Black dogfish
Encyclopedia
The black dogfish is a species
of dogfish shark
in the family
Etmopteridae
. It is common over the outer continental shelf
and continental slope at a depth of 180–2250 m (590.6–7,381.9 ft). Females generally inhabit deeper water than males, and depending on the region, smaller sharks may occur at a different depth than larger ones. This species is distributed widely in the Atlantic Ocean
, from Greenland
and Iceland
to Virginia
and West Africa
in the north, and off southwestern Africa and Argentina
in the south. The largest member of its family, the black dogfish typically measures 60–75 cm (23.6–29.5 in) long. It has a stocky, dark brown body that is darker below than above, and bears scattered minute bioluminescent
organs. Its two dorsal fin
s are preceded by stout spines, and the anal fin is absent.
Active and schooling
, the black dogfish is an opportunistic predator and scavenger
that mainly consumes bony fishes, crustacean
s, and cephalopod
s. It is aplacental viviparous, with females producing litters of 4–40 pups that are sustained to term
by a yolk sac
. There is no well-defined breeding season
, and mating and birthing take place year-round. The black dogfish contributes significantly to the bycatch
of deep-sea commercial fisheries operating in the North Atlantic; it is of little commercial value and is usually discarded. As large portions of its range see little deepwater fishing activity and its northwestern Atlantic population seems to be stable, the International Union for Conservation of Nature (IUCN) has listed this species under Least Concern
overall. It has been assessed as Near Threatened
in the northeastern Atlantic, where its numbers may have declined from heavy fishing pressure.
The first known specimen of the black dogfish was collected near Julianehåb in Greenland
and described by Danish zoologist Johannes Reinhardt
in his 1825 Ichthyologiske bidrag. Reinhardt gave it the name Spinax fabricii in honor of missionary
and naturalist
Otto Fabricius
, who pioneered the study of Greenlandic fishes. German biologists Johannes Müller
and Jakob Henle
, in their 1839–41 Systematische Beschreibung der Plagiostomen, created the new genus Centroscyllium
for this species.
According to the IUCN, further taxonomic
investigation is required to confirm that black dogfish in the North Atlantic and the southeastern Atlantic represent the same species. A 2010 phylogenetic study by Nicolas Straube and colleagues, based on nuclear
and mitochondrial DNA
, found that the black dogfish is the sister species of the whitefin dogfish
(C. ritteri), and that the two are in turn sister to the clade
formed by the granular dogfish
(C. granulatum) and combtooth dogfish
(C. nigrum).
waters of the Atlantic Ocean
; its range abuts, but does not extend into, the Arctic Ocean
. In the northeast, it occurs from Iceland
to Sierra Leone
, including the Faroe Islands
, southern Norway
, and the Rockall Trough and Porcupine Seabight
off Ireland
. In the northwest, it is found from southern Greenland
and Baffin Island
to Virginia
, being particularly abundant in the Laurentian Channel
, and may occur further south to the Gulf of Mexico
off Alabama
. In the southeast, it is found off Namibia
and South Africa
as far as Cape Agulhas
. In the southwest, it has been recorded from the Beagle Channel
at the southern tip of Argentina
.
Inhabiting the outer continental shelf
and continental slope, the black dogfish is found mostly near the bottom in water 180–2250 m (590.6–7,381.9 ft) deep. It is most common at depths of 800–1200 m (2,624.7–3,937 ft) off Iceland, 1250–1500 m (4,101–4,921.3 ft) in the Rockall Trough, 500–1300 m (1,640.4–4,265.1 ft) off Greenland, 350–500 m (1,148.3–1,640.4 ft) off northern Canada, and below 500 m (1,640.4 ft) off southern Africa. The species may venture closer to the surface in the northern extreme of its range, particularly during the dark, cold winter months. Depth segregation by sex has been documented in the North Atlantic, with females outnumbering males at depths greater than 1 km (0.621372736649807 mi). Depth segregation by size varies by region: larger sharks are generally found in deeper water off western Greenland, in shallower water off western Iceland, and without pattern with respect to depth off eastern Iceland. The black dogfish prefers water temperatures of 3.5–4.5 °C (38.3–40.1 F), though off northern Canada it is most abundant in water of 5–6.5 °C (41–43.7 F); it can tolerate temperatures down to 1 °C (33.8 °F). There is some evidence that this species conducts seasonal migrations
, spending winter and spring in shallower water. Sharks off northern Canada perform development-related movements (see below) not observed off western Greenland, suggesting the presence of two distinct stocks
in the northwestern Atlantic.
