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Biology

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Little is known about the big skate's mating behaviour but, like other skates, it is oviparous, or egg-laying, but it has unusually large egg capsules that contain up to seven eggs. Among skates, only the big skate and the closely related Raja pulchra have more than one egg per egg capsule. The egg capsules of the big skate are laid in pairs and usually contain three to four eggs, although up to seven have been recorded. Hatchlings are released from the egg capsule about nine months after being laid by the female. Males reach sexual maturity at approximately seven to eight years, females at 12 to 13 (4). The big skate feeds on marine invertebrates such as shrimps, worms and clams, as well as on crustaceans and fish (3) (4). The positioning of the mouth on the underside of the body is perfect for sucking up animals hiding in the sand.
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Conservation

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Presently, this skate is classified only as Lower Risk/near threatened (LR/nt) on the IUCN Red List 2004, and no direct conservation measures are currently in place for the species (1). However, more population data and close monitoring of this species are required to accurately assess the impact fisheries are having on its abundance and distribution.
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Description

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Aptly named, the big skate is the largest skate in North American waters (4). As with all skates, the body is flattened and disc-shaped, with the pectoral fins broadly expanded and joined to the head and body (5). In this species, the tip of the snout and tips of the pectoral fins are acutely pointed, forming a diamond-shaped disc (4) (5). The tail is distinctly demarcated from the disc, relatively narrow, and about as long as body length (5). An irregular row of approximately 33 thorns run from the end of the back, down the tail to the first of two dorsal fins. The small eyes are positioned on the upper surface relatively far back, while the mouth appears on the underside, along with the five gill slits (4). Mottled colouration on the back includes browns, reddish-browns, dark greys and blacks, with occasional small pale spots and scattered dark blotches (4), while the underside is white (6). The species' name 'binoculata' means two eyes, referring to the prominent dark ocellus (eye-like spot) on the upper surface of each pectoral fin (4). Biologists believe this illusion of eyes may confuse potential predators by making the skate appear much larger than it is (4) (7).
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Habitat

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Occurring along the coast in estuaries, bays and over the continental shelf. Commonly found on sandy and muddy bottoms to depths of 120 m (2) (4). Usually seen lying on the bottom partially covered with bottom sediments, with eyes protruding above the remainder of the body and sediments (4) (5) (7).
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Range

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Found in temperate waters of the north-eastern Pacific Ocean from Alaska to central Baja, California (1) (5). This range includes the eastern Bering Sea and Aleutian Islands, west to Unalaska Island and South to Baja, California (U.S.) near Cedros Island (4).
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Status

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Classified as Lower Risk/near threatened on the IUCN Red List (1).
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Threats

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The big skate is fished for its fins, which are marketed fresh and frozen (3), but is only of minor importance to commercial fisheries (4). However, this species is also taken incidentally as bycatch, primarily by bottom trawlers in the waters off the coast of California (U.S). Indeed, during the 1990s, the skate catch off the coast of California increased nearly ten-fold, partly targeted and partly taken as bycatch by trawl fisheries that supplement their income by marketing incidentally caught skates and rays (4). Data are currently inadequate to determine the precise impact fisheries are having on big skate populations, but as one of the larger, slow maturing species with a low reproductive rate, this skate is potentially vulnerable to population collapses caused by over-fishing (1).
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Diagnostic Description

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Dorsal fins well back on tail, small; caudal and anal fins absent; pectorals broad, attached to snout and incorporated with body; pelvic fins large, moderately concave on free margins (Ref. 6885). Posterior sides of tail with a small fleshy keel on either side (Ref. 6885).
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Cristina V. Garilao
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Life Cycle

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Up to 7 embryos per egg case (Ref. 2850). Oviparous, paired eggs are laid. Embryos feed solely on yolk (Ref. 50449). Distinct pairing with embrace. Young may tend to follow large objects, such as their mother (Ref. 205).
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Morphology

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Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0
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Trophic Strategy

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Feeds on fish and crustaceans (Ref. 2850).
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Biology

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Largest skate in North America (Ref. 2850). Feed on crustaceans and fishes (Ref. 6885). Oviparous. Distinct pairing with embrace. Young may tend to follow large objects, such as their mother (Ref. 205). Young hatch at 18-23 cm TL (Ref. 114953). Eggs are oblong capsules with stiff pointed horns at the corners deposited in sandy or muddy flats (Ref. 205). Egg capsules are 22.8-30.5 cm long and 11.0-19.4 cm wide (Ref. 41249, 41300, 41357). Pectoral fins utilized for human consumption (Ref. 2850). Marketed fresh and frozen; eaten fried and baked (Ref. 9988).
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Importance

