|Scientific Name:||Beringraja binoculata (Girard, 1855)|
Dipturus binoculata (Girard, 1855)
Raja binoculata Girard, 1855
|Taxonomic Source(s):||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.|
|Taxonomic Notes:||Ishihara et al. (2012) established the new genus Beringraja for the two species B. binoculata (previously Raja binoculata Girard, 1855) and B. pulchra (previously Raja pulchra Liu 1932).|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Farrugia, T.J., Goldman, K.J., King, J.R. & Ormseth, O.A.|
|Reviewer(s):||Barnett, L.A.K. & Lawson, J.|
|Contributor(s):||Ellis, J.R., Dulvy, N.K. & Jang, J.J.|
|Facilitator/Compiler(s):||Kyne, P.M., Lawson, J. & Walls, R.H.L.|
The Big Skate (Beringraja binoculata, formerly Raja binoculata) is a large-bodied demersal skate that occurs primarily on soft-sediment habitats in coastal waters on the continental shelf in the Northeast Pacific and the Eastern Central Pacific, from northern Baja California to Alaska. They are one of the largest species of skate and, as with the Common Skate (Dipturus batis) and Barndoor Skate (Dipturus laevis), may be susceptible to overfishing given their large body size. The Big Skate may be one of the most fecund elasmobranchs and has an estimated generation length of 14.25 years. However, life-history traits differ between regions. This species is taken in commercial and recreational fisheries, and is monitored through formal stock assessments throughout much of its range. Indices of relative abundance of the populations found off British Columbia, Canada and in the Gulf of Alaska have remained relatively stable over time. On the west coast of the United States (Washington, Oregon and California), this species is managed under the federal Groundfish Fishery Management Plan. Given that available stock assessments indicate that populations of the Big Skate are stable, and that this species is managed throughout much of its range, this species is assessed as Least Concern.
|Previously published Red List assessments:|
The Big Skate is found along the western coast of North America, from the Gulf of California to the Bering Sea (Walford 1935, Roedel and Ripley 1950).
Native:Canada (British Columbia); Mexico (Baja California); United States (Alaska, Aleutian Is., California, Oregon, Washington)
|FAO Marine Fishing Areas:|
Pacific – eastern central; Pacific – northeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The population trend is estimated to be stable based on stock assessments from British Columbia, Canada and the Aleutian Islands (AI), Eastern Bering Sea (EBS), and Gulf of Alaska (GOA), in the United States. In Washington, Oregon, California, United States and Baja California, Mexico, no species-specific stock assessments are available and thus the population trend is unknown. In Californian waters the species is one of the three most important skates in the fisheries (Roedel and Ripley 1950, Martin and Zorzi 1993) and is caught incidentally by trawl, longline and trammel net gear (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 species ranged from 22.9 to 286.3 tonnes. Since 1916, skates have constituted 11.8% of the total weight of elasmobranchs landed (ranging from 1.9 to 89.5% annually). The skates that are landed in the Californian fishery are mostly juveniles (Roedel and Ripley 1950, Martin and Zorzi 1993), with larger individuals being discarded.|
A formal stock assessment for the Big Skate in British Columbia, Canada was published by Fisheries and Oceans Canada. The assessment concluded that the historical (1996-2011) levels of removal have had no significant impact on Big Skate abundance in the region based on available trawl and longline survey data (King et al. 2015).
Recent stock assessment data exist for the AI, EBS, and GOA and are based on bottom trawl surveys conducted by the U.S. National Marine Fisheries Service. Biomass of the Big Skate for the entire BSAI area (EBS shelf, EBS slope, AI) was 1,692 t in 2002, 1,373 t in 2004, 4,081 t in 2010 and 1,356 t in 2012 (Ormseth 2014a). In the GOA, the Big Skate is managed distinctly from the Longnose Skate (Raja rhina) and "Other Skates". Biomass of the Big Skate across the entire GOA has remained relatively stable at ~50,000 t since the 1990s , but a dramatic decline in biomass of the Big Skate has been recorded in the Central GOA since 2003 (Ormseth 2014b). Despite this area-specific decline the Big Skate is not considered to be overfished based on GOA-wide biomass estimates (Ormseth 2014b).
|Current Population Trend:||Stable|
|Habitat and Ecology:||The Big Skate is most common in soft-sediment habitats in coastal waters on the continental shelf (Bizzarro et al. 2014, Farrugia et al. in press 2016), although they have also been observed associating with hard substrates (Steinet al. 1992). They are most common at depths of less than 200 m (Day and Pearcy 1968, Love et al. 2005, Ormseth 2011), although they have been found to depths of 800 m (Martin and Zorzi 1993). In the GOA this species is the most commonly encountered species of skate in the inshore continental shelf waters at 100–200 m depth, and is most abundant in the central and western areas of the GOA (Ormseth 2014b; Bizzarro et al. 2014). Similarly, in central California, the Big Skate is aggregated on the continental shelf near the coast (Bizzarro et al. 2014).|
Despite being a demersal species that is considered to be relatively sedentary, the Big Skate is capable of large movements. For example, in British Columbia, a study revealed that ~75% of tagged individuals were recaptured within 21 km of the tagging locations, but 15 of the tagged individuals (0.1%) moved over 1,000 km (King and McFarlane 2010). In the Gulf of Alaska, satellite tags showed that over a one-year period six of the twelve tagged individuals observed in this study moved over 100 km, and a single individual moved 2,000 km (Farrugia et al. in press 2016).