s (protective third eyelids); they are followed a short distance behind by much smaller spiracle
s (accessory respratory
openings). The nostrils are anteriorly placed and preceded by short flaps of skin. The mouth is wide and evenly arched, with thin lips and short but deep furrows around the corners. There are around 34 tooth rows in either side of both jaws; each tooth has three (occasionally up to five) slender cusps
, with the central one the longest.
Both dorsal fin
s are immediately preceded by stout, grooved spines, with the second much longer than the first. The small first dorsal fin has a rounded apex and a nearly straight trailing margin, with its origin lying behind the pectoral fins. The second dorsal fin is rather angular and has about double the area of the first, with its origin located opposite the midpoint of the pelvic fin bases. The pectoral fins are small and rounded. The pelvic fins are about as large as the second dorsal fin, with rounded tips and nearly straight trailing margins. The caudal peduncle is short and leads to a broad caudal fin comprising less than a quarter of the total length; the upper lobe has a convex upper margin leading to a squared-off tip, while the lower lobe is indistinct. The skin is densely covered by tiny dermal denticles; each one is recurved and thorn-like, rising from an irregular star-shaped base. This species is a plain dark brown above, darkening to almost black below, with white dorsal fin spines. Juvenile sharks have white edges on the dorsal, pectoral, and pelvic fins. There are minute, luminescent
dots scattered about the skin without a regular pattern.
s that tend to be larger during the winter and spring. Though fairly active, its swimming muscles exhibit lower activity of glycolytic
enzyme
s and higher activity of creatine phosphokinase compared to the shallow-water spiny dogfish
(Squalus acanthias), suggesting a lesser capacity for bursts of speed. The lipid
-filled liver
comprises about one-fifth of its total weight and functions in maintaining neutral buoyancy
. Potential predators of the black dogfish are larger sharks and bony fishes. It is one of several deep-sea sharks parasitized by the barnacle
Anelasma squalicola, which attaches in front of the second dorsal fin and impairs the reproductive development of its host. Other known parasites of this species include the fluke
Otodistomum cestoides, the copepod
s Neoalbionella fabricii and Neoalbionella centroscyllii, and the protozoa
ns Haemogregarina delagei and Trypanosoma rajae.
Apparently opportunistic in feeding habits, the black dogfish typically hunts in open water but also scavenges off the bottom. The bulk of its diet consists of a variety of bony fishes, including rattail
s, whitings
, rockfish
es, lanternfish
es, and barracudina
s, as well as pelagic crustacean
s such as krill
and shrimp
, and cephalopod
s. Fish become a progressively more important food source as the shark ages, while crustaceans become less important. Infrequently, polychaete worms and jellyfish
are also eaten. In the northwestern Atlantic, Greenland halibut
(Reinhardtius hippoglossoides) and rattail offal
discarded from fishing vessels have become a major source of food for this species, particularly for older sharks that are capable of consuming larger pieces such as heads.
s are retained inside the uterus
and are sustained to term solely by yolk. Mature females have two functional ovaries
and two functional uteruses. Fertilized eggs are ovulated
into the uterus at a diameter of 3–4.5 cm (1.2–1.8 in), though a few may be retained in the ovary; the eggs are not enclosed in a capsule. The external yolk sac
is fully resorbed when the embryo is close to term, with the remaining yolk having been transferred to an internal yolk sac attached to the intestine
. The internal yolk sac serves to provision the newborn shark until it learns to feed. The litter size ranges from 4 to 40. Newborns measure 13–19 cm (5.1–7.5 in) long.
