|Scientific Name:||Platanista gangetica (Roxburgh, 1801)|
|Infra-specific Taxa Assessed:|
Delphinus gangetica Roxburgh, 1801
Platanista gangetica (Roxburgh 1801)
Platanista indi (Blyth 1859)
Platanista minor (Owen 1853)
|Taxonomic Notes:||The South Asian River Dolphin (Platanista gangetica) is the only species in the family Platanistidae (Rice 1998). The Indus and Ganges populations were long regarded as identical until Pilleri and Gihr (1971) divided them into two species (P. gangetica and P. minor). Kasuya (1972; cf. Reeves and Brownell 1989) reduced the two taxa to subspecies of P. gangetica, and that treatment is followed here. Shreshta (1995) has questioned the reality of the alleged differences between the two populations. Until the late Pliocene, the present-day Indus, Ganges and Brahmaputra (except for the upper reach, the Yarlung Zangpo Jiang) rivers constituted a single westward-flowing river called the Indobrahm (Hora 1950, 1953). Even up until historical times there was probably sporadic faunal exchange between the Indus and Ganges drainages by way of head-stream capture on the low Indo-Gangetic plains, between the Sutlej (Indus) and Yamuna (Ganges) rivers (Dey 1968).|
|Red List Category & Criteria:||Endangered A2abcde+3bcde+4abcde ver 3.1|
|Assessor(s):||Braulik, G.T. & Smith, B.D.|
|Facilitator/Compiler(s):||Lowry, L., Chiozza, F., Pollock, C.M.|
Considerable effort has been made to document the status of South Asian River Dolphins since the early 1970s, yet rigorous quantitative data on numbers, mortality, extent of occurrence, and area of occupancy are still lacking for some of the species’ range, especially in India and Bangladesh. The diversity and scale of threats—recent, ongoing, and projected—have far outpaced effort at documentation. Moreover, this species is the sole living representative of its family (which represents an ancient lineage in the order Cetartiodactyla), and therefore its extinction would mean not just the loss of a single species, but loss of an entire mammalian family regarded as a sister taxon to all other cetaceans. Based on available evidence, the species qualifies for listing as Endangered under criterion A.
Criterion C. Although it is possible that the total number of mature individuals is less than 2,500, current information from field surveys does not allow this criterion to be credibly applied. If future population assessments ultimately indicate that the population meets the <2,500 threshold, then it would qualify under subcriterion C1 because a continuing decline of at least 20% can be expected over the next 20–40 years (see "Threats" and "Conservation Actions").Criterion D. The population size is greater than 250 mature individuals, so this criterion does not apply.
Criterion E. No quantitative analysis of extinction probability has been attempted for this species.
|Previously published Red List assessments:|
This species occurs in the Indus, GBM, and KS river systems of the South Asian subcontinent, from the deltas upstream to where movement is blocked by rocky barriers, shallow water, fast currents, dams, or barrages (low, gated diversion dams). The three river systems are disjunct and therefore so are their respective dolphin subpopulations, although there may be occasional demographic interaction between the latter two during the high-water season if the freshwater plumes of the two systems meet. There is further subpopulation separation within the Indus and GBM systems, some of it natural but much of it caused by physical barriers (dams and barrages) constructed within the last 100 years.
