Thornback ray

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Thornback ray
Raja clavata (juv).jpg
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Rajiformes
Family: Rajidae
Genus: Raja
Species:
R. clavata
Binomial name
Raja clavata

The thornback ray (Raja clavata), or thornback skate, is a species of ray fish in the family Rajidae. [2]

Contents

Distribution

It is found in coastal waters of Europe and the Atlantic coast of western Africa and Mediterranean Sea coast of North Africa. It is native possibly as far south as Namibia and South Africa. [2]

Its natural habitats are open large seas and shallow seas. It is sometimes seen trapped in large estuarine pools at low tide. [2]

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 10–60 metres (33–197 ft). Juvenile fish feed on small crustaceans, particularly amphipods and bottom-living shrimps; adults feed on crabs, shrimps and small fish.

Description

Like all rays, the thornback ray has a flattened body with broad, wing-like pectoral fins. 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. [2] [3]

Adult fish can grow to 1 metre (3.3 ft) in length, although most are less than 85 centimetres (33 in). This ray can weigh from 4.5 to 8.75 lb (2 to 4 kg). [4]

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. [5] [6]

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. [6]

Personificated face of a Raja clavata . Raja clavata no.JPG
Personificated face of a Raja clavata .

Taxonomy

Raja clavata, the thornback ray (or thornback skate, roker), was named by Carl Linnaeus in the 10th edition of Systema Naturae in 1758, in the genus Raja of the Order Rajiformes in the Family Rajidae. [2]

It is one of about 13 species of skate (family Rajidae) that are known from the North Sea and adjacent Atlantic waters.

Common names

Raja clavata at the Aquarium de Vannes. Raie bouclee Raja clavata Vannes 20082012 2.jpg
Raja clavata at the Aquarium de Vannes.

Common names include: [7]

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.

Top side view of Thornback ray on a white background. Thornback ray on a white background.jpg
Top side view of Thornback ray on a white background.

Life cycle

Oviparous. Polyandrous 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. [2] This is one of the fish used by the marine leech Pontobdella muricata as a host. [8]

British Isles population
Skeletal mount Nagelrochen nhm.jpg
Skeletal mount

A search about the growth and maturation of Raja clavata in the Solway Firth (part of the border between Cumbria, England and Dumfries and Galloway, 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. [9]

See also

Related Research Articles

Skate (fish) Family of fishes

Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. More than 150 species have been described, in 17 genera. Softnose skates and pygmy skates were previously treated as subfamilies of Rajidae, but are now considered as distinct families. Alternatively, the name "skate" is used to refer to the entire order of Rajiformes.

Rajiformes order of fishes

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, with a generally flattened body. The undulatory pectoral fin motion diagnostic to this taxon is known as rajiform locomotion. The eyes and spiracles are located on the upper surface of the head and the gill slits are on the underside of the body. Most species give birth to live young, although some lay eggs with a horny capsule.

Prickly dogfish species of fish

The prickly dogfish is a poorly known species of dogfish shark in the family Oxynotidae, inhabiting temperate Australian and New Zealand waters. Reaching a length of 75 cm (30 in), this brown to gray shark has a very thick body with a prominent "humpback" and extremely rough skin. It is further characterized by two enormous, sail-like dorsal fins placed relatively close together. Both dorsal fins have a spine embedded mostly within the fleshy leading portion of the fin; the first dorsal spine is tilted forward.

<i>Raja</i> (fish) genus of fishes

Raja is a genus of skates in the family Rajidae containing 16 species. Formerly a wastebasket genus, many species historically placed here have been moved to other genera in the family, such as Amblyraja, Beringraja, Dipturus, Leucoraja and Rostroraja. Raja are flat-bodied, cartilaginous fish with a rhombic shapes due to their large pectoral fins extending from or nearly from the snouts to the bases of their tails. Their sharp snouts are produced by a cranial projection of rostral cartilage. The mouth and gills are located on underside of the body. They may be either solid-coloured or patterned, and most skates have spiny or thorn-like structures on the upper surface, and some species contain weak electrical organs within their tails. Mating typically occurs in the spring and the female lays numerous eggs per clutch which are encapsulated in leathery cases, commonly known as "mermaid’s purses". Species vary in size, ranging from about 40 to 140 cm (1.3–4.6 ft) in length. These bottom-dwellers are active during both day and night, and typically feed on molluscs, crustaceans and fish. Raja skates are found in the East Atlantic, including the Mediterranean, and western Indian Ocean, ranging from relatively shallow water to a depth of 800 m (2,600 ft). Skates and related species have fossil records dating from the Upper Cretaceous period, thus this well adapted species is quite ancient.

<i>Mullus barbatus</i> species of fish

Mullus barbatus is a species of goatfish found in the Mediterranean Sea, Sea of Marmara, the Black Sea and the eastern North Atlantic Ocean, where its range extends from Scandinavia to Senegal. They are fished, mostly by trawling, with the flesh being well regarded. The International Union for Conservation of Nature has assessed their conservation status as being of "least concern".

Deepsea skate species of fish

The deepsea skate is a species of softnose skate, in the family Arhynchobatidae, found in deep water from 362 to 2,906 m, usually on the continental slope. They are distributed from off northern Baja California around Coronado Island and Cortes Bank, north to the Bering Sea, and west to Japan. It is fairly common below 1,000 m, and is taken as bycatch in deepwater trawls and traps. The species name abyssicola comes from the Greek abyssos meaning "bottomless", and cola meaning "living at depths".

Big skate species of fish

The big skate is the largest species of skate in the waters off North America. They are found along the Pacific Coast from Alaska to Baja California, typically from the intertidal zone to a depth of 120 m (390 ft), and feed on benthic invertebrates and small fishes. They are unusual among skates in that their egg cases may contain up to seven eggs each. This species is one of the most commercially important skates off California and is sold for food.

