The thornback ray (''Raja clavata''), or thornback skate, is a species of

ray fish Batoidea is a superorder of cartilaginous fishes, commonly known as rays. They and their close relatives, the sharks, comprise the subclass Elasmobranchii. Rays are the largest group of cartilaginous fishes, with well over 600 species in 26 fa ...

in the family Rajidae.Fishbase.org: ''Raja clavata''
/ref>

Distribution

The Thornback ray is found in the Atlantic

coastal The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...

waters of Europe and western Africa. It is also present from south Africa to the southwestern Indian Ocean and in the Mediterranean and Black Seas. It is native possibly as far south as Namibia and South Africa. Its natural

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s are open large

sea The sea, connected as the world ocean or simply the ocean, is the body of salty water that covers approximately 71% of the Earth's surface. The word sea is also used to denote second-order sections of the sea, such as the Mediterranean Sea, ...

s and shallow seas. It is sometimes seen trapped in large

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

pools at low tide. The thornback ray is probably one of the most common rays encountered by divers.

Habitat

The thornback ray is usually found on sedimentary seabeds such as mud, sand or gravel at depths between 10-60m. Juvenile fish feed on small

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 ...

s, particularly

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...

s and bottom-living

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

s; adults feed on

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

s, shrimps and small fish.

Description

Like all rays, the thornback ray has a flattened body with broad, wing-like

pectoral 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 ...

s. The body is kite-shaped with a long, thorny tail. The back is covered in numerous thorny spines, as is the underside in older females. Adult fish can grow to in length, although most are less than . This ray can weigh from 4.5 to 8.75 lb (2 to 4 kg). Their colours vary from light brown to grey with darker blotches and numerous small darker spots and yellow patches. Sometimes the yellow patches are surrounded by small dark spots. The underside is creamy-white with a greyish margin. When threatened they can appear black.Oceanario.pt: ''Raja clavata''
/ref> In sexually mature fish, some of the spines are thickened with button-like bases (known as bucklers). These are particularly well developed on the tails and backs of sexually mature females. Raja clavata no

Taxonomy

''Raja clavata'', the thornback ray (or thornback skate, roker), was named by

Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

in the

10th edition of Systema Naturae The 10th edition of ''Systema Naturae'' is a book written by Swedish naturalist Carl Linnaeus and published in two volumes in 1758 and 1759, which marks the starting point of zoological nomenclature. In it, Linnaeus introduced binomial nomencla ...

in 1758, in the genus

Raja ''Raja'' (; from , IAST ') is a royal title used for South Asian monarchs. The title is equivalent to king or princely ruler in South Asia and Southeast Asia. The title has a long history in South Asia and Southeast Asia, being attested f ...

'' of the Order

Rajiformes Rajiformes is one of the four orders in the superorder Batoidea, flattened cartilaginous fishes related to sharks. Rajiforms are distinguished by the presence of greatly enlarged pectoral fins, which reach as far forward as the sides of the head ...

in the Family Rajidae. It is one of about 13 species of

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 ...

(family Rajidae) that are known from the

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

and adjacent Atlantic waters.

Common names

Raie bouclée Raja clavata Vannes 20082012 2

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 contrast ...

s include: * Danish — Sømrokke. * Dutch — Stekelrog. * English — Roker / Thornback ray / Dorn. * Estonian — Astelrai. * Faeroese — Naglaskøta. * Finnish — Okarausku. * French — Raie bouclée. * German — Nagelrochen. * Icelandic — Dröfnuskata. * Latvian — Dzelkņraja. * Norwegian — Piggskate. * Polish — Raja nabijana a. ciernista. * Portuguese — Raia lenga / Raia brocheada * Russian — Колючий скат. * Spanish — Raya de clavos. * Swedish — Knaggrocka.

