| Citation |
Kyne, P.M., Gledhill, K. & Jabado, R.W. 2019. Rhynchobatus djiddensis. The IUCN Red List of Threatened Species 2019: e.T39394A121035795. http://dx.doi.org/10.2305/IUCN.UK.2019-2.RLTS.T39394A121035795.en. Downloaded on 01 August 2019. |
Description |
RANGE DESCRIPTION
The Whitespotted Wedgefish is widespread in the Western Indian Ocean from South Africa to Oman and the Arabian/Persian Gulf, but it may not be present further east (Last et al. 2016). However, the species distribution may not be fully defined due to confusion with other members of the Rhynchobatus djiddensis species-complex.
DESCRIPTION
Where rhinopristoid rays (sawfishes [Pristidae], wedgefishes [Rhinidae], giant guitarfishes [Glaucostegidae], and guitarfishes [Rhinobatidae]) have been targeted or exploited as incidental catch, severe declines, population depletions, and localized disappearances have occurred (e.g., Tous et al. 1998, Dulvy et al. 2016, Moore 2017, Jabado 2018). However, there are no species-specific time-series data available for wedgefish species that can be used to calculate population reduction. This is due to a lack of species-specific reporting as well as taxonomic and identification issues, particularly around the whitespotted wedgefish (i.e., Rhynchobatus djiddensis) species-complex. The name Rhynchobatus djiddensis was used widely for wedgefishes across the Indo-West Pacific prior to clarification of species distributions and recognition that R. djiddensis is restricted to the Western Indian Ocean (see Last et al. 2016).
Despite the lack of species-specific data, there are a number of relevant historical accounts and contemporary datasets for landings and catch rates, and although landings data are not a direct measure of abundance, these can be used to infer population reduction where landings have decreased while fishing effort has remained stable or increased. In nearly all cases presented below, there is no reason to suspect that overall effort has decreased (although directed fishing effort may have shifted in response to resource collapse/depletion). In fact, as the human coastal population continues to grow and as fishing technology and market access improves, fishing effort and power is continuing to increase globally (Anticamara et al. 2011, Watson et al. 2013). To infer population reduction for Indo-West Pacific wedgefishes, there are several relevant historical accounts and more contemporary datasets on landings and catch rates (i.e., datasets including some period of the 2000s) (see the Supplementary Information for details). For the five contemporary datasets, there is no information to suggest that overall effort would have decreased such that declining catches represent changes in the fishery. Rather, they likely indicate reductions in abundance. While only one of the contemporary datasets is from the known range of the Whitespotted Wedgefish (the landings dataset from Iran), these are considered informative for understanding population reduction in wedgefishes more broadly.
These historical accounts and datasets show: (1) a 93% decline in Rhinobathidae (which probably equals guitarfishes generally) catch rate in the Gulf of Thailand from peak catches in 1968 to 1972 (Ritragsa 1976, Pauly 1979); (2) the collapse of Indonesian targeted wedgefish fisheries (Chen 1996, Suzuki 2002); (3) the depletion of rays (which can be used to infer declines in wedgefishes) in in the Java Sea (Blaber et al. 2009) (recent trawl surveys in the Java Sea and North Natuna Sea recorded only three Rhynchobatus; Tirtadanu et al. 2018, Yusup et al. 2018); (4) declines in landings from Iran (see below), Pakistan, and Indonesia, which are the equivalent of 81-99% population reduction over the last three generation lengths (30–45 years) (DGCF 2015, 2017, FAO 2018, M. Gore unpubl. data) (see the Supplementary Information); and, (5) significant declines in landings of guitarfishes (which includes wedgefishes) in Tamil Nadu (86% decline for a 5-year period) and catch rates of rays (which does not include wedgefishes, but is representative of declines in demersal batoids) in Maharashtra (63% decline for a 15-year period) in India (Mohanraj et al. 2009, Raje and Zacharia 2009) (see the Supplementary Information).
To expand on point four above in relation to Iran (a range state of the Whitespotted Wedgefish), landings data for the giant guitarfish category are available for 1997-2016 (20 years; Table 2 in the Supplementary Information) (FAO 2018). This grouping likely includes all rhinids and glaucostegids occurring locally, including Bowmouth Guitarfish (Rhina ancylostoma), Bottlenose Wedgefish (Rhynchobatus australiae), Whitespotted Wedgefish (R. djiddensis), and Smoothnose Wedgefish (R. laevis). Landings declined by 66% over this period, which is the equivalent of a 91% population reduction over the last three generations of the Whitespotted Wedgefish (45 years).
While this is the only time-series data available for the range of the Whitespotted Wedgefish, fishing pressure (‘actual levels of exploitation’) is high across the range of this species with the exception of South Africa (see Threats section), and there is nothing to suspect that similar declines have not occurred across large areas of the Western Indian Ocean. The following provides some species-specific examples of the situation relevant for the Whitespotted Wedgefish which supports this conclusion.
In southern Mozambique, anecdotal reports suggest that artisanal longline fishing led to declines in the Whitespotted Wedgefish (which was one of the main target species of the fishery) as this species was abundant on reefs before longline fisheries began in the early 2000s and subsequently are only seen in low numbers (Pierce et al. 2008). In Zanzibar, fisher interviews indicated that there were perceived declines in wedgefish or that they are rare (Schaeffer 2004); wedgefishes were a retained bycatch of commercial prawn trawling in Tanzania (Rose 1996), and intense fishing pressure across the Tanzanian shelf is likely resulted in population reduction mirroring those outlined above for the Indo-West Pacific more broadly. In Madagascar, there was a decrease in the size of wedgefish caught in artisanal fisheries over time (Humber et al. 2017), thought, in part, could be due to the targeting of larger individuals. A steep decline in catch-per-unit-effort (CPUE) can be inferred from reported catch reductions from 10-20 sharks per day in 1992 to 1-3 sharks per day in 1995 in Morondava, West Madagascar, with fishers moving further afield to fish (Cooke 1997). Whitespotted Wedgefish, a high-value target species, would likely have declined by a similar order of magnitude.