Various authors have reported the size at maturity as between 46 and 63 cm (18.1 and 24.8 in) for males and 51 and 70 cm (20.1 and 27.6 in) for females, reflecting differences between geographical areas. Off northern Canada, females give birth in the portion of the Laurentian Channel less than 400 m (1,312.3 ft) deep. As the young grow they migrate into the deeper parts of the Channel, and eventually a long distance northward over the Grand Banks or the Labrador Shelf
, to the deep continental slope. This movement pattern has not been observed in black dogfish inhabiting adjacent waters off western Greenland. A number of anomalous hermaphroditic
specimens have been documented.
by commercial
deep-sea trawl, gillnet
, and longline fisheries operating throughout the North Atlantic, including the Icelandic Greenland halibut fishery, the French mixed-species trawl fishery, and the Canadian Greenland halibut, crab
, redfish
, monkfish
, and witch fisheries. Captured sharks are usually discarded, though in recent years this and other small deepwater sharks have been increasingly retained and utilized for fishmeal. Reported catches by European countries, of which France made the largest contribution, have followed a declining trend from 486 tons in 2001 to 35 tons in 2006. The average catch by Canadian fisheries was 68 tons per year from 1996 to 2005. The black dogfish occurs mostly too deep for fisheries off southern Africa; in the remainder of its range there is little information available on fishery impact.
The International Union for Conservation of Nature (IUCN) has listed the black dogfish under Least Concern
worldwide; it is minimally affected by fishing activity across many parts of its range, while its population in the northwestern Atlantic presently seems to be stable and may have increased from 1978 to 1995. By contrast, the intensity of deepwater fisheries in the northeastern Atlantic has led the IUCN to give this species a regional assessment of Near Threatened
. The reproductive characteristics of the black dogfish, such as a large female maturation size, may render it susceptible to overfishing
, though it is more fecund
than other deep-sea dogfish sharks. In the northwestern Atlantic, catches of this species are managed as part of the total allowable catch (TAC) for deep-sea sharks set by the International Council for the Exploration of the Sea (ICES).
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
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...
Etmopteridae
Etmopteridae
Etmopteridae is a family of sharks in the order Squaliformes, commonly known as lantern sharks. Their name comes from the presence of light-producing photophores on their bodies. The members of this family are small, under long, and are found in deep waters worldwide. There are 45 species in five...
. It is common over 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 continental slope at a depth of 180–2250 m (590.6–7,381.9 ft). Females generally inhabit deeper water than males, and depending on the region, smaller sharks may occur at a different depth than larger ones. This species is distributed widely in 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...
, from Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
and Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
to Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
and 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:...
in the north, and off southwestern Africa and 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 south. The largest member of its family, the black dogfish typically measures 60–75 cm (23.6–29.5 in) long. It has a stocky, dark brown body that is darker below than above, and bears scattered minute bioluminescent
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
organs. Its two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s are preceded by stout spines, and the anal fin is absent.
Active and 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...
, the black dogfish is an opportunistic predator and scavenger
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
that mainly consumes bony fishes, 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, and 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. It is aplacental viviparous, with females producing litters of 4–40 pups that are sustained to term
Full Term
Full Term in the universities of Oxford and Cambridge refers to the eight weeks within the longer academic term during which lectures are given and students are required to be in residence...
by a 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...
. There is no well-defined breeding season
Breeding season
The breeding season is the most suitable season, usually with favourable conditions and abundant food and water, for breeding among some wild animals and birds . Species with a breeding season have naturally evolved to have sexual intercourse during a certain time of year in order to achieve the...
