|Scientific Name:||Bathyraja aleutica (Gilbert 1896)|
Raja aleutica Gilbert, 1896
|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):||Davis, C.D., Ebert, D.A., Ishihara, H., Orlov, A., Compagno, L.J.V., Farrugia, T.J. & Tribuzio, C.A.|
|Reviewer(s):||Haas, D.L. & Clerkin, P.J.|
|Facilitator/Compiler(s):||Lawson, J., Walls, R.H.L. & Dulvy, N.K.|
The Aleutian Skate (Bathyraja aleutica) is a large, deepwater skate, that is widely distributed in the North Pacific. This species inhabits the outer continental shelf and upper slopes and occurs at depths between 15-1,602 m. It is taken as bycatch in commercial trawl and longline fisheries, operating in the upper part of its bathymetric distribution. Biomass estimates from scientific surveys suggest that biomass may have increased in the eastern Bering Sea in recent years. Few time series data are available for other areas of its range. Given that the Aleutian Skate appears to be more abundant in deeper waters, outside the range of current fishing pressure, and in the absence of any evidence to suggest significant declines, it is assessed as Least Concern. However, few species-specific data are available and increasing interest in skate fisheries within this species’ range is of concern. Aleutian Skates exhibit limiting life-history characteristics, similar to other large skate species and may be susceptible to overfishing, should a directed fishery develop. Species-specific monitoring is required to determine catch levels and trends. If fisheries expand further across this species’ range, or if a long-term target fishery was to develop, then this assessment should be revisited.
|Previously published Red List assessments:|
The Aleutian Skate is common in the Northwest and northeast Pacific Ocean. It is widespread, from Chiba Prefecture, Japan to Cape Navarin, western and northern Sea of Okhotsk, Russia in the Northwest Pacific. It is also common in the Bering Sea, Aleutian Islands and Gulf of Alaska, USA and in British Columbia, Canada. Its range continues to Cape Mendocino, northern California, USA (Ishihara 1990, Dolganov 1999, Hoff 2002, Mecklenburg et al. 2002, Ebert 2003, Stevenson 2004, Orlov et al. 2006).
Native:Canada (British Columbia); Japan (Honshu); Russian Federation (East European Russia, Kamchatka, Kuril Is., Magadan, Sakhalin); United States (Alaska, Aleutian Is., California)
|FAO Marine Fishing Areas:|
Pacific – northwest; Pacific – northeast
|Range Map:||Click here to open the map viewer and explore range.|
Surveys which report biomass estimates for the Aleutian Skate are varied depending on the jurisdiction with inconsistent time series between areas. The only bottom trawl surveys carried out in Russian waters were between 1977 and 1997, and estimated an average annual biomass estimate of 87,700 t, comprising of 27,800 t in the western Bering Sea, 5,100 t off the Kuril Islands and Kamchatka and 54,800 t in the Sea of Okhotsk, with no significant trend over time (Dolganov 1999). A positive trend in catch per unit effort (CPUE) survey data was observed in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka between 1993 and 2000, however a slight decline in CPUE was detected in 2000 (Orlov et al. 2006).
In Alaskan waters, Bathyraja species comprise the majority of the skate biomass based on fishery independent bottom trawl surveys. The Aleutian Skate is the majority of the total skate biomass in the Gulf of Alaska (GOA) and in the eastern Bering Sea (EBS) slope, however, the Alaska Skate (Bathyraja parmifera) dominates skate biomass on the EBS shelf (Stevenson and Lewis 2010, Ormseth and Matta 2011, Ormseth and Matta 2012, Ormseth 2013). Biomass estimates in the GOA increased from 11,293 t in 1999 to 15,945 t in 2011, with a peak of 25,399 t in 2007 (Ormseth and Matta 2011). However, this increase could be due to the increased survey coverage and accuracy of species identification, rather than a true increase in population biomass. Spatial analyses of the distribution of skates in the Gulf of Alaska have shown hotspots of Aleutian Skate abundance in Shelikof Strait and west of Kodiak Island (Bizzarro et al. 2014). On the EBS slope, where the Aleutian Skate is the most abundant skate species, the overall skate biomass has stayed fairly constant between 30,000 and 40,000 t since 2002, with the Aleutian Skate fluctuating between 14,000 and 22,000 t (Ormseth and Matta 2012). On the EBS shelf, the Aleutian Skate is a much smaller proportion of the skate biomass and in most years with reliable species identification, their survey biomass varies between 1,000 and 6,000 t, except in 2003 when it was estimated at 18,000 t (Ormseth and Matta 2012). In the Aleutian Islands (AI), the Aleutian Skate abundance varied between 3,000 and 11,000 t from 2000 to 2012 (Ormseth and Matta 2012). Overall, when surveys were conducted in all three areas (EBS slope, EBS shelf and AI) in the same years (2002, 2004, 2010, 2012), the total biomass estimates increased from 26,261 to 33,293 t, but these biomass estimates were associated with fairly large coefficients of variation (0.1-0.2).
Virtually nothing is known about the population status or abundance of this species in other parts of its range including the west coasts of Canada and the United States.
|Current Population Trend:||Stable|
|Habitat and Ecology:|
The Aleutian Skate is a large deepwater skate, reaching a maximum size of 154 cm total length (TL) (Ebert 2005). It inhabits the outer continental shelf and upper slope on muddy substrates (Ebert 2003), and occurs at depths of 15 to 1,602 m (Sheiko and Fedorov 2000, Mecklenburg et al. 2002, Ormseth and Matta 2011).
