|Scientific Name:||Rhynchobatus djiddensis (Forsskål, 1775)|
Raja djiddensis Forsskål, 1775
|Taxonomic Source(s):||Forsskål, P. 1775. Descriptiones animalium, avium, amphibiorum, piscium, insectorum, vermium; quae in itinere orientali observavit Petrus Forsskål. Post mortem auctoris edidit Carsten Niebuhr. Havenai, Mölleri.|
|Taxonomic Notes:||The species previously referred to as the wide-ranging Rhynchobatus djiddensis is a species complex of at least four species (L.J.V. Compagno pers. comm. in: Cavanagh et al. 2003). The current known range of R. djiddensis is in the Western Indian from the Eastern Cape Province, South Africa, to the Red Sea. It is not known whether it occurs off Madagascar, where at least two other species of Rhynchobatus do occur (L.J.V. Compagno pers. comm. 2003).|
|Red List Category & Criteria:||Vulnerable A2d+3d+4d ver 3.1|
|Assessor(s):||Dudley, S.F.J. & Cavanagh, R.D.|
|Reviewer(s):||Kyne, P.M., Heupel, M.R. & Simpfendorfer, C.A. (Shark Red List Authority)|
A large (reaching 310 cm total length) Western Indian Ocean inshore guitarfish, distributed from the Red Sea to South Africa. There is little information available on the biology of the species. It does however have a low fecundity of four pups/litter and preliminary tagging data indicate very slow growth rates. In general, the large size and nearshore habitat of this species make it highly susceptible to artisanal fishing with gillnets and other gear, and to shallow water demersal trawling. Off Tanzania Rhynchobatus djiddensis is exploited commercially, primarily for fins, in bottom-set gillnets and possibly also by spearfishermen, and is also a component of the bycatch in prawn trawls. Although species-specific data are not provided, it is likely that R. djiddensis is an important component of coastal elasmobranch catches in Kenya where artisanal gillnetting as well as prawn trawling occurs, together with an established trade in shark fins. By inference the same would apply for Mozambique, where similar fisheries occur and where fins are the main product supporting shark fishing. Additionally, there are presently some 150 to 200 foreign vessels targeting shark fin off East Africa and the Middle East in the Western Indian Ocean. One of the primary target species of these mostly Taiwanese flagged vessels is giant guitarfish. This fishery is operating over a large proportion of the species' range and is known to be poaching from territorial waters where surveillance and policing are often insufficient. Recent arrests of foreign vessels illegally fishing off Mozambique have confirmed large catches of giant guitarfish occurring in this area. The only catch data series available for this species are from the protective shark nets and recreational angling in KwaZulu-Natal (KZN), South Africa, neither of which indicates a significant decline in catch, and from these fisheries significant numbers of R. djiddensis are released alive. In addition, prawn trawlers operating off central KZN take this species as bycatch. Most individuals are alive and released, although subsequent survival is unknown. Although the species faces less threats in this area, and the population there appears stable, catches are seasonal and it is possible the animals may also move to Mozambique, where they are being increasingly caught. The exceptionally high value of (among the most valuable of all elasmobranchs) and demand for the fins, palatability of the flesh and limiting life history characteristics, render the species vulnerable to overexploitation throughout much of its range. Although little data is available on the species' population status, given its susceptibility to capture by multiple gear types, the known heavy fishing pressure from local and foreign vessels in parts of its range and its high value fins, it is highly likely that numbers have been significantly reduced. Serious declines have occurred in populations of similar species for the same reasons, thus R. djiddensis is assessed as Vulnerable globally due to inferred population declines and continuing, unregulated high levels of exploitation. Information is required on this species from the Red Sea region, and species-specific monitoring and assessment of population status is essential throughout its range as a basis for regulation of its exploitation and trade.