, and mating and birthing take place year-round. The black dogfish contributes significantly to 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 deep-sea commercial fisheries operating in the North Atlantic; it is of little commercial value and is usually discarded. As large portions of its range see little deepwater fishing activity and its northwestern Atlantic population seems to be stable, the International Union for Conservation of Nature (IUCN) has listed this species under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
overall. It has been 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...
in the northeastern Atlantic, where its numbers may have declined from heavy fishing pressure.
Taxonomy and phylogeny
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
and described by Danish zoologist Johannes Reinhardt
Johan Reinhardt
Johannes Christopher Hagemann Reinhardt was a professor in zoology at the University of Copenhagen.Born in Rendalen parish in Norway, his father, Johannes Henrik Reinhardt, was a priest, and his mother, Johanne Elisabeth Mommesen, was from Holmestrand . He was not baptized Johannes, but adopted...
in his 1825 Ichthyologiske bidrag. Reinhardt gave it the name Spinax fabricii in honor of missionary
Missionary
A missionary is a member of a religious group sent into an area to do evangelism or ministries of service, such as education, literacy, social justice, health care and economic development. The word "mission" originates from 1598 when the Jesuits sent members abroad, derived from the Latin...
and naturalist
Naturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Otto Fabricius
Otto Fabricius
Otto Fabricius was a Danish missionary, naturalist, ethnographer and explorer of Greenland. He was sent to Greenland 1768–1773 and during this brief period he made enormous amounts of observations and collections. The facilities at his command were primitive to the extreme...
, who pioneered the study of Greenlandic fishes. German biologists Johannes Müller
Johannes Peter Müller
Johannes Peter Müller , was a German physiologist, comparative anatomist, and ichthyologist not only known for his discoveries but also for his ability to synthesize knowledge.-Early years and education:...
and Jakob Henle
Friedrich Gustav Jakob Henle
Friedrich Gustav Jakob Henle was a German physician, pathologist and anatomist. He is credited with the discovery of the loop of Henle in the kidney. His essay "On Miasma and Contagia" was an early argument for the germ theory of disease...
, in their 1839–41 Systematische Beschreibung der Plagiostomen, created the new genus Centroscyllium
Centroscyllium
Centroscyllium is a genus of big-eyed deepwater dogfishes with no anal fin, a grey or black-brown body, and dorsal spines, with the second one being much larger than the first. There are seven extant species.-Species:...
for this species.
According to the IUCN, further taxonomic
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
investigation is required to confirm that black dogfish in the North Atlantic and the southeastern Atlantic represent the same species. A 2010 phylogenetic study by Nicolas Straube and colleagues, based on nuclear
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
and mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
, found that the black dogfish is the sister species of the whitefin dogfish
Whitefin dogfish
The whitefin dogfish is a species of deep-sea dogfish shark in the family Etmopteridae. It has only been found in the northwest Pacific Ocean off the southeastern coast of Japan, between the latitudes of 35°N and 32°N. It inhabits continental slopes and seamounts at a depth of 320 to 1,100 m ....
(C. ritteri), and that the two are in turn sister to the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
formed by the granular dogfish
Granular dogfish
The granular dogfish, Centroscyllium granulatum, is a little-known very small dogfish shark of the family Dalatiidae, endemic to the Falkland Islands.-Physical characteristics:...
(C. granulatum) and combtooth dogfish
Combtooth dogfish
The combtooth dogfish, Centroscyllium nigrum, is a little-known deepwater dogfish shark.-Physical description:The combtooth dogfish has no anal fin, grooved dorsal spines, two dorsal fins of about same size, pointed nose, large eyes, small gill slits, a short abdomen, short caudal peduncle, and is...
(C. nigrum).
Distribution and habitat
The black dogfish is a common species with a wide but non-continuous distribution in the temperateTemperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
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...
; its range abuts, but does not extend into, the Arctic Ocean
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...
. In the northeast, it occurs from Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
to Sierra Leone
Sierra Leone
Sierra Leone , officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea to the north and east, Liberia to the southeast, and the Atlantic Ocean to the west and southwest. Sierra Leone covers a total area of and has an estimated population between 5.4 and 6.4...
