|Scientific Name:||Centrophorus granulosus|
|Species Authority:||(Bloch & Schneider, 1801)|
Squalus granulosus Bloch & Schneider, 1801
|Taxonomic Notes:||The distribution of C. granulosus, as understood here, is difficult to establish due to remaining confusion to the genus. Worldwide reports made under C. uyato have often been synonymized with C. granulosus but affinities of these specimens need further study. Taxonomic resolution between species of the genus with sessile dermal denticles like C. granulosus is required, particularly for C. niaukang, C. lusitanicus, C. harrissoni, C. tessellatus, C. atromarginatus and even some probable undescribed species (Guallart 2003, Compagno in prep. a). Until that is managed, identity of each worldwide OTU reported under the name C. granulosus outside the Mediterranean Sea can be considered as pending of being checked.
Two nominal species of Centrophorus have been reported in the Mediterranean Sea, C. granulosus and C. uyato, which some authors consider to be synonymous, and others consider them valid species. Although considerable taxonomic controversy of the genus still persists, the present assessment is based on the agreement of most Mediterranean authors that there is only one species of Centrophorus in the Mediterranean Sea (e.g., Tortonese 1969, Tortonese and Capapé 1971, Rancurel 1983, Capapé 1985, Muñoz-Chapuli and Ramos 1989, Guallart 1998, Compagno in prep.). In the western North Atlantic two forms have been traditionally identified as C. granulosus and C. uyato. The two species differ trenchantly in reproductive biology, reaching sexual maturity at greatly different sizes and differing in size of ova. (Burgess unpub. data).
The same species or a similar "granulosus-type" has been observed in Taiwanese waters, but critical taxonomic comparison with other "granulosus-type" material from the Atlantic has not been conducted.
|Red List Category & Criteria:||Vulnerable A2abd+3d+4d ver 3.1|
|Assessor/s:||Guallart, J., Serena, F., Mancusi, C., Casper, B.M., Burgess, G.H., Ebert, D.A., Clarke, M. & Stenberg, C.|
|Reviewer/s:||Cavanagh, R.D., Fowler, S.L. & participants of the Shark Specialist Group Northeast Atlantic Workshop (Shark Red List Authority)|
A rare deepwater dogfish with a widespread global distribution, inhabiting the upper continental slopes and outer continental shelf area. Believed to have the lowest reproductive potential of all elasmobranch species; its reproductive biology is characterized by a late onset of maturity (12 to 16 years in females), only one pup per litter and a two-year gestation period with occasional resting periods. This makes it extremely vulnerable to overexploitation and population depletion. Despite a lack of data for certain regions within its geographic range, this species is globally assessed as Vulnerable on the basis of its limiting life history traits and the global increase in unmanaged fishing effort to exploit deeper waters.
This species is extremely rare in the Mediterranean, which in combination with the documented localized depletion subsequent to brief targeted fishing efforts and the species? inherent vulnerability to exploitation even in moderate numbers though bycatch, leads to an assessment of Vulnerable in this region. A decline of 80 to 95% from baseline has been estimated for the Northeast Atlantic population. Due to the low level of recruitment (resulting from a low fecundity and low reproductive output), this species is assessed as Critically Endangered within the Northeast Atlantic.
Taxonomic issues, in combination with a paucity of data have hampered this species? assessment. Elsewhere as a result, it cannot be assessed beyond Data Deficient for the North and South west Atlantic. There is an urgent call for further research on a global level, but in particular to collect further data for these aforementioned areas, monitoring of the extent to which this species is affected by bycatch is also required. The taxonomic issues relating to this species need to be resolved and the Centrophorus spp. examined to determine the proper identification of the species involved within these regions.
|Range Description:||Thought to be a circumglobal species, in temperate and tropical waters, however considerable taxonomic confusion of the genus still persists (see Taxonomy). This species occurs in the following regions and countries:
Northeast Atlantic: France, Spain, Portugal, Madeira.
Mediterranean: Albania, Algeria, France, Greece, Italy, Morocco, Spain, Tunisia and Turkey. Absent from the Black Sea. (Baino et al. 2001, Boutan 1926, Maurin 1968, Jardas 1984, Fischer et al. 1987, Papakonstatinou 1988, Ungaro et al. 1994, Kabaskal 2002).
West Africa: Canary Islands, Morocco, Sahara Republic, Senegal, Liberia, Ivory Coast to Nigeria, Cameroon to Congo.
Sub Equatorial Africa: Angola, Namibia, and the west coast of South Africa (Northern Cape Province. Southern Mozambique, Madagascar, Aldabra Island.
Indian Ocean: Yemen, Somalia (the Gulf of Aden), nominal records from India, which are at least in part based on Centrophorus atromarginatus.
Australia and Oceania: Probably Australia (temperate waters off Western Australia, South Australia, Victoria, Tasmania, and New South Wales as C. uyato, but possibly including other species).
