|Scientific Name:||Rhinoraja albomaculata (Norman, 1937)|
Bathyraja albomaculata (Norman, 1937)
|Taxonomic Notes:||Compagno (1999, 2005) reallocated this species from Bathyraja to the genus Rhinoraja but the validity of this move remains unconfirmed. Both are currently in use, until a definitive systematic revision of these genera is conducted.|
|Red List Category & Criteria:||Vulnerable A4bcd ver 3.1|
|Assessor(s):||McCormack, C., Lamilla, J., San Martín, M.J. & Stehmann, M.F.W.|
|Reviewer(s):||Haywood, M., Kyne, P.M. & Valenti, S.V. (Shark Red List Authority)|
Bathyraja albomaculata is a medium sized (to 96 cm TL), wide-ranging skate from the Southwest Atlantic off Uruguay, Argentina and the Falkland/Malvinas Islands and more rarely recorded off Chile in the Southeast Pacific. This species is known from a wide depth range (between 55 m and 861 m) with higher densities at depths that differ latitudinally in the Southwest Atlantic. It is reportedly taken as bycatch in deepwater benthic trawl teleost target fisheries and also in the Dipturus chilensis directed skate fishery off Argentina. There is little species-specific trawl landing information available but fishing pressure off Argentina 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. A decline in the biomass of B. albomaculata captured during fishery-independent investigations at 45° to 55°S was also reported off Argentina from 1998 to 1999, however the second phase of investigations employed gear which likely reduced the capture of rays. In longline fisheries targeting Dipturus chilensis off Argentina and Chile, they are thought to comprise up to 10% (on deeper water trips) and <5% of the landed catch, respectively. In the multispecies skate trawl fishery north of the Falkland/Malvinas Islands, B. albomaculata is the second most important species forming 28% of the catch. In the early 1990s the fishery experienced dramatic declines, especially in the southern area which was closed to the rajid fleet in 1996. Between 1993 and 1997 B. albomaculata replaced B. griseocauda as the dominant species in the catch in the northern fishery area. A recent assessment of the northern ray population, utilizing observer data, has shown no significant trend in CPUE for this species. There have been no studies to determine the abundance of B. albomaculata in the southern area since the rajid fishery closure; however, it is also caught as bycatch by finfish trawlers that operate around the Falkland/Malvinas Islands and within the southern rajid closure. In an extensive study of the abundance of B. albomaculata in the Southwest Atlantic between 1998 and 2003, the species was generally absent between 48°S and 52°S, where it was formerly abundant, coincident with heavy fishing pressure in the area. B. albomaculata displays slow growth and late maturity and can be susceptible to overfishing if not closely monitored. Although more information is required to assess the magnitude of past declines, the vulnerability the species has shown to overfishing in the past and the continued fishing pressure through much of its range justifies an assessment of Vulnerable, on the basis of observed and inferred past and suspected future declines.
|Range Description:||Distributed in the Southwest Atlantic over the southern Patagonian shelf between 52°S and 54°S, around the Falkland/Malvinas Islands and the Burdwood Bank (Menni and Stehmann 2000). North of 52°S, it occurs on the outer shelf and upper slope as far north as 41°S, with its northern most record off Uruguay (Ruocco et al. 2006). In the south it is present both in shallower shelf areas and in deeper water, but in the north it is restricted to deeper water, following the Malvinas Current (Ruocco et al. 2006). In the Southeast Pacific off Chile from Taltal (26°10'S) (Lamilla unpubl. data) to the Strait of Magellan (56°S) (Pequeño 2000) and off Guamblin Island (45°04'S, 75°27'W) (Lamilla 1986).|
Native:Argentina; Chile; Falkland Islands (Malvinas); Uruguay
|FAO Marine Fishing Areas:|
Atlantic – southwest; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The population size of this species is unknown, however, it is the second most common skate caught in the skate fishery north of the Falkland/Malvinas Islands (Ruocco et al. 2006) suggesting that it is abundant, at least in those waters. |
Specimens from the Falkland/Malvinas Islands have been found to mature at a smaller size than those off Argentina despite using the same methods for assessing length at maturity (Ruocco et al. 2006). Ruocco et al. (2006) suggested that there may be separate populations within the species' range, however further research on larger sample sizes is required to test this hypothesis.
Ruocco et al. (2006) found that B. albomaculata was most abundant on the outer continental shelf and slope between 36°30' and 45°S. In contrast, it was generally absent between 48°S and 52°S, a region where it was formerly reported as abundant. This could be related to the recent higher fishing pressure around the Falkland/Malvinas Islands (Ruocco et al. 2006).
There have also been reports that the biomass of B. albomaculata south of 45°S declined by 83% between 1998 and 1999 (García de la Rosa et al. 2000), however the second phase of investigations employed gear which likely reduced the capture of rays.
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Recorded from a wide depth range from 55 m to 861 m (J. Pompert pers. comm.) in bottom temperatures ranging from 2.8 to 6.8°C (Menni and Stehmann 2000). |
In the Southwest Atlantic, Ruocco et al. (2006) found the depth distribution of the species differed latitudinally. In the north (north of 41°S), the species was found from 65 to 310 m, with higher densities from 250 to 310 m. In the central area of its Southwest Atlantic distribution (41°S and 48°S), the species was found in shallower water from 70 to 140 m with high densities from 100 to 130 m. In the south (south of 48°S), B. albomaculata was found over a broader depth range from 70 to 310 m, with higher densities from 160 to 190 m.
