The spiny dogfish (''Squalus acanthias''), spurdog, mud shark, or piked dogfish is one of the best known

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of the

Squalidae Squalidae, more commonly known as dogfish, dog sharks, or spiny dogfish, are one of several families of sharks categorized under Squaliformes, making it the second largest order of sharks, numbering 119 species across 7 families. Having earned t ...

(dogfish)

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

s, which is part of the

Squaliformes The Squaliformes are an order of sharks that includes about 126 species in seven families. Members of the order have two dorsal fins, which usually possess spines, they usually have a sharp head, no anal fin or nictitating membrane, and fiv ...

order. While these common names may apply to several species, ''Squalus acanthias'' is distinguished by two spines (one

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

to each

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

) and no

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

. It lives in shallow waters and further offshore in most parts of the world, especially in temperate waters. Those in the northern Pacific Ocean were reevaluated in 2010 and found to constitute a separate species, now called the Pacific spiny dogfish (''Squalus suckleyi'').

Description and behaviour

The spiny dogfish has dorsal fins, no anal fin, and white spots along its back. The

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

fin has asymmetrical lobes, forming a

heterocercal Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

tail. The species name ''acanthias'' refers to the shark's two spines. These are used defensively. If captured, the shark can arch its back to pierce its captor with spines near the dorsal fins that secrete a mild venom into its predator. This shark is known to hunt in packs that can range up into the thousands. They are aggressive hunters and have a sizable diet that can range from squid, fish, crab, jellyfish, sea cucumber, shrimp and other invertebrates. Dogfish sharks experience one of the longest gestation periods of any organism, which can last from around 18 to 24 months. During spawning season, which occurs during the colder months of winter, females can lay anywhere from 2 to 12 eggs, which develop ovoviviparously and the pups are birthed as live young, with about 5 to 6 in each litter of pups, mainly depending on the size of the female. Reproduction occurs in the winter in offshore waters, while pups are normally born in the warmer and deeper offshore waters where it is harder for humans and predators to reach them. The reproductive cycle begins when females produce several large eggs of yellow coloring, which become fertilized once they pass through the shell gland and are wrapped in what is called a "candle", or a kind of reproductive capsule. One can determine if an egg is fertilized when the

blastoderm A blastoderm (germinal disc, blastodisc) is a single layer of embryonic epithelial tissue that makes up the blastula. It encloses the fluid filled blastocoel. Gastrulation follows blastoderm formation, where the tips of the blastoderm begins the fo ...

is visible. The candle passes through the rest of the reproductive tract until it reaches the uterus. Attached to the gill region of the pup is a yolk sac which provides nutrients for them as they develop, which they absorb as they grow. Even after fully absorbing the yolk sac, the pups may live in the uterus for a period of time afterwards during the gestation period. Both sexes are greyish brown in color and are

countershaded Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, an ...

. Males are identified by a pair of pelvic fins modified as sperm-transfer organs, or "claspers". The male inserts one clasper into the female cloaca during copulation. In females the size of ova and the state of uteri determines whether sexual maturity has been reached, while in males, clasper length and calcification is the determination factor. Many of the growth patterns show a isometric growth pattern, as the pups have very similar features to the adults. Sexual maturity does not match body size development, they mature quite earlier than one would expect. Most males reach sexual maturity at an earlier ages of around 10 years, growing to be about 60–65 cm in length. Females take a longer period of time, around 16 years, to reach sexual maturity, and can grow to about at that time. Some dogfish have been seen to live nearly 70 years, but the average lifespan is around 30–40 years. Male Spiny dogfish use their

clasper In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's c ...

s to impregnate females, which take time to develop properly, and before reaching sexual maturity, tend to be longer than their

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two ...

s. During this time, the testes develop, but no sperm will exist inside until later stages are reached, and genital ducts are deformed compared to adult ducts. Once the adult stage is reached, claspers have elongated, and are now hardened with calcium and are still slightly longer than their pelvic fin. At this point testes are fully developed, and sperm exist within the seminal vesicles, and genital ducts conform to a twisted shape we commonly see in adults. Spiny dogfish are bottom-dwellers. They are commonly found at depths of around , but have been found deeper than . Life span estimates based on analysis of vertebral centra and annuli in the dorsal spines range from 35 to 54 years. Aiguillat commun (tete).jpg, Head Squalus acanthias jaws.jpg, Jaws Squalus acanthias upper teeth.jpg, Upper teeth Squalus acanthias lower teeth.jpg, Lower teeth

Commercial use

Spiny dogfish are sold as food in Europe, the United States, Canada, New Zealand, Venezuela and Chile. The meat is primarily eaten in England, France, Italy, the Benelux countries, Germany, and as an unwitting houndshark in Greece. The fins and tails are processed into

fin needles A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

for cheaper versions of shark fin soup in Chinese cuisine. In England, dogfish are bought in fish and chip shops as "huss", and previously as "rock salmon" until the term was outlawed. In France, they are sold as "small salmon" (''saumonette'') and in Belgium and Germany as "sea eel" (''zeepaling'' and ''Seeaal'', respectively). In Greece, all small dogfish are commercially called ''galéos'', after the critically endangered

Galeorhinus galeus The school shark (''Galeorhinus galeus'') is a houndshark of the family Triakidae, and the only member of the genus ''Galeorhinus''. Common names also include tope, tope shark, snapper shark, and soupfin shark. It is found worldwide in temperate ...

that produces a seasonal dish; other small sharks as the spiny dogfish substitute it. Spiny dogfish bodies are ground into fertilizer, liver oil and pet food. Because of their availability, cartilaginous skulls and small sizes, they are popular

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

dissection specimens in high schools and universities. Reported catches varied between 31,700 tonnes in 2000 and 13,800 tonnes in 2008. Bottom trawlers and sink

gillnet Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...

s are the primary tools. In Mid-Atlantic and Southern New England fisheries, they are often caught with larger

groundfish Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes (the demersal zone).Walrond Carl . "Coastal fish - Fish of the open sea floor"Te Ara - the Encyclopedia of New Zealand. Updated 2 March 2009 They oc ...

