In India, the Ganges Shark is one of 10 species of chondrichthyans protected under Schedule I, Part II A of the Indian Wildlife (Protection) Act, 1972 (Government of India Ministry of Environment and Forests 2006). However, the effectiveness of this measure is unknown, with ongoing issues in enforcement and compliance. In Bangladesh, the Ganges Shark has been protected since 2012 under Schedule I of the Wildlife (Conservation and Security) Act, 2012, however the effectiveness of this measure is limited due to a general lack of awareness of the protection among fishers and traders (Haque and Das 2019). The species could benefit from some protection in the Sundarbans World Heritage Area, if regulations are enforced. In Myanmar, two shark reserves were designated in the Myeik Archipelago in 2004 where targeting sharks and rays is prohibited (Notification 2/2004) (Howard et al. 2015). In 2008, a nationwide ban on the targeting of sharks was announced. Despite the nationwide ban, sharks and rays continue to be captured in large numbers, partly because there is little or no enforcement, and little knowledge of the ban in fishing communities (MacKeracher et al. 2020).
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 is needed to help understand population trends and inform management.
The Ganges Shark has a patchy distribution across the Indo-West Pacific (Li et al. 2015). It is difficult to ascertain its historical distribution. In Pakistan, there are several records from fishers and jaw traders in the Karachi, Sindh Province of Pakistan (mostly from 2001 to 2005) that are likely from south of Karachi and lower Indus River and the adjacent inshore coast (Jabado et al. 2018). There is no suitable habitat for the species west of the Indus River (Jabado et al. 2017). There is a single record of an adult landed in Mumbai in 2016 on the west coast of India, although it is unlikely to have been caught locally (Jabado et al. 2018). It is known from the lower Ganges River Basin, West Bengal, India with most historic records from the Hooghly River, and east to at least the Bangladesh-Myanmar border (Ebert et al. 2013, Chowdhury et al. 2017, Haque and Das 2019). In Myanmar, it is known from a single 19th century specimen collected in the Yangon River (originally described as Carcharhinus siamensis) (Li et al. 2015). In Sabah, Borneo, the species is known from 14 specimens collected from the Kinabatangan River in 1996–2003 (described as Glyphis fowlerae) and it was previously recorded from Borneo around the turn of the 20th century (Compagno 1984, Compagno et al. 2010, Last et al. 2010). In Indonesia, a set of jaws obtained in Cirebon, Java, were identified as Ganges Shark (Li et al. 2015). Due to a lack of local suitable habitat, and Cirebon’s position as a major trading node of fish products, it is likely that this specimen originated elsewhere.
Bangladesh, India, Malaysia
Genetic data indicate contemporary gene flow in the Ganges Shark between Pakistan, India, Bangladesh, Myanmar, and Borneo (Li et al. 2015). However, gene flow is contemporary in an evolutionary sense and these data cannot yet resolve the time frame within the past 10,000 years (G.J.P. Naylor pers. comm. 2021). High resolution genetic population analyses of two congeners, the Northern River Shark (Glyphis garricki) and Speartooth Shark (Glyphis glyphis) revealed a very high degree of population differentiation over a small geographic scale. There was a significant differentiation of populations separated by just 200 km and these data are consistent with genetically distinct subpopulations in each of the separate areas of their ranges (Feutry et al. 2020). This may also be the case for the Ganges Shark and it is likely that there are possible subpopulations in each of the separate parts of its known range. Records of the Ganges Shark are sparse and the species is considered extremely rare (Jabado et al. 2017). Extensive surveys of sharks and rays have recorded few additional records of this species across its known range, including around the western India, Bay of Bengal, Indo-Malay Archipelago, and the South China Sea. These surveys include: India (e.g., Akhilesh et al. 2014, Raje et al. 2015, Jabado et al. 2018), Bangladesh (Haque and Das 2109, S. Chakma pers. comm. 10 November 2018), Thailand (e.g., Arunrugstichai et al. 2018), Borneo (e.g., Last et al. 2010, Manjaji-Matsumoto et al. 2016), eastern Indonesia (e.g., >21,000 sharks recorded in over six years of surveys but this species not recorded; White 2007), southern China (e.g., Lam and Sadovy de Mitcheson 2011), and the Philippines (e.g., Compagno et al. 2005). Photographs of a carcharhinid from the Philippines in 2000 "may possibly be this species" but were insufficient to confirm the identification (Compagno et al. 2005).
The historical population size is unknown, but there is little doubt the population has been severely depleted due to a long history of intensive and largely unregulated riverine and coastal fisheries and other threats in its habitat (Compagno and Cook 1995). There has been a significant increase in coastal fishing effort and engine power in the Indo-Pacific region and there has been increased demand for sharks since the 1970s due to growing coastal human population densities and international trade in shark products, including the fin trade (e.g., Henderson et al. 2007, Jabado et al. 2015).
