|Scientific Name:||Zearaja chilensis (Guichenot, 1848)|
Dipturus chilensis (Guichenot, 1848)
Dipturus flavirostris (Philippi, 1892)
Raia chilensis Guichenot, 1848
Raja flavirostris Philippi, 1892
|Taxonomic Notes:||Often referred to as the synonyms Dipturus flavirostris or Raja flavirostris.|
|Red List Category & Criteria:||Vulnerable A4bd ver 3.1|
|Assessor(s):||Kyne ,P.M., Lamilla, J., Licandeo, R.R., Jimena San Martín, M., Stehmann, M.F.W. & McCormack, C.|
|Reviewer(s):||Valenti, S.V. & Gibson, C.G. (Shark Red List Authority)|
Zearaja chilensis is a large skate (reportedly to 210 cm TL, but more commonly to ~125 cm TL) distributed in the Southwest Atlantic from Uruguay, Argentina and around the Falkland/Malvinas Islands (and doubtfully from southern Brazil) and in the Southeast Pacific from central to southern Chile (30° to 56°S). It occurs on the continental shelf and upper slope at depths of 28 to 435 m in the Southwest Atlantic and 40 to 500 m off Chile. Maximum ages of 27 years for females and 23 years for males have been estimated, with females maturing at 14 years of age. The vulnerability of large skates to overexploitation and subsequent population depletion is well documented and in the case of Z. chilensis, both directed and bycatch fishing pressure from commercial and artisanal activities are impacting this K-selected species. In Chile, overall biomass of Dipturus trachydermus and Zearaja chilensis has decreased by 51% and spawning biomass by 34% since fishing began in 1979. Landing statistics are not separated by species, but research has shown that Z. chilensis makes up 85% of catches. Catches are now regulated by quota in Chile and there may be some refuge for the species in the more remote regions of southern Chile. In the Southwest Atlantic there is heavy fishing pressure across most of the species' distribution, and in the coastal and continental shelf waters of Argentina, fishing pressure on all skate species has increased rapidly due to international demand, with landings rising from <1,000 t prior to 1994 to 17,465 t in 2003. Zearaja chilensis is the target species of a Korean longline vessel operating off Mar del Plata, and is also taken in various multispecies fisheries off Argentina. During fishery-independent investigations, a 53% decline in the biomass of Z. chilensis captured from 45° to 55°S during summer surveying in 1999 was reported compared to 1998. It was acknowledged, however, that during the second phase of the investigations, new gear was employed which likely reduced the capture of rays, and as such these estimates should be viewed with some caution. In the multispecies skate trawl fishery north of the Falkland/Malvinas Islands, Z. chilensis is one of four species dominating commercial catches. In the early 1990s the fishery experienced dramatic declines, especially in the southern area which was closed to the skate fleet in 1996. Agnew et al. (2000) found that between 1993 and 1996 there was some evidence that Z. chilensis declined in catches, but showed an increase again in 1997. It did however, show the greatest decrease in mean and maximum size from 1993 to 1997 of any species (mean size from 76.76 cm DW in 1993 and 58.49 cm DW in 1997) (Agnew et al. 2000). A recent assessment of the northern ray population, utilizing observer data, showed an increasing trend in CPUE for this species (Wakeford et al. 2004). Precautionary management in the Falkland/Malvinas Islands has resulted in recovery of overall skate stocks, and so fishing pressure will continue on all species, including those less likely to sustain heavy exploitation such as Z. chilensis. Furthermore, overall CPUE trends may mask localised declines or depletions of individual species (Wakeford et al. 2004). Globally, documented biomass declines off Chile, the vulnerable life-history of the species and continuing heavy fishing pressure over most of the species' range, particularly in the Southwest Atlantic, warrant an assessment of Vulnerable on the basis of past and future declines. More robust biomass estimates and catch monitoring in the Atlantic may indeed show that the species has declined more significantly than suspected and may fall into a higher threat category in the future, particularly as directed fishing pressure continues.
|Range Description:||Southwest Atlantic: From southern Brazil (doubtful), Uruguay, Argentina and around the Falkland/Malvinas Islands. The species occurs with certainty from at least 34°35´S (Uruguay), but occurrence to the north is unconfirmed and as such the reports for Southern Brazil are doubtful as they may correspond to a species complex which is still under study, mainly including Dipturus leptocaudus (Krefft and Stehmann 1975) (J. Soto pers. comm).
Southeast Pacific: Chile from Coquimbo (30°S) to Punta Arenas (56°S).
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:||Reportedly one of the most abundant skate species of the Southwest Atlantic, however exact details of population size are unknown.