The Big Skate attains a maximum total length (TL) of about 290 cm (McFarlane and King 2006), although specimens over 180 cm TL (90 kg) are unusual (Martin and Zorzi 1993), especially outside of British Columbia waters. Length-weight relationships (Zeiner and Wolf 1993, Downs and Cheng 2013), age and growth parameters have been established in California (Zeiner and Wolf 1993), British Columbia (McFarlane and King, 2006), and the Gulf of Alaska (Gburski et al. 2007, Ebert et al. 2008). In California and the Gulf of Alaska, big skates reach about 250 cm TL and live to about 15 years, whereas in British Columbia they can grow up to 290 TL cm and live to 26 years. It is important to note that age estimates are based on an unvalidated method and geographic differences in size or age may reflect differences in sampling or ageing criteria. Age and size at maturity also differs between regions. In the Gulf of Alaska, females big skates reach 50% maturity at 150 cm TL (10 years) and at 120 cm TL (7 years) for males (Gburski et al. 2007, Ebert et al. 2008). In British Columbia, females reach 50% maturity at 90 cm TL (8 years) and at 72 cm TL (6 years) for males (McFarlane and King 2006). The Big Skate is oviparous and deposits egg cases on the sea floor that have embryos that develop in 6 to 20 months, depending on water temperature (Hoff 2007). Fecundity estimates are difficult to obtain because the Big Skate is one of only two skates to have more than one embryo per egg case. Aquarium observations have shown that the most common number of embryos per egg case is two (Chiquillo et al. 2014), but the range is from 1 to 7 (DeLacy and Chapman 1935, Hitz 1964). The number of egg cases that can be produced per female each year is uncertain, but observations in aquaria indicate that females can deposit over 350 egg cases per year (Ebert et al. 2008). This indicates that big skates may be one of the most fecund elasmobranchs. In the wild, only a few areas where egg cases are deposited have been observed, in Oregon (Hitz 1964) and the Gulf of Alaska (Thomas Farrugia, pers. obs. 2014), in which egg cases can reach densities of 7.5 egg cases per 100 m². Estimates of generation length range from 11.5 to 17 years (Zeiner and Wolf 1993, McFarlane and King 2006) with an average of 14.25 years.
|Generation Length (years):||11.5-17|
|Use and Trade:||This species is utilized for its meat.|
Commercial and recreational fisheries are most likely the main threat to this species. In Californian waters the species was one of the three most important rajids in commercial and recreational fisheries along with the California Skate (Dipturus inornata) and Longnose Skate (Raja rhina; Roedel and Ripley 1950, Martin and Zorzi 1993) and is landed as bycatch from trawlers, longline and trammel nets (Zeiner and Wolf 1993, California Department of Fish and Wildlife 2015). Martin and Zorzi (1993) analysed trends in the commercial landings of skates from 1916-1990 and reported that annual landings of Rajidae ranged from 22.9-286.3 t. 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.
In British Columbian and Alaskan waters ongoing direct and indirect take of the Big Skate occurs. Since the global market for skates is increasing, there is likely going to be a increasing demand for skate fisheries in the Northeast Pacific (Farrugia et al. in press 2016).
Stock assessments are used to inform status and management of fisheries throughout much of the range of the Big Skate. On the west coast of the United States (Washington, Oregon and California), groundfisheries are managed by a federal Groundfish Fishery Management Plan. This species is one of the six shark and ray species that are managed under a Fishery Management Plan (PFMC 2014). In the Gulf of Alaska, an Allowable Biological Catch (ABC) based on fishery-independent biomass estimates and natural mortality estimates is generated annually (Ormseth 2014a,b). Additionally, in California, a network of 29 marine protected areas (MPAs) were implemented in 2007 under California's Marine Life Protection Act, representing approximately 204 square miles (~18%) of state waters in the central coast region (California Department of Fish and Wildlife 2015). Due to these MPAs, most trawlers are restricted to operating in deeper waters, and only in central and northern California. As a result, fishing effort in the California trawl fishery has been reduced, and southern California is largely closed to trawl fishing.
In British Columbia, Canada, catch limits are set based on mean historic catch with consideration of estimates of trends and Maximum Sustainable Yield is estimated (King et al. 2015).
|Citation:||Farrugia, T.J., Goldman, K.J., King, J.R. & Ormseth, O.A. 2016. Beringraja binoculata. The IUCN Red List of Threatened Species 2016: e.T44183A80679344.Downloaded on 23 October 2017.|
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