|Range Description:||Western Indian Ocean from the Red Sea to the Eastern Cape in South Africa.|
Native:Djibouti; Egypt; Eritrea; Kenya; Mozambique; Oman; Saudi Arabia; Somalia; South Africa; Sudan; Tanzania, United Republic of; Yemen
|FAO Marine Fishing Areas:|
Atlantic – southeast; Indian Ocean – western
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||In South Africa, although it reaches the Eastern Cape Province, it is common only in KwaZulu-Natal (KZN).|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Occurs on the continental shelf to 70 m (generally to 35 m). A large (reaching 300 cm TL) inshore guitarfish. Relatively little information is available on this species across its range. Off KwaZulu-Natal (KZN), South Africa it occurs mainly off sandy beaches during summer (van der Elst 1988), where it is especially abundant in the surf zone but does occur along the edges of deeper reefs down to 30 m. Tagged animals have been shown to travel a mean distance of only 49 km, reflecting local movement during the summer (Mann 2003). It is unknown where the animals go in winter but it is possible that they move north into the warmer waters of Mozambique.
Over the period 1981 to 2000 R. djiddensis catches constituted 33.5% of the total batoid catches in the protective shark nets of KZN, South Africa (Young 2001). Females dominated by 1.95:1, significantly different from unity. Catches are strongly seasonal, occurring primarily (77%) in the summer months of December to April. The median size of females caught (175 cm precaudal length; PCL) was significantly greater than that of males (148 cm PCL) and there was no significant change in size of animals caught between 1981 and 2000.
Initial indications from tagging data are that growth is very slow (Bullen and Mann 2003). This species is aplacental viviparous, with low fecundity (four pups/litter; van der Elst 1988), but little other details of reproductive biology are known.
Diet includes crabs, bivalve molluscs and small fish (van der Elst 1988).
Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length): 150 cm TL (sex not specified; van der Elst 1988).
Longevity (years): Unknown.
Maximum size (total length): 310 cm TL (Compagno et al. 1989).
Size at birth: 60 cm TL (van der Elst 1988).
Average reproductive age (years): Unknown.
Gestation time (months): Unknown.
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: 4 pups/litter (periodicity not given; van der Elst 1988).
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
The restricted coastal habitat, limited life history characteristics, susceptibility to capture in various gear types, and ever growing demand place coastal rhynchobatids amongst the most vulnerable chondrichthyan fishes.
Most detailed information on catches of R. djiddensis is from South Africa and further data are required from throughout its range where the species faces a number of threats.
The mean annual catch in the KZN protective shark nets, South Africa, over the period 1981-2000 was 118 individuals, of which 74% were released alive (Young 2001). There was no significant trend overall (Young 2001) but catch and catch rate declined during the 1990s. Survival of released animals is unknown but, of 460 netted animals tagged and released between 1988 and 2002, 32 (7%) were recaptured (Natal Sharks Board unpublished data). There was no change in the mean size of animals caught in the nets during the time period examined (Young 2001).
Catch rate (number of fish per angler hour) in competition shore angling in KZN showed an increase over the period 1977-2000, as did the mean mass of animals caught (Pradervand 2003). By contrast, anecdotal reports from anglers indicate that the species is less commonly caught than in previous years (Mann 2003). Pradervand (2003) notes that targeting biases do occur in competition shore angling. Hence it is possible that such biases may mask any decline in abundance. A popular target species for shore anglers because of its fighting ability, it has become common practice to release these fish (van der Elst 1988). Of a total of 3,426 animals tagged (including those caught in the shark nets), 198 (5.8%) have been recaptured (Mann 2003).
Rhynchobatus djiddensis is taken as bycatch by demersal prawn trawlers operating in 20 to 45 m depth on the Tugela Bank off central KZN, primarily in summer and at a rate of 123 to 231 per year (Fennessy 1994). Most (82%) of those caught in a sample of 100 trawls were alive and released, although subsequent survival is not known.
