|Scientific Name:||Dipturus oxyrinchus|
|Species Authority:||(Linnaeus, 1758)|
|Taxonomic Notes:||In Mediterranean there are some doubts about the validity of historical identification. This species could be potentially confused with Dipturus batis, despite morphological and colour differences (Ragonese et al. 2003).|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Ungaro, N., Serena, F., Dulvy, N.K.D., Tinti, F., Bertozzi, M., Mancusi, C., Notarbartolo di Sciara, G & Ellis, J.E.|
|Reviewer(s):||Cavanagh, R.D. & Valenti, S.V. (Shark Red List Authority)|
Dipturus oxyrinchus is benthic and found on sandy or muddy bottoms at depths of 90 to 900 m, mainly around 200 m and was most frequently captured at depths of 200 to 500 m in the MEDITS surveys. Dipturus oxyrinchus is moderately abundant in the Mediterranean with a standing stock biomass estimated at 1,899 t in the western, northern and eastern Mediterranean. The overall biomass index assessed by the Mediterranean International Trawl Surveys (MEDITS) was 3.7 kg/km² throughout this area (Baino et al. 2001). In Italian waters there has been no indication of a decline in abundance in the last 20 years (Relini et al. 2000). However, it does not appear to have been captured by research surveys from the Gulf of Lions since 1984 (Aldebert 1997) and it is now rarely captured in the Adriatic Sea shelf areas (Jukic-Peladic et al. 2001). However, Dipturus oxyrinchus mostly inhabits deep areas (known to occur down to at least 900 m, mostly around 200 to 500 m) where fishery exploitation is presently at low levels in the Mediterranean, thus it is assumed these areas are currently refuges for much of the population. There is a need for precaution given its relatively large body size indicating a low intrinsic rate of population increase and thus a low capacity to withstand even moderate fishing pressure. This, together with the evidence of dramatic declines and apparent disappearance in some localized areas (likely due to fisheries pressure), leads to the assessment of this species as Near Threatened in the Mediterranean. The situation must be closely monitored to ensure that its conservation status is not raised into the Vulnerable category in the future, particularly if deepwater fisheries were to develop. This species in now very rare on continental shelves but its depth range extends down the continental slope to 900 m. There is some evidence to infer that this species was captured historically in the Irish Sea and may now be locally extinct from the Irish Sea. Nothing is known of the status of this species along Norway and in Iceland and the Faroes or the French and Iberian waters. Nothing is known of current population trends in the northeast Atlantic region. The large body size and inferred low intrinsic rate of population increase suggests this will be highly vulnerable to bycatch mortality from demersal trawls and deepwater longline and gillnet fisheries, and consequently we have assigned this species as Near Threatened in the northeast Atlantic.
This species may have been found on continental shelf areas including the Irish Sea and Northern North Sea and shelf edge habitats in this area from central Norway southwards (Hientz 1962). Long-nose skate was recorded occasionally in the northern North Sea and Celtic sea in waters of 111 to 159 m in the UK groundfish surveys between the late 1960s and 2002. Catch rates of the long-nose skate over this time period were very low ranging between 0.01 and 0.11 individuals captured per hour of trawling (an encounter rate of one individual per 9-100 hours of survey (Ellis et al. 2005).
The long-nose skate is inferred to be locally extinct from the Irish Sea (Dulvy and Reynolds 2002). This is based on knowledge of the presence of this species in catches of a long-line fishery based in the Isle of Man in the central Irish Sea in the 1880s, and its current absence from recent trawl surveys of the area. There are no further corroborating evidence supporting its former presence in the Irish Sea and the question of uncertain species identification remains.
Nothing is known of the status of these species in Iceland and the Faroe islands and the French waters and Iberian waters.
