The common skate (''Dipturus batis''), also known as the blue skate, is the largest

skate Skate or Skates may refer to: Fish *Skate (fish), several genera of fish belonging to the family Rajidae * Pygmy skates, several genera of fish belonging to the family Gurgesiellidae * Smooth skates or leg skates, several genera of fish belongin ...

in the world, attaining a length of up to .Griffiths AM, Sims DW, Cotterell SJ, El Nagar A, Ellis JR, Lynghammar A, McHugh M, Neat FC, Pade NG, Queiroz N, et al. 2010. Molecular markers reveal spatially-segregated cryptic species in a critically endangered fish, the common skate Dipturus batis. Proceedings of the Royal Society of London B 277: 1497–1503. Historically, it was one of the most abundant skates in the northeast

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

and the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...

. Despite its name, today it appears to be absent from much of this

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

. Where previously abundant, fisheries directly targeted this skate and elsewhere it is caught incidentally as bycatch. The species was uplisted to critically endangered on 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 biol ...

in 2006 and it is protected within the EU.ICES (11 October 201
5.3.12 Common skate (Dipturus batis-complex (blue skate (Dipturus batis) and flapper skate (Dipturus cf. intermedia)) in subareas 6–7 (excluding Division 7.d) (Celtic Seas and western English Channel)
. ICES Advice 2016, Book 5. Research published in 2009 and 2010 showed that the species should be split into two, the smaller southern ''D.''

cf. The abbreviation ''cf.'' (short for the la, confer/conferatur, both meaning "compare") is used in writing to refer the reader to other material to make a comparison with the topic being discussed. Style guides recommend that ''cf.'' be used onl ...

''flossada'' (blue skate), and the larger northern ''D.'' cf. ''intermedius'' (flapper skate).Is 80-Year-Old Mistake Leading to First Species to Be Fished to Extinction?
ScienceDaily 17 Nov 2009Iglesias SP, Toulhoat L, Sellos DY. 2009. Taxonomic confusion and market mislabelling of threatened skates: important consequences for their conservation status. Aquatic Conservation: Marine and Freshwater Ecosystems 20: 319–333. Under this taxonomic arrangement, the name ''D. batis'' is discarded.White W.T. and P.R. Last. 2012. A review of the taxonomy of chondrichthyan fishes: a modern perspective. Journal of Fish Biology 80: 901–917. Alternatively, the scientific name ''D. batis'' (with ''flossada'' as a synonym) is retained for the blue skate and ''D. intermedius'' for the flapper skate.

Description

The common skate can reach up to in length, in width, and in weight, making it the largest

in the world. Overall shape features a pointed snout and rhombic shape, with a row of spines or thorns along the tail. The top surface is generally coloured olive-grey to brown, often with a pattern of spots, and the underside is lighter blue-grey. It can be confused with several other skates in its range, such as '' D. nidarosiensis'', '' D. oxyrinchus'', and '' Rostroraja alba''.

Range, habitat, and ecology

The common skate is native to the northeast Atlantic. It is a bottom dwelling species mainly found at depths of 100-200m, but it can occur as shallow as 30m and as deepth as 1000m. Now, their population and range are severely depleted and fragmented, with disappearances being reported on several places. This species is found in northeastern Atlantic from Norway and Iceland to Senegal. Its presence in the

is questionable since earlier records could concern ''D. intermedius'' recently considered as a distinct species.

Growth and reproduction

The common skate can reach an estimated age of 50–100 years and maturity is reached when about 11 years old. The size where they reach maturity depend on sex and population. In ''D.'' cf. ''flossada'' (blue skate) males reach maturity when about long and females when about long.ICES (October 2012). . Retrieved 31 December 2017. In ''D.'' cf. ''intermedia'' (flapper skate), males reach maturity when about long and females when about long. The sex ratio is 1:1, but this can vary depending on geography and season. When hatching, juveniles measure up to long. Once they have reached sexual maturity, they reproduce only every other year. They mate in the spring, and during the summer, females lay about 40 egg cases in sandy or muddy flats. The eggs develop for 2–5 months before hatching.

Egg case

Egg cases measure up to long, excluding the horns, and wide. They are covered in close-felted fibers and often wash up on the shore. Egg case hunts have been done throughout the general distribution of the common skate. In the British Isles, egg cases were found only in northern

Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

and the north of Ireland. In the 19th and 20th centuries, egg cases were seen along the entire British coastline in high numbers, but now they are found only in a few areas.

Diet

Like other skates, the common skate is a bottom feeder. Its diet consists of

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

clam Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two shel ...

oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...

s, snails,

bristle worm Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ...

s, cephalopods, and small to medium-sized fish (such as

sand eel Sand eel or sandeel is the common name used for a considerable number of species of fish. While they are not true eels, they are eel-like in their appearance and can grow up to in length. Many species are found off the western coasts of Europe ...

, flatfish,

monkfish Members of the genus ''Lophius'', also sometimes called monkfish, fishing-frogs, frog-fish, and sea-devils, are various species of lophiid anglerfishes found in the Atlantic and Indian Oceans. ''Lophius'' is known as the "monk" or "monkfish" ...

, catsharks,

spurdog ''Squalus'' is a genus of dogfish sharks in the family Squalidae. Commonly known as spurdogs, these sharks are characterized by smooth dorsal fin spines, teeth in upper and lower jaws similar in size, caudal peduncle with lateral keels; upper ...

