|Scientific Name:||Rioraja agassizii (Müller & Henle, 1841)|
Rioraja agassizi (Müller & Henle, 1841)
|Red List Category & Criteria:||Vulnerable A4d ver 3.1|
|Assessor(s):||Kyne, P.M., San Martín, J. & Stehmann, M.F.W.|
|Reviewer(s):||Chiaramonte, G.E. & Valenti, S.V. (Shark Red List Authority)|
Rioraja agassizi has a relatively restricted distribution on the continental shelf off southern Brazil, Uruguay and northern Argentina (~30° to 43°S). This coastal and shelf skate is found at depths of 10 to 100 m and reaches a maximum size of 71 cm TL. The majority of its geographic and bathymetric distribution is subjected to fairly intensive trawl fishing. This species is taken off Argentina and Uruguay in a multi-species coastal demersal fishery where skate landings have increased considerably since 1994. Indeed, increasing international demand for skates has resulted in growing fishing pressure on skate species along the coastal and shelf waters of Argentina and Uruguay. This species is included in an annual quota in Argentina, which has been exceeded in recent years, highlighting its inadequacy as a management measure. Declines in the overall biomass estimates of the coastal skate assemblage have been recorded and considerable declines in the biomass of some skate species have been documented off Buenos Aires Province, Argentina and Uruguay (34° to 41°S) (i.e., the similarly sized Atlantoraja cyclophora and the smaller Sympterygia acuta), an area where trawl fishing is intensive. Furthermore, a reduction of 5 cm on the TL of R. agassizi landed at Puerto Quequén (38°37'S, 58°50'W) between 2001 and 2005 was recently detected (Perez et al. unpublished). Fishing pressure is also known to be intense where the species is taken as by-catch in artisanal and industrial southern Brazil. In this region it composes 5 to 20% landings, the proportion of this species is considered to have declined in captures and the population is likely to have declined. While specific data are lacking, the overall high fishing pressure on the range of R. agassizi, together with increasing demand for skates in the region, and documented declines of other coastal and shelf species, R. agassizi is assessed as Vulnerable based on inferred past and expected future declines due to actual and potential levels of exploitation.
|Range Description:||Endemic to the Southwest Atlantic, between ~30° and 43°S (Menni and Stehmann 2000). Its absence in Patagonian waters has been confirmed (Menni and Stehmann 2000).|
Native:Argentina (Buenos Aires); Brazil (Rio Grande do Sul); Uruguay
|FAO Marine Fishing Areas:|
Atlantic – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||One of the most abundant skates on the continental shelf off Uruguay-Buenos Aires, Province, Argentina (Colonello et al. 2003).|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||A coastal and shelf skate, occurring at depths of 10 to 130 m (Figueiredo 1977). Reaches a maximum size of ~71 cm TL (Cousseau et al. 2000) and has an annual reproductive period, with egg-laying from November to July, but with a peak in January and February in south Brazilian waters (Peres and Vooren 1993). There are apparent nearshore movements of adults for reproductive activities during the summer.|
The majority of the species' geographic and bathymetric distribution is subjected to fairly intensive trawl fishing.
Off Argentina and Uruguay, Rioraja agassizi is taken by the multi-species fleet that exploits the coastal demersal fish assemblage (Massa et al. 2003, 2004). Furthermore, since 2000, one vessel has been specifically targeting skates off Argentina. There are no data on specific catches as all species of batoids are registered in fishery statistics as "unidentified rays and skates". Increasing international demand for skates has resulted in growing fishing pressure on skate species along the coastal and shelf waters of Argentina and Uruguay. 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). There has been a 31% reduction in overall coastal skate biomass estimates from 1994 (when active exploitation commenced) to 1999/2003 (Massa et al. 2004). While this data is not species-specific, it highlights the pressure placed on the coastal skate assemblage, of which R. agassizi is a dominant component. Considerable declines in the biomass of other coastal and shelf skate species have been documented off Buenos Aires Province, Argentina and Uruguay (34° to 41°S) (i.e., the similarly sized Atlantoraja cyclophora and the smaller Sympterygia acuta) (Massa and Hozbor 2004, Massa et al. 2006), an area where trawl fishing is intensive.
In an observer program of the Puerto Quequén coastal benthic trawl fishery in Buenos Aires Province, Argentina, R. agassizi was found to constitute only a small component of batoids captured (0.3% by number, 0.1% by mass, 2.7% frequency of occurrence) (Tamini et al. 2006).
Fishing pressure is also known to be intense where the species occurs off southern Brazil and demersal trawlers in that region land skates as part of multi-species fisheries. This species is taken as by-catch in artisanal and industrial fisheries in southern Brazil, and composes 5 to 20% of captures (Lessa et al. 1999). Lessa et al. (1999) reported that the proportion of this species has declined in captures and there is a risk of a population decline.
|Conservation Actions:||In Argentina, the species is included in the annual maximum permitted catch (MPC) of the fishery for coastal skates, established by the Argentine fisheries authorities. In recent years the landings were higher than the quotas, and at present this is not an adequate management measure. Species-specific catch data are required as at present all species of batoids are registered in the fishery statistics as "unidentified rays and skates". Specific catch information is also required from southern Brazil.|
|Citation:||Kyne, P.M., San Martín, J. & Stehmann, M.F.W. 2007. Rioraja agassizii. The IUCN Red List of Threatened Species 2007: e.T63109A12607686.Downloaded on 26 April 2018.|