|Scientific Name:||Raja asterias|
|Species Authority:||Delaroche, 1809|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Serena, F., Abella, A., Walls, R. & Dulvy, N.|
|Facilitator/Compiler(s):||Walls, R., Pardo, S.A. & Dulvy, N.|
Starry Skate (Raja asterias) is distributed primarily in the Mediterranean Sea. It is caught as bycatch by bottom trawl, trammel net, and gill net fisheries especially in the Italian, French and Spanish seas. This skate is relatively fast growing with an early age of maturity (the three generation span is ~ 19 years), high fecundity and a short life span, which indicates that it is relatively productive and resilient to fishing pressure. There have also been steep declines in landings over a 25 year period (1969-1994) in the Gulf of Lions. It is suspected that these trends are likely to be representative throughout its range. Starry Skate is inferred to have undergone a decline of 20% throughout its distribution, and it is therefore assessed as Near Threatened as it is close to qualify as threatened under Criterion A2. Further information on its status in the southern Mediterranean Sea is needed.
Starry Skate (Raja asterias) can probably be considered endemic in the Mediterranean Sea, but may also occur in the Atlantic, near the southern coast of Portugal (Serena 2005). It has been reported for the northern and southern areas of the Balearic Islands of the western Mediterranean Sea (Massutì and Moranta 2003), in the Tyrrhenian Sea of the northern Mediterranean (Romanelli et al. 2007), as well as along the Tunisian coasts (Capapé 1977), and in the central Tyrrhenian Sea (Minervini et al. 1985).
Native:Albania; Algeria; Bosnia and Herzegovina; Cyprus; Egypt (Egypt (African part), Sinai); France (Corsica, France (mainland)); Greece (East Aegean Is., Greece (mainland), Kriti); Israel; Italy (Italy (mainland), Sardegna, Sicilia); Lebanon; Libya; Monaco; Montenegro; Morocco; Slovenia; Spain (Baleares, Spain (mainland)); Syrian Arab Republic; Tunisia; Turkey (Turkey-in-Asia)
|FAO Marine Fishing Areas:||
Present - origin uncertain:
Atlantic – eastern central; Atlantic – northeast; Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
Genetic analysis suggests at least two distinct clusters: Western and Eastern Mediterranean basin, and Sicilian coast and Algeria, and possibly other countries in North Africa (Gerotto 2013). This species was captured in both the GRUND (Italian waters) and MEDITS (northern Mediterranean basin) trawl surveys (Relini 1998, Bertrand et al. 2000), which began in 1985 and 1994 respectively. In the south Ligurian and north Tyrrhenian Sea it was captured over muddy bottoms, in restricted coastal areas from nine to 190 m depth, but mainly concentrated at 100 to 150 m depth. From 1999 to 2004 the difference between the Biomass Index and Density Index decreased, which may indicate a change in the population structure with a predominance of smaller specimens (Serena et al. 2005). The species has a higher relative abundance on the Italian and Corsican continental shelves (Baino and Serena 2000, Serena et al. 2005). Nursery areas are located very close to the coast at two to 15 m depth (Abella and Serena 2005).
Landings of Starry Skate in the southwest North Sea and eastern English Channel, as reported by France, are likely the result of misidentification or incorrect use of species codes (ICES 2012).
Catches in the Aegean Sea MEDITS bottom trawl surveys, from 1998 to 2008, ranged from 24 specimens (9.85kg) in 1998, to nine (2.01kg) in 2003, to 34 (13.91kg) in 2008. Inter-annual variability was high, but there was no overall trend for the time series (Tserpes et al. 2013).
There have been estimated declines in the MEDITS program in the Adriatic Sea (Ferretti et al. 2013), and landings declined over 25 years (1969-1994) in the Gulf of Lions despite no apparent decrease in fishing effort, and in this region the species disappeared entirely from catches in waters >150 m between 1957 and 1995. In waters <150 m deep, it declined by approximately 20%. The same negative trend is reported for the Spanish Mediterranean area. It is suspected that these trends are likely to be representative throughout the species’ range, and thus the species is inferred to have undergone a decline of 20% throughout its distribution during the three-generation period (19 years).
|Habitat and Ecology:||
Starry Skates are found predominantly on the Italian and Corsica continental shelves between shallow waters and 150 m depth (Baino and Serena 2000). In the eastern Ionian Sea, the species is found down to depths of 343 m (Mytilineou et al. 2005), although this is probably due to misidentifications. The species prefers muddy and sandy bottoms (Vannucci 2005).
Maximum size is estimated at 72 cm total length (TL) for males and of 76 cm TL for females (Bono et al. 2005, Serena and Abella 1999). Barone et al. (2006) and Serena et al. (2005) estimate length at maturity at 51.7 cm TL for males and 56.1 cm TL for females, and Serena and Abella (1999) and Bauchot (1987) reported length at maturity at 45 to 54 cm TL for males and 60 cm TL for females. Age at maturity is reported at three to four years for both males and females (Serena and Abella 1999, Bono et al. 2005). The species is egg laying, with 34 to 112 egg cases laid depending on individual size, and egg cases can reach 45 mm in length and 30 mm width (Bauchot 1987). Juveniles are about 8 cm TL when they emerge from the egg cases in January. The sex ratio is about 1:1 (Minervini et al. 1985, Abella et al. 1997). Juveniles move quickly into shallow waters from 5-7 m depth soon after birth and then move into deeper waters progressively as they grow (Abella and Serena 2002, Catalano et al. 2003).
Recent preliminary tagging experiments (Catalano et al. 2003) suggest a faster growth rate than described in previous literature (Serena and Abella 1999). As this species reaches maturity relatively early (~3 years) and has a short lifespan (~10 years) it is considered to be relatively productive, even though it is only moderately fecund.