This species was previously found throughout the Mediterranean Sea (Stehmann and Burkel 1984). However, it now appears to be absent from the Gulf of Lions, Eastern Mediterranean. Comparative trawl surveys indicate Dipturus oxyrinchus was historically present in both shelf and slope trawl surveys and is now absent from comparable surveys. Dipturus oxyrinchus was captured in 10% of hauls (n=27) in shelf surveys, occurring between 1959 and 1972 (coast to 150 m depth) and was also present in a survey between 1980-1984. This species was not subsequently recorded from 628 hauls from four trawl surveys spanning 1985-1995 (Aldebert 1997).
Native:Albania; Algeria; Bosnia and Herzegovina; Croatia; Cyprus; Denmark; Egypt (Sinai); France (Corsica); Greece (East Aegean Is., Kriti); Guernsey; Israel; Italy; Jersey; Lebanon; Libya; Malta; Mauritania; Montenegro; Morocco; Norway; Portugal (Azores, Madeira, Selvagens); Senegal; Spain (Baleares, Canary Is.); Syrian Arab Republic; Tunisia; Turkey (Turkey-in-Europe); United Kingdom (Great Britain, Northern Ireland); Western Sahara
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northeast; Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
This is one of the largest-bodied species of skate and it has been found to have undergone declines from other shelf seas, notably the Irish Sea (Dulvy et al. 2000). The large body size (150 cm), and presumably slow growth and later maturation and likely low intrinsic rate of population increase of this species render it especially vulnerable to exploitation such as trawling and at risk of local extinction (Dulvy and Reynolds 2002).
Nothing is known of the population status or trends in its abundance from this area.
The MEDITS International trawl surveys cover the north Mediterranean coast almost continuously from western Morocco and Spain in the west Mediterranean to the Aegean Sea in the eastern Mediterranean (Baino et al. 2001). Trawl surveys are carried out each year during the summer period in the coastal areas of four arbitrary, geographically defined areas: Western (Morocco, Spain, France), Western Central (Tyrrhenian, Corsican, Sardinia and Sicily coasts), Eastern Central (Adriatic, Ionian and Albanian coasts) and the Eastern (Aegean Sea). A total of 6,336 tows were performed between 1994 and 1999 in depths ranging from 10 to 800 m, including much of the known distribution of this species. The sharpnose skate is the second most abundant skate in the Mediterranean and was recorded in 301 (3%) hauls in this area. The total standing stock biomass has been estimated as 1,899 t using a swept area method, assuming full catchability (Baino et al. 2001). Assuming an average individual weight of either 10 or 5 kg this would represent approximately 189,900 to 379,800 individuals. This species was found between 50 and 800 m, but was caught most frequently between 200 and 500 m and it was most commonly captured in the western central area and in the Aegean Sea (Baino et al. 2001).
In the Adriatic Sea, historical trawl survey results from the "Hvar" survey in 1948 showed D. oxyrinchus present in 3.2% of hauls carried out in the shelf bottoms, while in the comparable (MEDITS) survey in 1998 it did not appear in any shelf hauls (Jukic-Peladic et al. 2001). The MEDITS surveys of the area began in 1994 while another study of the Adriatic Sea began in 1985: the National Group for Demersal Resource Evaluation (GRUND). During this time D. oxyrinchus has been captured with occurrence lower than 0.1% in the MEDITS surveys in the Adriatic and has been captured in only 1% of hauls in 1994 in the central and northern Adriatic and in 2.6% of hauls in 1995 in the southern Adriatic during GRUND surveys (Marano et al. 2003). However, it should be noted that the MEDITS net is thought to have a low sampling efficiency of truly benthic species (Jukic-Peladic et al. 2001).
