|Scientific Name:||Dipturus mennii Gomes & Paragó, 2001|
Dipturus diehli Soto & Mincarone, 2001
|Taxonomic Notes:||Dipturus diehli (Soto & Mincarone 2001) as known only from the holotype taken off Santa Catarina, Brazil (29°39´S, 47°50´W) at a depth of 480 m is likely a synonym of D. mennii and is treated here as such.|
|Red List Category & Criteria:||Vulnerable A4d ver 3.1|
|Reviewer(s):||Kulka, D.W., Valenti, S.V. & participants at Expert Panel Meeting, Newbury, UK (Shark Red List Authority)|
A large (to 160 cm TL) skate endemic to Brazil with a restricted distribution between the states of Rio Grande do Sul and Rio de Janeiro (approximately 22°S to 34°S). Inhabits the outer continental shelf and upper slope at depths of 133 to 500 m, and as such occupies a relatively narrow band of available habitat. Little specific information available on the biology or ecology of the species, but its large size suggests it shares the slow life history characteristics other large skates, including slow growth, late maturity, low fecundity and long lifespan. Brazil recently developed a deep-sea fishing program on the slope at depths of 200 to 900 m off southern Brazil. As such the entire geographical and bathymetrical distribution of the species has been subject to a gillnet fishery for monkfish Lophius gastrophysus, in which Dipturus mennii was the most common elasmobranch bycatch species. Furthermore, otter trawlers operating in the same area also capture skate. Deepsea longlining in the area is restricted to >600 m and so is outside the depth range of D. mennii. The vulnerability of large skates to overexploitation and subsequent population depletion is well documented, and serious concern is expressed for D. mennii given its limited distribution, the entirety of which has been subject to intensive fishing pressure. However, considerable management arrangements have recently been implemented in these fisheries which resulted in the ceasing of fishing by foreign vessels in 2002, a quota management and effort limitation system for domestic vessels, no gillnetting shallower than 250 m and two no-fishing areas. The conservation status of this species will rely heavily upon the success of these management arrangements. Full observer coverage onboard domestic vessels provide a real opportunity to collect future catch trend data. As such, this assessment should be updated as this data become available.
|Range Description:||Dipturus mennii is endemic to southern Brazil, between the states of Rio Grande do Sul and Rio de Janeiro. These states are bounded by latitudes ~22°S to ~34°S. As such, the species is restricted to ~12° of latitude, and given its occurrence on the outer shelf and upper slope, it is restricted to a relatively narrow band of available habitat. Previous references to D. trachydermus off southern Brazil such as those summarised in Menni and Stehmann (2000) probably refer to D. mennii (Gomes and Paragó 2001). Following then, it is likely that references to D. trachydermus in the Brazilian monkfish fishery by Perez and Wahrlich (2005) also refer to D. mennii.|
Native:Brazil (Paraná, Rio de Janeiro, Rio Grande do Sul, Santa Catarina, São Paulo)
|FAO Marine Fishing Areas:|
Atlantic – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Nothing known about population structure.|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Dipturus mennii has been found on the outer continental shelf and upper slope in depths of 133 to 500 m, but is primarily distributed on the upper continental slope. Nothing is known of its ecology and reproductive biology, except that it is oviparous like other skates. Given its large size (maximum ~160 cm total length (TL), 120 cm disk width (DW)) it is likely to exhibit life history characteristics of large chondrichthyans (including large skates) such as slow growth, late size and age at maturity, low fecundity and long lifespan. Ebert (2005) showed that some skates may be restricted to a very small number of spawning seasons, as low as one. The acquisition of such biological data for D. mennii is required. Dipturus mennii has been found on the outer continental shelf and upper slope in depths of 133 to 500 m, but is primarily distributed on the upper continental slope. Nothing is known of its ecology and reproductive biology, except that it is oviparous like other skates. Given its large size, it is likely to exhibit life history characteristics of large chondrichthyans (including large skates) such as slow growth, late size and age at maturity, low fecundity and long lifespan. Ebert (2005) showed that some skates may be restricted to a very small number of spawning seasons, as low as one. The acquisition of such biological data for D. mennii is required.|
Demand for skates is increasing on the international market, with recent increased exploitation in the southwest Atlantic, resulting in the retention and marketing of skates taken as non-target bycatch in Brazilian deepwater fisheries (Perez et al. 2003, Perez and Wahrlich 2005). In addition, the vulnerability of large skates to overexploitation and subsequent population depletion is well documented (Dulvy and Reynolds 2002).
In 1998 the Brazilian government initiated a deep-sea fishing program in order to remove some pressure from the shelf environment and explore unexploited resources on the slope (Perez et al. 2003). Fishing activities employing chartered foreign vessels began in 2000 using demersal gear, specifically longlines, otter trawls, gillnets and pots at depths of <200 to 900 m. Longlining was later (2001) restricted to depths >600 m (Perez et al. 2003) and as such is outside the depth of D. mennii. The gillnet fishery for monkfish Lophius gastrophysus which was developed as part of this deepwater fishing program, operated over the entire geographical and bathymetrical distribution of Dipturus mennii. Perez and Wahrlich (2005) surveyed bycatch in this fishery between 22°44´S and 34°21´S and at depths of 132-607 m, recording D. mennii and D. trachydermus (see note in Geographic Range section) as the abundant elasmobranch bycatch species. Skates are also taken and retained in the deepwater trawl fishery which operates in the same region (Perez et al. 2003). Perez et al. (2003) reported trawlers operating down to depths of 460 m. Foreign vessels were unauthorized to operate after October 2002 and a management plan implemented for the fishery (see Conservation Actions section below). These management arrangements should greatly reduce the level of impact on the species, but it will continue to be taken as bycatch.
A management plan was developed for the gillnet monkfish fishery in 2002 and approved in June 2005. Foreign chartered fishing vessels were unauthorized to operate after October 2002 and an annual TAC of 1,500 t and an effort limitation of nine vessels implemented for the domestic fleet. Further management arrangements included a permanent VMS tracking system, 100% observer coverage, logbooks and a ban on fishing shallower than 250 m. Furthermore, two no-take zones were implemented, one in the southern and the other in the northern sections of the fishing area and range of D. mennii (Perez et al. 2002, Perez pers. comm). The conservation status of this species will rely heavily upon the success of these management arrangements. Full observer coverage onboard domestic vessels should provide accurate monitoring of trends in the future.
The restriction of the southern Brazilian deepwater longline fishery to depths of >600 m places it outside the known bathymetric distribution of D. mennii.
|Citation:||Kyne, P.M. 2007. Dipturus mennii. The IUCN Red List of Threatened Species 2007: e.T63124A12616691.Downloaded on 19 October 2017.|
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