, including the Faroe Islands
Faroe Islands
The Faroe Islands are an island group situated between the Norwegian Sea and the North Atlantic Ocean, approximately halfway between Scotland and Iceland. The Faroe Islands are a self-governing territory within the Kingdom of Denmark, along with Denmark proper and Greenland...
, southern Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
, and the Rockall Trough and Porcupine Seabight
Porcupine Seabight
The Porcupine Seabight is a deep-water basin in the Porcupine Bank in the northeastern Atlantic Ocean. It lies southwest of Ireland and is approximately 180 nautical miles by 100 nautical miles . The feature is shaped roughly like an amphitheatre with the deepest point lying to the southwest...
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...
. In the northwest, it is found from southern Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
and Baffin Island
Baffin Island
Baffin Island in the Canadian territory of Nunavut is the largest island in the Canadian Arctic Archipelago, the largest island in Canada and the fifth largest island in the world. Its area is and its population is about 11,000...
to Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
, being particularly abundant in the Laurentian Channel
Laurentian Channel
The Laurentian Channel is a submarine valley in eastern Canada.The channel is of glacial origin and is the submerged valley of the historic St. Lawrence River, running 1400 km from a sharp escarpment downstream from the confluence of the St. Lawrence with the Saguenay River, past Anticosti Island...
, and may occur further south to 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...
off Alabama
Alabama
Alabama is a state located in the southeastern region of the United States. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its inland...
. In the southeast, it is found off 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...
and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
as far as Cape Agulhas
Cape Agulhas
Cape Agulhas is a rocky headland in the Western Cape, South Africa. It is the geographic southern tip of Africa and the official dividing point between the Atlantic and Indian oceans...
. In the southwest, it has been recorded from the Beagle Channel
Beagle Channel
thumb|right|300px|Aereal view of Beagle Channel. The Chilean [[Navarino Island]] is seen in the top-right while the Argentine part of [[Isla Grande de Tierra del Fuego]] is seen at the bottom-left....
at the southern tip of 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...
.
Inhabiting 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 continental slope, the black dogfish is found mostly near the bottom in water 180–2250 m (590.6–7,381.9 ft) deep. It is most common at depths of 800–1200 m (2,624.7–3,937 ft) off Iceland, 1250–1500 m (4,101–4,921.3 ft) in the Rockall Trough, 500–1300 m (1,640.4–4,265.1 ft) off Greenland, 350–500 m (1,148.3–1,640.4 ft) off northern Canada, and below 500 m (1,640.4 ft) off southern Africa. The species may venture closer to the surface in the northern extreme of its range, particularly during the dark, cold winter months. Depth segregation by sex has been documented in the North Atlantic, with females outnumbering males at depths greater than 1 km (0.621372736649807 mi). Depth segregation by size varies by region: larger sharks are generally found in deeper water off western Greenland, in shallower water off western Iceland, and without pattern with respect to depth off eastern Iceland. The black dogfish prefers water temperatures of 3.5–4.5 °C (38.3–40.1 F), though off northern Canada it is most abundant in water of 5–6.5 °C (41–43.7 F); it can tolerate temperatures down to 1 °C (33.8 °F). There is some evidence that this species conducts seasonal migrations
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...
, spending winter and spring in shallower water. Sharks off northern Canada perform development-related movements (see below) not observed off western Greenland, suggesting the presence of two distinct stocks
Fish stock
Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters are the only significant factors in determining population dynamics, while extrinsic factors are considered to be insignificant.-The stock concept:All species have geographic limits to their...
in the northwestern Atlantic.
