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Bathyraja trachura

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES ARHYNCHOBATIDAE

Scientific Name: Bathyraja trachura
Species Authority: (Gilbert, 1892)
Common Name(s):
English Roughtail Skate, Black Skate
Synonym(s):
Raja microtrachys Osburn and Nichols 1916
Raja trachura Gilbert 1891

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2009
Date Assessed: 2004-09-07
Assessor(s): Davis, C.D., Ebert, D.A., Orlov, A. & Ishihara, H.
Reviewer(s): Valenti, S.V. & Goldman, K.J. (Shark Red List Authority)
Justification:
This widespread, moderate-sized (91 cm TL) deep-sea skate is known from the north Pacific Ocean, from the Sea of Okhotsk to northern Baja California. The Roughtail Skate (Bathyraja trachura) occurs at depths of 213-2,550 m, but the majority of the population appears to exist below 600 m depth, with abundance increasing at greater depths. It is occasionally taken as bycatch in trawl fisheries, but is discarded as it is not commercially valuable. The bulk of the population is thought to occur beyond the range of current fisheries and in the absence of any information to suggest that declines have occurred; the species is currently assessed as Least Concern. The very wide depth distribution of the species likely provides refuge from anthropogenic effects; however the situation should be monitored as fisheries continue to expand into greater depths in the future. Given that this species, like other deepwater skates, has limiting life-history characteristics that would make it vulnerable to depletion, this assessment should be revisited if fisheries expand further and deeper across its range.

Geographic Range [top]

Range Description: North Pacific: The Roughtail Skate inhabits waters in northern Baja California, Mexico including the Sea of Okhotsk, Pacific waters of the Kuril Islands and Kamchatka; Bering Sea and Gulf of Alaska (Isakson et al. 1971, Parin 2001, Mecklenburg et al. 2002).
Countries:
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:
Native:
Pacific – eastern central; Pacific – northeast; Pacific – northwest
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Biomass estimates in Russian waters, based on bottom trawl surveys conducted between 1977 and 1997 comprised 18,500 mt; including 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).

The estimated biomass of this skate on the eastern Bering Sea slope was 1,677 mt in 2004 (Matta et al. 2006) and 139 mt in the Gulf of Alaska in 2005 (Gaichas 2006). Population numbers cannot be estimated as there are no data on mean body weight.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: The Roughtail Skate is a deep-sea skate that inhabits waters from 213-2,550 m (Ebert 2003, Stevenson 2004) but the bulk of population occurs at greater depths. Dolganov (1998d) reported that the species is most common at 600-1,400 m depth and surveys that sample below 1,200 m depth in the eastern Pacific suggest that it becomes more abundant with depth (D.A. Ebert pers. obs.). Females reach age at maturity at 5-6 years of age and 72.8-81.5 cm total length (TL); males at five years and 71.7-78.3 cm TL (Dolganov 1998c). Maximum size is 91 cm TL (Davis et al. 2007), and size at birth is 9-16 cm (Ebert 2003). Preferred temperature range is 1.9-3.6°C (Dolganov 1998a). Egg capsules measure 68-69 x 59-61 mm (Dolganov 1998c); egg capsule measurements from eastern Bering Sea 67-77 x 63-71 (Ebert 2005). Reported to feed on benthic invertebrates such as shrimps, crabs and worms, and small fishes such as rattails and flatfishes but a more detailed feeding study is needed (Dolganov 1998b, Ebert 2003).

Age at maturity in the eastern north Pacific is 11-14 years for males and 7-13 years for females; size range at maturity is 58.0-72.0 cm TL for males and 58.0-77.0 cm TL for females (from Davis 2006). Reproductive cycle appears to be continuous (Davis 2006). Size at maturity in the eastern Bering Sea is 73.5 cm TL females and 75.5 cm TL males (Ebert 2005).
Systems: Marine

Threats [top]

Major Threat(s): This species is taken occasionally as bycatch but discarded as it is not commercially valuable (Ebert 2003). There are no species specific data available to determine the quantity taken, however a significant portion of the population is thought to occur beyond the range of current fisheries. Trawl and longline fisheries operate down to 600-800 m depth in Russian waters and may take this species in the upper part of its bathymetric distribution, but it is more common below these depths (A.M. Orlov pers. obs.). In the eastern Pacific most groundfish fisheries operate at shallower depths. At present, the very wide depth distribution of the species likely offers a refuge beyond anthropogenic affects. The situation should be monitored, and this assessment may need to be re-visited if fisheries expand into deeper waters.

Conservation Actions [top]

Conservation Actions: No management or conservation efforts are currently in place. Where taken, catches require monitoring, particularly as deepwater fisheries expand worldwide.

The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and management of all chondrichthyan species in the region.

Citation: Davis, C.D., Ebert, D.A., Orlov, A. & Ishihara, H. 2009. Bathyraja trachura. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 21 November 2014.
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