Age and length at maturity have been estimated at 10 years for females and 11 years for males (Henderson et al. 2004). Ruocco et al. (2006) found sizes at maturity off Argentina of 65.3 cm total length (TL) and 62.8 cm TL for females and males, respectively, whereas the estimates of Henderson et al. (2004) from the Falkland/Malvinas Islands were smaller (around 57.2 cm TL and 59.4 cm TL for females and males, respectively). These studies used the same methods to assess age at maturity and Ruocco et al. (2006) suggested that different populations might occur within the species range.
The oldest specimen reported was 17 years and the maximum length has been estimated at 96 cm TL (Agnew et al. 2000).
Like other skates, B. albomaculata is oviparous. Henderson et al. (2004) found ovarian fecundity ranged from four to 32 with a mean of 14 and size at hatching was estimated at 9.8 cm and 10.5 cm DW for females and males, respectively. Gravid and post-partum females were observed all year-round and throughout the species' depth range but there was an increase in the proportion of gravid and post-partum females during autumn and winter (Henderson et al. 2004). Ruocco et al. (2006) also found females carrying eggs in April, September and October suggesting that year-round egg laying may occur.
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. 2006).
A highly specific feeder on benthopelagic gammarid and polychaetes (Brickle et al. 2003) and to a lesser extent on isopods.
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 1,000 t, however, since that year skate landings increased considerably, reaching >15,000 t in 2001 and 17,465 t in 2003 (Massa et al. 2004).
Bathyraja albomaculata is a regular bycatch in bottom trawl fisheries for bony fishes. It has been captured during fishery-independent investigations for hake Merluccius hubbsi and other species (García de la Rosa et al. 2000). García de la Rosa et al. (2000) reported a 83% decline in the biomass of B. albomaculata captured from 45° to 55°S during the summer investigations of 1999 compared to 1998, however, it was acknowledged that during the second phase of the investigations, new gear was employed which likely reduced the capture of rays. During 1999, there was a decrease in the captures of rays by the deep sea fishing fleet of around 15% with regard to 1998 (García de la Rosa et al. 2000).
The species is also taken in the Dipturus chilensis directed skate fishery off Argentina which currently comprises a single vessel. Onboard observation of the fishing operation in 2000 and 2001 indicated that the vessel fished from 37° to 44°S off Argentina in two regions; around 50 m of depth and along the 100 m isobath. At greater depths, the processed catch composition varied between trips and comprised from around 5 to 10% of B. albomaculata (Colonello et al. 2002). Species-specific bycatch data are not generally collected for this fishery, however, and remain a priority for this and the trawl fishery.
Since 1989, rajids have been targeted by a Korean fleet utilizing demersal trawls around the Falkland/Malvinas Islands. Although approximately 11 skate species are regularly taken, commercial catches are dominated by four species including B. albomaculata. 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. Agnew et al. (2000) found that between 1993 and 1997 B. albomaculata replaced B. griseocauda as the dominant species in the catch in the northern fishery area. According to Agnew et al. (2000) B. albomaculata (and also B. brachyurops) should be able to sustain higher fishing pressures than B. griseocauda and D. chilensis because it matures earlier and grows faster relative to these other species. However, Henderson et al. (2006) noted that B. albomaculata displays quite a low fecundity compared to other rajid species and combined with its slow growth and late maturity, this species could be susceptible to overfishing if not closely monitored.
Following declines in CPUE in the early 1990s, the southern area was closed to the ray fleet in 1996 and the fishery now concentrates in the northern area. A more recent assessment of the northern ray population, utilizing observer data, has shown little indication of an increasing or decreasing trend in CPUE for this species (Wakeford et al. 2004). Bathyraja albomaculata is currently the second most important species, comprising 28% of the catch (Ruocco et al. 2006). 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. As such, pressure will continue on all species, including those less able to sustain heavy fishing pressure, such as B. albomaculata.
There have been no studies to determine the abundance of this species in the southern area since the skate fishery closure. However, this species is also caught as bycatch by finfish trawlers targeting Micromesistius australis, Macruronus magellanicus, Merluccius hubbsi, M. australis and Salilota australis around the Falkland/Malvinas Islands (Brickle et al. 2003) and within the southern rajid closure. While vessels fishing under general finfish licenses are prohibited from targeting rajids, a small bycatch (below 10%) is allowed so rajids to the south of the Islands are continuing to face bycatch fishing pressure.
Bathyraja albomaculata is also a regular bycatch of the Dipturus chilensis longline fishery off Chile. 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 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 exists within the area and at the depth range fished and could potentially be caught as bycatch in the fishery.
In Argentina, species-specific assessments of direct and indirect catches are a priority. 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).
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 a seasonal fishery closure for the entire Chilean coast between December 1 and February 28 to protect the reproductive season of Dipturus trachydermus. It is unknown whether this measure also protects the reproductive season of B. albomaculata.
|Citation:||McCormack, C., Lamilla, J., San Martín, M.J. & Stehmann, M.F.W. 2007. Rhinoraja albomaculata. The IUCN Red List of Threatened Species 2007: e.T63102A12604017.Downloaded on 21 January 2018.|