| Citation |
Kyne, P.M., Rigby, C.L., Dharmadi & Jabado, R.W. 2019. Rhynchobatus australiae. The IUCN Red List of Threatened Species 2019: e.T41853A68643043. http://dx.doi.org/10.2305/IUCN.UK.2019-2.RLTS.T41853A68643043.en. Downloaded on 31 July 2019. |
Description |
JUSTIFICATION
The Bottlenose Wedgefish (Rhynchobatus australiae) is a large (to ~300 cm total length) shark-like ray which is widespread in the Indo-West Pacific from Mozambique to the Solomon Islands and north to Taiwan. It occurs in coastal and continental shelf waters from close inshore to depths of at least 60 m. The taxonomy of the whitespotted wedgefish species-complex (which includes several Indo-West Pacific wedgefishes) is not fully resolved, and the distribution of the Bottlenose Wedgefish may be refined when more information comes to light. Wedgefishes have limited biological productivity; the Bottlenose Wedgefish has litter sizes of 7-19 pups and an estimated generation length of 15 years. The ‘white’ fins of shark-like rays (including sawfishes, 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. The meat is of high quality and generally consumed locally. There is a high level of fisheries resource use and increasing fishing pressure across the range of the Bottlenose Wedgefish, and as a result, targeted and incidental fishing effort is placing significant pressure on all wedgefish species in the Indo-West Pacific. Where wedgefishes and giant guitarfishes have been targeted or exploited as incidental catch, severe declines, population depletions, and localized disappearances have occurred. Severe population reduction in the Bottlenose Wedgefish is inferred from actual levels of exploitation, as well as several historical accounts and contemporary datasets from Iran, Pakistan, India, Thailand, and Indonesia. While some parts of Australasia provide refuge from intense fishing effort, this proportion of the species’ range is not considered to be large enough relative to the global range to lower the assessment. It is inferred that the Bottlenose Wedgefish has undergone a >80% population reduction over the last three generations (45 years) and it is assessed as Critically Endangered A2bd.
RANGE DESCRIPTION
The Bottlenose Wedgefish is widespread in the Indo-West Pacific from Mozambique through the Western Indian Ocean, the Arabian Sea, Southeast Asia, and extending north to Taiwan, south to Australia (where it is wide-ranging across the north of the continent), and east to the Solomon Islands (Last et al. 2016, Hylton et al. 2017). 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 e.g. the Aru Islands gillnet fishery). 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, with some of the highest increases in the Asian region (Anticamara et al. 2011, Watson et al. 2013). To infer population reduction for Indo-West Pacific wedgefishes, four relevant historical accounts are presented below, followed by five 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.
With regards to historic perspectives, firstly, research trawl survey data from the Gulf of Thailand showed a 93% decline in catch rates of Rhinobathidae (a name that is likely to include wedgefishes and guitarfishes broadly) from peak catches in 1968 to a low in 1972 (Ritragsa 1976, Pauly 1979). Similarly, catch rates of rays declined by 92% from 1963 to 1972. Secondly, the Indonesian Aru Islands wedgefish gillnet fishery rapidly expanded from its beginnings in the mid-1970s to reach its peak in 1987 with more than 500 boats operating before catches then declined very rapidly with only 100 boats left fishing in this area in 1996 (Chen 1996). Thirdly, investors in Indonesia withdrew from a wedgefish fishery in the Malaku and Arafura Seas because the resource had been overfished by 1992 resulting in limited returns for their investment (Suzuki 2002). Lastly, research trawl surveys in the Java Sea showed the decline of rays between 1976 and 1997 by at least an order of magnitude (i.e., a decline of at least 90%) (Blaber et al. 2009). It is worth noting that recent trawl surveys in the Java Sea recorded only a single individual Rhynchobatus (Tirtadanu et al. 2018), and in the North Natuna Sea (which is north of the Java Sea), trawl surveys recorded only two individuals (Yusup et al. 2018).
Five contemporary datasets are available for landings data or catch rates at varying levels of taxonomic resolution (e.g., whitespotted wedgefish, guitarfishes etc.) from Iran, Pakistan, western and eastern India, and Indonesia. These datasets likely include various species of wedgefishes and in each case probable species are listed. One dataset (Raje and Zacharia 2009) does not include wedgefishes but rather presents landings data for myliobatoid rays (stingrays, eagle rays, butterfly rays, and devil rays). However, this can be used to infer declines in wedgefishes given overlapping distributions, habitat, and susceptibility to capture in the same fishing gear. Data used to calculate proportional declines, annual proportional change, and population reduction over three generation lengths are provided in the Supplementary Information.
Firstly, landings data for the giant guitarfish category are available from Iran 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, Whitespotted Wedgefish (Rhynchobatus 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 Bottlenose Wedgefish (45 years).