Age and growth characteristics are somewhat similar between the eastern Bering Sea (EBS) and Gulf of Alaska (GOF). In the EBS, longevity is 16 years for males and 17 years for females, whereas in GOA longevity is 18 and 19 years, respectively (Haas 2011). Females mature at 9-10 years (Dolganov 1998), at a size of 112-133 cm TL, averaging 125 cm in the GOA (Dolganov 1998, Ebert 2003). Males mature at 8-9 years (Dolganov 1998), at a size of 108-116cm TL, averaging 113 cm TL in the GOA (Dolganov 1998, Ebert 2003). However, there seems to be a difference in the age of maturity of 3.5 years between EBS and GOA Aleutian Skates, with EBS skates maturing at 10.4 years and GOA skates at 13.7 years (Haas 2011).
Reproductive characteristics are also variable across the range of the species. Ovarian fecundity in the EBS ranged from 7 to 60 ova per female, compared to 3-36 ova in GOA (Haas 2011). In the EBS, egg cases are deposited between June and November, at depths of 250-500 m (Teshima and Tomonaga 1986, Ebert 2003, Hoff 2010), whilst in Asian waters, they are reportedly deposited all year round, with no depth range reported (Dolganov 1998, Glubokov and Orlov 2000). Two nursery areas have been identified in the EBS, both near shelf breaks and associated with a nearby underwater canyon. Nursery grounds in the southern part of its range are unknown (Ebert 2003). Egg capsules measure 117-136 x 73-97 mm and size at birth is 120-150 mm TL (Dolganov 1998).
Demographic analyses, which take into account growth and reproductive rates, have been conducted on the species. Aleutian Skates in Alaska have a relatively high population growth rate when compared to other skates, with a finite population growth rate of 1.252 (Ebert et al. 2007). These results suggest that it is a relatively productive skate species and less vulnerable to population declines compared to B. trachura for example (Barnett et al. 2013). This analysis did not estimate population growth rates for the species in different regions (i.e. EBS or GOA), thus it is not possible to determine if the species has differences in vulnerability across its range. However, Haas (2011) found that skates from the GOA had greater longevity, later age at maturity, and lower potential fecundity than skates from the EBS, which could indicate increased vulnerability to fishing pressure.
|Use and Trade:||In Japan, skate wings (in which this species is likely to be included) are marketed fresh and frozen for human consumption.|
Commercial fisheries pose the greatest potential threat to the Aleutian Skate. This species is taken as bycatch of commercial trawl and longline fisheries in the EBS, AI, and GOA (Gaichas et al. 2003, Ormseth and Matta 2012, Ormseth 2013), and probably elsewhere throughout its range in the eastern North Pacific. A target fishery for skates (mainly Longnose Skate (Raja rhina) and Big Skate (Beringraja binoculata)) was developed in the GOA between 2003 and 2005, and in Prince William Sound, Alaska between 2009 and 2010, but Bathyraja species constituted only a small proportion of the catch of this fishery (Ormseth 2011). About 30% of the catch of Aleutian Skate is retained in the EBS (Ormseth and Matta 2011). Depth analysis of observed catch in longline fisheries targeting Pacific cod in the EBS, suggest that most of the skate catch (98%) occurs <200 m depth (Ormseth and Matta 2011). Therefore this species’ deep bathymetric distribution may offer refuge, outside the range of current fisheries. Although there is no target fishery at present, there has been interest in developing markets for skates in Alaska and continued interest in skates as a potential future target in the GOA, EBS and AI is expected (Farrugia et al. in review).
In Russian waters, this skate is a common bycatch of bottom trawl and longline fisheries (targeting halibut and rockfishes; Tokranov et al. 2005). Deepwater bottom trawl and longline fisheries are present in the northern Sea of Okhotsk, western and eastern Kamchatka, western Bering Sea and northern Kuril Islands, but the fishing pressure is relatively low. These fisheries usually operate down to 600 – 800 m, i.e., within the upper part of species' bathymetric range (Ormseth and Matta 2011). There are no fisheries activities in the southern and western Sea of Okhotsk, off Commander and southern Kuril Islands. There has also been interest in this skate as a potential fishery target in Russia (Orlov 2004).
Commercial fisheries likely catch this species in other regions, but catch data is limited. The Aleutian Skate is regularly taken as bycatch in offshore bottom trawl fisheries around Japan but no time series data are available to determine catch levels (H. Ishihara pers. obs. 2007). Catch of Aleutian Skate in Canadian and west coast US waters is minimal as it is mostly captured as a non-target species and usually discarded.
No information is currently available on post-discard survivorship for this species after being caught in different gear types. Studies of other skate species have shown about a 19% short-term mortality after discard from a trawl net (Mandelman et al. 2013).
The Aleutian Skate has not been a conservation concern in any of the regions that it inhabits. Since 2010, targeted fishing of all skate species has been prohibited in the GOA (Ormseth 2011). Bathyraja species are presently managed within the GOA ‘other skates assemblage’, but continued, accurate monitoring of skate landings is required to ensure that any increased commercial interest in Bathyraja spp. is identified in time for appropriate management measures to be implemented (Ormseth and Matta 2011). Skates are targeted in the Pacific Canadian waters, but the fishery targets big and longnose skates, and bycatch of the Aleutian Skate is minimal.Improved catch monitoring is important throughout the species range, 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., Ishihara, H., Orlov, A., Compagno, L.J.V., Farrugia, T.J. & Tribuzio, C.A. 2015. Bathyraja aleutica. The IUCN Red List of Threatened Species 2015: e.T161661A80674005.Downloaded on 23 May 2018.|
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