide texture, while the taste comes from the other ingredients. It is commonly served at special occasions such as weddings and ba ...
, and is also used as a source of meat, liver oil, and
fishmeal Fish meal (sometimes spelled fishmeal) is a commercial product made from whole wild-caught fish, bycatch, and fish by-products to feed farm animals, such as pigs, poultry, and farmed fish.R. D. Miles and F. A. Chapman.FA122: The Benefits of Fish ...
. Traditionally, it has comprised a part of the
bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...
of pelagic longline fisheries targeting
swordfish The swordfish (''Xiphias gladius''), also known as the broadbill in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are the sole member of the Family (biology), family Xiphiidae. They ...
(''Xiphias gladius'') and
tuna A tuna (: tunas or tuna) is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae ( mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bul ...
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, about 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 A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted rept ...
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 of night
shark meat Shark meat is a seafood consisting of the flesh of sharks. Several sharks are fished for human consumption, such as porbeagles, shortfin mako shark, requiem shark, and thresher shark, among others. Shark meat is popular in Asia, where it is oft ...
per day could result in the ingestion of several times the daily mercury content judged safe by the
World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...
. The
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...
has assessed the night shark globally as
Endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...
, citing its slow reproductive rate and historical declines under fishing pressure. It has also been listed as vulnerable by the American Fisheries Society. This species was once a significant part of the Cuban
artisanal An artisan (from , ) is a skilled craft worker who makes or creates material objects partly or entirely by hand. These objects may be functional or strictly decorative, for example furniture, decorative art, sculpture, clothing, food ite ...
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 Marlins are fish from the family Istiophoridae, which includes between 9 and 11 species, depending on the taxonomic authority. Name The family's common name is thought to derive from their resemblance to a sailor's marlinspike. Taxonomy T ...
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 The bigeye tuna (''Thunnus obesus'') is a species of true tuna of the genus ''Thunnus'', belonging to the wider mackerel family (biology), family Scombridae. In Hawaiian language, Hawaiian, it is one of two species known as ahi, the other being t ...
(''Thunnus obesus''). No fishery information on the night shark is available for the eastern Atlantic, leading to an IUCN assessment of
data deficient A data deficient (DD) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as offering insufficient information for a proper assessment of conservation status to be made. This does not necessaril ...
for that region. In 1997, the U.S.
National Oceanographic and Atmospheric Administration The National Oceanic and Atmospheric Administration (NOAA ) is an American scientific and regulatory agency charged with forecasting weather, monitoring oceanic and atmospheric conditions, charting the seas, conducting deep-sea exploration ...
National Marine Fisheries Service The National Marine Fisheries Service (NMFS), informally known as NOAA Fisheries, is a United States federal agency within the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) that is responsible for the ste ...
(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 The Endangered Species Act of 1973 (ESA; 16 U.S.C. § 1531 et seq.) is the primary law in the United States for protecting and conserving imperiled species. Designed to protect critically imperiled species from extinction as a "consequence of e ...
(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.Bolden, S. (January 16, 2009)
Species of Concern: Night Shark
NOAA Fisheries Office of Protected Resources: Proactive Conservation Program. Retrieved on September 14, 2009.
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.


References

{{Good article night shark Fish of the Western Atlantic Fish of the Americas Fish of the Dominican Republic Marine fish of Africa Marine fish of West Africa Vulnerable fish Vulnerable biota of Africa Vulnerable biota of South America night shark