In the south Ligurian and north Thyrrenian sea this species is distributed across a relatively narrow range (164 to 580 m depth), mostly concentrated on the outside margin of the slope (300 to 400 m). The trend of the relative biomass and density indexes shows some fluctuations characterized by not abundant but constant captures. In the last period the trend for the biomass decrease while the abundance one is nearly stable. This fact suggests a change in the population structure with predominant presence of young individuals. Moreover the ecological aspects and the distribution pattern of this species are very different from the other skate species and there is no competition or overlapping geographical distribution and is supposed to exist from the moment it is confined only in the bathyal area (Serena et al. 2005).
|Habitat and Ecology:||
Dipturus oxyrinchus is benthic and found on sandy or muddy bottoms at depths of 90 to 900 m, mainly around 200 m (Stehmann and Burkel 1984), and was most frequently captured at depths of 200 to 500 m in the MEDITS surveys (Baino et al. 2001).
Females mature at >90 cm and males between 70 and 80 cm in total length (TL) (N. Ungaro pers. comm). However, in the north Thyrrenian sea, a female and male measuring 83 and 77.5 cm TL respectively, were recorded as immature 77.5 cm in TL were reported (C. Mancusi and F. Serena pers. comm). Within the Italian Seas, the size range recorded was 17 to 112 cm TL in the south Ligurian Sea and north Thyrrenian sea, while in the south part of Italy (Sicily strait) it was 105 to 115 cm (Serena et al. 2003, Ragonese et al. 2003). In the northern part of the Thyrrenian sea the disc width (DW) range was 10.5 to 53 cm. From these data it seems that the TL is approximately 1.5 times the DW. Consequently, we inferred that specimens with maximum TLs recorded in the Italian seas, with the maximum total lengths of 112 to 115 cm, had a DW of 74 to 76 cm (C. Mancusi pers. comm). Stehmann and Burkel (1984) recorded a maximum size of 150 cm, therefore as above a DW of 100 cm is inferred (C. Mancusi pers. comm).
Further details on the size at birth, age at maturity and longevity are unknown for this species. It has a spawning period from February to April (Stehmann and Burkel 1984, Bauchot 1987, Notarbartolo di Sciara and Bianchi 1998), however Serena (2005) reported spawning to occur between February and May, with egg cases measuring between 100 and 150 cm in length. The reproductive age, gestation time, reproductive periodicity, litter size, rate of population increase and natural mortality are also unknown.
A study on the feeding habits of rays in the south Ligurian and North Thyrrenian Seas show this species feeds mainly on crustaceans and cephalopods, in particular Cephalopoda decapoda (Sepietta owenian was the only specimen identified to a species level). Crustaceans included in this ray's diet belonged to the Amphida (Gammaridea n.d.), Euphasiacea (Meganyctiphanes norvegica), Isopoda (Isopoda n.d.) Mysidiacea (Lophogaster typicus) and Decapoda (Pasiphea sivado, Pontocaris lacazei, Pontophilus pinosus, Solenocera membranacea, Plesionika spp.) orders. Due to the small number of specimens analysed (n = 14) it was not possible to undergo a more accurate analysis to determine whether there was any difference between the feeding habits of different size classes of this skate. The only difference observed was that females seemed to prefer cephalopods and the males that feed mainly on crustaceans, in particular L. typicus (Vannucci 2005).
Dipturus oxyrinchus is captured as bycatch by trawl nets and offshore bottom long lines. Catches are occasional and specimens are sometimes discarded at sea (N. Ungaro pers. comm). Rajids are an important component of the demersal fisheries of Northwest Europe (Holden 1977) and skates have traditionally been landed due to their large size. The situation appears similar in the Mediterranean, where D. oxyrinchus is probably captured as part of the bycatch of multispecies trawl fisheries. Over the last 50 years, benthic trawl effort has increased numerically and technologically in the shelf and slope area of the Mediterranean. For example, the Gulf of Lions area was initially exploited by small-scale benthic trawl fisheries composed of 27 small, low powered boats (total nominal horse power of 2,700 hp), more recently effort has increased to a total nominal horsepower of 19,940 hp (1974 to 1987). Since then half of the fishing effort has been displaced into targeting small pelagic fish (Aldebert 1997). The Adriatic Sea is subject to trawling mainly by Italian, Croatian, Slovenian, and Albanian fleets, however, no landings data are available (Jukic-Peladic et al. 2001).