The range of the Ganges subspecies (Ganges Dolphin) has declined progressively since the nineteenth century when it was mapped by Anderson (1879). Historically it occurred through several thousand kilometres of free-flowing river in India, Bangladesh, Nepal, and possibly Bhutan. The downstream effects of at least ten dams and barrages constructed in the Ganges mainstem and tributaries have severely reduced and fragmented dolphin habitat (Smith and Reeves 2000). Dolphins have undergone roughly a 100 km decline in their range in the Ganges River since the late 1800s, and disappeared from the upper Ganges between Haridwar and Bijnor, and Narora and Kanpur. Historically, they were found year-round in the Yamuna River approximately 400 km upstream to Delhi (Anderson 1879), but in recent years, dolphins have not been reported in this river above the Chambal River confluence during the dry season because upstream channels have become too shallow and polluted to support dolphins (Sinha 2000). In the northern Ganges tributaries, of the six dolphin subpopulations that were isolated above or between barrages, three have been extirpated (in the Gandak River above the Gandak Barrage, in the Sarda River above the upper and lower Sarda barrages and the Sone River) (Sinha et al. 2000) and one has been reduced to insignificant numbers (in the Kosi River above the Kosi Barrage) (Smith 1994, Sinha and Kannan 2014). A few Ganges Dolphins were still present during the mid-1990s as far downstream in the Hoogly River as Kakdwip (Sinha 1997), and more recent surveys suggest their continued presence between Farraka and the Bay of Bengal in West Bengal, India (Chowdhury et al. 2016). The lack of adequate of water being released downstream of Farraka Barrage has eliminated dry-season habitat for more than 300 km, or until the Ganges (Padma)-Brahmaputra confluence in Bangladesh (Smith et al. 1998).
Occasional reports of dolphins in the reservoir behind Kaptai Dam (built in 1961) of the KS system occurred until the mid-1990s (Ahmed 2000), but surveys in the late 1990s found no evidence that any Ganges Dolphins survive there (Smith et al. 2001). Thus, the dam's construction likely caused a substantial reduction in the subspecies’ range in southeastern Bangladesh, but the absence of any historical information on occurrence in the upper Karnaphuli makes any quantitative estimate of range reduction impossible
Dolphins are expected to have been extirpated from the Subansiri River because of periodic dramatic declines in river discharge from the newly completed Lower Subansiri hydroelectric project (Baruah et al. 2012).
The map produced by Sinha and Kannan (2014) shows where the species occurred as of that time
Native:Bangladesh; India; Nepal; Pakistan
|Range Map:||Click here to open the map viewer and explore range.|
Published data on abundance consist primarily of uncorrected counts conducted within discrete portions of the vast network of riverine and deltaic habitat occupied by these dolphins. Few rigorous estimates of absolute abundance, with measures of precision, are available. Combining current knowledge on abundance from the Indus and Ganges we make an educated guess that the entire species numbers less than 5,000 individuals of all ages. More specific information on each of the subspecies is provided below:
The highest encounter rates of Ganges Dolphins have been observed in the Ganges mainstem between Maniharighat and Buxar (1.6/km) (Sinha and Kannan 2014); and within this segment, particularly in the Vikramshila Gangetic Dolphin Sanctuary in the lower Ganges (3.3/km; (Chaudhary et al. 2012), 1.13/km in the middle reaches of the Gandak River, and 1.4/km in the lower Sangu River, Bangladesh (Smith et al. 2001). An encounter rate of 0.23 dolphins/km was recorded in the entire Brahmaputra River (Wakid 2009).
Compiling direct counts and abundance estimates from numerous surveys by different groups over approximately the last ten years, Sinha and Kannan (2014) tabulated a total of 3,526 individuals for the Ganges River subspecies. However, it is not clear how accurate this is because the various researchers cited did not follow consistent and robust methods and at least some of the counts are likely to be negatively biased. In addition, many tributaries north of the Ganges River, such as Mahananda, Mechi, Bagmati, Kamala, Balan, and Burhi Gandak, have not yet been surveyed, of which Mahananda and Bagmati are large rivers (Sinha and Kannan 2014). Similarly, the Indian portion of the Sundarbans Delta and some large and many small rivers in Bangladesh have not been assessed, so the true total could be much higher.
|Current Population Trend:||Unknown|
|Habitat and Ecology:|
South Asian River Dolphins are generally concentrated in counter-current pools below channel convergences and sharp meanders and above and below mid-channel islands. Annual monsoon-driven flooding causes great variability in the dolphins’ access to large parts of their range. Isolation in seasonal lakes or deep river channels sometimes occurs, as does "escapement" from the rivers into canals and reservoirs. Deltaic (brackish) waters are a component of the total range, but Ganges Dolphins are not generally known to occur in salinities greater than 10 ppt.
