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Raja binoculata

(Black sand skate)


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Largest skate in North America[1]. Feed on crustaceans and fishes [2]. Oviparous . Distinct pairing with embrace. Young may tend to follow large objects, such as their mother[3]. Eggs are oblong capsules with stiff pointed horns at the corners deposited in sandy or muddy flats[3]. Egg capsules are 22.8-30.5 cm long and 11.0-19.4 cm wide[4][5][6]. Pectoral fins utilized for human consumption [1]. Marketed fresh and frozen; eaten fried and baked[7].

Near Threatened

Threat status

Common Names

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Click on the language to view common names.

Common Names in Danish:

Stor rokke

Common Names in Dutch:

Grote rog, Zwarte zandrog

Common Names in English:

big skate, Black sand skate, Boeseman's skate

Common Names in French:


Common Names in Japanese:


Common Names in Korean:


Common Names in Mandarin Chinese:

Hé shì yáo, 双斑鳐, 雙斑鰩, 鮑氏老板鯆, 鮑氏鰩, 鲍氏老板鯆, 鲍氏鳐

Common Names in Polish:

Raja wielka

Common Names in Russian:

Skat, скат боль, скат большой калифорнийский

Common Names in Salish:

K´ak´ew´, K'ak'ew'

Common Names in Spanish:

Raya Brava, raya bruja gigante, Raya gigante

Common Names in Spanish, Castilian:

Raya bruja gigante, Raya gigante

Common Names in Tsimshian:

Gandah, K´andah, K'andah

Common Names in Vietnamese:

Cá Ðu?i, Cá Đuối


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Physical Description

Species Raja binoculata

Distinctive Features: The big skate has a flattened diamond-shaped body with a stiff snout tapering to a blunt point . The small eyes are positioned on the dorsal surface some distance from the pointed snout with large spiracles just posterior to the eyes.

The mouth is on the ventral surface along with the five gill slits . The pectoral fins are not clearly distinct , attaching the snout with the body. These fins have a concave anterior edge between the snout and pointed tips of the fins. The two small dorsal fins are located on the tail while the anal and caudal fins are absent. The pelvic fins are large and moderately concave and weakly notched along the free margins . The tail is long and narrow and has a fleshy keel on either side.

Dentition: The teeth of the big skate are small. They are arranged in rows with bases touching and raised cusps .

Denticles : There is an irregular row of approximately 33 middorsal thorns that runs down the back and tail to the first dorsal fin. There is a single middorsal thorn located just behind the orbits. Also, orbital thorns are located between the eyes but may remain buried under the skin in some individuals. These thorns may become more prominent as the skate ages.

Small, placoid scales are present, although rather sparsely, on the body, tail and posterior portion of the head .


The big skate has mottled coloration on the dorsal surface including brown, reddish brown, dark gray and black. There may also be small pale spots and scattered dark blotches. There are two large black spots, resembling eyes, on the dorsal surface of the pectoral fins. Each spot has a pale border and dark center. Biologists believe that these "eyes" may confuse potential predators , with the skate appearing much larger than it is. The ventral surface ranges from white to a muddy white sometimes with dark blotches.


Aptly named the "big" skate, this species is the largest skate in North American waters. The maximum reported size of the big skate is 7.9 feet (2.4 m ) total length, however this species usually does not reach lengths beyond 6 feet (1.8 m) and weights of 200 pounds (91 kg ). Males reach maturity at approximately 7-8 years of age and lengths of 3.2-3.6 feet (0.9-1.1 m); females mature at about 12-13 years of age and lengths of 4.3-4.6 feet (1.3-1.4 m).


In waters from the intertidal range to depths of 394 feet (120 m ), the big skate is found along the coast in estuaries, bays , and over the continental shelf. Although this skate is sometimes observed in low stands of kelp, it is more common on sandy and muddy bottoms . It is usually seen hiding motionless in the bottom sediments with only eyes protruding, camouflaged from potential predators . When it does move, swimming occurs by the undulation of the pectoral fins, which makes the skate appear as though it is "flying" gracefully through the water.