There is no data available on threats, however it is inferred that, similar to other large-bodied skates, this species may be captured and retained as bycatch of demersal trawl and long-line fisheries, particularly in deeper water.
The large body size in combination with the presumably slow growth rate, low fecundity and large size of juveniles of this species makes it especially vulnerable to fishing exploitation when compared to other rajids (Walker and Hislop 1998, Dulvy et al. 2000, Dulvy and Reynolds 2002). Moreover, although only large individuals may be landed for consumption, most size classes are likely to be taken in fishing nets as the legal mesh size used in much of the Mediterranean is approximately 20 mm (knot to knot).
The potential threat of development of deepwater fisheries within this species range is a possible cause for concern in the future. Although the General Fisheries Commission for the Mediterranean (GFCM), the main intergovernmental decision-making body on fishery management in the Mediterranean, has made the decision to refrain from expanding deep water fishing operations beyond the limit of 1,000 m, this species occurs mostly from 200-500 m and down to 900 m. For more information, see: Mediterranean Conservationists and Fishermen Work Together to Protect Deep Seas.
Ungaro (pers. comm.) recommends the avoidance of fishery activities below the depths of 500 m. Potential management efforts to protect this species are hampered by the low commercial value of skate in general and its full retention within the cod end of the gear types currently in use, employing a mesh size with 20 mm opening within the Mediterranean. Baring this in mind, at present the only management measure which could promote the sustainability of the Dipturus oxyrinchus population within the Mediterranean would be to define suitable non-trawling zones and to enlarge these closed areas to encompass a proportion of the Dipturus oxyrinchus population, including this ray's eggs (which are often found in the trawl net cod-end) (Ragonese et al. 2003).
The global increase of fishing effort and the ensuing depletion of populations have been the subject of the debate by the international bodies charged with the management and conservation of marine resources. Relevant is the formulation by FAO of the "International Plan of Action on the management and conservation of cartilaginous fishes" (IPOA-Sharks). According to the Plan, all the states that capture sharks, rays or chimaeras, either as target species or as bycatch, shall implement a national action plans to ensure suitable use, conservation and recovery of threatened species (Vacchi and Notarbartolo 2000). In this context the FAO SAC Subcommittee on the Environment and Ecosystem proposed a recommendation to activate the necessary tools and regional agreements towards the formulation of a Mediterranean Action Plan for the Management and Conservation of Cartilaginous Fishes. A project for record data proceeding from all Mediterranean basin and regarding large elasmobranchs (MEDLEM) has been discussed and adopted at the last SAC meeting held in Rome (FAO 2005). Also the EC prepared a draft proposal for the European Community Plan of Action that encourages research programs aimed at the assessment of the conservation status of cartilaginous fishes in the Mediterranean Sea (Serena et al. 2002). Italy must act urgently to establish a plan of action for the conservation and management of its chondrichthyan fauna, in tight coordination with other Mediterranean riparian countries. The Italian National Action Plan (PAN-SHARKS) draft was formulated by a scientific committee coordinated by ICRAM (Central Institute for the Marine Research) and was conceived in order to provide Italy with the necessary tools for the ratification of the SPA protocol, in the respect of the guidelines formulated within the EC Draft Action Plan and the FAO IPOA-Sharks recommendation (Serena et al. 2002, Vacchi and Notarbartolo 2000).
In England and Wales waters this species has been proposed for protection under the Wildlife and Countryside Act 1981. If this species was scheduled this would prohibit a wide range of activities and practices including the intentional killing, injuring or taking, the possession and the trade in wild animals. At the time of writing the status of this proposal is pending.
|Citation:||Ungaro, N., Serena, F., Dulvy, N.K.D., Tinti, F., Bertozzi, M., Mancusi, C., Notarbartolo di Sciara, G & Ellis, J.E. 2007. Dipturus oxyrinchus. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 04 March 2015.|
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