|Scientific Name:||Prionace glauca (Linnaeus, 1758)|
Carcharhinus macki (Phillipps, 1935)
Carcharias glaucus (Linnaeus, 1758)
Carcharias gracilis Philippi, 1887
Carcharias hirundinaceus Valenciennes, 1835
Carcharias pugae Pérez Canto, 1886
Carcharias rondeletii (Risso, 1810)
Carcharinus glaucus (Linnaeus, 1758)
Galeus thalassinus Valenciennes, 1835
Glyphis glaucus (Linnaeus, 1758)
Hypoprion isodus Philippi, 1887
Isurus glaucus (Linnaeus, 1758)
Prionace mackiei Phillipps, 1935
Squalus glaucus Linnaeus, 1758
Squalus adscensionis Osbeck, 1765
Squalus caeruleus Blainville, 1816
Squalus rondeletii Risso, 1810
Thalassorhinus vulpecula Valenciennes, 1839
|Taxonomic Source(s):||Weigmann, S. 2016. Annotated checklist of the living sharks, batoids and chimaeras (Chondrichthyes) of the world, with a focus on biogeographical diversity. Journal of Fish Biology 88(3): 837-1037.|
|Red List Category & Criteria:||Critically Endangered A2bd (Regional assessment) ver 3.1|
|Assessor(s):||Sims, D., Fowler, S.L., Ferretti, F. & Stevens, J.|
|Reviewer(s):||Dulvy, N.K. & Allen, D.J.|
|Facilitator/Compiler(s):||Walls, R.H.L. & Dulvy, N.K.|
Mediterranean regional assessment: Critically Endangered (CR)
The Blue Shark (Prionace glauca) is found throughout pelagic waters of the Mediterranean Sea from the surface to as deep as 1,160 m. It is a large (up to 380 cm total length), relatively fast-growing and fecund oceanic shark, with one of the highest maximum annual rates of population increase of all commercially-fished oceanic shark species (at 29% per year). Despite this, the Mediterranean subpopulation has undergone a decline of 78–90% over the past 30 years (three-generation period). The Blue Shark is taken in large numbers in the region by both artisanal and commercial fisheries, mainly as bycatch but more recently it has also been targeted and increasingly retained as valued bycatch. Many catches are unreported in the Mediterranean region, all are unregulated, and fishing effort is not declining. The Blue Shark is therefore listed as Critically Endangered in the Mediterranean Sea based on a past decline of up to 90% over three generations resulting from ongoing overfishing.
|Range Description:||The Blue Shark occurs throughout pelagic waters of the Mediterranean Sea (Megalofonou et al. 2005a,b). The Mediterranean subpopulation is inferred to be distinct from the north Atlantic subpopulation on the basis of i) very limited exchange confirmed using ordinary tags in the past; and ii) zero exchange based on recent satellite tracking. The implications of this lacking connectivity between regions include reduced population regrowth in the face of overexploitation.|
Data from tag-recapture programs and satellite tags suggest very little exchange of Blue Shark individuals between the north Atlantic and the Mediterranean Sea. Kohler and Turner (2008) analysed 39 years of tag-recapture data from 1962–2000. Of 90,752 individuals tagged in the north Atlantic, only two were recaptured in the Mediterranean Sea: one coming from the Northwest, and one from the Northeast Atlantic. Additionally, of the 698 sharks tagged in the Mediterranean Sea, 25 were recaptured there and only one was recovered in the Northeast Atlantic. On average there was less than one migrant per generation, with only two individuals crossing into the Mediterranean Sea and one leaving in four generation spans. A similar synthesis of tag-recapture data was conducted by Fitzmaurice et al. (2005). Of 16,719 specimens tagged and released by the Irish rod and reel fishery between 1970 and 2001, only two individuals were recaptured in the Mediterranean Sea (Fitzmaurice et al. 2005). Again this is less than the one individual per generation threshold. Finally, Stevens (1990) reported tag-recapture locations of 2,585 Blue Shark individuals all tagged off the United Kingdom between 1970 and 1981 in cooperation with the Shark Angling group of Great Britain; none were recaptured in the Mediterranean Sea.
Tag and recapture data need to be interpreted with caution because relocations depend on the range of fishing fleets and they do not provide information on the actual movements of the tagged sharks. Recent analyses of telemetry data obtained from satellite pop-off tags on Blue Shark individuals tagged off Portugal (47 individuals), and southeast England (six individuals) show larger clockwise movements throughout the eastern Atlantic adjacent to the Gibraltar Straits, but no incursions into the Mediterranean Sea (Queiroz et al. 2012, Vandeperre et al. 2014).
