Thorny skate Thorny Skate (Amblyraja radiata) - MywallpapersMobi

Thorny skate Thorny Skate (Amblyraja radiata)

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Canadian Marine Life Encyclopedia

Thorny Skate

Amblyraja radiata

  • Canadian Marine Life Encyclopedia

Also known as

Thorny back, thornback, maiden ray, starry ray, starry skate

Distribution

North Atlantic; Northwest Atlantic from Greenland and Hudson Bay South Carolina

Ecosystem/Habitat

Soft bottoms

Feeding Habits

Active predator

Conservation Status

Special concern/data deficient

Taxonomy

Order Rajiformes (skates & relatives); Family Rajidae (skates)

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Skates may look similar to flatfish, but they are actually much more closely related to sharks. Like sharks, a skate’s skeleton is made up of cartilage, which is softer and more flexible than bone. Skates commonly have small spines or modified scales on their bodies, but the thorny skate is aptly named because it is practically covered in these tiny thorny looking spines. They have a row of 10 to 20 large, conspicuous spines that run along their midline down their back and reaching their tail. They also have one large spine in front of and one behind each eye, large spines on each shoulder, and numerous smaller spines on their snout, pectoral fins and tail.

  • Description
  • Life Cycle
  • Fishing
  • Conservation Status
  • Further Reading

Thorny skates are flat and shaped like a rhomboid. They have a bluntly triangular snout and tail that is shorter than their body, with two dorsal fins at the end. Their eyes are on the dorsal (top) side of their body and their gills and mouth are on the ventral (under) side. Thorny skates are typically brown on their dorsal side with irregular dark spots, while their ventral side is white. They are rather large and can grow to just over 100 centimetres long from their snout to the tip of their tail; however their size varies greatly depending on geography.

Thorny skates, like many other sharks, skates and rays, are slow-growing, late to mature and long-lived. It is believed that thorny skates can live to be at least 28 years old, however 16 to 20 years old is more common. They reach maturity at around 11 years and are able to reproduce year-round. Females lay approximately 40 to 56 egg cases per year, which are also called “mermaid’s purses.” These egg cases are rectangular capsules with tendrils at each corner to help secure them to seaweed or rocks. Each containing a single skate embryo, or baby skate, which will feed off of the yolk sac inside the egg capsule. When the baby skate reaches about 10 to 12 centimetres long it is fully formed and will emerge from the capsule. At this stage, the young skate mainly feeds on amphipods, which are extremely small, shrimp-like crustaceans. As they grow, their diet shifts more toward other bottom-dwelling organisms including polychaete worms, decapods (such as crabs, lobster, shrimp) and fish. 

Currently, there is only one active fishery that targets thorny skates, which occurs on the Grand Banks off the southeast shore of Newfoundland. There also used to be a mixed fishery for both thorny skates and winter skates on the eastern Scotian Shelf, however that fishery was closed after both species saw great declines in abundance. Even so, thorny skates are caught as bycatch (incidental catch) in trawl, long line and gillnet fisheries across their range. Oceana Canada is campaigning to reduce bycatch in Canadian waters and help protect species like skates. Find out more at Oceana.ca/Bycatch .

Thorny skates were assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as of Special Concern in 2012. They were assessed as such because of population declines from the 1970s to 1990s due to high fishing pressure from groundfish fisheries. Population declines leading to closure of many groundfish fisheries in the 1990s has halted the decline of thorny skates in many regions. Although many populations of are now considered stable, they are still found in low numbers compared to historical averages. Bycatch is the greatest threat to the recovery of thorny skates in Canada today. Help protect skates from becoming bycatch at Oceana.ca/bycatch .

  • COSEWIC. (2012) COSEWIC assessment and status report on the Thorny skate, Amblyraja radiate, in Canada. Retrieved from: http://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_raie_epineuse_thorny_skate_1012_e.pdf
  • DFO. (2016, December 19). Thorny skate; Amblyraja radiata. Retrieved from: http://www.dfo-mpo.gc.ca/species-especes/skates/species/thorny-eng.html
  • DFO. (2012, March). Status updates for the Thorny skate in the Canadian Atlantic and Arctic Oceans and Smooth skate (Laurentian-Scotian and Funk Island Deep designatable units). Can. Sci. Advis. Sec. Sci. Response 2017/011. Retrieved from: http://www.dfo-mpo.gc.ca/csas-sccs/Publications/ScR-RS/2017/2017_011-eng.pdf
  • DFO. (2017, April 20). Species at risk public registry; Species profile; Thorny skate. Retrieved from: http://www.registrelep-sararegistry.gc.ca/species/speciesDetails_e.cfm?sid=1181
  • Fishbase. (n.d.). Amblyraja radiate; Starry ray. Retrieved from: http://www.fishbase.se/summary/2565
  • Kulka, D.W., Sulikowski, J., Gedamke, J., Pasolini, P. & Endicott, M. 2009. Amblyraja radiata. The IUCN Red List of Threatened Species 2009: e.T161542A5447511. Retrieved from: http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161542A5447511.en
  • NOAA. (2009, May 19). Species of concern; Thorny skate. Retrieved from: http://www.nmfs.noaa.gov/pr/pdfs/species/thornyskate_detailed.pdf
  • NOAA Fisheries. (n.d.). Thorny skate. Retrieved from: https://www.greateratlantic.fisheries.noaa.gov/protected/pcp/soc/thorny_skate.html