Outside South Africa:
Various fishing activities impact R. djiddensis over most of its range outside of South Africa. In most, if not all cases, however specific data are limited. Increased local and foreign targeting and landing of giant guitarfish threatens the species across its range.
The fins from large animals of this species and other members of its genus fetch exceptionally high prices, creating a significant incentive for bycatch to be retained. The species is exploited commercially, primarily for its fins, off Tanzania in bottom-set gillnets and possibly also by spearfishermen (Barnett 1997, Saleh Yahya pers. comm. Institute of Marine Sciences, Zanzibar, September 2003). Given the ready accessibility of the species (due to its size and inshore habitat) and the high value of its fins, these catches are cause for particular concern (Barnett 1997). It is also taken as bycatch by prawn trawlers off Tanzania (Barnett 1997). In neighbouring Kenya there is artisanal gillnetting as well as prawn trawling, and there is an established trade in shark fins (Marshall 1997). Although species-specific data are not provided, it is likely that R. djiddensis is an important component of coastal elasmobranch catches in Kenya.
Similar fisheries occur in Mozambique (Sousa et al. 1997) and where fins were the main product supporting the shark fishing industry (Mihara and Donato 1986 in Sousa et al. 1997). Large Rhynchobatus djiddensis are landed for their fins by artisanal fisherman in southern and central Mozambique and this practice is increasing (Andrea Marshall, University of Queensland, pers. comm). Furthermore, catches of R. djiddensis by recreational anglers have also been recorded in southern Mozambique (Sousa et al. 1997).
Inshore fisheries (including gillnet and trawl) are also prevalent in the Red Sea, where it is an important landed species (Bonfil and Abdallah 2004). Catch data from this area are required.
It is not, however, solely local fishing activities that impact upon R. djiddensis. Of great concern is the large number of foreign vessels targeting guitarfish fin in the region. At the time of writing, there was some 150 to 200 Taiwanese operated fishing vessels (most Taiwanese flagged vessels, some Indonesian flagged) fishing for shark fin off East Africa and the Middle East in the Western Indian Ocean (IOTC 2005). The main target species for these fishers is reportedly hammerhead sharks and giant guitarfish (IOTC 2005). The fishing grounds targeted by these vessels can be divided into two areas: 1). Offshore Mozambique, Tanzania and Madagascar (almost year-round fishing season), and 2). Offshore Oman, Yemen and Somalia (April to July) (IOTC 2005). These areas represent large proportions of the giant guitarfish's range. These foreign vessels are known to be poaching from territorial waters where surveillance and policing are insufficient (IOTC 2005). A recent report of illegal fishing by foreign vessels in Mozambican waters included a seizure of an entire cargo consisting of sharks, mostly R. djiddensis. See: South Africa And Mozambique Tighten Noose On Foreign Vessels For Illegal Fishing.
Habitat modification/degradation, including to inshore nursery areas, from human activities (fisheries, pollution, coastal impacts) are likely affecting this species given its inshore occurrence.
Monitoring and documentation and direct and indirect artisanal and commercial catches is required where the species is being fished. Species-specific catch and effort data should be collected throughout its range, which will require capacity-building, education and training programmes. Further investigation into the taxonomy, population and range, biology and ecology of R. djiddensis is urgently required. Harvest and trade management is needed, including control of fin trading activities where they occur and as such precautionary curtailment of commercial exploitation throughout its range is recommended given that it will not be able to sustain intense and uncontrolled targeting.
The recreational line fishery in South Africa is managed by a bag limit of one/species/person/day for unspecified chondrichthyans, which includes R. djiddensis.
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 management of all elasmobranch species in the region. See Anon. (2004) for an update of progress made by nations in the range of R. djiddensis.
|Citation:||Dudley, S.F.J. & Cavanagh, R.D. 2006. Rhynchobatus djiddensis. The IUCN Red List of Threatened Species 2006: e.T39394A10197912.Downloaded on 15 December 2017.|