Wakeford et al. (2004) suggests that the species does not form a resident population in the Falkland/Malvinas Islands, but has a broad distribution in the Southwest Atlantic. As such, exploitation off Patagonian Argentina may be impacting upon the abundance and population structure of the species around the Falkland/Malvinas Islands (Agnew et al. 2000). Few small individuals of Zearaja chilensis are found around the Falkland/Malvinas Islands and the seasonal movement of the species westward out of the Falkland/Malvinas Islands region towards the end of the year is suggested by Wakeford et al. (2004).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Found on the continental shelf and upper slope. In the Southwest Atlantic it has been recorded at depths of 28 to 435 m at temperatures of 3.5 to 18.8°C (Menni and Stehmann 2000) and in Chile, inhabits sandy and muddy bottoms at depths of 40 to 500 m (Quiroz 2005). Like other skates, this species is oviparous, with a peak in reproductive activity in summer (Mariotti et al. 2003). From examined longline catches off Chile, females were observed between 47 and 126 cm TL, and males between 52 and 109 cm TL, with 42% of specimens in the size range 80 to 90 cm TL with a sex ratio of 1:2 (F:M) (Lamilla et al. 2001, 2002). Maximum size estimated as 160 cm TL for the Falkland/Malvinas Islands (Agnew et al. 2000) and 210 cm TL for Chile (Quiroz 2005), but the species is usually observed much smaller than these reported sizes. For example, the largest individual reported by Licandeo et al. (2006) was 125 cm TL, and by (Lamilla et al. 2001, 2002) was 126 cm TL.
Various maximum ages have been estimated for Zearaja chilensis from Chile. Gili et al. (1999) provided estimates of maximum ages of 21 years for females and 20 years for males, but these may have been derived from a mix of two species (D. trachydermus and Z. chilensis) and these figures should thus be viewed with caution (Lamilla et al. 2002). Fuentealba (1989) estimated maximum ages of 25 years for females and 26 years for males, and Licandeo et al. (2006) 27 years for females and 23 years for males (these latter figures are taken as the most reliable). Age and size at 50% maturity were estimated by Licandeo et al. (2006) as 14 years and 106 cm TL for females and 11 years and 86 cm TL for males. Other estimates of age and size at maturity from Chile, Argentina and Uruguay are given in the life history table below. Differences in reported sizes at maturity may be attributed to geographical variation, different stocks, different sampling and analytical methodologies or levels of exploitation.
The vulnerability of large skates to overexploitation and subsequent population depletion is well documented (Dulvy and Reynolds 2002). The three generation period for the species is 61.5 years (3 x 20.5 years), calculated with published estimated maximum age and age at maturity for females (Licandeo et al. 2006).
This species faces both directed and bycatch fishing pressure in Chile. Since 1979 there have been industrial and artisanal landings in Chile of up to >4,000 t/year of Z. chilensis combined with D. trachydermus. These two species are not separated in catch landing statistics (Roa and Ernest 1999, 2000). Between 1999 and 2000 there was an important increase in mainly artisanal landings, with a maximum landing of 4,151 t during 2000, which then dropped to 3,000 t in 2001 (SERNAPESCA 1989-2003). In Chile, overall biomass has decreased by 51% and spawning biomass has decreased by 34% since fishing began in 1979 (Quiroz 2005).
In the artisanal multispecies longline fishery off Central and Southern Chile (39°15' to 41°28.6'S) the catch is regulated by quota for Z. chilensis and D. trachydermus. Since 2000, 30% of artisanal landings within this fishery (between IX and X Regions) have been monitored (Lamilla et al. 2001, 2002). Landings comprise 85% Z. chilensis, 10% D. trachydermus, with the remaining 5% made up of Bathyraja albomaculata, B. brachyurops, B. griseocauda and Rajella sadowskyii (Lamilla et al. 2001, 2002).
South of the above-mentioned fishing grounds (that is, south of 41°28.6'S), both Z. chilensis and D. trachydermus are taken as bycatch in commercial fisheries for southern hake Merluccius australis and in artisanal fisheries for golden kingclip Genypterus blacodes. Captures in 2002 were of ~2,000 t for both Dipturus trachydermus and Zearaja chilensis combined and since 2005 there have been quotas put in place in these southern fishing grounds.
Off southern Chile, artisanal fishing activities generally only operate close to small towns such as Chiloé, Aysén and Punta Arenas and as such there may be some refuge for the species in the extensive coastline of southern Chile which consists of many fjords and canals where fishing activities are not operating at present.
Zearaja chilensis is also a minor bycatch of the Chilean deepsea crustacean fisheries for yellow squat lobster Cervimunida johni and deepsea shrimp Heterocarpus reedi (Acuña and Villarroel 2002).
Argentina and Uruguay
In the coastal and continental shelf waters of Argentina, fishing pressure on all skate species is rising due to increasing demand on the international market. Subsequently, catches have been rising since 1994. Skates, principally Z. chilensis, are directly targeted by a licensed Korean longliner on the continental shelf off Mar del Plata, Argentina (Colonello et al. 2002) and are also taken in coastal fisheries (Massa et al. 2004a, b). While, species-specific catch time-series for these fisheries are unavailable, skate landings for Argentina were <1,000 t prior to 1994, rising to >15,000 t in 2001 and 17,465 t in 2003 (Colonello et al. 2002, Massa et al. 2004a, b). Skates are exploited over much of the Argentinean continental shelf (i.e., see Figure 4 in García de la Rosa et al. 2000).