Typically found in water with a depth of 0 to -4,869 meters (0 to -15,974 feet).[8]

Biome: Marine .

Ecology: The Big Skate attains a maximum total length (TL ) of 240 cm, although specimens over 180 cm TL (90 kg ) are unusual (Martin and Zorzi 1993). Zeiner and Wolf (1993) examined 171 specimens and reported on the weight¬length relationship , maturity and growth parameters . Males were found to mature at 100?110 cm TL (10?11 years) and females at more than 130 cm TL (10?12 years). The fecundity has not been determined.

The reproductive biology of Big Skate is unusual in that it produces large egg cases that contain multiple (1?7) embryos (DeLacy and Chapman 1935, Hitz 1964). There is some evidence that spawning beds are used, and Hitz (1964) reported that large numbers of eggs may be caught by scallop dredge . He observed that egg cases were most abundant at a depth of 60?65 m , and in one instance 152 cases were taken in one 30 minute drag . Hitz (1964) recorded two spawning beds, each at 35 fathoms (64 m), one off Tillamook Head and the other between the Siuslaw and Siltcoos Rivers . Several embryological studies have been undertaken on D. binoculata (e.g. , Manwell 1958, McConnachie and Ford 1966, Read 1968, Ford 1971, Evans and Ford 1976). These have utilised egg cases taken off Comox, at 16 fathoms (29 m) off Tsawassen in the Straits of Georgia, British Columbia and from the waters of the San Juan Islands.

Although little is known about the absolute abundance of Big Skate, there have been several published accounts of its comparative abundance . Ebert (1986) captured nine specimens by rod and line in San Francisco Bay and this species accounted for 2% (by number) of the elasmobranch assemblage in this area. The demersal fish assemblages of Oregon have been well studied (Day and Pearcy 1968, Pearcy et al. 1989, Stein et al. 1992). Day and Pearcy (1968) captured 7,689 fish from 67 species and of these, only four specimens of D. binoculata were recorded (0.05% of the catch ) and these were taken in water of less than 200 m depth. Pearcy (1989) studied the ichthyofauna of the Heceta Bank, Oregon, using a submersible and, over 16 dives, observed four specimens of D. binoculata. By numbers, Big Skate accounted for approximately 0.1?0.8% of the fish assemblage (Pearcy et al. 1989). More recently, Stein et al. (1992) undertook a similar survey and recorded 10 specimens, most of which were found on mud or mud/boulder substrates.

The ichthyofauna of British Columbia has been well documented and in these waters D. binoculata is relatively abundant. Fargo and Tyler (1991) reported on the species compositions of four distinct fish assemblages (Reef Island, Butterworth, Bonilla and Moresby Gully) and D. binoculata was found to be an important member of the Reef Island assemblage (Perry et al. 1994), constituting 0.10?0.17% of the biomass (Fargo and Tyler 1991). In British Columbian waters, D. binoculata favours shallow (26?33 m) and warmer (7.6?9.4°C) waters (Perry et al. 1994).[9].

List of Habitats :


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The big skate feeds on marine invertebrates such as shrimp, worms, and clams as well as on fishes including the great sculpin (Myoxocephalus polyacanthocephalus).


The big skate is an oviparous , or egg-laying species. It has probably the largest egg capsules in the Rajidae family , with each measuring 9-12 inches (22.8-30.5 cm) long and 4-7 inches (11.0-19.4 cm) wide. The egg capsules are oblong in shape with horns at each corner. The only known egg capsules to contain more than one egg inside are those of the big skate and mottled skate (R. pulchra). The egg capsules of the big skate commonly contain 3-4 eggs, although up to 7 have been documented. The female releases the egg capsules in pairs on sandy or muddy substrate. The egg capsules release the hatchlings about nine months after being released from the female. The empty black egg cases, referred to as mermaid's purses , sometimes wash ashore and are found by beach walkers.



Large predatory bony fishes and sharks consume big skates . One such documented predator is the sevengill shark (Notorynchus cepedianus). The egg capsules are sometimes eaten by elephant seals.


