|Scientific Name:||Rhinobatos rhinobatos|
|Species Authority:||(Linnaeus, 1758)|
Raja rhinobatos Linnaeus, 1758
|Red List Category & Criteria:||Endangered A4cd ver 3.1|
|Assessor(s):||Notarbartolo di Sciara, G., Bradai, M.N., Morey, G., Marshall, A.D., Compagno, L.J.V., Mouni, A., Hicham, M., Bucal, D., Dulvy, N., Heenan, A. & Rui Coelho.|
|Reviewer(s):||Cavanagh, R.D., Ducrocq, M. & Valenti, S.V. (Shark Red List Authority)|
A guitarfish known from the southern Bay of Biscay, southwards to Angola, including the Mediterranean Sea. Although the distribution is fairly wide, it is subjected to fishing pressures throughout most of its range. Its existence along coastal inshore areas makes this species an easy target for subsistence fisheries. Limited data are available on the biology, but it is large and is likely to have a relatively unproductive and vulnerable life history. Off the west African coasts, this species is taken as bycatch of international shrimp trawl fleets, bottom trawl cephalopod fisheries and in artisanal gill net fisheries. It is targeted for its meat, which is salted, dried and exported within the region and its fins are used to supply the Asian fin trade market. Other guitarfishes and wedgefishes have undergone severe declines (Rhynchobatis luebberti, Rhinobatos cemiculus) and the future fishing pressure in shallow coastal habitats is unlikely to decrease. The common guitarfish is believed to face similar threats as the blackchin guitarfish Rhinobatos cemiculus. In the northern Mediterranean, where both species used to be quite common (see for example Doderlein (1884), concerning their daily presence on the Palermo fish market); both disappeared from bottom trawl surveys, from Alboran to Aegean sea within the MEDITS international programme, both disappeared from the landings in Mazzara del, and appear to have been extirpated. In the Balearic Islands both species were considered as typical inhabitants of unvegetated sandy bottoms. Old fishermen reported their relative frequency during the first half of the 20th century, but nowadays they seem to be extinct in the area. In areas of the southern Mediterranean (e.g., Gulf of Gabés, but perhaps elsewhere along the still underfished Mediterranean African coast) both species are still present in the catch, but with a large fraction of immatures. Given evidence for regional extinctions in the northern Mediterranean Sea and intense and continuing fishing pressure throughout this species' habitat along the west African coasts, observed declines in its congener R. cemiculus, and its likely vulnerable life history characteristics, there is no reason to suspect that this species will not suffer similar declines to those observed in the northern Mediterranean throughout the rest of its range. Therefore this species is assessed as Endangered on the basis of past and suspected future declines. The status of this species should be monitored carefully. At present, this species is not subject to any conservation or management measures. It recommended that species specific landings data, and fishing effort should be recorded and analysed.
Global: the common guitarfish distribution extends between 44°N to 17°S, 19°W to 36°E from the southern Bay of Biscay southwards to Angola (including the Mediterranean), this guitarfish appears to prefer warmer waters (Fredj and Maurin 1987).
Mediterranean: occurs throughout the Mediterranean coasts, but appears more prevalent in the southern and eastern regions (Capapé 1989, Whitehead et al. 1984), in particular around the Gulf of Gabes, on the East coast of Tunisia (Quignard and Capapé 1971).
East Atlantic: Morocco, Mauritania, Senegal, Gambia, Guinea Bissau southwards possibly to Namibia.
Native:Albania; Algeria; Angola (Angola); Benin; Bosnia and Herzegovina; Bulgaria; Cameroon; Cape Verde; Congo; Côte d'Ivoire; Croatia; Cyprus; Denmark; Egypt; Equatorial Guinea; France; Gabon; Germany; Ghana; Greece; Guinea; Guinea-Bissau; Iceland; Ireland; Israel; Lebanon; Liberia; Libya; Mauritania; Monaco; Montenegro; Morocco; Namibia; Nigeria; Norway; Portugal (Azores, Madeira); Senegal; Sierra Leone; Slovenia; South Africa; Spain; Syrian Arab Republic; Togo; Tunisia; United Kingdom; Western Sahara
|FAO Marine Fishing Areas:||
Atlantic – northeast; Atlantic – southeast; Atlantic – eastern central; Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Due to widespread and unregulated fishing throughout the range the population is expected to be declining.
