|Scientific Name:||Bathyraja brachyurops|
|Species Authority:||(Fowler, 1910)|
|Taxonomic Notes:||Until B. cousseauae was described recently, this was often identified as B. brachyurops.|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor/s:||McCormack, C., San Martin, M.J., Stehmann, M. & Lamilla, J.|
|Reviewer/s:||Haywood, M., Kyne, P.M. & Valenti, S.V. (Shark Red List Authority)|
A poorly known large skate (to 125 TL) distributed in the Southwest Atlantic off Argentina and around the Falkland/Malvinas Islands and also in the Southeast Pacific off Chile. Known from depths of 28 to 604 m. Taken as regular bycatch in bottom trawl fisheries for Merluccius hubbsi and Dissostichus eleginoides off Argentina. There is little species-specific bycatch information available for these fisheries however fishing pressure has increased substantially over the past decade and in 1999, there was a decrease in the captures of rays by the deep sea fishing fleet of around 15% with regard to 1998. There was a reported decline in the biomass of B. brachyurops captured during fishery-independent investigations at 45° to 55°S off Argentina from 1998 to 1999, however the second phase of investigations employed gear which likely reduced the capture of rays. Bathyraja brachyurops is taken by one longliner targeting Dipturus chinlensis off Argentina, where it has been observed to comprise more than 20% on some trips in deeper water. The species is also taken in the Dipturus chilensis longline fishery operating to 300 m off Chile, where it comprises <5% of the catch. Overall biomass of the target species in the Chilean fishery has declined by 51% since fishing began in 1979 and declines are thus also likely to have occurred for bycatch species. The species also has the potential to be caught as bycatch by longliners targeting D. eleginoides below depths of 300 m off Chile. Around the Falkland/Malvinas Islands, this species is one of four dominating commercial catches in the multispecies skate fishery where its proportion in catches increased as the proportion of B. griseocauda decreased. This has been attributed to the early maturation and fast growth of the species and indicates that B. brachyurops may be able to sustain higher fishing pressure than other species. Following declines in the fishery in the early 1990s, the area to the south of the Falkland/Malvinas Islands has been closed to the commercial ray fleet and fishing now occurs north of 52°S. There have been no studies to determine the abundance of B. brachyurops in the southern area since the closure; however, it is may also be taken as bycatch by finfish trawlers operating around the Falkland/Malvinas Islands and within the skate closure area. A recent assessment of the northern ray population showed no increasing or decreasing trend in the CPUE of B. brachyurops over the period from 1992 to 2001. Given that this species is relatively wide-ranging compared with its congeners in the region and appears to have increased in proportion in some catches, it is assessed as Least Concern. However, past declines in biomass in the Falkland/Malvinas Islands fishery and continued fishing pressure throughout the species? range confirm the need for close monitoring and the collection of species-specific catch and bycatch data where none currently exists.
|Range Description:||B. brachyurops is widely distributed off Argentina from 40°30?S, including the Falkland/Malvinas Islands and occasionally at the coasts of the Buenos Aires Province and southern Brazil (Menni and Stehmann 2000). It is also found off Chile south of Valdivia (40°S) to the Strait of Magellan (Menni and Stehmann 2000). Colonello and Massa (2004) reported that the distribution of B. brachyurops was not uniform, at least over the area surveyed (from 45° to 41°S), with two areas of higher density identified north of 44°S below the 100 m isobath and south of 44°S at around 200 m.|
Native:Argentina; Brazil; Chile; Falkland Islands (Malvinas)
|FAO Marine Fishing Areas:||
Atlantic – southwest; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
The population size is unknown, however, this species is the third most important in the rajid trawl fishery north of the Falkland/Malvinas Islands forming around 20% of the catch (Wakeford et al. 2004).
This fishery initially operated in two areas, one to the north and one to the south of the islands. Following heavy fishing pressure during the early 1990s, Agnew et al. (2000), found that the species composition of the catch had changed so that the larger, late-maturing B. griseocauda had been replaced as the dominant species in the catch B. brachyurops to the south of the Islands. The southern area has since been closed to the rajid fishery and there have been no studies on the status of B. brachyurops in this area since. A recent assessment of the ray population in the northern area which is still open to the rajid fleet, showed no significant trend in CPUE for this species (Wakeford et al. 2004).
|Habitat and Ecology:||
Reported to depths of 28 to 604 m in a range of bottom temperatures from 3.0°C to 12.5°C (Menni and Stehmann 2000).
Age at maturity has been estimated at approximately eight years (Agnew et al. 2000). Size at maturity is estimated at around 64 cm TL for females and 58 cm TL for males (Stehmann et al. unpubl. data) with maximum and minimum lengths of 125 cm TL (FIFD unpubl. data) and 13 cm TL (Norman 1937) respectively. Like all skates, it is oviparous. Further information on the life history of the species may become available in the near future as the ECORAYA project is finalised (M. Stehmann pers. comm).
Smaller individuals feed opportunistically on benthic gammarid amphipods and polychaetes and larger specimens are active predators feeding primarily on fish (e.g., Patagonotothen ramsayi) and cephalopods (e.g., Loligo gahi) (Brickle et al. 2003).