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Thorny Skate

Amblyraja radiata

SARA Status
No Status

NS
Special Concern

SC
Threatened

TH
Endangered

EN
Extirpated

EX

SARA Status

  • No Status NS
  • Special Concern SC
  • Threatened TH
  • Endangered EN
  • Extirpated EX
COSEWIC Status
Not at Risk

NR
Special Concern

SC
Threatened

TH
Endangered

EN
Extirpated

EX

COSEWIC Status

  • Not at Risk NR
  • Special Concern SC
  • Threatened TH
  • Endangered EN
  • Extirpated EX

Description

Thorny Skate (Amblyraja radiata) belongs to the Class Chondrichthyes, which includes all shark and skate species. Thorny Skate is a relatively large skate; it can reach up to 90 cm total length (7.5 kg) on the Labrador Shelf, 110 cm (12.5 kg) on the Grand Banks, and 100 cm (10 kg) in the Gulf of St. Lawrence, Scotian Shelf, and Gulf of Maine. It varies among regions in overall size, body proportions, number of thorns (except on its midline), growth, and age at maturity. It is distinguished from other skates in the Northwest Atlantic Ocean primarily by a row of 11–19 large thorns on the midline of its back and tail. The upper body colour can be highly variable among individual Thorny Skate, ranging from yellow-edged dark spots on light brown to an almost uniform dark brown. The underside of its body is uniformly white, rarely with a few small, non-symmetrical, darkly pigmented markings. Its average age at maturity is 11 years, and it lives at least 20–30 years.

Habitat

Thorny Skate live on the ocean bottom over a wide range of depths (18–1200 m) and usually in water temperatures of 0–10 °C. They can be found on a variety of bottom types, such as sand, gravel, mud, and broken shells.

Thorny Skate is the most widely distributed and abundant skate species in the North Atlantic Ocean. In Canadian waters, it is among the most widespread and abundant bottom-dwelling fish species and is continuously distributed from Baffin Bay, Davis Strait, Labrador Shelf, Grand Banks, Gulf of St. Lawrence, Scotian Shelf, and Bay of Fundy to Georges Bank. The highest concentrations of this fish in these waters are found along the southern Grand Banks off Newfoundland and on the eastern portion of the Scotian Shelf.

Approximate boundary of Thorny Skate distribution in Canada, as adapted from COSEWIC 2012.

Map depicting the Canadian distribution of Thorny Skate. In Canadian waters, it is continuously distributed from Baffin Bay, Davis Strait, Labrador Shelf, Grand Banks, Gulf of St. Lawrence, Scotian Shelf, and Bay of Fundy to Georges Bank. This map was adapted from the Committee on the Status of Endangered Wildlife in Canada ( COSEWIC) 2012 assessment and status report on the Thorny Skate (Amblyraja radiata) in Canada.

‘>Thorny Skate distribution

Approximate boundary of Thorny Skate distribution in Canada, as adapted from COSEWIC 2012.

Map depicting the Canadian distribution of Thorny Skate. In Canadian waters, it is continuously distributed from Baffin Bay, Davis Strait, Labrador Shelf, Grand Banks, Gulf of St. Lawrence, Scotian Shelf, and Bay of Fundy to Georges Bank. This map was adapted from the Committee on the Status of Endangered Wildlife in Canada ( COSEWIC) 2012 assessment and status report on the Thorny Skate (Amblyraja radiata) in Canada.

Threats

COSEWIC states that threats include both directed fishing and bycatch, as well as predation in the south (e.g., southern Gulf of St. Lawrence). Although fishing effort and catches have generally decreased, Thorny Skate continue to be caught in a directed fishery (around Newfoundland and Labrador and outside Canada’s Exclusive Economic Zone (EEZ) in the Northwest Atlantic Fisheries Organization (NAFO) Regulatory Area) and as bycatch in other groundfish fisheries (both inside and outside Canadian waters).

Further Information

For more information, visit the Species at Risk registry . 

Thorny Skate

Thorny Skate

Illustration of a Thorny Skate viewed from the side. It is a flattened fish with a disc-shaped body covered in thorns and a slender tail. This species is distinguished from other skates in Canadian waters primarily by a row of 11–19 large thorns on the midline of its back and tail. The upper body colour can be highly variable among individual Thorny Skate (ranging from yellow-edged dark spots on light brown to an almost uniform dark brown). The underside of its body is uniformly white, rarely with a few small, non-symmetrical, darkly pigmented markings.

Scientific name: Amblyraja radiata
SARA Status: No Status
COSEWIC Status: Special Concern
Region: Nunavut, Quebec, New Brunswick, Prince Edward Island, Nova Scotia, and Newfoundland and Labrador

Did You Know?

Thorny Skate reproduce by laying an embryo in a hard-shelled egg case (“Mermaid’s purse”) on the bottom of the ocean, and each female produces between 6 and 40 egg cases per year. Hatching success rate is estimated at 38%, meaning approximately 15 hatchlings survive per female each year. Little is known about predators of Thorny Skate, but the embryo developing inside of an egg case has sometimes been found eaten by a shell-drilling gastropod, while juveniles and adults may be eaten by marine mammals, other skates, and larger fish. Thorny Skate have a highly varied diet of bottom-dwelling fish and invertebrates, which changes with prey availability and skate body size; small skates eat more squid, marine worms, and amphipods (“sea lice”), while larger skates eat Sand Lance, Capelin, smaller Haddock, and Snow Crab.

Related information

  • COSEWIC assessment and status report on the Thorny Skate Amblyraja radiata in Canada (2013)

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