, classified as

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 ...

, and discarded. Recreational fishing accounts for an insignificant portion of the spiny dogfish catch. The Cape Cod Commercial Fishermen's Alliance promotes sustainable use of the dogfish in restaurants and fish markets in the

Cape Cod Cape Cod is a peninsula extending into the Atlantic Ocean from the southeastern corner of mainland Massachusetts, in the northeastern United States. Its historic, maritime character and ample beaches attract heavy tourism during the summer mont ...

area of

Massachusetts Massachusetts (Massachusett: ''Muhsachuweesut Massachusett_writing_systems.html" ;"title="nowiki/> məhswatʃəwiːsət.html" ;"title="Massachusett writing systems">məhswatʃəwiːsət">Massachusett writing systems">məhswatʃəwiːsət'' En ...

, as of 2017, paid for by the

National Oceanographic and Atmospheric Administration The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...

. It aims to persuade diners to buy less-popular fish.

Conservation status and management

Once the most abundant shark species in the world, populations of ''Squalus acanthias'' have declined significantly. They are classified in the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biolo ...

of threatened species as Vulnerable globally and Critically endangered in the Northeast Atlantic, meaning stocks around Europe have decreased by at least 95%. This is a direct result of

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in t ...

to supply northern Europe's taste for rock salmon, saumonette, and zeepaling. Despite these alarming figures, very few management or conservation measures are in place for ''Squalus acanthias''. In EU waters, a

Total Allowable Catch The Common Fisheries Policy (CFP) is the fisheries policy of the European Union (EU). It sets quotas for which member states are allowed to catch each type of fish, as well as encouraging the fishing industry by various market interventions. I ...

(TAC) has been in place since 1999, but until 2007 it only applied to ICES Areas IIa and IV. It was also set well above the actual weight of fish being caught until 2005, rendering it meaningless. Since 2009 a maximum landing size of has been imposed in order to protect the most valuable mature females. The TAC for 2011 was set at 0 tons, ending targeted fishing for the species in EU waters. It remains to be seen if populations will be able to recover. In the recent past the European market for spiny dogfish has increased dramatically, which led to the

and decline of the species. This drastic increase led to the creation and implementation of many fishery management policies placing restrictions on the fishing of spiny dogfish. However, since the species is a late-maturing fish, it takes a while to rebuild the population. In 2010, Greenpeace International added the spiny dogfish to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries." In the same year, the

Convention on Migratory Species The Convention on the Conservation of Migratory Species of Wild Animals, also known as the Convention on Migratory Species (CMS) or the Bonn Convention, is an international agreement that aims to conserve migratory species throughout their r ...

(CMS; also known as the

Bonn Convention The Convention on the Conservation of Migratory Species of Wild Animals, also known as the Convention on Migratory Species (CMS) or the Bonn Convention, is an international agreement that aims to conserve migratory species throughout their r ...

) listed the species (Northern Hemisphere populations) under Annex I of its Migratory Shark Memorandum of Understanding. In recent years, however, the US has implemented fishing controls and The proposed quota for 2011 was with a trip limit of , an increase over past years in which the quota has ranged from , with trip limits from . In 2010, NOAA announced the Eastern US Atlantic spiny dogfish stocks to be rebuilt, and in 2011, concerns about dogfish posing a serious predatory threat to other stocks resulted in an emergency amendment of the quota with nearly being added. In June 2018, the New Zealand

Department of Conservation An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as Ministry of the Environment ...

classified ''Squalus acanthias'' Linnaeus as "Not Threatened" with the qualifier "Secure Overseas" under the

New Zealand Threat Classification System The New Zealand Threat Classification System is used by the Department of Conservation to assess conservation priorities of species in New Zealand. The system was developed because the IUCN Red List, a similar conservation status system, had some ...

Fossil range

''Squalus acanthias'' fossils are known from the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

of Denmark and the Netherlands, dating from approximately 11 million years ago. As with other cartilaginous fish, the fossil record of ''Squalus acanthias'' consists predominantly of dental material, as cartilage does not fossilize well. The teeth of ''S. acanthus'' can be hard to differentiate from those of other squaliforme sharks, making identification difficult.

References

External links

Spiny dogfish
at ''Animal Diversity Web'' * *

3D model of a spiny dogfish splanchnocranium
{{Authority control spiny dogfish Fish of the Americas Marine fish of Europe Marine fish of New Zealand Fish of the Mediterranean Sea Fish of the Black Sea Marine fauna of North Africa Marine fauna of East Asia Marine fish of South Africa Marine fish of Southern Australia Cosmopolitan fish spiny dogfish spiny dogfish Species endangered by use as food