|Scientific Name:||Raja binoculata|
|Species Authority:||Girard, 1855|
Dipturus binoculata Girard, 1855
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Ellis, J. & Dulvy, N.|
|Reviewer(s):||Musick, J.A. & Fowler, S.L. (Shark Red List Authority)|
This assessment is based on the information published in the 2005 shark status survey (Fowler et al. 2005).
This large-bodied demersal skate occurs in the north-eastern Pacific, from California to Alaska. The Big Skate (Raja binoculata) has not been subject to meaningful study and there are insufficient data on the population to determine its status. It is, however, one of the larger species of skate and, as with the Common Skate (Dipturus batis) and Barndoor Skate (D. laevis), may be susceptible to overfishing.
|Range Description:||The Big Skate is a large rajid found along the western coasts of North America, from the Gulf of California to the Bering Sea and Alaska (Walford 1935, Roedel and Ripley 1950). Although it may be found to depths of 800 m (Martin and Zorzi 1993), it is most common at moderate depths of less than 200 m (Day and Pearcy 1968) and the visual pigments are suited to these comparatively shallow waters (Beatty 1969).|
Native:Canada; United States (California, Oregon, Washington)
|FAO Marine Fishing Areas:||
Pacific – eastern central; Pacific – northeast
|Range Map:||Click here to open the map viewer and explore range.|
|Habitat and 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).
|Major Threat(s):||In Californian waters the species is, with the California skate Dipturus inornata and longnose skate Raja rhina, one of the three most important rajids in commercial and recreational fisheries (Roedel and Ripley 1950, Martin and Zorzi 1993) and is a bycatch from trawlers, longline and trammel nets (Zeiner and Wolf 1993). Martin and Zorzi (1993) analysed trends in the commercial landings of skates from 1916-1990 and reported that annual landings of Rajidae spp. Ranged from 22.9-286.3 t. Since 1916, rajids have constituted 11.8% of the total weight of elasmobranchs landed (ranging from 1.9-89.5% annually). The skates that are landed in the Californian fishery have tended to be juvenile fish (Roedel and Ripley 1950, Martin and Zorzi 1993), with larger individuals being discarded.|
|Citation:||Ellis, J. & Dulvy, N. 2005. Raja binoculata. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 05 July 2015.|
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