Ganges Dolphins are generally concentrated in counter-current pools below channel convergences and sharp meanders (Smith 1993, Smith et al. 1998) and above and below mid-channel islands, bridge pilings, and other engineering structures that cause scouring. Several studies have demonstrated that Ganges Dolphins are concentrated into deep pool habitat in the dry season, which increases their conflict with fisheries that also concentrate in these productive areas (Kelkar et al. 2010, Bashir et al. 2012). Their fidelity to counter-current pools is probably greatest in fast-flowing channels. Isolation in seasonal lakes sometimes occurs (especially in the Brahmaputra basin). Deltaic (brackish) waters are a major component of the total range of this subspecies, but the animals are not generally known to occur in salinities greater than 10 ppt, although they have been observed in waters as saline as 23 ppt.
Indus Dolphins generally occur in the deepest river channel and are less common in secondary channels and small braids (Braulik 2006). During the low-water season (October to April), barrages divert almost all river water such that dolphin habitat downstream of Sukkur Barrage and in some tributary segments has been eliminated and so have the dolphins. As water levels drop in the winter, dolphins are concentrated in the remaining deep areas, including the head ponds upstream of barrages. A comprehensive habitat study demonstrated that Indus Dolphins selected locations in the river with significantly greater mean depth, maximum depth, cross-sectional area, and hydraulic radius, and significantly narrower river width and a lower degree of braiding than areas where dolphins were absent (Braulik et al. 2012). Channel cross-sectional area was the most important factor affecting dolphin presence and abundance, with the area of water less than 1 m in depth exerting the greatest influence. Indus Dolphins avoided channels with small cross-sectional area (<700m2), presumably owing to the risk of entrapment and reduced foraging opportunities.
Male South Asian River Dolphins attain sexual maturity at a body length of about 170 cm and physical maturity at 200-210 cm. Females attain sexual maturity at similar or slightly larger body lengths but physical maturity at about 250 cm. The generally larger rostrum of females accounts for this sexual dimorphism. Length at birth is estimated to be about 70 cm. Gestation lasts approximately one year, with possible peak birthing seasons in early winter and early summer. Young begin feeding on small prey at about one or two months and are weaned within a year (Kasuya 1972). Brownell (1984) estimated age at sexual maturity to be roughly 6-10 years in this species.
|Continuing decline in area, extent and/or quality of habitat:||Yes|
|Generation Length (years):||10-20|
|Movement patterns:||Not a Migrant|
|Use and Trade:||
The Ganges subspecies is hunted locally for food, and to extract oil which is used as a fish attractant. The Indus Dolphin is no longer used by humans or for trade.
Water development projects such as dams and irrigation barrages (diversion dams) have dramatically affected the habitat, abundance, and population structure of this species throughout its range. Barrages and dams are physical barriers that isolate dolphins into small sections of river, fragmenting the population. In addition to fragmentation, dams and barrages have degraded downstream habitat and created impoundments with high sedimentation and altered assemblages of fish and invertebrate species. Canals branching from the river channels upstream of barrages represent population "sinks", as dolphins enter them with little or no prospect of safe return; this problem has been especially well documented in Pakistan. More dams and barrages are either under construction or in advanced planning stages. Water diversion and use in the South Asian subcontinent, including intra- and inter-basin transfers, will continue to be driven principally by the escalating demands for water from agriculture, industry, and municipalities; by strategic considerations; and by the need to control flooding. The range of the South Asian River Dolphin will probably continue to decline as subpopulations are extirpated due to habitat loss related to escalating water demands, large engineering structures (e.g., high dams, barrages, and embankments), and long-term climate changes (Smith et al. 2010, Chaudhary et al. 2012, Braulik et al. 2014).
