|Scientific Name:||Dipturus trachydermus (Krefft & Stehmann, 1975)|
Raja trachyderma Krefft & Stehmann, 1975
|Red List Category & Criteria:||Vulnerable A4bd ver 3.1|
|Assessor(s):||Lamilla, J. & Massa, A.|
|Reviewer(s):||Cavanagh, R.D., Kyne, P.M. & Acuna, E. (Shark Red List Authority)|
As presently known D. trachydermus has a relatively limited distribution in the Southeast Pacific off Chile (36°20' S to 41°30' S) and in the Southwest Atlantic off Argentina (45°36.1' S to 51°6.8' S). However, it has also been recorded in the Beagle Channel (54°51' S) and following Leible and Stehmann (1987) it is presumed to be continuously distributed south through Patagonia in the Atlantic and up to Central Chile in the Southeast Pacific. A large skate (at least 235 cm TL, estimated to 250 cm TL) of the outer shelf and upper slopes at depths of 93 to 450 m, but recorded from shallower waters in the Beagle Channel (20 to 22 m). Little information is available on the biology of the species. The vulnerability of large skates to overexploitation and subsequent population depletion is well documented and in the case of D. trachydermus, both directed and bycatch fishing pressure from commercial and artisanal activities are impacting the species. In Chile, overall biomass of Dipturus spp. (D. trachydermus and D. 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 D. trachydermus makes up 10% of catches. Directed and bycatch catches in commercial and artisanal fisheries in Chile are managed through an annual quota system, which has been decreasing in recent years. There may be some refuge for adults at depths beyond the reach of the artisanal longline fishery off Central and Southern Chile; however, continued catches of immature animals will limit recruitment to the reproductive population. Although little specific data is available for the Southwest Atlantic (where it is not abundant), there has been increasing direct targeting of skates in that region as international demand increases. Globally then, with documented biomass declines off Chile and direct targeting continuing throughout its range, the species is assessed as Vulnerable on the basis of past and future declines of greater than 30% for the three generation period (estimated at 50.4 years).
|Range Description:||Occurs in the Southwest Atlantic off Argentina. Occurrence off Uruguay and southern Brazil uncertain; previous references to the species off southern Brazil such as those summarised in Menni and Stehmann (2000) probably refer to the recently described D. mennii (Gomes and Paragó 2001). Also occurs in the Southeast Pacific off Chile. Lloris and Rucabado (1991) also recorded the species from the Beagle Channel (54°51' S), and Leible and Stehmann (1987) presumed that it is continuously distributed south through Patagonia in the Atlantic.|
Native:Argentina (Chubut, Santa Cruz); Brazil; Chile
|FAO Marine Fishing Areas:|
Atlantic – southwest; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||While the species is documented south to 51°6.8' S in the Atlantic, south to 41°30' S in the Pacific, and in the Beagle Channel (54°51' S) (Lloris and Rucabado 1991), this assessment follows the presumption of Leible and Stehmann (1987) that it is continuously distributed south through Patagonia in the Atlantic and up to Central Chile in the Southeast Pacific. Thus the assessments here are treated as regional assessments and not subpopulation assessments.
There are no abundance estimates but the species is apparently not abundant in Argentinean waters.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Distributed in deep temperate waters of the continental shelf and upper slope, between 93 m (Menni and Gosztonyi 1977) and 450 m (Leible 1984) depth, but also recorded in 20 to 22 m in the Beagle Channel (Lloris and Rucabado 1991). Inhabits sandy and muddy bottom sediments.
The following life history data from Chile is drawn from Lamilla et al. (2001, 2002), unless otherwise stated.
From examined longline catches off Chile, females were observed between 98.5 and 225 cm TL, and males between 82 and 235 cm TL, with 35.8% of specimens in the size class 160 to 180 cm TL. Sex ratio was 1:1. Maximum size is estimated at 250 cm TL.
There are no reproductive or aging studies for this species, but ages up to 20 years for males and 21 years for females have been suggested (Gili et al. 1999). However, these may have been derived from a mix of two species (D. trachydermus and D. chilensis) and these figures should thus be viewed with caution (Lamilla et al. 2002).
The feeding habits are mainly piscivorous (Macrouronus magellanicus, Helicolenus lengerichi, Merluccius australis and Merluccius gayi), but also crustaceans (mainly Pterygosquilla armata) in shallower depths.
An age at maturity for the species was estimated at 12.6 years if Amat (age at maturity) is 60% of Amax (maximum age) based on ages for D. laevis (Gedamke et al. 2005). Average reproductive age for D. trachydermus was estimated using the following calculation: (((21-12.6)/2)+12.6) = 16.8 years.
No information is available on the biology of the species from Argentina.
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 50.4 years (3 x 16.8 years), calculated with published estimated maximum age for females (Gili et al. 1999) and estimated female age at maturity (60% of maximum age based on ages for Dipturus laevis in Gedamke et al. (2005).
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 D. trachydermus combined with D. chilensis. 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 multi-species longline fishery off Central and Southern Chile (39°15'-41°28.6'S) the catch is regulated by quota for D. trachydermus and D. chilensis. 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% D. 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). Anecdotal evidence suggests that larger individuals of D. trachydermus were more abundant in previous years. However, research in 2002 recorded mostly immature specimens, suggesting that larger mature specimens may occur in deeper depths beyond the reach of the artisanal fishery (Lamilla et al. 2002).
South of the above-mentioned fishing grounds, both D. trachydermus and D. chilensis are taken as bycatch in commercial fisheries for southern hake (Merluccius australis) and in artisanal fisheries for golden kingclip (Genypterus blacodes). Captures were of ~2,000 t for both Dipturus species combined in 2002 and since 2005 there have been quotas put in place in these southern fishing grounds.
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, particularly D. chilensis and D. trachydermus, are directly targeted by a licensed Korean longliner off Argentina. Species-specific catch data are however, unavailable.
Similarly, species-specific catch data from multi-species demersal fisheries which operate within the range of D. trachyderma and likely take the species as bycatch are unavailable. Cedrola et al. (2005), however, recorded D. trachydermus as bycatch in the Patagonian red shrimp (Pleoticus muelleri) fishery. This industrial fishery 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).
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 its reproductive season.
Regulations and management tools utilised also need to be species-specific, due to differing life histories and abundance patterns of D. trachydermus and D. chilensis.
In Argentina, the assessment of direct and indirect catches is a priority.
|Citation:||Lamilla, J. & Massa, A. 2007. Dipturus trachydermus. The IUCN Red List of Threatened Species 2007: e.T63116A12611753.Downloaded on 23 May 2018.|