|Scientific Name:||Bathyraja trachura|
|Species Authority:||(Gilbert, 1892)|
Raja microtrachys Osburn and Nichols 1916
Raja trachura Gilbert 1891
|Taxonomic Source(s):||Eschmeyer, W.N. and Fricke, R. (eds). 2015. Catalog of Fishes: genera, species, references. Updated 1 October 2015. Available at: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp. (Accessed: 1 October 2015).|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Vásquez, V.E., Davis, C.D., Ebert, D.A., Ishihara, H. & Orlov, A.|
|Reviewer(s):||Winton, M.V., Jang, J.J. & Lawson, J.|
|Facilitator/Compiler(s):||Walls, R.H.L. & Dulvy, N.K.|
The Roughtail Skate (Bathyraja trachura) is a moderate-sized deepwater skate that is widely distributed in the North Pacific Ocean, from the Sea of Okhotsk to northern Baja California, Mexico. This species is found at depths ranging from 213 to 2,550 m, with abundance increasing at depths >600 m. It is occasionally taken as bycatch in trawl fisheries, but is typically discarded as it has no commercial value. Its life history strategy gives it the potential to be vulnerable to commercial fishing activity and other impacts, but population biomass is estimated to be stable in the eastern Bering Sea, the Aleutian Islands, and the Gulf of Alaska, and this species was assessed as Least Concern in the coastal waters of the Russian Federation. The wide depth distribution of the species likely provides some degree of refuge from anthropogenic effects, as the bulk of the population occurs beyond the range of many current fisheries. Given the absence of evidence to suggest that declines have occurred, the management that is taking place throughout the eastern part of its range, and given that only a portion of the population may be exposed to threats, this species is assessed as Least Concern. However, given that this species, like other deepwater skates, has life history characteristics that may make it vulnerable to overexploitation, this assessment should be revisited if fisheries expand further and deeper across its range.
|Previously published Red List assessments:|
|Range Description:||The Roughtail Skate inhabits waters from northern Baja California, Mexico, to the Gulf of Alaska, Bering Sea, and the Sea of Okhotsk, including the Pacific waters of the Kuril Islands and Kamchatka (Isakson et al. 1971, Parin 2001, Mecklenburg et al. 2002, Ebert 2003).|
Native:Canada (British Columbia); Mexico (Baja California, Baja California Sur); Russian Federation (Kamchatka, Kuril Is.); United States (Alaska, California, Oregon, Washington)
|FAO Marine Fishing Areas:|
Pacific – eastern central; Pacific – northeast; Pacific – northwest
|Range Map:||Click here to open the map viewer and explore range.|
In Alaska, population information for the Roughtail Skate is available from trawl surveys and population modelling conducted by the U.S. National Marine Fisheries Service. This species was surveyed in the Aleutian Islands (AI), and on the Eastern Bering Sea (EBS) shelf and slope, as part of the BSAI (Bering Sea and Aleutian Islands) skate complex. Although biomass trends for the Roughtail Skate are considered to be stable in the EBS shelf, EBS slope, and AI, it is noted that the available timeseries are too short for proper evaluation (Ormseth 2014a). Population growth rates show estimated for this species in the eastern Bering Sea suggest that this species is likely among the least productive of the members of the Alaskan skate assemblage (population growth rate of 1.045 yr-1) due to its late age at maturity and consequently long generation times (Barnett et al. 2013, Winton et al. 2013).
This species was most abundant on the EBS slope. Species-specific total biomass on the EBS slope was ~1,650 tonnes (t) in 2002 and 2004 (Matta et al. 2006) and increased to ~2,200 t in 2008, 2010 and 2012, but decreased in the AI from a peak of 976 t in 1986 to 0-2 t in 2010 and 2012 (Ormseth 2014a). Overall total skate biomass was estimated to have undergone a dramatic increase from from 106,535 t in 1983 to 371,004 t in 1989, although skates were not identified to species during this period (Ormseth 2014a). Population modelling indicates that this increase is consistent with a period of large year classes (i.e. increased recruitment) in the late 1970s and early 1980s (Ormseth 2014a).
In the Gulf of Alaska (GOA), estimates from bottom trawl surveys suggest that the Roughtail Skate biomass has fluctuated in the eastern, western and central GOA from 1984-2013 (Ormseth 2014b). Because of these fluctuations, it is difficult to establish a trend, however "other skate" biomass (skates excluding the Big Skate (Beringraja binoculata)) increased in the GOA in 2013, which reversed a declining trend that occurred between 2005-2011 (Ormseth 2014b).
In Russian waters, data from bottom trawl surveys (at depths of 50–2,000 m, between 1977 and 1997) estimated that the biomass of this species was 18,500 metric tons (mt; 16,700 mt in the western Bering Sea, 100 mt off Kuril Islands and Kamchatka, and 1,700 mt in the Sea of Okhotsk; Dolganov 1999).