Bottlenose skate Rostroraja alba

The bottlenose skate, spearnose skate, or white skate is a species of skate in the family Rajidae. It is a benthic fish native to the coastal eastern Atlantic Ocean. Due to overfishing, it has been depleted or extirpated in many parts of its former range in the northeastern Atlantic and the Mediterranean Sea, and is now endangered.

Broad skate species of fish

The broad skate is a poorly known species of skate in the family Rajidae. It occurs at depths of 846 to 2,324 metres, and has been observed via remotely operated underwater vehicle by the Monterey Bay Aquarium Research Institute as deep as 3,167 metres (10,390 ft), making it one of the deepest-occurring skates known. It is sporadically distributed in the Pacific Ocean, from the Gulf of Panama to British Columbia and the Bering Sea, to the Tohoku Slope off northern Honshu and the Okhotsk Slope off Hokkaido. The species name, badia, comes from the Latin batius meaning "brown", referring to its color.

Undulate ray species of fish

The undulate ray is a species of ray and cartilaginous fish found in the Mediterranean and East Atlantic from southern Ireland and England to the Gulf of Guinea. It is found in areas with mud or sand, and may occur as deep as 200 m (660 ft), though it prefers shallower depths. It is considered endangered due to overfishing.

Shagreen ray species of fish

The shagreen ray, also known as shagreen skate or fuller's ray, is a species of skate in the family Rajidae. This ray is found in the eastern Atlantic Ocean, from Murmansk, Russia through Norway, southern Iceland, the Faroe Islands, the Celtic Sea, the northern North Sea and Skagerrak, to northern Morocco, including (infrequently) the western Mediterranean Sea and the Madeira Islands. It is absent from the shallow waters off England and Wales.

Mottled skate species of fish

The mottled skate is a species of skate in the family Rajidae. An inhabitant of shallow coastal waters, it is found in the northwestern Pacific Ocean off Korea, Japan, and China. This species grows to 1.12 m (3.7 ft) long and has a diamond-shaped pectoral fin disc with a long snout. It is characterized by a covering of prickles above and below its snout, but not elsewhere on its body, and a dark ring in the middle of each "wing".

Jensen's skate, also known as the shortail skate, is a poorly known species of fish discovered in 2004 during a study of bottom ichthyofauna aboard the Norwegian RV G.O. Sars, where four species were identified, including A. jensieni.

Black scorpionfish species of fish

The black scorpionfish is a venomous scorpionfish, common in marine subtropical waters. It is widespread in the Eastern Atlantic Ocean from the British Isles to the Azores and Canary Islands, near the coasts of Morocco, in the Mediterranean Sea and the Black Sea.

Clearnose skate species of fish

The clearnose skate is species of cartilaginous fish in the family Rajidae. R. eglanteria is also known by other common names such as the brier skate and summer skate. Clearnose skates are easily identified by the translucent patches on either side of their snouts and their mottled dorsal surface. They are found along the Atlantic and Gulf coasts of the United States in shallow waters of the continental shelf.

Pita skate species of fish

The pita skate is a medium-sized skate in the family Rajidae. The holotype and only known specimen was found in the northern Persian Gulf, in Iraqi waters. It was collected at a depth of less than 15 m (49 ft).

<i>Raja texana</i> species of fish

The roundel skate or Texas clearnose skate is a species of cartilaginous fish in the family Rajidae. It is found in the Gulf of Mexico, Southeast Florida and the Yucatan Peninsula.

<i>Raja straeleni</i> species of fish

Raja straeleni, the biscuit skate or spotted skate, is a species of marine fish in the skate family of order Rajiformes. It is native to the eastern Atlantic Ocean.

<i>Raja stellulata</i> species of fish

Raja stellulata, commonly known as the Pacific starry skate, rock skate, prickly skate, or starry skate, is a species of cartilaginous fish in the family Rajidae. It is found on rocky bottoms at 18–982 m depths in the Northeast and Eastern Central Pacific, from Coronado Bank in northern Baja California in Mexico to Barkley Sound in British Columbia, Canada. Females reach a maximum total length of 76.1 cm and a maximum age of 15 years, while males can be up to 71.7 cm long and live up to 14 years; the total length at birth is 15.5–22.5 cm. This skate prefers cold water with a temperature of 4.1–11.6°C.

<i>Pontobdella muricata</i> species of annelid

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.

References

  1. Ellis, J. (2016). "Raja clavata". IUCN Red List of Threatened Species . IUCN. 2016: e.T39399A103110667. doi: 10.2305/IUCN.UK.2016-3.RLTS.T39399A103110667.en . Retrieved 14 December 2017.
  2. 1 2 3 4 5 6 Fishbase.org: Raja clavata
  3. Filaman.ifm: Morphology of Raja clavata
  4. Kindersley, Dorling (2001,2005). Animal. New York City: DK Publishing. ISBN   0-7894-7764-5.Check date values in: |year= (help)
  5. Shark-references.com: Lists/literature by V.A. Vanov
  6. 1 2 Oceanario.pt: Raja clavata
  7. http://www.ices.dk/explore-us/projects/EU-RFP/EU Repository/ICES ICES Fish Map: species factsheet for Raja clavata
  8. "Pontobdella muricata Linnaeus, 1758". SeaLifeBase. Retrieved 27 December 2019.
  9. Nottage, A. S. (1983). "Growth and maturation of roker Raja clavata L. in the Solway Firth". Journal of Fish Biology. 23: 43–48. doi:10.1111/j.1095-8649.1983.tb02880.x.