Secondly, landings data for the rhinobatid category are available from Pakistan for 1993-2011 (19 years; Tables 3 and 4 in the Supplementary Information) covering the country’s two coastal provinces (M. Gore unpubl. data). This grouping likely includes all rhinids, glaucostegids, and rhinobatids occurring locally, including Bowmouth Guitarfish, Bottlenose Wedgefish, and Smoothnose Wedgefish. Data from Sindh province (Table 3) showed a 72% decrease from peak landings in 1999 to a low in 2011, and data from Balochistan province (Table 4) showed an 81% decrease from landings in 1994 to a low in 2011. These decreases are the equivalent of 98-99% population reduction over the last three generations of the Bottlenose Wedgefish (45 years).
Thirdly, catch data for myliobatoid rays (this includes a variety of demersal rays, but does not include rhinopristoids) are available from Maharashtra, western India for 1990-2004 (15 years; Table 5 in the Supplementary Information) (Raje and Zacharia 2009). The catch rate declined by 63% over this period, while fishing effort doubled, which is the equivalent of a 95% population reduction over the last three generations of the Bottlenose Wedgefish (45 years).
Fourthly, landings data for guitarfishes are available from Tamil Nadu, eastern India for 2002-2006 (5 years; Table 6 in the Supplementary Information) (Mohanraj et al. 2009). This grouping was reported in the paper to include Bowmouth Guitarfish and R. djiddensis, and hence would therefore include Bowmouth Guitarfish, Bottlenose Wedgefish, and Smoothnose Wedgefish. Landings declined by 86% over this period. Furthermore, species-specific trawl landings data were reported for R. djiddensis (i.e. Bottlenose Wedgefish and Smoothnose Wedgefish), with a decline of 87% over this period. This time-period is too short to derive equivalent population reduction over three generations.
Lastly, landings data for whitespotted wedgefishes are available from Indonesia for 2005-2015 (11 years; Table 7 in the Supplementary Information) (DGCF 2015, 2017). This grouping likely includes Bowmouth Guitarfish, Bottlenose Wedgefish, Clown Wedgefish (R. cooki), Eyebrow Wedgefish (R. palpebratus), and Broadnose Wedgefish. Landings declined by 88% over this period, which is the equivalent of a >99% population reduction over the last three generations of the Bottlenose Wedgefish (45 years). An additional data point available for 2016 is excluded from this analysis. This datum suggests a massive increase in reported landings which is an artefact of the inclusion of a wider range of batoids in the reported figure (DGCF 2017).
The one region in which the Bottlenose Wedgefish may be in a better state than most of their range is Australia, where fishing effort is relatively low, Turtle Exclusion Devices reduce catches of large rays by 94% (Brewer et al. 2006), and there are controls on their catch and retention. Estimates of fishing mortality rates in the Northern Prawn Fishery (the main fishery to interact with this species) for this, and similar species, are well below those that would lead to significant population declines (Zhou and Griffiths 2008).
Fishing pressure (actual levels of exploitation) is high across the range of this species (see Threats section), and the above information can be considered representative of population reduction throughout the Indo-West Pacific (with the exception of some parts of Australasia). Australia and Papua New Guinea provide some refuge for the species, however, this proportion of the species’ range is not considered to be large enough relative to the global range to lower the assessment. Overall, it is inferred that the Bottlenose Wedgefish has undergone a >80% population reduction over the last three generations (45 years) and it is assessed as Critically Endangered A2bd.
HABITAT AND ECOLOGY
The Bottlenose Wedgefish occurs from close inshore to depths of at least 60 m on the continental shelf (Last et al. 2016). It occurs over soft substrates, but can also be associated with coral reefs. Maximum size is ~300 cm total length (TL); males mature at 110-130 cm TL; females mature at ~155 cm TL (White and Dharmadi 2007, Last and Stevens 2009, Last et al. 2016). Reproduction is lecithotrophic viviparous with litter sizes of 7-19 pups (mean of 14); size at birth is 46–50 cm TL (White and Dharmadi 2007, Last and Stevens 2009). Generation length is estimated as 15 years (see the Supplementary Information).
THREATS
Globally, wedgefishes are subject to intense fishing pressure on their coastal and shelf habitats that is unregulated across the majority of their distributions. Wedgefishes are captured in industrial, artisanal, and subsistence fisheries with multiple fishing gears, including gillnet, trawl, hook and line, trap, and seine net and are generally retained for their meat and fins (Bonfil and Abdallah 2004, White and Sommerville 2010, Moore 2017, Jabado 2018). There is a high level of fisheries resource use and increasing fishing pressure across the range of the Bottlenose Wedgefish, and demersal coastal fisheries resources have been severely depleted in significant areas of the Indo-West Pacific, including India and Southeast Asia (Stobutzki et al. 2006, Mohamed and Veena 2016). Fishing pressure is however considerably lower across northern Australia.