In Pakistan, significant declines in shark catches have been reported for the last 15 years (Khan 2012). While there is limited information available on the Ganges Shark in the Pakistan region, its large size and the presence of intensive fisheries mean that, like many other large carcharhinids in the region, it is likely to have severely declined. There have been no known records from Pakistan since 2005. The last known record for Pakistan was a set of jaws collected from commercial gillnet landings at the Manora Basin in 2005, estimated to be from an individual approximately 275 cm total length (M. Harris pers. comm. 9th June 2017). In 2001–2002, a small number of jaws were also collected from commercial gillnet landings in Karachi, with most from sharks estimated to be approximately 180–200 cm total length. This species is likely to have occurred in similar habitats to the Pondicherry Shark (Carcharhinus hemiodon) which was formerly found in the Indus river in the 1950–1960s and searches for that species, since 1980s, have failed to find it (Kyne et al. 2021, M. Moazzam Khan pers. comm. 6 February 2017). Further, the catch of Pakistani fishing vessels has been extensively monitored at major landing centres since 1987 but neither this species nor the Pondicherry Shark have been recorded (M. Moazzam Khan pers. comm. 6 February 2017). Given this level of search effort, records of Ganges Shark would be expected to have appeared and been recorded if present, and it is possibly recently locally extinct in Pakistan.
In India, landing site surveys have failed to record this species (e.g., Akhilesh et al. 2014, Raje et al. 2015). There is only one recent record in west Indian waters (Jabado et al. 2018), indicating (like elsewhere in its range), that the Ganges Shark is extremely rare. Furthermore, reports from India indicate that several shark stocks, including small-bodied and relatively resilient whaler sharks, such as Spadenose Shark (Scoliodon laticaudus), Milk Shark (Rhizoprionodon acutus), and 'blacktip' sharks (Carcharhinus spp.), are either declining or have already collapsed (Mohamed and Veena 2016), likely as a result of dramatic increases in fishing pressure. Across India, landings of elasmobranchs have declined by 44% from 1998–2018 (CMFRI 1999, 2019; Gupta et al. 2020). There have been steep declines in sharks and rays that are captured in trawl and gillnet fisheries. For example, the Milk Shark is a small resilient shark yet the overall stock biomass was estimated to have reduced by 55% of unexploited levels based on a stock assessment of this species from landings during 2012–2014 in Gujarat, India (Sen et al. 2017).
In Bangladesh, reconstructed elasmobranch landings data showed a 34% decline in landings over 15 years from 2000–2014. Catches gradually rose from 195 t in 1950 to 7,540 t in 1973 then declined to 3,500 t in the mid-1980s, rose steeply to a peak of 10,909 t in 2000 followed by a fluctuating decline to 7,163 t in 2014 (Pauly et al. 2020). Surveys of Bangladeshi fisheries and markets in 2016–2017 identified three records of the Ganges Shark; one from a landing site and two from fins at shark processing centres; a possible few more specimens were present: however, they need further identification (Haque and Das 2019, A.B. Haque unpubl. data 2021). The tidal river systems of the Sundarbans and the coastal waters of Bangladesh provide suitable habitat for the Ganges Shark and there is possibly a population of this species in Bangladesh that has not been detected due to a lack of systematic surveys and species level identifications (Haque and Das 2019). Communications with local scientists and surveys of local fishers have revealed that there has been a significant decline in carcharhinid catch and size over the last 5–10 years in Bangladesh (A. B. Haque pers. comm. 15 October 2020). In 2010–2016 there were 7–8 trawlers that were targeting larger sharks (carcharhinids) but with a decline in catch, these vessels have been forced to target other species.
In Myanmar, there have been no recent records of this species and recent landings surveys in nearby Thailand have failed to record this species (e.g., Arunrugstichai et al. 2018). In Malaysian Borneo, this species was originally described from 15 specimens, with all but one collected from the Kinabatangan River. Most specimens were collected during 1996–1997 surveys with the remainder of the specimens collected in 1999 and 2003 (Compagno et al. 2010). Recent targeted surveys designed to detect this species and sawfishes in the known area of occurrence in the Kinabatangan River in Borneo failed to document any individuals (Manjaji-Matsumoto et al. 2016). Sixteen sites were sampled (using rod and line, longline, and gillnets) along the Kinabatangan River from 18–23 September 2015. During this survey two individual elasmobranchs were captured; a Giant Freshwater Stingray (Urogymnus polylepis) and a Bull Shark (Carcharhinus leucas). The authors document that, "fishermen report that catches of Ganges Shark are very rare (rarer than Giant Freshwater Stingray), and are reportedly caught more often in the dry season" (Manjaji-Matsumoto et al. 2016). Further fieldwork on 20–24 August 2016 resulted in three additional captures of Giant Freshwater Stingray. Further sporadic field work in Northeast Borneo (Pitas District, within the Kudat-Banggi Priority Conservation Area) resulted in an unverified record of a river shark from Bengkoka River, based on interview with a local fisher (Manjaji-Matsumoto et al. 2016). Further work in the Pitas District rivers estuaries and nearshore areas in March, April, and May 2016 revealed only captures of rays and brief surveys of local fishers and fish markets failed to reveal any Ganges Sharks (Manjaji-Matsumoto et al. 2016). The reports of local fishers suggest that the Ganges Shark may still persist in the Kinabatangan River (Manjaji-Matsumoto et al. 2016); however, without any confirmed recent identifications, it is possible that the Ganges Shark has recently become locally extinct in Sabah, Borneo. It is also possible that the species has become locally extinct in Myanmar.