Copepods parasitize a variety of marine fishes with the big skate being no exception. The copepod Lepeophtheirus cuneifer sp. nov. is one such documented parasite of the big skate.


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Dipturus binoculataDipturus binoculata (Girard • Okamejei boesemaniOkamejei boesemani (Ishihara, 1987) • Raja (Okamejei) boesemani Ishihara 1987 • Raja cooperi Girard


Name Status: Accepted Name .

First described: Girard, C. Abstract of a report to Lieut. James M. Gilliss, U.S.N., upon the reptiles collected during the U.S.N. Astronomical Expedition to Chili. Proc. Acad. Nat. Sci. Philadelphia 7 [1854]: 226-227., 1855.

Last scrutiny: Data last modified by FishBase 27-Sep-1999

Similar Species

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Species similar in appearance and sharing habitat with the big skate include:

California skate (R. inornata) which has a pointed snout, deeply notched pelvic fins, and slightly convex anterior edges of the pectoral fins.

Sandpaper skate (R. kincaidi) which lacks orbital thorns and has a thorn on the shoulders in center of body on each side of the midline of the skate.

Longnose skate (R. rhina) which has deeply concave anterior margins of the pectoral fins and deeply notched pelvic fins. Starry skate (R. stellulata) which has small ocelli and convex anterior edges of the pectoral fins as well as is covered with thorns. Roughtail skate (R. trachura) which has no large thorns on the body and is dark gray or black both on the dorsal and ventral surfaces.

Members of the genus Raja

ZipcodeZoo has pages for 132 species and subspecies in this genus. Here are just 100 of them:

R. abyssicola (Deep-Sea Skate) · R. ackleyi (Ocellate River Stingray) · R. acutispina (Sharpspine Skate) · R. africana (African Ray) · R. alba (White Bottle-Nose Skate) · R. albomaculata (White-Dotted Skate) · R. aleutica (Aleutian Skate) · R. altavela (Spiny Butterfly Ray) · R. annandalei (Indonesian Round Skate) · R. aquila (Spotted Eagle Ray) · R. asperrima (Roughskin Stingaree) · R. asterias (Atlantic Starry Skate) · R. australis (Sydney Skate) · R. badia (Broad Skate) · R. bahamensis (Bigelow's Skate) · R. bathyphila (Deepwater Skate) · Rajella bathyphila (Abyssal Skate) · R. batis (Common European Skate) · R. binoculata (Boeseman's Skate) · R. birostris (Giant Atlantic Manta) · R. bonasus (Cow-Nosed Ray) · R. brachyura (Blonde Ray) · R. brachyurops (Broadnose Skate) · R. bullisi (Tortugas Skate) · R. castelnaui (White-Spotted Skate) · R. centroura (Rough-Tailed Northern Stingray) · R. cervigoni (Venezuela Skate) · R. clarkii (Madagascar Skate) · R. clavata (Thornback Skate) · R. cortezensis (Cortez Ray) · R. cruciata (Crossback Stingaree) · R. cyclophora (Eyespot Skate) · R. diabolus (Lesser Devil Ray) · R. dipterygia (Spottail Electric Ray) · R. djiddensis (White Spotted Shovelnose Guitarfish) · R. eatonii (Equatorial Skate) · R. eglanteria (Clear-Nosed Summer Skate) · R. equatorialis (Equatorial Skate) · Psammobatis extenta (Little Skate) · R. flagellum (Longheaded Eagle Ray) · R. fluviatilis (Gangetic Stingray) · R. fuliginea (Sooty Skate) · R. fullonica (Fuller's Shagreen Ray) · R. garmani (Rosetted Skate) · R. garricki (San Blas Skate) · R. georgiana (Antarctic Starry Skate) · R. gigas (Giant Skate) · R. griseocauda (Graytail Skate) · R. guttata (Longnose Stingray) · R. halavi (Halavi's Guitarfish) · R. herwigi (Cape Verde Skate) · R. hollandi (Yellow-Spotted Skate) · R. hyperborea (Darkbelly Skate) · R. imbricata (Schneider's Scaly-Stingray) · R. ingolfiana (New Zealand Smooth Skate) · R. inornata (California Skate) · R. interrupta (Sandpaper Skate) · R. jenseni (Travancore Skate) · R. kincaidi (Sandpaper Skate) · R. koreana (Ocellate Spotskate) · R. kujiensis (Dapple-Bellied Softnose Skate) · R. laevis (Barn-Door Winter Skate) · R. lemprieri (Whitedappled Skate) · R. lentiginosa (Speckled Skate) · R. lima (Filetail Fanskate) · R. lintea (Sharp-Nosed Skate) · R. lymma (Blue Spotted Fantail Stingray) · R. macloviana (Patagonian Skate) · R. maculata (Dark-Spotted Electric Ray) · R. maderensis (Madeira Skate) · R. magellanica (Magellan Common Ray) · R. mamillidens (Prickly Skate) · R. meerdervoortii (Bigeye Skate) · R. microocellata (Smalleyed Skate) · R. micrura (Short-Tailed Lesser Butterfly Ray) · R. miraletus (Homelyn Mirror Ray) · R. montagui (Spotted Homelyn Ray) · R. multispinis (Multispine Skate) · R. murrayi (Murray's Skate) · R. naevus (Butterfly Skate) · R. narinari (White-Spotted Eagle Ray) · R. nasuta (New Zealand Rough Skate) · R. nidarosiensis (Norwegian Skate) · R. nitida (Roughback Skate) · R. brachyura (Winter Skate) · R. olseni (Spreadfin Skate) · R. oregoni (Hooktail Skate) · R. oxyrhyncha (Longnosed Skate) · R. oxyrinchus (Long-Nosed Burton Skate) · R. parmifera (Flathead Skate) · R. pastinaca (Common Stingray) · R. percellens (Southern Guitarfish) · R. philippii (Pita Skate) · R. platana (La Plata Skate) · R. poecilura (Long-Tailed Butterfly Ray) · R. polyommata (Argus Skate) · R. polystigma (Speckled Skate) · R. powelli (Indian Ringed Skate) · R. pulchra (Smoothback Skate) · R. purpuriventralis (Purplebelly Skate)