Little is known of the population sizes of the common guitarfish. However, there has been a marked decline in the abundance of this guitarfish in the Northern regions of the Mediterranean, based on a combination of fisherman' s knowledge and data from the Mediterranean International Trawl Survey (MEDITS). These experimental trawl surveys carried out in the North of the Mediterranean (from the Alboran to the Aegean Sea) between 1994 and 1999 failed to catch any common guitarfish, indicating that they have disappeared from this area (Baino et al. 2001). Indeed, Relini and Piccinetti (1991) reported the common guitarfish species extinct within the northern regions of the Mediterranean. Observations from the 1970s and 1980s indicate that the common guitarfish was prevalent within the south and eastern basins of Mediterranean (Whitehead et al. 1984, Quignard and Capapé 1971, M.N. Bradai pers. comm.), however the demersal nature of this species and the localized decline within the northern Mediterranean indicate that there are low levels of interconnectivity between the geographical sub-populations.
No information is available on the population size of this species along the west African coasts.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The common guitarfish is a bottom dwelling species with an aplacental viviparous mode of reproduction mode (the maternal adult gives birth to live young which do not have a yolk sac placenta). It can be found over sandy, muddy, shell and occasionally macro-algal covered substrates (Whitehead et al. 1984, De Buen 1935). It inhabits shallow waters in the intertidal zone to waters of up to 180 m in depth. This guitarfish tends to swim slowly along the sea bottom or partially buries itself under the substrate, feeding upon benthic invertebrates and fish (Patokina and Litvinov 2005). Scientific trawl surveys in Moroccan waters recorded the depth range of the common guitarfish as 17 to 80 m in depth (M. Hicham and A. Mouni pers. comm. 2006). Bottom trawl surveys carried out off the coast of Sierra Leone indicate that this is a sublittoral species which occurs between 10 and 100 m in depth. It was only found in waters deeper than 50 m during the summer and autumnal months and during the winter-spring seasons this guitarfish moves northwards (Litvinov 1993).
Whitehead et al. (1984) reported the maximum size of the common guitarfish as approximately 100 cm in total length (TL). However, within the Southern Mediterranean (the Gabés Gulf), the maximum reported sizes were slightly larger with 140 cm TL for males and 162 cm TL for females (Capapé et al. 1996). Males reach maturity at 75 cm in TL, females at 85 cm TL. The age at maturity is not known for either sex, nor the longevity of this species. The females have between one and two litters per year, with the gestation period spanning four months. Between 4 and 6 pups are produced per litter, measuring 30 cm at birth.
There is no information available on the natural rate of mortality that this species population experiences, or any further details on its population and reproductive biology.
This species' biology and inshore habitat make it highly susceptible to population depletion. The distribution of this species is fairly wide but it would be subjected to fishing pressures throughout most of its range, as its coastal habitat make this rhinobatid easy target for artisanal fisheries and it is likely to be caught as bycatch of commercial fisheries of all kinds, operating along the majority of the Mediterranean coastline, for example the Egyptian commercial trawl fishery off the coast of Alexandria.
Guitarfish are vulnerable to fisheries given their life history. There is also little known about their biology or habitat requirements but it is likely that habitat requirements especially for young (nursery grounds) is being influenced by humans causing habitat degradation in many of these areas.
Other species of guitarfish are now regularly caught as by-catch in local fisheries in the Red Sea and Western Indian Ocean, including much of Africa. They are used for their flesh or fins but often are discarded.