Pollutant loads in South Asian rivers are increasing and can be expected to continue to do so with industrialization and the spread of intensive agricultural practices facilitated by irrigation with river water. The capacity of these rivers to dilute pollutants (e.g., arsenic, DDT, industrial effluents) and salinity has already been drastically reduced because of upstream water abstraction, diversion, and impoundment. Again, this problem is bound to worsen as more development takes place and with few controls on pollutant discharges.
Deliberate killing of River Dolphins has declined in many areas but still occurs at least occasionally. Dolphins are hunted by tribal people in the upper Brahmaputra for their meat and by fishermen in the middle reaches of the Ganges for their oil, which is used as a fish attractant.
A high dam has been planned for some time just upstream of the dolphins' current (or at least recent) range in the Karnali River, Nepal. If built, this structure would almost certainly eliminate the small amount of dolphin habitat in Nepal’s last river with a potentially viable dolphin population (Smith and Reeves 2000). Disturbance and environmental degradation associated with geotechnical feasibility studies and bridge and road construction for the dam already may have contributed to a decline in the number and range of dolphins above the Nepal-India border (Smith 1993, 1994). Another high dam has been proposed for the Surma River in Cachar, India, which would certainly affect dolphins downstream in the Kalni-Kushiyara distributary.
organisms, degradation of prey spawning habitat etc., (e) contaminant flux leading to significant changes in chronic and/or acute exposure to toxins, (f) loss of complexity (channelization, sediment entrapment upstream of dams, etc.) making the rivers less habitable for dolphins and (g) downstream effects on the ecology of the delta (e.g., saline encroachment, loss of sediment). A related initiative is a series of projects planned under the Indian National Waterways Act 2016. This initiative has raised concerns regarding the possible negative impacts of these developments and the associated lack of water, capital dredging, construction of additional barrages, increased vessel traffic, and pollution.
Embankments cause sediments to be deposited in the riverbed instead of on the floodplain, thereby eliminating or reducing the extent of the eddy counter-currents where dolphins are generally found (Smith et al. 1998). They also restrict access to floodplain habitat critical to the reproduction and growth of riverine fish species. Approximately 3,500 km of embankments have been constructed in the Ganges mainstem and the Gandak, Buri Gandak, Bagmati, Kamala, Yamuna, and Son tributaries (Mishra 1999). Dolphins were apparently extirpated from at least 35 km of the Punpun tributary of the Ganges after embankments were constructed in 1975 (Sinha et al. 2000).
Other sources of habitat degradation in the GBM system include dredging (Smith et al. 1998) and the removal of stones (Shrestha 1989), sand (Mohan 1989), and woody debris (Smith 1993). These activities compromise the ecological integrity of the riverine environments, especially small tributaries where suitable habitat is limited and disproportionately vulnerable to local disturbance. Although the long-term implications of reduced dry-season flows in the Ganges are catastrophic for the survival of both River Dolphins and a major portion of the world’s human population that inhabits the Ganges basin, minimum flow requirements to maintain ecological integrity have only been superficially assessed and even if minimum flows were prescribed in principle or in law, there is little prospect of their being implemented. Meanwhile, new projects to divert dry-season flow, such as Kanpur Barrage in the upper Ganges, continue to be constructed (Sinha et al. 2000).
It has been suggested that dolphins sometimes move through barrage gates and between subpopulations (Reeves et al. 1991). The only solid evidence of this is from a single radio-tracked dolphin released above Sukkur Barrage during canal closure that traversed the barrage
in both upstream and downstream directions several times (Toosy et al. 2009). The barrage gates were eventually closed, leaving the animal below the barrage, trapped in a new subpopulation downstream from its origin. The potential implications of large-scale movements of animals through barrages are great. If animals are more likely to move downstream than upstream, the result would be the gradual attrition of upstream subpopulations and the augmentation of those downstream. Migration of this type could dramatically deplete upstream subpopulations over time, especially as many of these are already very small, potentially leading to their gradual extirpation (Reeves et al. 1991).