, and other skates). The size of the individual can affect its diet. Larger ones eat larger things like fish. The bigger the skate is, the more food will be needed to sustain its large body size. The activity level determines how much it eats; the more active it is, the more it eats. The common skate does not feed only on creatures at the bottom of the ocean, as some do ascend to feed on mackerel, herring, and other

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

fish, which are caught by rapidly moving up from the seabed to grab the prey.

Threatened status

The common skate is listed as a critically endangered species by the IUCN and it is threatened both in the Atlantic Ocean and Mediterranean Sea. The common skate's population has drastically decreased because of overfishing and it likely will disappear entirely unless more is done to preserve it. It has both been targeted directly and caught incidentally as bycatch. Due to the profitability of trawl fishing, bycatch likely will remain a serious problem for the common skate. The species is

extirpated Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...

in the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and ...

. Remaining strongholds where it remains locally common are off western Scotland and in the

Celtic Sea The Celtic Sea ; cy, Y Môr Celtaidd ; kw, An Mor Keltek ; br, Ar Mor Keltiek ; french: La mer Celtique is the area of the Atlantic Ocean off the southern coast of Ireland bounded to the east by Saint George's Channel; other limits includ ...

.ICES (2017). . Retrieved 31 December 2017. A stronghold along the coast of Norway has been suggested, but recent studies indicate the species is rare there and many previous records are the result of misidentifications of other skates. Because the common skate is long-lived and slow to mature, it may be slow to repopulate, but experience with the related

barndoor skate The barndoor skate (''Dipturus laevis'') is a species of marine cartilaginous fish in the skate family Rajidae of the order Rajiformes. It is native to the northwestern Atlantic Ocean, and is found from the Grand Banks of Newfoundland and the ...

(''D. laevis'') of the northwest Atlantic indicates that a population recovery may be possible in a relatively short time. The common skate is strictly protected within the EU, making it illegal for commercial fishers to actively fish for it or keep it if accidentally landed. Like other

elasmobranchs Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of gil ...

, it is believed to have a good chance of surviving if released after being caught.

Taxonomy

Distinct genetic and morphological differences exist within the common skate as traditionally defined, leading to the recommendation of splitting it into two species: The smaller (up to about in length) southern ''D.''

''flossada'' (blue skate), and the larger and slower-growing northern ''D.'' cf. ''intermedius'' (flapper skate). Under this taxonomic arrangement, the name ''D. batis'' is discarded. Alternatively, the scientific name ''D. batis'' (with ''flossada'' as a synonym) is retained for the blue skate and ''D. intermedius'' for the flapper skate. A formal request of preserving the name ''D. batis'' (with ''flossada'' as a synonym) for the blue skate has been submitted to the International Commission on Zoological Nomenclature, but as of 2017 a decision is still pending. Based on molecular

phylogenetics In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...

, ''D.'' cf. ''intermedius'' is very close to '' D. oxyrinchus'', while the relationship to ''D.'' cf. ''flossada'' is more distant. ''D.'' cf. ''intermedius'' has dark olive-green eyes and the blotch on each wing consists of a group of pale spots. ''D.'' cf. ''flossada'' has pale yellow eyes, and the blotch on each wing is relatively large, roughly round, dark and with a pale ring around it. Additional differences between the two are found in the thorns on their tails and other

morphometric Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...

features. Both are found around the British Isles, and their ranges broadly overlap in the seas around this archipelago, but ''D.'' cf. ''intermedius'' is the most frequent species in the northern half (off Scotland and

Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...

), and ''D.'' cf. ''flossada'' is the most frequent in the southwest (Celtic Sea) and at

Rockall Rockall () is an uninhabitable granite islet situated in the North Atlantic Ocean. The United Kingdom claims that Rockall lies within its exclusive economic zone (EEZ) and is part of its territory, but this claim is not recognised by Ireland. ...

.ICES (October 2012). . Retrieved 31 December 2017. The primary—possibly only—species in Ireland is ''D.'' cf. ''flossada'' based mainly on the ICES International Bottom Trawl Survey and

zoological specimen A zoological specimen is an animal or part of an animal preserved for scientific use. Various uses are: to verify the identity of a (species), to allow study, increase public knowledge of zoology. Zoological specimens are extremely diverse. Exampl ...

s, the species off Norway is ''D.'' cf. ''intermedius'' (no confirmed records of ''D.'' cf. ''flossada'', but it might occur), and based on limited data the main in the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...

Skagerrak The Skagerrak (, , ) is a strait running between the Jutland peninsula of Denmark, the southeast coast of Norway and the west coast of Sweden, connecting the North Sea and the Kattegat sea area through the Danish Straits to the Baltic Sea. T ...

and

Kattegat The Kattegat (; sv, Kattegatt ) is a sea area bounded by the Jutlandic peninsula in the west, the Danish Straits islands of Denmark and the Baltic Sea to the south and the provinces of Bohuslän, Västergötland, Halland and Skåne in Sweden ...

is ''D.'' cf. ''intermedius'' (although at least one record of ''D.'' cf. ''flossada'' in this region, off west Sweden, has been reported). Uncertainty exists about the exact species involved in the southern half of the range, but a preliminary morphological study indicates that the one in the

Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...

is ''D.'' cf. ''intermedius''.

References

External links

* * {{Taxonbar, from=Q1421947 common skate Endangered fish Fish of the East Atlantic Fish of the North Sea common skate common skate