Description
Adult black dogfish typically measure 60–75 cm (23.6–29.5 in) in length and can reach 1.1 m (3.6 ft), making it the largest member of its family. Females attain a larger ultimate size than males. The shark has a rather stocky and laterally compressed body, with a moderately long, thick, and flattened snout that forms a very broad arch at the front. The sizable, horizontally oval eyes are a reflective green in life and lack nictitating membraneNictitating 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...
s (protective third eyelids); they are followed a short distance behind by much smaller spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s (accessory respratory
Breathing
Breathing is the process that moves air in and out of the lungs. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose. Breathing is only one process that delivers oxygen to where it is needed in the body and...
openings). The nostrils are anteriorly placed and preceded by short flaps of skin. The mouth is wide and evenly arched, with thin lips and short but deep furrows around the corners. There are around 34 tooth rows in either side of both jaws; each tooth has three (occasionally up to five) slender cusps
Cusp (dentistry)
A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
, with the central one the longest.
Both dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s are immediately preceded by stout, grooved spines, with the second much longer than the first. The small first dorsal fin has a rounded apex and a nearly straight trailing margin, with its origin lying behind the pectoral fins. The second dorsal fin is rather angular and has about double the area of the first, with its origin located opposite the midpoint of the pelvic fin bases. The pectoral fins are small and rounded. The pelvic fins are about as large as the second dorsal fin, with rounded tips and nearly straight trailing margins. The caudal peduncle is short and leads to a broad caudal fin comprising less than a quarter of the total length; the upper lobe has a convex upper margin leading to a squared-off tip, while the lower lobe is indistinct. The skin is densely covered by tiny dermal denticles; each one is recurved and thorn-like, rising from an irregular star-shaped base. This species is a plain dark brown above, darkening to almost black below, with white dorsal fin spines. Juvenile sharks have white edges on the dorsal, pectoral, and pelvic fins. There are minute, luminescent
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
dots scattered about the skin without a regular pattern.
Biology and ecology
The black dogfish forms shoals or schoolShoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
s that tend to be larger during the winter and spring. Though fairly active, its swimming muscles exhibit lower activity of glycolytic
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s and higher activity of creatine phosphokinase compared to the shallow-water spiny dogfish
Spiny dogfish
The spiny dogfish, spurdog, mud shark, or piked dogfish, Squalus acanthias, is one of the best known of the dogfish which are members of the family Squalidae in the order Squaliformes. While these common names may apply to several species, Squalus acanthias is distinguished by having two spines ...
(Squalus acanthias), suggesting a lesser capacity for bursts of speed. The 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...
-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...
comprises about one-fifth of its total weight and functions in maintaining 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...
. Potential predators of the black dogfish are larger sharks and bony fishes. It is one of several deep-sea sharks parasitized by the barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
Anelasma squalicola, which attaches in front of the second dorsal fin and impairs the reproductive development of its host. Other known parasites of this species include the fluke
Trematoda
Trematoda is a class within the phylum Platyhelminthes that contains two groups of parasitic flatworms, commonly referred to as "flukes".-Taxonomy and biodiversity:...
Otodistomum cestoides, 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 Neoalbionella fabricii and Neoalbionella centroscyllii, and the protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
ns Haemogregarina delagei and Trypanosoma rajae.
Rattail
Grenadiers or rattails are generally large, brown to black gadiform marine fish of the family Macrouridae...
s, whitings
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...
, rockfish
Sebastes
Sebastes is a genus of fish in the family Sebastidae , most of which have the common name of rockfish. Most of the world's almost 110 Sebastes species live in the north Pacific, although two live in the south Pacific/Atlantic and four Sebastes is a genus of fish in the family Sebastidae (though...
es, 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, and 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, as well as pelagic 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 such as krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
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...
, and 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. Fish become a progressively more important food source as the shark ages, while crustaceans become less important. Infrequently, polychaete worms and jellyfish
Scyphozoa
Scyphozoa is a class within the phylum Cnidaria, sometimes referred to as the "true jellyfish".The class name Scyphozoa comes from the Greek word skyphos , denoting a kind of drinking cup and alluding to the cup shape of the organism....
are also eaten. In the northwestern Atlantic, Greenland halibut
Greenland halibut
The Greenland halibut or Greenland turbot belongs to the Pleuronectidae family , and is the only species of the genus Reinhardtius. It is a deepwater fish distributed from 200 to 1600 m but has been caught at depths more than...