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fisheries: commercial; aquarium: public aquariums
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Big skate

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The big skate (Beringraja binoculata) is the largest species of skate (family Rajidae) 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.[2]

Taxonomy

This species was described by Charles Frédéric Girard in 1855; its specific epithet binoculata is derived from the Latin bi meaning "two", and oculatus meaning "eyed", referring to the two prominent eyespots on its wings. Girard also described what would later be determined to be a junior synonym of B. binoculata, R. cooperi, based on notes made by James G. Cooper on a decaying big skate found ashore near the entrance of Shoalwater Bay, Washington.[3] In some older literature, this species is placed in the genus Dipturus.[4] In 2012, the big skate was moved from Raja to the new genus Beringraja together with the mottled skate (B. pulchra).[5]

Distribution and habitat

The big skate is found in the north-eastern Pacific Ocean, from the eastern Bering Sea and the Aleutian Islands, as far south as Cedros Island off central Baja California. It is rare south of Point Conception, California. It occurs in coastal bays, estuaries, and over the continental shelf, usually on sandy or muddy bottoms, but occasionally on low strands of kelp. Though reported to a depth of 800 m (2,600 ft), it is usually found no deeper than 120 m (390 ft). It frequents progressively shallower water in the northern parts of its range.[2][3] This species is abundant off British Columbia, where it prefers a depth of 26–33 m (85–108 ft) and a temperature of 7.6–9.4 °C (45.7–48.9 °F).[6]

Description

The maximum known length of a big skate is 2.4 m (7.9 ft), though this species usually does not exceed 1.8 m (5.9 ft) and 91 kg (201 lb). This species has a flattened, diamond-shaped pectoral fin disk slightly wider than it is long, with a long, moderately pointed snout. The eyes are small and placed just ahead of the large spiracles. The teeth are small with raised cusps, numbering 24-48 rows in the upper jaw and 22–45 in the lower. Two small dorsal fins are on the tail, the anal fin is absent, and the caudal fin is reduced to a simple fold. There is a weak notch in each pelvic fin.[2][3]

A juvenile has smooth skin, while an adult has small prickles on its dorsal surface and the underside of the snout, between the gill slits, and on the abdominal region. It has two or three thorns on the middle of the back, a row of 12-55 (usually 13–17) thorns along the midline of the tail, and an interdorsal thorn. Some older individuals have a thorn above each eye. The back is colored a mottled brown to reddish brown, olive-brown, or gray, with rosettes of small white spots or scattered dark blotches. Two large dark spots with pale borders occur, one on each wing. The ventral side is white, sometimes with dark spots or blotches.[2][3]

Biology and ecology

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A male big skate resting on the sea floor off Mt. Pinos

Big skates are usually seen buried in sediment with only their eyes showing. They feed on polychaete worms, molluscs, crustaceans, and small benthic fishes. Polychaetes and molluscs comprise a slightly greater percentage of the diet of younger individuals. A known predator of big skates is the broadnose sevengill shark (Notorhynchus cepedianus); the eyespots on the skates' wings are believed to serve as decoys to confuse predators. Juvenile northern elephant seals (Mirounga angustirostris) are known to consume the egg cases of the big skate. Known parasites of the big skate include the copepod Lepeophtheirus cuneifer.[2][3]

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The egg capsule ("mermaid's purse") of a big skate

This species is oviparous, and is one of the few skate species that typically has more than one embryo within each egg capsule, commonly called "mermaid's purses" when they are found washed up on beaches. The egg capsule of a big skate is the largest of any skate, measuring 23–31 cm (9–12 in) long and 11–19 cm (4–7 in) wide. Each capsule is oblong in shape and has a highly arched dorsal surface, nearly flat ventral surface, and parallel lateral edges that become somewhat concave towards the center of the case. At the corners of the case, four blunt, broad horns are seen, with the posterior pair being slightly longer. A single egg capsule may contain one to seven (usually three or four) eggs.[3]

The female deposits her eggs in pairs on sandy or muddy flats; the breeding season is indiscrete, and egg-laying occurs year-round.[3] Females may use distinct spawning beds, as large numbers of egg cases have been found in certain localized areas.[6] The young emerge after 9 months and measure 18–23 cm (7–9 in). Female big skates mature at 1.3–1.4 m (4 ft 3 in – 4 ft 7 in) long and 12–13 years old, while males mature at 0.9–1.1 m (2 ft 11 in – 3 ft 7 in) long and 7–8 years old.[2] The growth rates of big skates in the Gulf of Alaska are comparable to those off California, but differ from those off British Columbia. The lifespans of big skates off Alaska are up to 15 years, while those off British Columbia are up to 26 years.[7][8]