Native:Albania; Algeria; Bosnia and Herzegovina; Croatia; Cyprus; Egypt (Egypt (African part), Sinai); France (Corsica, France (mainland)); Greece (Greece (mainland), Kriti); Israel; Italy (Italy (mainland), Sardegna, Sicilia); Lebanon; Libya; Malta; Montenegro; Morocco; Palestinian Territory, Occupied; Slovenia; Spain (Baleares, Spain (mainland), Spanish North African Territories); Syrian Arab Republic; Tunisia; Turkey
|FAO Marine Fishing Areas:|
Mediterranean and Black Sea
|Population:||Mediterranean-based population trends have been inferred from an index appropriate for the Blue Shark. Since the mid-20th century the Blue Shark has declined in abundance by three to four orders of magnitude in this region. It was regularly caught in the tuna trap of Camogli in small numbers, but has not been caught at all over the past six decades (Ferretti et al. 2008). Recent observations from the same gear confirm that no individuals were taken from 2006 to the present day (Cattaneo-Vietti et al. 2014). The Blue Shark was the most abundant of the large predatory sharks taken in pelagic fisheries in the Mediterranean Sea, but catch rates in the region have declined considerably. In the northern Ionian Sea, there were significant declines in abundance and biomass over 21 years (1978–99). In Spanish waters, catch rates in biomass declined steeply over 25 years as well (1979–2004). Pelagic fishing pressure in the region remains high and catches unregulated. Taking into consideration other local trend estimates in abundance and biomass, a meta-analytical estimate of these trend analyses suggested that the abundance of the Blue Shark has declined by ~78–90% over the past 30 years (three-generation period).|
The population decline in the Mediterranean region may be partly attributed to the exploitation of immature individuals. During a study of large pelagic fisheries in the Mediterranean Sea from 1998–99, 91.1% of 3,771 Blue Shark individuals measured were <215 cm total length (TL) and 96.3% were <257 cm TL, indicating that the majority had not yet reached maturity (Megalofonou et al. 2005a). These data indicate that the Blue Shark is unlikely to have had sufficient opportunity to reproduce in these waters before capture in fisheries, leaving this discrete subpopulation depleted with questionable population regrowth.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The Blue Shark is oceanic and pelagic, found from the surface to at least 1,160 m depth (Queiroz et al. 2012). It occasionally occurs inshore where the continental shelf is narrow, preferring temperatures of 12–20°C; it is found at greater depths in tropical waters (Last and Stevens 2009). The Blue Shark is highly migratory with complex movement patterns and spatial structure related to reproduction and the distribution of prey. There tends to be a seasonal shift in population abundance to higher latitudes associated with oceanic convergence or boundary zones, as these are areas of higher productivity.|
This oceanic shark reaches a maximum size of ~380 cm TL. About 50% of males in the Atlantic are sexually mature at 218 cm TL, although some may reach maturity as small as 182 cm TL. Females are sub-adult from 173–221 cm TL and fully mature from 221 cm TL (Pratt 1979).
This placental live-bearing shark produces litters averaging ~35 pups (maximum recorded 135 pups) after a gestation period of nine to 12 months. At birth, the pups are 35–50 cm TL. Reproduction has been reported as seasonal in most areas, with the young often born in spring or summer (Pratt 1979, Stevens 1984, Nakano 1994) although the periods of ovulation and parturition may be extended (Strasburg 1958, Hazin et al. 1994). Females can store sperm in their nidamental glands for extended periods, for later fertilisation (Pratt 1979). Ageing studies estimate longevity to be ~20 years, with males maturing at four to six and females at five to seven years (Stevens 1975, Cailliet et al. 1983, Nakano 1994). Smith et al. (1998) estimated the intrinsic rate of population increase at maximum sustainable yield (MSY) to be 0.061. The maximum annual rate of population increase is the highest of all commercially-fished oceanic shark species at 29% per year. The generation period (average age of mature females in an unfished population) is estimated as 10 years (Dulvy et al. 2008).
|Generation Length (years):||10|
|Movement patterns:||Full Migrant|
|Use and Trade:||Blue Shark fins are the most prevalent in the Hong Kong shark fin market (Clarke et al. 2006a) and comprise at least 17% of the overall market; an estimated 10.7 million individuals (0.36 million tonnes) are killed for the global fin trade each year (Clarke et al. 2006a,b). This species has increased in commercial value and incidental catches are now rarely discarded (Megalofonou et al. 2005a), with the meat marketed in Greece, Italy, and Spain, and fins exported to Asia.|
|Major Threat(s):||The Blue Shark is rarely a targeted commercial species but a major bycatch of longline and driftnet fisheries, particularly from nations with high-seas fleets. Much of this bycatch is unrecorded, and much of it is likely to be valued and retained as 'byproduct'. This species was the target of big game tournaments in the Adriatic Sea and is an incidental catch of tuna traps.|
There are currently no species-specific catch limits or other protections in place in the Mediterranean Sea. Furthermore, the trade in the Blue Shark's meat and fins is not monitored, despite the species' prominence in international trade (Rose 1996; Clarke et al. 2006a,b). The Blue Shark's trans-oceanic migrations strongly support arguments for regional and international management (Camhi et al. 2009).
In 2013, the European Union (EU) banned removal of shark fins on board vessels (Regulation No. 605/2013), in line with advice from the International Union for the Conservation of Nature’s Shark Specialist Group and other shark fishery experts, in order to enhance enforcement of the 2003 EU ban on shark finning (Regulation No. 1185/2003) and facilitate improved shark fishery data collection. Since this species has been subject to high rates of finning in the past, well-enforced shark finning bans could help to reduce mortality.
|Citation:||Sims, D., Fowler, S.L., Ferretti, F. & Stevens, J. 2016. Prionace glauca. The IUCN Red List of Threatened Species 2016: e.T39381A16553182.Downloaded on 24 March 2018.|
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