In the Central Tyrrhenian Sea, length at 50% maturity values estimated by Romanelli et al. (2007) were 56.5cm TL and 50.5cm TL for females and males, respectively. In the south Ligurian Sea, males mature by 45 cm TL and females may mature by 53 cm TL (Barone et al. 2007). Total length at 50% maturity was estimated to be 51.7 cm and 56.1 cm TL for males and females respectively. In the Catalan Sea, the size at first maturity for females was assessed to be around 48.1 cm TL, while males showed a maturing phase from 45 to 51 cm TL (Coll et al. 2013). These estimates are lower than the ones reported in the Gulf of Tunisia (Capapé 1977). The annual rate of population increase is 0.247 year-1, and estimated generation time is 4.36 years; the time taken to double the population is 2.81 years (Abella et al. 2011). The estimated generation length is around 6 years.
|Use and Trade:||There is no information available on the use and trade of this species.|
The species is mainly caught by beam trawls, bottom trawls, trammel, and gill nets. Near the Corsican coast in particular, fishing pressure is low because only a few Corsican trawlers, as well as a few Italian vessels, operate in this area (Abella and Serena 2002). A reduced number of trawlers belonging to the La Spezia fleet operate on the same grounds northwards to Viareggio harbour (the most important fishing port of the north Tyrrhenian- south Ligurian Sea). The Livorno fleet operating in the same area is also relatively small. Trawlers concentrate their effort mainly on the grounds at depths between 100 and 400 m and therefore there is a little overlap with areas in which the Viareggio fleet operate.
Off Tuscany (Ligurian Sea), it is mainly landed as bycatch of beam trawlers, targeting common sole and turbots, however very few of these operate in this area (Abella and Serena 2002). Most small individuals caught near shore with trammel and gill nets by these artisanal fisheries are landed. However the ban on trawling within three miles of the coast in this area of the Mediterranean Sea affords protection for this species' shallow nursery areas. Moreover, a general reduction in fishing effort on the grounds traditionally exploited by the Viareggio fleet occurred during the last 15 years because the number of vessels in operation reduced from 107 in 1985, to 78 in 2000 (Abella and Serena 2002).
Little information is available on the probability of survival of discarded juveniles. Preliminary experiments performed with individuals caught and successively put into marine water pools have demonstrated high rates of survival for released individuals caught with bottom trawl nets (Catalano et al. 2003).
Although this skate is one of the more exploited species in the Ligurian Sea, it is apparently relatively resilient to fishing pressure as a result of its life history characteristics. It is relatively productive due to its early age of first maturity (about three years) and relatively short lifespan (about 10 years), even if it is only moderately fecund (Abella and Serena 2002).
Data available for Starry Skate in the North Sea and eastern English Channel are thought to be unreliable owing to confusion between this species and Blonde Skate (R. brachyura) (ICES 2012).
Fishing mortality calculated from the model in 1978 was assessed to be 74% of total mortality, much higher than the mortality of this group due to predation (Coll et al. 2013).
In the northwest Mediterranean Sea, bottom-trawling operations capture large amounts of juvenile fish due to their low selectivity (Sardà et al. 2004) and Starry Skate is sensitive to the type of non-selective commercial trawling operating throughout the Mediterranean Sea from hatchling to adult sizes (Coll et al. 2013). Results from Coll et al. (2013) confirmed that the species has been and still is highly affected by fishing in the Catalan Sea, particularly trawling, and is very sensitive to increasing fishing effects. Under the current situation and under situations of increasing fishing effort in the future, this skate may disappear from the Catalan Sea, as it has already happened with other rays and skates in highly exploited areas of the North Atlantic (Brander 1981; Casey and Myers 1998, Dulvy et al. 2000). Fishing effects in the Mediterranean Sea are high, and it is likely populations are at low levels.
Continental shelves and coastal areas of the whole Mediterranean Sea are currently subjected to a high fishing pressure from a highly diversified fishing fleet (Coll et al. 2010), therefore posing high threat to populations of Mediterranean endemic rays and skates (Aldebert 1997, Ferretti et al. 2010). Starry Skate primarily occupies these areas, and frequently occurs at smaller depths than the depth benchmark of 63 metres for White Skate (Rostroraja alba), which is now locally extinct in parts of the Atlantic and Mediterranean Sea owing to overfishing (Dulvy and Reynolds 2002). Additionally, Starry Skate has a smaller latitudinal range than White Skate and a restricted geographic range, thus making it perceivably more sensitive to fishing (Notarbartolo Di Sciara 1998; Dulvy and Reynolds 2002). Finally, strong declines have been documented in regions where immediate deeper refuges are not available, such as in the Gulf of Lions and the Adriatic Sea (Aldebert 1997, Jukić-Peladić et al. 2001).
A recent regional analysis of human effects in the Mediterranean Sea illustrated that fishing intensity is currently high in most coastal and continental shelf systems where this skate is distributed (Coll et al. 2010), therefore fishing effects may be higher than previously evaluated. However, Coll et al. (2013) showed that Starry Skate may respond well under decreasing trawl fishing effort and could substantially recover in the Mediterranean Sea if this were to occur.
The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species in the region.
The Portuguese Administration adopted a national legislation in October 2011 (Portaria no 315/2011) that prohibits, along the whole continental Portuguese Exclusive Economic Zone, during the whole month of May, the catch, the maintenance on board and the landing of any skate species belonging to the genera Raja or Leucoraja (ICES 2012). Additionally, each fishing trip is allowed a maximum of 5% bycatch, in weight, of those species to be maintained on board or landed.
Further research and monitoring of the population where it is fished is required to prevent declines in the future.
|Citation:||Serena, F., Abella, A., Walls, R. & Dulvy, N. 2015. Raja asterias. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 04 July 2015.|