More Info

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Further Reading

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Data Sources

Accessed through GBIF Data Portal March 02, 2008:



  1. Eschmeyer, W.N., E.S. Herald and H. Hammann (1983). A field guide to Pacific coast fishes of North America. Houghton Mifflin Company, Boston, U.S.A. 336 p. [back]
  2. Hart, J.L. (1973). Pacific fishes of Canada. Fish. Res. Board Can. Bull. 180:1-740. [back]
  3. Breder, C.M. and D.E. Rosen (1966). Modes of reproduction in fishes. T.F.H. Publications, Neptune City, New Jersey. 941 p. [back]
  4. Ishihara, H. (1990). Study on the systematics and fishery resources of the North Pacific skates (Pisces: Chondrichthyes: Rajidae). Tokyo University. 186 p. Ph.D. dissertation. [back]
  5. Cox, K.W. (1963). Egg-cases of some elasmobranchs and a cyclostome from California waters. Calif. Fish Game 49(4):271-289. [back]
  6. DeLacey, A.C. and W.M. Chapman (1935). Notes on some elasmobranchs of Puget Sound, with descriptions of their egg cases. Copeia 1935(2):63-67. [back]
  7. Frimodt, C. (1995). Multilingual illustrated guide to the world's commercial coldwater fish. Fishing News Books, Osney Mead, Oxford, England. 215 p. [back]
  8. Mean = -368.720 meters (-1,209.711 feet), Standard Deviation = 790.670 based on 541 observations. Ocean depth information for each observation from British Oceanographic Data Centre. [back]
  9. Ellis, J. & Dulvy, N. 2005. Raja binoculata. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. <>. Downloaded on 04 February 2012. [back]
Last Revised: 2015-02-06