The Largetooth Sawfish (Pristis pristis) formerly occurred in rivers in eastern Borneo, with the last record confirmed from the Kinabatangan River in 1996 (Manjaji-Matsumoto et al. 2016). There have been no verified sightings of sawfishes (Pristidae spp.) from either the Kinabatangan River or rivers in the Kudat-Banggi Priority Conservation Area, yet they were formerly present there (Manjaji 2002). While the sawfishes are potentially more sensitive to fishing mortality and more readily captured due to their toothed rostra than the Ganges Shark, the local extinction of Largetooth Sawfish and Dwarf Sawfish (Pristis clavata) from Malaysia gives an indication of the high levels of fishing mortality in rivers in Borneo, and Southeast Asia more generally (Yan et al. 2021).
Overall, based on historic and ongoing intensive and largely unregulated riverine and coastal fisheries in its habitat and no refuge from fishing pressure, it is suspected that the species has undergone a population reduction of >80% over the past three generation lengths (54 years). It is possibly locally extinct in Pakistan, Myanmar, and Borneo with the limited recent records only from west and east India and Bangladesh. In addition, given the rarity of contemporary records, it is estimated that the number of mature individuals of the Ganges Shark is very small (<250) with small numbers (<50) of mature adults in each subpopulation and an inferred continuing decline due to ongoing intensive and unmanaged fishing pressure and habitat threats across its entire range. The species is assessed as Critically Endangered A2cd; C2a(i).
The species is caught as bycatch in subsistence, small-scale, and industrial fisheries and retained for its meat and fins. The Ganges Shark occupies large tidal rivers, estuaries and coastal areas. The habitat specificity of the Ganges Shark increases its susceptibility to the impacts of human activities, particularly fishing and habitat modification. The habitat of this species is subject to intense anthropogenic pressure, from river and coastal fisheries, habitat degradation and pollution (including untreated discharge from industrial and chemical plants), increasing river use, sand mining in rivers, power plants, and the construction of dams and barrages which alter flow and affect river productivity (Compagno and Cook 1995, Sen and Mandal 2019). For example, in Pakistan, there are four large dams and 22 barrages on the Indus River, with several more proposed (Braulik et al. 2015). Barrages have fragmented the river habitat, with fragment size declining steadily as more barrages were built (Braulik et al. 2015). The construction of barrages also led to the collapse of the commercial Hilsa Shad (Tenualosa ilisha) fishery due to the disruption of their migration (Braulik et al. 2015). Due to habitat overlap it is likely that this fishery caught juvenile Ganges Shark as bycatch, while net entanglement would be an ongoing threat in the river if juvenile Ganges Sharks persist. Ganges Sharks landed in Karachi and the Manora Basin in the early 2000s were caught by a commercial gillnet fishery that operated mostly in shallow coastal waters south of Karachi, and around the Indus River mouth (M. Harris pers. comm. 9 June 2017).
In India, there is a high level of fisheries exploitation with most stocks fully exploited (FAO 2020). The number of trawlers operating in the Indian state of Gujarat (one of the major shark catching regions) has almost doubled from ~ 6,600–11,582 for the period 2000–2010 (Zynudheen et al. 2004, CMFRI 2010). There are over 80,255 active fishers operating along the West Bengal coast, with most of the mechanized vessels using gill nets (CMFRI 2012). Bangladesh has a substantial artisanal and subsistence fishing fleet that operates throughout the Sundarbans and coastal regions (Haque and Das 2019). In 2017–2018 there were 67,669 vessels reported to be operating in addition to illegal, unreported, and unregulated fishers (Shamsuzzaman et al. 2017, DoF 2018). Fishing effort has increased substantially since 1950 and dramatically in recent years, with a four-fold increase from 2000 to 2014 (Ullah et al. 2014, Pauly et al. 2020). Three specimens of Ganges Shark were caught as bycatch and retained by artisanal fishers in Bangladesh using a range of fishing gear which may have included drift gillnets, trammel nets, and long lines (Haque and Das 2019). Severe habitat degradation is ongoing throughout the Sundarbans and associated rivers. This is driven by high human population density resulting in pollution (general, agricultural, chemical, sewage, and industrial), over-harvesting of fisheries resources, vegetation removal, and upstream river engineering (e.g., Barman 2007, Sen and Mandal 2019, Sievers et al. 2020).
In Myanmar, fishing effort has been increasing since 1950 across subsistence, artisanal, and industrial fisheries (Pauly et al. 2020). The number of vessels across all sectors has increased substantially from 2,000 vessels in 1950 to 125,222 vessels in 2014, with >80% of the fleet subsistence fisheries (Pauly et al. 2020). In Malaysian Borneo, hydroelectric and reservoir dams, and habitat degradation through land clearing and pollution throughout the area (Chong et al. 2010) may be a significant threat to this species in addition to fishing pressure (Compagno et al. 2010).