Morphometrics

Dorsal spines : 0; Anal spines: 0; Anal soft rays: 0. ; disc-width 1,25 to 1,36 times in its length, its length 1,70 to 1,83 times in total length; pectoral fins with clear angles on lateral side; triangular pelvic fins . Dorsally prickly; large females also prickly throughout their ventral surface; young and large males prickly along the borders of their discs and the underside of their snout. 30-50 thorns form a median row from the nape to the first dorsal fin; additional large 'buckler' thorns with swollen bases scattered on upper surface of disc in adults . Max length : 105 cm male/unsexed; 139.0 cm (female); common length : 85.0 cm ; max. weight: 18.0 kg. Thornback ray on a white background

Life cycle

Oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

Polyandrous Polyandry (; ) is a form of polygamy in which a woman takes two or more husbands at the same time. Polyandry is contrasted with polygyny, involving one male and two or more females. If a marriage involves a plural number of "husbands and wives" ...

species. Paired eggs are laid and deposited on shallow sand, mud, pebble or gravel bottoms . Up to 170 egg cases can be laid by a single female in a year, average fecundity around 48-74 eggs. In northwestern Europe, egg cases are laid during spring, and in the Mediterranean during winter and spring. Egg cases are oblong capsules with stiff pointed horns at the corners, each containing one embryo. Capsules are 5.0-9.0 cm long without the horns and 3.4-6.8 cm wide. Egg cases are anchored with an adhesive film. Embryos feed solely on yolk. Egg cases hatch after about 4–5 months and pups are about 11–13 cm. Mating season is from February to September, peaking in June. Adults observed to form same-sex aggregations during the mating season with females moving to shallower inshore waters approximately a month before the males. Mating does not occur in the Baltic Sea. This is one of the fish used by the marine leech ''

Pontobdella muricata ''Pontobdella muricata'' is a species of marine leech in the family Piscicolidae. It is a parasite of fishes and is native to the northeastern Atlantic Ocean, the Baltic Sea, the North Sea, and the Mediterranean Sea. Description ''Pontobdella mu ...

'' as a

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman * Michel Host ...

. ;British Isles population Nagelrochen nhm

A search about the growth and maturation of ''Raja clavata'' in the

Solway Firth The Solway Firth ( gd, Tràchd Romhra) is a firth that forms part of the border between England and Scotland, between Cumbria (including the Solway Plain) and Dumfries and Galloway. It stretches from St Bees Head, just south of Whitehaven in ...

(part of the border between

Cumbria Cumbria ( ) is a ceremonial and non-metropolitan county in North West England, bordering Scotland. The county and Cumbria County Council, its local government, came into existence in 1974 after the passage of the Local Government Act 1972. Cumb ...

, England and

Dumfries and Galloway Dumfries and Galloway ( sco, Dumfries an Gallowa; gd, Dùn Phrìs is Gall-Ghaidhealaibh) is one of 32 unitary council areas of Scotland and is located in the western Southern Uplands. It covers the counties of Scotland, historic counties of ...

, Scotland) shows that the males and females appear to mature at 42 and 45 cm in disc width respectively. The Solway population is heavily exploited by an unrestricted commercial fishery and a considerable proportion (48.6%) of the retained catch is immature. It is suggested that fishing pressure has brought about a reduction in the size at which female fish mature.

References

* Picton, B.E. & Morrow, C.C., 2005. — ''Encyclopedia of Marine Life of Britain and Ireland''.
Habitas.org.uk: ''Raja clavata'' (Thornback ray)

External links

*
Fishbase.org Database: ''Raja clavata'' IUCN Red List of all current Threatened Species
* {{Authority control

thornback ray The thornback ray (''Raja clavata''), or thornback skate, is a species of ray fish in the family Rajidae. Distribution The Thornback ray is found in the Atlantic coastal waters of Europe and western Africa. It is also present from south Afri ...

Fish of the East Atlantic Fish of the Mediterranean Sea Fish of the North Sea Near threatened biota of Africa Near threatened biota of Europe

Taxonomy articles created by Polbot