There are limited species-specific conservation or management measures in place for giant guitarfishes. 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 Sharpnose Guitarfish is protected in Bangladesh under Schedule I of the Bangladesh Wildlife (Conservation and Security) Act, 2012. However, this legislation has not been implemented (Haque et al. 2018).
Kuwait bans the catches of all rays. 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), 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, and Iran. 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.
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.
Location InformationThe Sharpnose Guitarfish is moderately widespread in the northern Indian Ocean, where it occurs from the Arabian/Persian Gulf to Myanmar (Last et al. 2016b). This species has been confused with the Giant Guitarfish (Glaucostegus typus) and Pacific Ocean records of the Sharpnose Guitarfish are probably referable to that species.
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 giant guitarfish 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.
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 giant guitarfishes, 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. All of the historical accounts, and one of the five contemporary datasets are outside the known range of the Sharpnose Guitarfish, but are informative for understanding population reduction in giant guitarfishes more broadly.
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) (it is suspected that this fishery caught giant guitarfishes as well as wedgefishes). 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).
Five contemporary datasets are available for landings data or catch rates at varying levels of taxonomic resolution (e.g. 'guitarfishes' etc.) from Iran, Pakistan, western and eastern India, and Indonesia. These datasets likely include various species of giant guitarfishes and in each case probable species are listed. One dataset (Raje and Zacharia 2009) does not include giant guitarfishes 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 giant guitarfishes 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 Sharpnose Guitarfish and Halavi Guitarfish (Glaucostegus halavi). Landings declined by 66% over this period, which is the equivalent of a 91% population reduction over the last three generations of the Sharpnose Guitarfish (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 Sharpnose Guitarfish, Halavi Guitarfish, and Widenose Guitarfish (G. obtusus). 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 Sharpnose Guitarfish (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 Sharpnose Guitarfish (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 Sharpnose Guitarfish and Widenose Guitarfish but was also likely to include Giant Guitarfish (G. typus) and Clubnose Guitarfish (G. thouin). Landings declined by 86% over this period. Furthermore, species-specific trawl landings data were reported for the Sharpnose Guitarfish, with a decline of 94% 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 may include giant guitarfishes, but in any case, the trends can be considered representative of glaucostegids as well as rhinids. Landings declined by 88% over this period, which is the equivalent of a >99% population reduction over the last three generations of larger glaucostegid species (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).
Additionally, during research trawl surveys in United Arab Emirates (UAE) waters, the Sharpnose Guitarfish was the most common guitarfish in 2002, but was not captured during similar surveys in 2016 (Edwin Grandcourt, pers. comm., 08/02/17).
Fishing pressure ('actual levels of exploitation') is high across the range of this species (see Threats section), and while some of these datasets are outside the range of the Sharpnose Guitarfish, they can be considered representative of population reduction throughout the Indo-West Pacific (with the exception of some parts of Australasia). Overall, it is inferred that the Sharpnose Guitarfish has undergone a >80% population reduction over the last three generations (45 years) and it is assessed as Critically Endangered A2bd.
Globally, giant guitarfishes are subject to intense fishing pressure on their coastal and shelf habitats that is unregulated across the majority of their distributions. Giant guitarfishes 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 Sharpnose Guitarfish, 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).
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 Indian state of Gujarat for example, 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. Pakistan (2,000 trawlers) and Sri Lanka (24,600 gillnet vessels operating in 2004).
Sharks and rays, including giant guitarfishes, 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 giant guitarfish species in the Indo-West Pacific. Furthermore, the high value of fins is driving retention and trade of giant guitarfishes globally (Moore 2017, Jabado 2018). The Sharpnose Guitarfish is landed throughout its range (e.g., Moore et al. 2012) and several countries within the distribution of this species rank among the top 20 shark fishing nations globally, specifically India, Pakistan, Sri Lanka, and Iran (Lack and Sant 2011).
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).