Asia and the Northwest Pacific: Taiwan Island and Japan.
Northeast Pacific: Possibly Hawaiian Islands.
Northwest Atlantic: Northern Gulf of Mexico (United States).
Central America: possibly wide ranging in the Gulf of Mexico and the Caribbean (the north coast of Cuba, Puerto Rico and the Caribbean off the Lesser Antilles (Burgess pers. comm.), possibly Colombia and Venezuela, and off French Guiana.
South America: Brazil (Northern).
Note that the species from the SE Atlantic may not be the same as found elsewhere, or may represent two or more species. The species needs to be critically evaluated from different regions. This or a similar species has also been found in Taiwanese waters (D.A. Ebert, unpubl. data).
Native:Albania; Algeria; Angola (Angola); Brazil; Cameroon; Congo; Côte d'Ivoire; Cuba; Dominica; Dominican Republic; France; Greece; Italy; Japan; Liberia; Madagascar; Mexico; Morocco; Mozambique; Namibia; Nigeria; Portugal (Madeira); Puerto Rico; Senegal; Somalia; South Africa (Northern Cape Province, Western Cape); Spain (Canary Is.); Taiwan, Province of China; Tunisia; Turkey; United States; Yemen
|FAO Marine Fishing Areas:||
Present - origin uncertain:
Atlantic – eastern central; Atlantic – northeast; Atlantic – northwest; Atlantic – southeast; Atlantic – southwest; Atlantic – western central; Indian Ocean – eastern; Indian Ocean – western; Mediterranean and Black Sea; Pacific – northeast; Pacific – northwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The determination of the range and population of this species is hindered by unresolved taxonomic issues (see taxonomy section). Within the Mediterranean, there is no evidence of the existence of different populations. No information is available on relationships between Mediterranean and Atlantic populations of Centrophorus. However, like most Mediterranean deepwater species, some degree of isolation is expected due to the barrier of the Straits of Gibraltar. Analysis of the Mediterranean International Trawl Survey (MEDITS) data from 1994 to 1999 show a low frequency of occurrence (only 2% of total hauls), for C. granulosus. Its overall biomass was estimated to be 2.9 kg/km², with a presence throughout the Mediterranean, though more abundant in the western central and in the western area (5.5 and 2.7 kg/km² respectively). The depth distribution of the biomass index show values of less than 0.1 from 50 to 100 m of depth and between 1 to >10 kg/km² between 200 to 800 m. Baino et al. give a standing stock biomass estimate of only 1,528 t (3%) for the west, north and east Mediterranean from 0?800 m depth. These data clearly indicate that this species is very rare. The MEDITS experimental trawl program surveys waters up to 800 m in depth. The depth range of this demersal deepwater shark extends from 100 to 1,490 m, however it is most commonly recorded between 300 and 800 m, therefore this data can serve as a good indicator of the abundance of this species.|
|Habitat and Ecology:||
A large deepwater species inhabiting the upper continental slopes and outer continental shelves. Usually demersal or benthopelagic, at depths from 100 to 1,490 m (Mediterranean Sea), with most records between 300 to 800 m depth (Baino et al. 2001, Compagno 1984, Gilat and Gelman 1984, Guallart 1998).
It is thought to have schooling habits (Maurin 1962, Gilat and Gelman 1984, Compagno 1984, Compagno in prep. a) because of the abundance in some catches or by the simultaneous presence of several individuals in baited cameras set over the bottom. It may also aggregate in particular areas of the slope, particularly in the margins of submarine canyons (Guallart 1998). Some evidence suggests that individuals present in the lower half of the depth range are mainly juveniles (Guallart 1998).
Age at maturity is estimated at 12 to 16 years (females) and 7 to 8 years (males) (Guallart 1998) with earlier estimates of 4 to 5 years for both males and females (Rizzo et al. 1995). Estimates of female size at maturity are 89 to 102 cm (93 cm when half mature) (Gullart 1998) and earlier estimates range between 70 to 95 cm (Capapé 1985, Fischer et al. 1987). Mature male size estimates are 79 to 85 cm (80 cm at half maturity) (Guallart 1998) and 70 to 80 cm (Capapé 1985, Fischer et al. 1987, Rizzo et al. 1995). Maximum recorded size is about 120 cm (Fischer et al. 1987, Guallart 1998). Size at birth range from 30 to 46 cm (Guallart and Vicent 2001, Fischer et al. 1987) and C. granulosus can live for over 30 years (Guallart 1998). The average reproductive age of this species is unknown.
A lecitotrophic aplacental viviparous (ovoviviparous) species (Ranzi 1932, Guallart and Vicent 2001, C. granulosus has an extremely low reproductive rate, with only one pup/litter (Tortonese 1956, Capapé 1985, Guallart 1998), a gestation period of about two years and occasional resting periods between pregnancies (Guallart 1998). The three-generation period is estimated to be about 50 to 60 years. This probably makes it the elasmobranch species with the lowest reproductive potential.