In general, fishing effort and the number of fishers has increased in recent decades across the range of this species, with demand for shark and ray product increasing over the same period due to the shark fin trade (Chen 1996, Jabado et al. 2017). In the Red Sea for example, the number of traditional boats tripled from 3,100 to 10,000 from 1988 to 2006 (Bruckner et al. 2011), and in the Indian state of Gujarat, the number of trawlers increased from about 6,600 in the early 2000s to 11,582 in 2010 (Zynudheen et al. 2004, CMFRI 2010, Jabado et al. 2017). All Indian states have high numbers of trawlers (e.g. as reported in 2010: Maharashtra, 5,613 trawlers; Kerala, 3,678 trawlers, Tamil Nadu, 5,767 trawlers; total trawlers in India: 35,228) and a high number of gillnetters (total of 20,257 as reported in 2010), and most countries have significant fishing fleets operating in coastal waters e.g. Oman (19,000 artisanal boats), Pakistan (2,000 trawlers), Sri Lanka (24,600 gillnet vessels operating in 2004), and Indonesia (~600,000 fishing vessels in marine waters) (Dissanayake 2005, CMFRI 2010, KKP 2016, Jabado et al. 2017).
Sharks and rays, including wedgefishes, are often targeted and now heavily exploited across the region by net and trawl fisheries and increasing fishing effort has put significant pressure on all wedgefish species in the Indo-West Pacific. Furthermore, the high value of fins is driving retention and trade of wedgefishes globally and the targeting of wedgefishes for their fins has also been reported in numerous countries, including Indonesia, Malaysia, Mozambique, and Tanzania (Barrowclift et al. 2017, Moore 2017, Jabado 2018). The Bottlenose Wedgefish is landed throughout its range (e.g. White and Dharmadi 2007, Last et al. 2010, Jabado 2018) and several countries within the distribution of this species rank among the top 20 shark fishing nations globally, specifically Indonesia, India, Taiwan, Pakistan, Malaysia, Thailand, Sri Lanka, and Iran (Lack and Sant 2011). Wedgefishes have been targeted in Indonesia since the 1970s, and these target fisheries have shifted spatially in response to localized depletions (Chen 1996, White and Dharmadi 2007, White and Sommerville 2010, Last et al. 2016, W.T. White, pers. comm. 2015).
Fishing pressure is considerably lower across northern Australia and in Papua New Guinea, which provides some refuge for this species. The degree of connectivity with Indonesia and elsewhere is unknown, and if animals regularly move into Indonesian waters they would face significantly higher levels of fishing pressure there. There are no target fisheries for this species in Australia, but it is taken as bycatch in numerous non-target fisheries (e.g. Stobutzki et al. 2002, White et al. 2013). The introduction of Turtle Exclusion Devices in northern and eastern Australian prawn trawl fisheries is likely to have significantly reduced this species mortality in trawl fishing gear (Brewer et al. 2006).
Illegal, unreported, and unregulated (IUU) fishing is known to occur in some parts of the range, for example by foreign and regional trawlers in Somalia and Yemen, with wedgefish specifically targeted off East Africa (IOTC 2005, Jabado et al. 2017). In northern Australia, wedgefish account for a minor component of the IUU fishing. The IUU activity peaked in the mid-2000s, and although vessel numbers have declined since then, there is still some illegal fishing in the region (Field et al. 2009, Marshall 2011, Harward and Bergin 2016).
The shallow, inshore soft-bottom habitat preferred by the species is threatened by habitat loss and environmental degradation (Stobutzki et al. 2006, White and Sommerville 2010, Moore et al. 2012, Jabado et al. 2017, Moore 2017). In the Arabian Sea and adjacent waters, dredging and coastal land reclamation has increased in recent years and has resulted in almost total loss of mangroves in some areas, such as Bahrain (Sheppard et al. 2010, Jabado et al. 2017), while Southeast Asia has seen an estimated 30% reduction in mangrove area since 1980 (FAO 2007, Polidoro et al. 2010).
USE AND TRADE
Wedgefishes are heavily utilized across their range for the meat and fins. The exception for this species is Australia where wedgefishes are generally not utilized or traded. 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 Bottlenose Wedgefish was listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS) in 2017 which aims to provide a framework for the coordination of measures adopted by Range States to improve the conservation of the species. 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). 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). Furthermore, the bans enacted under this legislation have not been implemented (Haque et al. 2018).
Kuwait bans the catches of all rays, and all sharks and rays are protected in Israel (although both countries represent a very small part of the species range). Balochistan province in Pakistan protects all guitarfishes and wedgefishes and therefore this species is specifically protected in that province, while in Sindh province there are protections for juvenile guitarfishes and wedgefishes (less than 30 cm), including this species. The United Arab Emirates (UAE), Qatar, and Oman have banned trawling in their waters (since 1980, 1993 and 2011, respectively), Malaysia has banned trawling in inshore waters, 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, Israel, and Australia. 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. In Australia, Queensland has a recreational possession limit of one shark or ray, and the Northern Territory a possession limit of three.
In the major prawn trawl fisheries of northern and eastern Australia, the bycatch of large elasmobranchs has been significantly reduced since 2000 with the use of Turtle Exclusion Devices in trawl nets (e.g. Brewer et al. 2006). In Queensland commercial net fisheries, there is a trip limit of five wedgefishes (DAFF 2009) and in the Northern Territory and Western Australia there are prohibitions on retention of any shark product in several non-target shark fisheries.
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. |