In South Africa, although the Whitespotted Wedgefish reaches the Eastern Cape Province, it is common only in KwaZulu-Natal (KZN). There was a marked decline in CPUE of the species in shark bather protection nets in KZN during the period 1979-2017 (Nomfundo Nakabi, KZN Sharks Board, pers. comm. 2018). This decline is not considered to be a good indicator of population reduction as it may be explained, at least partially, by shift in gear deployment whereby nets were gradually lifted off the substrate (which would reduce the capture of demersal rays).
Overall, it is inferred that this species has undergone a >80% population reduction due to actual levels of exploitation over the last three generations (45 years) and it is assessed as Critically Endangered A2bd.
HABITAT AND ECOLOGY
The Whitespotted Wedgefish occurs from close inshore (including the surf zone) to depths of 70 m on the continental shelf (usually shallower than 35 m) (van der Elst 1988, Last et al. 2016). Maximum size is 310 cm total length (TL) (typically smaller); males mature at ~150 cm TL (Last et al. 2016). Reproduction is lecithotrophic viviparous with a small litter size ~4 pups; size at birth is ~60 cm TL (van der Elst 1988, Last et al. 2016). Generation length is estimated as 15 years (see the Supplementary Information). The species appears to be partially migratory, as it is common in coastal waters of KwaZulu-Natal, South Africa during the summer, with tagged animals traveling a mean distance of 49 km, reflecting locals movements only, while it occurs in much lower numbers during the winter; presumably it migrates northwards into warmer waters (van der Elst 1988, Young 2001, Mann 2003).
USE AND TRADE
Wedgefishes are heavily utilized across their range for the meat and fins. While little species-specific information is available, the following provides a generalized account of use and trade globally. The meat is of good quality and a food source for many coastal communities in tropical countries where it is generally consumed locally, although it also enters the international trade in dried and salted form (e.g. Moore 2017, Jabado 2018). Large whole wedgefishes (>200 cm total length; TL) have been traded for a high value of up to US$680 each, however, smaller specimens can sell for low value (e.g. Jabado 2018). The ‘white’ fins of shark-like rays (including wedgefishes and giant guitarfishes) are considered the best quality fins for human consumption and are among the highest valued in the international shark fin trade (Suzuki 2002, Dent and Clarke 2015, Moore 2017). Fin prices in the literature include US$396/kg for wedgefish fins (Chen 1996) and an average price of US$276/kg and US$185/kg for Qun chi (fins from shark-like rays) in Guangzhou (mainland China) and Hong Kong, respectively (Hau et al. 2018). The skin may be dried and traded internationally as a luxury leather product (Haque et al. 2018). The eggs of shark-like rays are sometimes dried and consumed locally while the heads may also be dried and used as either fish meal or fertilizer (Haque et al. 2018, R.W. Jabado unpubl. data).
CONSERVATION ACTIONS
There are limited species-specific conservation or management measures in place for wedgefishes. Some localized protections, trawl bans, finning bans, as well as general fisheries management and marine protected areas likely benefit this species, although in some areas, effective enforcement is an ongoing issue. The Whitespotted Wedgefish is protected in South Africa; catching or possession of the species is not legal without a valid permit. India has protected Rhynchobatus djiddensis since 2001 under Schedule 1 of the Wildlife (Protection) Act of 1972 making its capture, landing, and trade illegal (Jabado et al. 2017). However, the reclassification of wedgefishes (Last et al. 2016) indicated that R. djiddensis does not occur in India, but the species present there are R. australiae and R. laevis, which are currently not listed under the Act. The Bangladesh Wildlife (Conservation and Security) Act, 2012 protects Rhynchobatus djiddensis under Schedule I, but again, the species occurring in Bangladesh are R. australiae and R. laevis (Last et al. 2016).
In the Arabian/Persian Gulf, Kuwait bans the catches of all rays; and in the Red Sea, all sharks and rays are protected in Israel (although both countries represent a very small part of the species range). The United Arab Emirates (UAE), Qatar, and Oman have banned trawling in their waters (since 1980, 1993 and 2011, respectively), and other countries have seasonal trawl closures that may benefit the species. Finning (i.e. removing fins and discarding the body at sea) has been banned in several range states including the UAE, Oman, Iran, and Israel. This may have reduced the retention of animals solely for their fins, but fins are still traded when whole animals are landed. A Ministerial Decree issued by the UAE Ministry of Climate Change and Environment (MOCCAE) in 2019 imposes a permanent ban on fishing in UAE waters for shark species listed on CITES, and on CMS.
Annex 1 of the Memorandum of Understanding on the Conservation of Migratory Sharks (Sharks MOU) lists species that have an unfavourable conservation status and would significantly benefit from collaborative international conservation action. Currently (February 2019) 36 shark and ray species are included in Annex 1 of the Sharks MOU, including Rhynchobatus australiae, R. djiddensis, and R. laevis.
To conserve the population and to permit recovery, a suite of measures will be required which may include species protection, spatial management, bycatch mitigation, and harvest and trade management measures (including international trade measures). Effective enforcement of measures will require ongoing training and capacity-building (including in the area of species identification). Catch monitoring, including in artisanal fisheries, is needed to help understand population trends and inform management. Finally, taxonomy needs to be further resolved to improve certainty of species identification.
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