Feeds on a variety of prey, mainly fishes but also cephalopods and other invertebrates, both benthic and mesopelagic; also probable scavenging habits (Boutan 1926, Capapé 1985, Guallart 1998).
This is a widespread species that is reported to be heavily fished and caught as bycatch in the Northeast Atlantic, the Northwest Pacific and other regions. As the global fishing fleet tends towards deeper and deeper unexploited fishing grounds, the threat from incidental catch to this species grows.
In the Northeast Atlantic this species is caught with bottom trawls, long lines, fixed bottom nets, hook and line and pelagic trawls (Compagno in prep). For this region, landings data were obtained from ICES (2006) for the Portuguese coast (main distribution range). These show a strong decline in catch from about 1,000 t in 1990 to less than 100 t in 2004. As a crude index of abundance a delury depletion model was implemented, assuming constant effort over the time series. The results of this suggest that the stock has declined by between 80 and 95% of its initial size when fishing began. This is based on two assumptions of effort. This assumes that recruitment does not occur. Though this is clearly not true, the extreme low fecundity and reproductive output suggests that effect of recruitment is very low indeed.
Within the Mediterranean, one of the main threats facing this species is development of target fisheries with longlines and gillnets in areas on the continental slope, where this species tends to aggregate. However, the global trend for fisheries reaching deeper unexploited grounds may not necessarily be the case for within the Mediterranean, due to the relative low level of biomass found in the deepwaters of this sea and as the fishing fleets are composed mainly of artisanal vessels. Local factors such as the fleet characteristics, the distance from the coast to suitable substrates and the perceived appreciation of the flesh and other by products of this species may, in many countries limit the potential for a targeted fishery to develop. A number of authors have commented on the economic potential to develop a targeted fishery for Centrophorus species (e.g., Boutan 1926 in Algeria, Rancurel 1983 in France, Gilat and Gelman 1984 in Israel), however there is no information regarding potential developments at present. Given the record low reproductive potential of this species, it is highly vulnerable to overexploitation and population depletion under even moderate fishing pressure. Therefore extreme caution should be exercised before the development of any targeted fishery.
There are a few examples of fisheries targeting Centrophorus granulosus in the Balearic Sea over the last 10 years (Guallart pers. comm. 2003). One of which was an alternative fishery, which developed in periods when other target species had declined, this artisanal fleet used bottom longline gears. Abundance (catches of about 50?80 specimens or 300?400 kg/ship and journey) and price of flesh was comparable to that of the original target species. However, catches decreased dramatically within a matter of weeks. An increase in abundance within these depleted areas took place after several months, presumably by migration from other unexploited areas. In another example, a semi-industrial fishery was carried out for several years. One ship made trips of several days covering wide areas unexploited for this species. Catches reached up to 900 specimens (about 5,000 kg). Flesh, livers and tails (as lower quality shark fins) were marketed.
Within the Mediterranean this species is also caught as bycatch, with bottom longlines and bottom gillnets and in bottom trawls targeting red shrimp Aristeus antennatus (Fischer et al. 1987). Further information on the catch rates of this species by this trawling fleet are required before the impact that this has on the Centrophorus granulosus population can truly be assessed.
This species is widespread throughout the Western North Atlantic at appropriate depths where it is only taken as bycatch in longline fisheries. At this time it appears that it does not constitute significant numbers in the fisheries, but data is lacking.
In southern Africa it is occasionally taken as a bycatch and possibly in the experimental Namibian deepsea fishery. However, it is uncommon relative to several other species, e.g. C. squamosus, Centroscymnus spp. and Deania spp. which are taken in far greater numbers.
Along the west African coast, this species is widespread, but scattered. It is infrequently caught along the Namibian coast, but this may represent a different species and possibly two or more species may be involved in this taxonomic confusion. Proper identification of this species in southeastern Atlantic waters is critical before this species can be reassessed.
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. The decision was adopted at the 29th session of the GFCM held in Rome in February 2005. Unless objections from member countries arise, it will come into force in July 2005. For more information, see: Mediterranean Conservationists and Fishermen Work Together to Protect Deep Seas.
Further study is required for taxonomic resolution of the genus, and on reproductive cycle and general life history, validation of ageing methods, population identification, and determination of nursery areas, migrations and spatial distribution. Monitoring fishing pressure is essential. This must include recording specific fishery statistics (including bycatch), and monitoring possible plans for development of target fisheries or increasing fishing pressure in their habitat.
There are currently no conservation measures at this time in the Northwest or the Southeast Atlantic. Examination of the Centrophourus spp. which occur in the latter region is strongly recommended to determine the proper identification of the species involved.
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|Citation:||Guallart, J., Serena, F., Mancusi, C., Casper, B.M., Burgess, G.H., Ebert, D.A., Clarke, M. & Stenberg, C. 2006. Centrophorus granulosus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 07 March 2014.|
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