Pollution may be affecting the viability of the Indus subspecies, especially considering the decline in flushing and dilution due to reduced flows and increasing industrial effluent discharges. More than 75% of the dolphin population occurs downstream of the confluence with the Panjnad River, which receives a large pollution load from the industrialized cities of the Punjab. There are almost no facilities for treatment of municipal waste in Pakistan and few controls on industrial effluent. Massive fish kills from industrial pollution have reportedly become common in urban areas, and also human deaths from contact with toxic industrial discharges, not to mention increasing runoff of pesticides used on irrigated crops grown along the riverbanks. Commonly used pesticides – DDT, Cypermethrin, Deltamethrin and Endosulfan – were found in the tissue of three Indus Dolphins that died in Sukkur in January 2011 (WWF-Pakistan 2011). The pressures on river water supply and continued untreated discharge of pollutants imply that there will be a continuing decline in the amount and quality of dolphin habitat, and similar to Ganges River Dolphins, Indus Dolphins are likely to be exposed to very high levels of toxic contaminants that could compromise health.
Deliberate killing for meat and oil was a traditional and widespread practice until at least the early 1970s (Pilleri and Zbinden 1973-74). The Indus Dolphin became a protected species in the early 1970s and within a few years, and following some prosecutions in the courts, dolphin hunting largely ceased (Bhatti and Pilleri 1982).
Indus Dolphins are accidentally captured in nets when they stray into irrigation canals which, due to their narrow and shallow dimensions, are easily and heavily fished. Net entanglement is a major concern between Sukkur and Kotri barrages where the Indus flow is so severely depleted that fixed nets span the river. However, in general, the Indus River main channel has not been intensively fished as fishing activity is concentrated in side channels and adjacent pools that are reported to be warmer and have higher fish densities. However, entanglement is an increasing threat as boats become mechanised and better able to negotiate the main channel. In 2007, changes in fishery management led to larger numbers of fishermen using the river and a coincident jump in the number of dolphin deaths. From 1993 to 2010 a total of 35 dolphins were reported dead between Guddu and Sukkur, however in 2011 alone 45 dead dolphins were reported and another 15 from January to May 2012, with similar monitoring systems present in each year (Waqas et al. 2012). In 2011 at least six dolphins were killed when insecticides were dumped into the river to increase fish catch, a practice that is increasingly common (WWF-Pakistan 2011).
The species is legally protected in all range states and occurs in a number of national parks and other designated areas, including dolphin reserves or sanctuaries, where at least nominal enforcement takes place. In Pakistan, the enforcement of regulations prohibiting dolphin hunting appears to have arrested a rapid population decline in the Indus during the early 1970s. Also in Pakistan, a program exists to rescue dolphins trapped in irrigation canals and return them to the Indus main channel. Although sample sizes were limited, trials in India to determine the effectiveness of shark and scrap fish oils as catfish attractant were judged provisionally successful, but it is unclear to what extent fishermen have converted to using them instead of dolphin oil.
In 1972, Indus Dolphins were protected under the Wildlife Act of Sindh and in 1974 the government of Sindh declared the Indus River between the Sukkur and Guddu Barrages a dolphin reserve. The government of Punjab prohibited deliberate killing of dolphins in the Punjab Wildlife Protection Act in 1974 and established the Taunsa Wildlife Sanctuary and Chashma Wildlife Sanctuary in 1983 and 1984, respectively (Chaudhry 1989, Reeves et al. 1991, Reeves and Chaudhry 1998). Enforcement of regulations prohibiting dolphin hunting appears to have arrested the rapid population declines reported by Pilleri and Zbinden (1973-74) for these river segments. A long-term programme to rescue dolphins trapped in irrigation canals and return them to the Indus mainstem has had good success in reducing mortality.
|Citation:||Braulik, G.T. & Smith, B.D. 2017. Platanista gangetica. The IUCN Red List of Threatened Species 2017: e.T41758A50383612.Downloaded on 21 April 2018.|
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