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Bathyraja maculata 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Chondrichthyes Rajiformes Arhynchobatidae

Scientific Name: Bathyraja maculata Ishiyama & Ishihara, 1977
Common Name(s):
English Whiteblotched Skate
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).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2015
Date Assessed: 2015-07-27
Assessor(s): Ormseth, O.A., Foy, R., Davis, C.D., Ebert, D.A., Orlov, A. & Ishihara, H.
Reviewer(s): Chabot, C.L. & Lawson, J.
Facilitator/Compiler(s): Walls, R.H.L. & Dulvy, N.K.
Justification:
The Whiteblotched Skate (Bathyraja maculata) occupies deep waters (73-1,193 m depth) of the northern North Pacific Ocean (Sea of Japan to the Gulf of Alaska). It is a large species (maximum length 147 cm) that is long-lived and late-maturing (maximum observed age = 36 years; female age at 50% maturity = 26 years). 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 or increasing in the eastern Bering Sea and in the Aleutian Islands, and this species was assessed as Least Concern in the coastal waters of the Russian Federation. The majority of the population of this species occurs at depths below those where most fishing activity takes places (~300 m and above), and there are no known habitat impacts such as pollution or development. Given this information, and that this species is managed as part of the Bering Sea/Aleutian Islands skate stock complex in Alaska, the Commander Skate is assessed as Least Concern. Either a shift to fishing in deeper waters or the development of a targeted fishery have the greatest potential to threaten the status of this species.
Previously published Red List assessments:

Geographic Range [top]

Range Description:

The Whiteblotched Skate is distributed throughout the northern North Pacific Ocean, from the northern Sea of Japan to the eastern Gulf of Alaska (Mecklenburg et al. 2002, Stevenson et al. 2007, Bizzarro and Vaughn 2008). In Alaskan waters, this is the most abundant skate species in the Aleutian Islands (AI; 22,400 t in 2012) and the third-most abundant skate species on the eastern Bering Sea (EBS) slope (5,820 t in 2012; Ormseth 2014a), and it is rarely observed on the EBS shelf. It appears to be quite rare in the Gulf of Alaska (GOA; Bizzarro and Vaughn 2008, Ormseth 2014b). Reported depth ranges are from 73 to 1,193 m (Stevenson et al. 2007).

Countries occurrence:
Native:
Japan (Hokkaido); Russian Federation (East European Russia, Kamchatka, Kuril Is.); United States (Alaska, Aleutian Is.)
FAO Marine Fishing Areas:
Native:
Pacific – northeast; Pacific – northwest
Additional data:
Lower depth limit (metres):1193
Upper depth limit (metres):73
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Recent population data exist for the AI, EBS, and GOA and are based on bottom trawl surveys conducted by the U.S. National Marine Fisheries Service. In the AI biomass estimates are quite variable, with coefficients of variation (CVs) ranging from 15-30%. Early biomass estimates may also be suspect due to changes in survey methodology. Nevertheless the population of the Whiteblotched Skate in the AI appears to have increased substantially during the 1990s and early 2000s, from 7,989 t in 1994 to 29,715 t in 2006 (Ormseth 2014a). Similarly, the estimated biomass of this skate has increased recently on the EBS slope, from 3,927 t in 2002 to 5,820 t 2012 (Ormseth 2014a). Variability of the estimates is slightly lower on the EBS slope relative to the AI (CV 14-23%). The species is sufficiently rare on the EBS shelf and in the GOA that biomass estimates are available only occasionally and have extremely high CVs (Ormseth 2014a,b).
Current Population Trend:Unknown
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:

Although the reported depth range for this species is 73 to 1,193 m, it is likely that it prefers a narrower range. In the EBS and AI it appears to be limited to depths between 200 m and 800 m, with the highest relative abundance between 300 m and 400 m (Stevenson et al. 2008). Other species of skate on the EBS slope use small, discrete areas on the upper slope (145-380 m depth) as nursery areas where they deposit embryos in eggcases (Hoff 2010). It is unknown whether this species has similar nursery areas or where these might be located. Similarly, the known depth distribution in the EBS and AI is derived only from summer surveys, and seasonal movements are not known. 

The Whiteblotched Skate is a large skate, with a maximum observed length of 147 cm (Stevenson et al. 2007). The maximum age is reported to be 36 years, with an age at 50% maturity of 26 years for females (Maurer 2009). Natural mortality is estimated at 0.05-0.14, and the annual population growth rate was estimated at 1.079 (Barnett et al. 2013). When compared to the other deepwater skates examined in this paper, rate of natural mortality was similar to other deepwater Bathyraja species in the Bering Sea, and annual population growth rate was comparatively low (third slowest of fourteen species). It is clear that the Whiteblotched Skate is a long-lived, slow-growing, late-maturing species that therefore has a life history that is vulnerable to fisheries exploitation and other impacts.
Systems:Marine

Use and Trade [top]

Use and Trade: This species is not known to be utilized.

Threats [top]

Major Threat(s):

Commercial fishing is most likely the main threat to this skate. It is taken in small numbers as bycatch of commercial trawl and longline fisheries in the EBS, AI, and GOA (Olav Ormseth, unpublished data, 2015). The majority of these catches occur in longline fisheries that occur along the EBS slope and in the AI. Skates are often retained, with the rate of retention depending on skate size and market interest. In 2013 the overall retention rate for skates in the EBS was 29%, although most of these data come from the EBS shelf where this species is rare (Ormseth 2014a). Since at least the early 2000s there has been interest in directed fisheries for skates in the GOA, mainly for the Longnose Skate (Raja rhina) and Big Skate (Beringraja binoculata). Such fisheries occurred in federal waters in 2003 and 2004, and in state waters in 2009 and 2010. Although directed fishing for skates is currently prohibited, interest in these fisheries remains high. 

The catch of the Whiteblotched Skate in the western Bering Sea (WBS) is unknown; however a recent assessment of the conservation status of chondrichthyans in Russian waters determined that the IUCN status of this species in Russia was “Least Concern” (Grigorov and Orlov 2013). In both Alaska and Russia, this skate occurs at depths below those where most commercial fishing occurs. In the EBS relatively little fishing effort occurs below 300 m depth, so most of the population of this species would occur below fished depths. If the operating depth of fisheries increases, the Whiteblotched Skate may be subject to increased fishing pressure.

Other threats are unknown. Altered ocean conditions resulting from climate change are likely to affect the Whiteblotched Skate, but the impact of that threat cannot be determined at this time.

Conservation Actions [top]

Conservation Actions: In the EBS and AI, the Whiteblotched Skate is managed as part of a skate complex comprising 13 species. Annual catch limits are determined for the complex as a whole by multiplying the estimated biomass of all skates (from surveys) by a natural mortality rate of 0.1 (Ormseth 2014a,b). Species-specific catch rates for this skate in particular are not actively tracked, but the aggregate skate catch has been below the acceptable biological catch since 2011 when the current management measures were adopted. 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 Russia this species does not appear to have any active management measures, but was assessed as “Least Concern” in coastal Russian Federation waters when the IUCN criteria were applied (Grigorov and Orlov 2013).

Citation: Ormseth, O.A., Foy, R., Davis, C.D., Ebert, D.A., Orlov, A. & Ishihara, H. 2015. Bathyraja maculata. The IUCN Red List of Threatened Species 2015: e.T161350A80674766. . Downloaded on 20 September 2017.
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