There is no information on the population or abundance of this species in Mexican waters.
|Current Population Trend:||Stable|
|Habitat and Ecology:|
The Roughtail Skate is a deep-sea skate that inhabits slope waters at depths of 213-2,550 m (Ebert 2003, Stevenson 2004), with the bulk of population occurring at depths > 600 m. Dolganov (1998a) reported that the species is most common at 600-1,400 m depth. Surveys that sample below 1,200 m depth in the eastern Pacific suggest that the species’ abundance increases with depth (D.A. Ebert pers. obs.).
As with all skates, reproduction in this species is oviparous. Egg capsules range in size from 68-69 x 59-61 mm in Russian waters (Dolganov 1998b) and 67-77 x 63-71 mm in the eastern Bering Sea (Ebert 2005). Neonates range from 9-16 cm total length (TL; Ebert, 2003). The reproductive cycle appears to be continuous (Davis 2006).
Reported maximum sizes and ages-at-maturity vary quite widely by geographic area. In Russian waters, females reach age at maturity at 5-6 years of age and 72.8-81.5 cm TL; males mature at approximately 5 years and 71.7-78.3 cm TL (Dolganov 1998b). Estimated sizes at maturity in United States waters are similar, but studies conducted to date suggest that the species matures at later ages. In the eastern North Pacific off central California, size and age at 50% maturity has been estimated at 72 cm TL and 14 years for females and 77 cm TL and 13 years for males (Davis 2006, Davis et al. 2007), with a maximum reported size of 91cm TL and age of 20 years (Davis 2006, Davis et al. 2007). In the eastern Bering Sea, size- and age-at-50% maturity has been estimated at 80 cm TL and 25 years for females and 74 cm TL and 21 years for males (Winton et al. 2014). The maximum reported size and age from the Bering Sea are 94 cm TL and 36 years (Winton et al. 2014). The reported differences between regions may indicate latitudinal variability in growth rates (Winton et al. 2014).
|Use and Trade:||This species is not known to be utilized.|
The Roughtail Skate is taken occasionally as bycatch in fisheries targeting groundfish throughout its range, but is typically discarded as it is not commercially valuable (Ebert 2003). Species-specific catch records are lacking, but the wide depth distribution (213-2,550 m) of this species likely offers some degree of refuge from anthropogenic effects. At present, trawl and longline fisheries do operate in the upper portion of the species’ bathymetric distribution in Russian waters (to depths of 600 to 800 m); however, the species’ abundance is greater below these depths (A.M. Orlov pers. obs.). In the eastern North Pacific, most groundfish fisheries operate at shallower depths. From 2004-2008, this species was estimated to make up only 0.1% (by weight) of the observed skate bycatch (Stevenson and Lewis 2010) in the Alaskan groundfish fisheries. However, prior to 2004, 99% of skate bycatch in Alaskan fisheries was recorded as “unidentified skate” (Stevenson and Lewis 2010), making it difficult to determine whether changes in the composition of the catch have occurred over time (Barnett et al. 2013).
In Alaska's BSAI and GOA regions, the Roughtail Skate is managed as part of a skate complex comprising 13 species. Annual catch limits are determined for the complex as a whole. Prior to 2011, skates were managed as part of an “other species” complex that included animals with widely disparate life history types including octopus, sharks, sculpins, and skates (Ormseth 2014a,b). In the GOA, this skate is managed as part of an “other skates” complex with harvest specifications based on survey biomass estimates. Skate field identification guides and classroom training programs have been developed for fishery observers in Alaska (Stevenson and Lewis 2010). When these tools were implemented in 2004 and 2008, the number of skates that were categorized as "unidentified skate" dropped dramatically from ~99% by weight to < 3% in 2008 (Barnett et al. 2013, Stevenson and Lewis 2010).
On the United States west coast (Washington, Oregon and California), groundfisheries are managed by a federal Groundfish Fishery Management Plan. Although this species is not a focal species of the plan, and no species-specific data on the Roughtail Skate will be collected, other skates are being managed under this program. 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 catches of this species have also likely been reduced (D. Ebert pers. obs. 2007).
In Russia, the Roughtail Skate do not appear to have any active management measures, but the Roughtail Skate was assessed as having an Least Concern status when evaluated against the IUCN Criteria (Grigorov and Orlov 2013).
|Citation:||Vásquez, V.E., Davis, C.D., Ebert, D.A., Ishihara, H. & Orlov, A. 2015. Bathyraja trachura. The IUCN Red List of Threatened Species 2015: e.T161375A80676077.Downloaded on 29 July 2016.|
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