In the directed Z. chilensis fishery, onboard observation showed that in 2000 and 2001, the single longline vessel fished from 37° to 44°S off Argentina in two regions; around 50 m of depth and along the 100 m isobath (Colonello et al. 2002). Zearaja chilensis accounted for ~50%+ of the catch of skates both in the shallower and deeper fished areas (Colonello et al. 2002).
Zearaja chilensis is a bycatch (often retained) in several multispecies demersal fisheries which operate within its Southwest Atlantic range, however, species-specific catch data are generally unavailable. For example, it is a bycatch of benthic trawl fisheries for Argentine hake Merluccius hubbsi, flounder and white croaker (Cousseau et al. 2000, Koen Alonso et al. 2001, Buratti 2004), of the multispecies coastal benthic trawl fishery operating out of Puerto Quequén (Tamini et al. 2006), and of the Patagonian red shrimp Pleoticus muelleri fishery (Cedrola et al. 2005). The latter is an industrial fishery which has been operating since 1979, with target catches rising since 1998, and reaching a peak of 79,000 mt in 2001 (Cedrola et al. 2005).
During fishery-independent investigations, García de la Rosa et al. (2000) reported a 53% decline in the biomass of Z. chilensis captured from 45° to 55°S during summer surveying in 1999 compared to 1998. It was acknowledged, however, that during the second phase of the investigations, new gear was employed which likely reduced the capture of rays, and as such these estimates should be viewed with caution.
Colonello et al. (2002) and García de la Rosa (1998) provide detailed accounts of size distributions and sex ratios of Zearaja chilensis in relation to latitude and depth taken in commercial operations (Colonello et al. 2002) and research cruises (García de la Rosa 1998) off Argentina.
In Uruguay, this species, along with Sympterygia bonapartei, S. acuta and Atlantoraja castelnaui are the main target species of a bottom longline fishery (Paesch and Domingo 2003). Species-specific catch data are not available, but captures of this group of skates for the period 1999 to 2002 are estimated at ~1,100 tons per year (A. Domingo pers. comm).
Since 1989, skates 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 Z. chilensis (Agnew et al. 2000, Wakeford et al. 2004). 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 1996 there was some evidence that Z. chilensis declined in catches (as a proportion of the total catch weight, from 10% in 1993 to 6% in 1996), but in 1997 the proportion increased again. Zearaja chilensis did however, show the greatest decrease in mean and maximum size from 1993 to 1997 of any species. Mean size was 76.76 cm DW in 1993 and 58.49 cm DW in 1997 (Agnew et al. 2000). Agnew et al. (2000) suggests that this decline in size may not be the result of fishing pressure in the Falkland/Malvinas Islands alone, but a combination of exploitation there and in Argentina where the species is more abundant. 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 an increasing trend in the relative abundance of Z. chilensis in catches, with an increasing trend in CPUE from 1992-1993 to 1999-2001 (Wakeford et al. 2004). The Falkland/Malvinas Islands have in place a precautionary management system for the skate fishery (see Conservation Actions below), and together with the recovery of biomass (Agnew et al. 2000), this means 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 likely less able to sustain heavy fishing pressure, such as Z. chilensis (inferred from its life history and documented declines in the Southeast Pacific). Furthermore, it should be noted that localised depletions may be masked by overall CPUE trends (Wakeford et al. 2004). 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 southern blue whiting Micromesistius australis, hoki Macruronus magellanicus, hake Merluccius hubbsi and M. australis, and Patagonian cod Salilota australis around the Falkland/Malvinas Islands and within the southern skate closure. While vessels fishing under general finfish licenses are prohibited from targeting skates, a small bycatch (below 10%) is allowed so skates to the south of the Islands are continuing to face bycatch fishing pressure (J. Pompert pers. comm).
In Chile, catches are regulated by annual total quota. Following Lamilla et al. (2001, 2002), in the fishing grounds between 39°15' and 41°28.6'S, quotas were set at 600 t for 2002, 500 t for 2003. Afterwards, quotas have been 425 t for 2004, 400 t for 2005 and 370 t for 2006. Since 2005, there has also been an annual quota for Dipturus spp. south of 41°28.6'S of 2,000 t for that year and 1,430 t for 2006. 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. Regulations and management tools utilised need to be species-specific, due to differing life histories and abundance patterns of Dipturus trachydermus and Zearaja chilensis.
In Argentina, the assessment of direct and indirect catches is 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. comm).
The following information is taken from Agnew et al. (1999, 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 (south of 52°S) was closed to skate fishing and the fishery is now restricted 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 licenses are prohibited from targeting skates, although a small bycatch (below 10%) is allowed.
|Citation:||Kyne ,P.M., Lamilla, J., Licandeo, R.R., Jimena San Martín, M., Stehmann, M.F.W. & McCormack, C. 2007. Zearaja chilensis. The IUCN Red List of Threatened Species 2007: e.T63147A12623314.Downloaded on 15 December 2017.|