Based on anecdotal evidence, the common guitarfish, along with the blackchin guitarfish Rhinobatos cemiculus is a species which was historically common throughout the Northern Mediterranean. In the late 19th century Doderlain (1884) commented on the daily presence of this species in the Palmero fish market, while in the early 20th Century it was considered a typical resident over sandy substrates around the Baleric Islands (De Buen 1935). Furthermore, the perception of older fishermen operating this region was that of a relatively high frequency of occurrence in the first half of the 20th century, compared to the present apparent local extinction in this area (G. Morey pers. comm. 2003). The absence of this species from MEDITS bottom trawl survey further consolidates the apparent disappearance of this species from the northern regions of the Mediterranean.
In portions of the southern shore (e.g., Gulf of Gabés and potentially elsewhere along the Mediterranean African coast which has be subject to less intensive fishing pressure) both species are still present in the catch, but with a large proportion of immature juveniles.
The sizes of Rhinobatos rhinobatos individuals fished by bottom trawls vary from 300 to 1,200 mm TL with an average of 736 mm LT. The most common size of individuals landed in the gulf of Gabès is between 500 to 1,000 mm (females) and 600 to 900 mm (males). Of the landing 54.46% of specimens landed were females and 46.72% were immature males (M.N. Bradai and Ennajar pers. comm. 2003).
Rhinobatids are caught as bycatch of shrimp trawl fisheries operating in shallow inshore waters. They are also caught in artisanal bottom setnet fisheries and dried for export to Ghana where used for human consumption.
In Senegal the landings of guitarfish species have decreased dramatically. Landings peaked in 1997 at 4,218 t and have since gradually decreased to an estimated 821 t in 2005 (Ministry of Maritime Economy and International Marine Transport of Senegal unpub. data).
In Guinea-Bissau this species is one of the main targets of specialised shark fishing teams. Preliminary surveys from the IUCN Guinea-Bissau programme in collaboration with Centre of Applied Fisheries Research indicate that populations of the common guitarfish and the blackchin guitarfish have diminished substantially (cited in Fowler et al. 2005). These fisheries use gillnets to target Rhinobatos spp. (mainly Rhinobatus rhinobatus and Rhinobatos cemiculus), fishing between 1 and 40 m in depth (Bucal 2006). There has been a shift in mesh net size, 15 years ago the gillnet mesh size was reported to be 230 to 280 mm, at present it is 180 to 160 mm. This will increase the number of juveniles caught by this fishery. Also caught as bycatch for fisheries targeting Mujillidae (mullet) also using gillnets. They are caught by hooks catching Lutjanidae and Dentex (Sparidae, sea breams). Captures have decreased over the last 15 years and the size of specimens landed have decreased (D. Bucal pers. comm. 2006), however it is important to note the change in mesh size.
No target fishery is in operation off Morocco, however it is caught as bycatch by bottom trawlers (targeting octopus and cephalopods) at 20 to 150 m depth (A. Moumni and M. Hicham pers. comm. 2006). No information is available on the rate of catch or bycatch landings or discard survival rates.
Reportedly common in Sierra Leone. Caught as bycatch of shrimp trawl fisheries operating in shallow inshore waters 14 to 26 m. The bulk (80%) of the international fleet consists of shrimp trawlers (Seisay 2005). The catch rate of a recent discards survey programme indicates a bycatch rate of >1 specimen per two hour tow. The shrimp fishery catches individuals of up to 220 cm (female) and 178 cm (male) in total length. It is also caught in artisanal bottom set net fishery where individuals measuring from 199- ~175 cm are caught (male and female). Specimens are dried and exported to Ghana (M. Seisay pers. comm. 2006). Rhinobatids are the most dominant batoids landed within artisanal fisheries. The common guitarfish accounts for 16.58% of the number of batoids landed and 28.15% of the total batoids landed, by weight (Seisay 2005). On a less specific level, rays are also captured as bycatch to industrial shrimp and finfish fisheries, in Sierre Leone shark and rays bycatch landings make up an estimated 0.8-1.0% of the total reported catch (Seisay 2005) (see figure 1).