Throughout this section the term rajid refers to skates of both the families Rajidae and Arhynchobatidae.
Skate landings have been increasing considerably in Argentina due to international demand. Prior to 1994, skate captures were less than 1,000t, however, since that year skate landings increased considerably, reaching >15,000 t in 2001 and 17,465 t in 2003 (Massa et al. 2004). Among the species of rays exploited commercially is B. brachyurops (García de la Rosa et al. 2000).
Bathyraja brachyurops is one of the dominant species in the multi-species skate trawl fishery around the Falkland/Malvinas Islands which has been operating since 1989. The fishery initially operated over two main areas, one located on the shelf edge to the north of the Islands, and the other to the south of the Islands. Following heavy fishing pressure during the early 1990s, Agnew et al. (2000), found that the species composition of the catch had changed so that the larger, late-maturing B. griseocauda had been replaced as the dominant species in the catch by B. albomaculata to the north and B. brachyurops to the south. Agnew et al. (2000) suggested that B. brachyurops should be able to sustain higher fishing pressure than the larger and late-maturing species in the fishery.
In 1996, following these declines, the southern area (south of 52°S) was closed to the fleet and the fishery now operates north of the Islands. A more recent assessment of the northern ray population (Wakeford et al. 2004) indicated that there was no significant increasing or decreasing trend in the CPUE for B. brachyurops over the period from 1992 to 2001.
The Falkland/Malvinas Islands have in place a precautionary management system for the skate fishery (see Conservation Actions), and together with the recovery of biomass (Agnew et al. 2000), what this means is that the fishery will continue into the future, because overall stocks are stable or recovering.
There have been no studies to determine the abundance of this species in the southern area since the rajid fishery closure. However, this species is also caught as bycatch by finfish trawlers operating around the Falkland/Malvinas Islands and within the southern rajid closure, targeting Micromesistius australis, Macruronus magellanicus, Merluccius hubbsi, M. australis and Salilota australis (Brickle et al. 2003). While vessels fishing under general finfish licenses are prohibited from targeting rajids, a small bycatch (below 10%) is allowed and rajids to the south of the Islands are continuing to face bycatch fishing pressure.
Bathyraja brachyurops is also a regular bycatch of the Dipturus chilensis longlining fishery off Chile (Lamilla et al. 2001, 2002) which operates mainly at depths from 30 to 300m. Landings for the fishery comprise 85% D. chilensis and 10% D. trachydermus with the remaining 5% made up of Bathyraja albomaculata, B. brachyurops, B. griseocauda and Rajella sadowskii (Lamilla et al. 2001, 2002). Overall biomass of the target species (D. chilensis and D. trachydermus) has declined by 51% since fishing began in 1979 (Quiroz 2005) and declines are thus also likely to have occurred for bycatch species. There may be some refuge for B. brachyurops at greater depths where fishing does not occur. However, there is also an artisanal Patagonian toothfish longline fishery operating at depths of 300 to 2,500 m between Iquique (20°S) to Ladrillero Gulf (49°S) off Chile (Lamilla 2003). This species could potentially be caught as bycatch in the fishery.
There are theoretically TACs, minimum sizes and overall annual quotas for quite a number of elasmobranch species in Argentina, however, little attention is paid to these and there is no regular monitoring by authorities (M. Stehmann pers. obs. 2006). Species-specific assessments of direct and indirect catches are a priority.
The following information is taken from Agnew et al. (1999 and 2000) unless otherwise specified.
The Falkland/Malvinas Islands multispecies skate fishery is managed by limiting fishing effort. The effort that each vessel is likely to exert is calculated (based on size, duration of license and past fishing history) and since 1994 only a limited number of licenses are granted to ensure that the total allowable effort (determined from assessments of stock status) is not exceeded. Stock status assessments are not, however, species-specific and a sustainable total allowable effort for the entire stock may not translate to sustainable levels of effort for individual species.
Following declines in CPUE in the early 1990s, in 1996, the southern area (below 52°S) was closed to rajid fishing and the fishery is now resticted to the area north of the Islands. This closure is extended to 50°30´S (between 56°30W and 58°W) during the second season of each year to exclude the skate fishing fleet from Loligo gahi fishing grounds.
All licensed vessels are required to provide daily catch and effort details, including discards of commercial and non-commercial species to the Falkland Island Fisheries Department. There is, however, no requirement to report species-specific information. Scientific observers are deployed onboard skate vessels in order to quantify the catch composition by species and to obtain detailed biological data on individual species.
Vessels fishing under general finfish licences are prohibited from targeting rajids, although a small bycatch (below 10%) is allowed.
In Chile, since 2005, there has been an annual quota for Dipturus spp. caught south of 41°28?S. Each year, there is also a seasonal fishery closure for the entire Chilean coast between December 1 and February 28 to protect the reproductive season. It is unknown whether this measure also protects the reproductive season of B. griseocauda.
|Citation:||McCormack, C., San Martin, M.J., Stehmann, M. & Lamilla, J. 2007. Bathyraja brachyurops. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 20 May 2013.|
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