(Reinhardtius hippoglossoides) and rattail offal
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...
discarded from fishing vessels have become a major source of food for this species, particularly for older sharks that are capable of consuming larger pieces such as heads.
Life history
Reproduction in the black dogfish occurs year-round, with no well-defined seasonal pattern. This species is aplacental viviparous, in which the developing embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s are retained 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 are sustained to term solely by yolk. Mature 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. Fertilized eggs are ovulated
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...
into the uterus at a diameter of 3–4.5 cm (1.2–1.8 in), though a few may be retained in the ovary; the eggs are not enclosed in a capsule. The external 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 fully resorbed when the embryo is close to term, with the remaining yolk having been transferred to an internal yolk sac attached to the 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...
. The internal yolk sac serves to provision the newborn shark until it learns to feed. The litter size ranges from 4 to 40. Newborns measure 13–19 cm (5.1–7.5 in) long.
Various authors have reported the size at maturity as between 46 and 63 cm (18.1 and 24.8 in) for males and 51 and 70 cm (20.1 and 27.6 in) for females, reflecting differences between geographical areas. Off northern Canada, females give birth in the portion of the Laurentian Channel less than 400 m (1,312.3 ft) deep. As the young grow they migrate into the deeper parts of the Channel, and eventually a long distance northward over the Grand Banks or the Labrador Shelf
Labrador
Labrador is the distinct, northerly region of the Canadian province of Newfoundland and Labrador. It comprises the mainland portion of the province, separated from the island of Newfoundland by the Strait of Belle Isle...
, to the deep continental slope. This movement pattern has not been observed in black dogfish inhabiting adjacent waters off western Greenland. A number of anomalous hermaphroditic
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
specimens have been documented.
Human interactions
The black dogfish is harmless to humans and of little commercial value. Substantial numbers are caught incidentallyBycatch
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...
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...
deep-sea trawl, 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...
, and longline fisheries operating throughout the North Atlantic, including the Icelandic Greenland halibut fishery, the French mixed-species trawl fishery, and the Canadian Greenland halibut, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
, redfish
Sebastes
Sebastes is a genus of fish in the family Sebastidae , most of which have the common name of rockfish. Most of the world's almost 110 Sebastes species live in the north Pacific, although two live in the south Pacific/Atlantic and four Sebastes is a genus of fish in the family Sebastidae (though...
, monkfish
Monkfish
Monkfish is the English name of a number of types of fish in the northwest Atlantic, most notably the species of the anglerfish genus Lophius and the angelshark genus Squatina...
, and witch fisheries. Captured sharks are usually discarded, though in recent years this and other small deepwater sharks have been increasingly retained and utilized for fishmeal. Reported catches by European countries, of which France made the largest contribution, have followed a declining trend from 486 tons in 2001 to 35 tons in 2006. The average catch by Canadian fisheries was 68 tons per year from 1996 to 2005. The black dogfish occurs mostly too deep for fisheries off southern Africa; in the remainder of its range there is little information available on fishery impact.
The International Union for Conservation of Nature (IUCN) has listed the black dogfish under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
worldwide; it is minimally affected by fishing activity across many parts of its range, while its population in the northwestern Atlantic presently seems to be stable and may have increased from 1978 to 1995. By contrast, the intensity of deepwater fisheries in the northeastern Atlantic has led the IUCN to give this species a regional assessment of 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...
. The reproductive characteristics of the black dogfish, such as a large female maturation size, may render 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....
, though it is more fecund
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
than other deep-sea dogfish sharks. In the northwestern Atlantic, catches of this species are managed as part of the total allowable catch (TAC) for deep-sea sharks set by the International Council for the Exploration of the Sea (ICES).