See the Supplementary Material for Figure 1: Industrial fishery production (mt) of rays in Sierra Leone waters. Original data (Seisay 2005).
There is no information available on the fishing effort, which limits the conclusions that can be drawn from this data, however in the absence of further information, it can be used to provide a preliminary indication for the national bycatch shark landings of Sierra Leone. It is likely that the actual number of sharks landed as bycatch by industrial fisheries is far greater, as this represents only the reported landings of legal fisheries. Although this data is not species specific, it gives an indication of the quantity of sharks landed in this country. Similar fisheries operate throughout the rest of the region.
Frequently captured in Gambia (A. Mendy pers. comm. 2006). Along the Mauritanian coast, however it is more abundant within the Banc d'Arguin national park where it is afforded some protection, and where in 2004 it composed 2% of the shark catch. Flesh retained and fins dried and exported to Ghana (L. Camara pers. comm. 2006). Prior to the December 2003 Banc d'Arguin ban on elasmobranch targeted fisheries it was fished for its highly prized fins and caught with specialised nets. Today, it is still caught incidentally as bycatch in teleost gillnet fisheries. It is also bycatch of industrial demersal trawl fisheries targeting cephalops and crustaceans and coastal teleosts (K. Brahim pers. comm. 2006).
There are no species specific measures currently in place.
The Mediterranean Action Plan for the conservation of chondrichthyan fishes recognises the urgent need to assess the status of Rhinobatos species, as a species that may be at high risk of threat in the region (Anonymous 2003).
This species is protected as part of a ban on directly targeted elasmobranch fishing in the Banc d'Arguin, Mauritania, which was implemented in December 2003. In this national park, management measures specific to Rhinobatos cemiculus were also introduced (M. DuCrocq pers. comm. 2006). The fishery was closed from February to September, to avoid the parturition period and therefore the capture of pregnant females. After negotiations with local fishermen, gear restrictions were introduced (to stop fishing with bottom gillnets of 1 to 2 m height and 11 to 16 cm (one side) square mesh).
There are no species specific regulations for the management of shark and shark fisheries in the Sierra Leone. However, a licensing system for artisanal fishing canoes, both foreign and Sierra Leone owned is payable to the Ministry of Fisheries and Marine Resources and the Local Government Administration (Seisay 2005). A National Action Plan for the conservation and management of sharks is being proposed. Highlights of the recommended management measures include: area and seasonal closure to shark fisheries; effort limitation of shark fishery; return of immature and/or juvenile shark and ray species.
There are marine protected areas inside the Bijagos archipelago (the Formosa Islands UROK marine reserve), the PNO marine reserve (Orango Islands) and the PNMJVO marine reserve (Joao Vieira and Poilao Islands). Within these areas, trawling and the use of nets is forbidden, the only gear type allowed is fishing with longlines. Furthermore, fishing is only allowed for subsistence purposes, commercial fishing is disallowed (Bucal 2006).
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. Fishing effort within the region should be monitored and species specific landings should be recorded. Further study on the range of the species and the use of specific critical coastal habitats, in particular reference to the negative impact of trawling.
A seasonal ban on the targeted exploitation of this species elsewhere within the West African region would decrease the rate of capture of reproductively active individuals (M. Ducrocq pers. comm. 2006). A ban on finning and the dumping of carcasses should be considered, as this would represent the most effective method of decreasing the fishing pressure on this species (A. Mendy pers. comm. 2006). Otherwise, the implementation of licences for targeted and non targeted shark fishing and finning and a tax system on shark fins are recommended as measures to control the fishing pressure on this species.
|Citation:||Notarbartolo di Sciara, G., Bradai, M.N., Morey, G., Marshall, A.D., Compagno, L.J.V., Mouni, A., Hicham, M., Bucal, D., Dulvy, N., Heenan, A. & Rui Coelho. 2007. Rhinobatos rhinobatos. The IUCN Red List of Threatened Species 2007: e.T63131A12620901. . Downloaded on 29 June 2016.|
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