Fisheries and stock status

Big skates are frequently caught by recreational anglers, who usually release or discard them. They adapt well to captivity and are often displayed in public aquaria. This species is one of the three most important skates fished off the coast of California, though compared to other commercial fisheries, it is of only minor importance. This species is usually taken as bycatch in bottom trawls; the pectoral fins are sold as "skate wings" and are eaten baked or fried, often being labeled as imitation scallops. In the 1990s, the market value of skate wings rose to US$0.40-$1.00 per pound, and catches of the big skate off California increased 10-fold as the trawl fishery began marketing its skate and ray bycatch.[2] In 2003, a targeted fishery for the big skate and the longnose skate (Raja rhina) commenced in the Gulf of Alaska.[7]

Fisheries encountering Big Skate are managed separately in three areas: Alaska, the Canadian province of British Columbia, and the west coast of the contiguous United States (Washington, Oregon, and California). Stock assessments for Big Skate have been conducted in all these areas, none of which found that overfishing was occurring.[9][10][11][12] The size of the stock and the estimates of sustainable catch were uncertain in all cases. Big Skates are assessed as least concern by the World Conservation Union.[1]

References

  1. ^ a b Farrugia, T.J.; Goldman, K.J.; King, J.R.; Ormseth, O.A. (2016). "Beringraja binoculata". IUCN Red List of Threatened Species. 2016: e.T44183A80679344. doi:10.2305/IUCN.UK.2016-2.RLTS.T44183A80679344.en. Retrieved 17 November 2021.
  2. ^ a b c d e f g Bester, C. Biological Profiles: Big Skate. Florida Museum of Natural History Ichthyology Department. Retrieved on March 7, 2009.
  3. ^ a b c d e f g Ebert, D.A. (2003). Sharks, Rays, and Chimaeras of California. London: University of California Press. ISBN 0-520-23484-7.
  4. ^ Froese, Rainer; Pauly, Daniel (eds.) (2017). "Beringraja binoculata" in FishBase. January 2017 version.
  5. ^ Ishihara, H., Treloar, M., Bor, P.H.F., Senou, H. and Jeong, C.H. (2012). The comparative morphology of skate egg capsules (Chondrichthyes: Elasmobranchii: Rajiformes). Bulletin of the Kanagawa Prefectural Museum (Natural Science) 41: 9-25.
  6. ^ a b IUCN/SSC Shark Specialist Group (2005). Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes. IUCN. ISBN 2-8317-0700-5.{{cite book}}: CS1 maint: uses authors parameter (link)
  7. ^ a b Gburski, C.M., Gaichas, S.K. and Kimura, D.K. (October 2007). "Age and growth of big skate (Raja binoculata) and longnose skate (R. rhina) in the Gulf of Alaska". Environmental Biology of Fishes. 80 (2–3): 337–349. doi:10.1007/s10641-007-9231-8.{{cite journal}}: CS1 maint: uses authors parameter (link)
  8. ^ McFarlane, G.A. & King, J.R. (2006). "Age and growth of big skate (Raja binoculata) and longnose skate (Raja rhina) in British Columbia waters". Fisheries Research. 78 (2–3): 169–178. doi:10.1016/j.fishres.2006.01.009.
  9. ^ Ormseth, O.A. (2018), Assessment of the skate stock complex in the Gulf of Alaska in: Stock Assessment and Fishery Evaluation Report for the Groundfish Resources of the Gulf of Alaska Region. (PDF), North Pacific Fishery Management Council, 605 W. 4th Ave., Suite 306, Anchorage, AK 99501
  10. ^ Ormseth, O.A. (2018), Assessment of the skate stock complex in the Bering Sea and Aleutian Islands: Stock Assessment and Fishery Evaluation Report for the Groundfish Resources of the Bering Sea and Aleutian Islands Region (PDF), North Pacific Fishery Management Council, 605 W. 4th Ave., Suite 306, Anchorage, AK 99501
  11. ^ King, J.R., Surry, A.M., Garcia, S.,and Starr, P.J. (2015), Big Skate (Raja binoculata) and Longnose Skate (R. rhina) stock assessments for British Columbia (PDF), DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2015/070{{citation}}: CS1 maint: multiple names: authors list (link)
  12. ^ Taylor, I.G., Gertseva, V., Stephens, A., Bizzarro, J. (2019), Status of Big Skate (Beringraja binoculata) Off the U.S. Pacific Coast in 2019, Pacific Fishery Management Council, Portland, OR{{citation}}: CS1 maint: multiple names: authors list (link)
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Big skate: Brief Summary

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The big skate (Beringraja binoculata) is the largest species of skate (family Rajidae) 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.

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