|Scientific Name:||Platanista gangetica|
|Species Authority:||(Roxburgh, 1801)|
|Infra-specific Taxa Assessed:|
Platanista gangetica (Roxburgh, 1801)
Platanista minor Owen, 1853
|Taxonomic Notes:||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), but Kasuya (1972; cf. Reeves and Brownell 1989) reduced the two taxa to subspecies of a single species (P. gangetica), 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 ver 3.1|
|Assessor(s):||Smith, B.D. & Braulik, G.T.|
|Reviewer(s):||Reeves, R. & Taylor, B.L.|
Considerable effort has been made to document the status of Platanista gangetica since the early 1970s, yet rigorous quantitative data on numbers, mortality, extent of occurrence, and area of occupancy are still lacking for much of the species’ range, especially in India and Bangladesh. The diversity and scale of threats – recent, ongoing, and projected – have generally outpaced effort at documentation. Moreover, it is important to bear in mind that 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 the loss of more than just a single species. Applying precautionary reasoning to the evidence available, the species qualifies for listing as Endangered.
Only very limited data are available on life history. Age at first reproduction is probably between 6–10 years and maximum longevity may be close to 30. Therefore, generation time is probably well over 10 but possibly less than 20 years, which would mean that three generations equals at least 30 years (i.e., from 1974 counting backwards or until 2034 counting forwards) but less than 60 (i.e., from 1944 counting backwards or until 2064 counting forwards).
Criterion A. In the absence of rigorous quantitative estimates of abundance throughout the species’ range, declines in extent of occurrence have been used as proxies for population size reduction, to supplement the qualitative evidence of reduced abundance and habitat deterioration and loss.
Subcriterion A1 does not apply because even if the decline has been greater than 70%, the causes are not clearly reversible, understood, or ceased, all of which would have to be true.
Subcriterion A2 applies because a population size reduction of more than 50% since 1944 is inferred and suspected, given that nearly all of the critical dam and barrage construction associated with the large-scale decline in the area of occupancy of both subspecies has occurred since that time. Moreover, the reduction and its causes have not ceased (more barrages are planned and under construction, habitat quality is expected to deteriorate further, and mortality from hunting and net entanglement continue), are not fully understood, and may not be reversible. The basis could rest on any or all of (a) to (e).
Subcriteria A3 and A4 could also apply because a population size reduction of more than 50% can plausibly be projected over the next 30–60 years (A3), or inferred, projected, or suspected over a period of 30–60 years including both the past and the future (A4), with the causes uncertain, continuing, and possibly irreversible, again in either instance based on any or all of (a) to (e). Evidence for A4c is probably the strongest since a precautionary interpretation of life history data indicates a period of 60 years for three generations, which encompasses the dramatic effects of the Farakka Barrage completed in 1974, as well as at least 19 other barrages and 18 high dams constructed in the GBM and KS systems since 1956, and the projected declines in the area of occupancy, extent of occurrence, and/or quality of habitat that will undoubtedly occur if the proposed Ganges-Brahmaputra inter-link canal and dam project is completed by India in 2016, as planned. The cumulative effects of these projects indicate a probable population size reduction of more than 50% for the Ganges subspecies from 1956–2016. Even though the number of dolphins in the Sukkur-Guddu segment (and possibly also the Guddu-Taunsa segment) of the Indus may have increased following a hunting ban in the early 1970s (see above), this could have been partly or largely due to one-way immigration from upstream (the return movements having been blocked by barrages). Equally, the major changes in the Indus caused by water development since 1944 have greatly reduced the dolphins’ area of occupancy, reduced the overall carrying capacity for dolphins in the Indus basin, and caused a substantial net decline in population size. Thus, it is reasonable to infer declines of at least 50% in the populations of both subspecies.
Criterion B. It has not been possible to estimate the extent of occurrence or area of occupancy for the entire species because the potential total range of the Ganges subspecies is so large and poorly documented. Nevertheless, the aggregate population of Ganges dolphins has been severely fragmented, and there is great uncertainty about their continued occurrence in many parts of that potential range. The Indus subspecies qualifies as EN under this criterion as: (a) its extent of occurrence is estimated at only about 900 km², compared with the EN threshold of 5,000 km², (b) its population is severely fragmented and it occurs at less than five locations (defined as inter-barrage segments of river), and (c) a continuing decline can be inferred or projected in the quality of its habitat. With the two subspecies combined, it would be difficult to demonstrate that the extent of occurrence is less than 5,000 km², although the total population is severely fragmented and the quality of habitat is continuing to deteriorate.
Criterion C. The substantial investment made to date in surveys in Pakistan, India, Bangladesh, and Nepal has failed to explicitly account for more than about 2,500 animals of all ages. 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" below).
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 subspecies.
Consultation and Peer Review: The assessments for the two subspecies were subjected to review by the IUCN Cetacean Specialist Group, and this species assessment was derived from them.
|Previously published Red List assessments:|
|Range Description:||This species occurs in the Indus, Ganges-Brahmaputra-Megna, and Karnaphuli-Sangu river systems of the South Asian subcontinent, from the deltas upstream to where they are 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 all three systems, some of it natural but much of it caused by physical barriers constructed within the last 100 years.|
The subspecies P. g. minor is endemic to the rivers of the lower Indus basin in Pakistan. Historically it occurred in the Indus mainstem and the Sutlej, Beas, Ravi, Chenab, and Jhelum tributaries. It ranged from the Indus delta upstream to the Himalayan foothills where rocky barriers or shallow water prevented further upstream movement. Development of the vast Indus Basin Irrigation System has severely fragmented the dolphin population within a network of barrages (low, gated, diversion dams) and water diversion has dramatically reduced the extent of dolphin habitat. Current occupancy is effectively limited to three subpopulations in the Indus mainstem located between the Chashma and Taunsa, Taunsa and Guddu, and Guddu and Sukkur Barrages. A few individuals still remain above Chashma Barrage and below Sukkur Barrage (Braulik 2003, Reeves and Chaudhry 1998, Reeves 1998) (see Figure 1, in Supplementary Material).
The map shows where the species may occur. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.
Native:Bangladesh; India; Nepal; Pakistan
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Published data on abundance consist primarily of 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 estimates of precision, are available.|
The entire current range of the Indus subspecies was surveyed in 2001 and resulted in an estimate of 843–1,171 individuals, with a best estimate of about 965. The largest subpopulation, containing more than 60% of the total, is located in the Sindh Dolphin Reserve between the Guddu and Sukkur Barrages, at the downstream end of the subspecies’ range. The next largest, with about 27% of the total for the subspecies, is immediately upstream in the Guddu-Taunsa segment of the Indus.
Surveys of portions of the range of the Ganges subspecies have collectively accounted for 1,200–1,800 animals, but the true population is believed to be larger because some potentially important areas have yet to be surveyed (e.g., the Indian Sundarbans) and at least some of the counts and estimates were considered negatively biased. The greatest densities of Ganges dolphins have been observed in the Ganges mainstem in India between Maniharighat and Buxar (particularly the Vikramshila Gangetic Dolphin Sanctuary) and just downstream of there between Kahalgaon and Manihari Ghat, and in the lower Sangu River of Bangladesh.
Dolphin counts in the Guddu-Sukkur segment of the Indus showed an apparently increasing trend from 1974 to 1996. If this increase was real and not an artifact of variable sighting biases, it could be explained by recovery after implementation of a hunting ban in 1974 or by permanent immigration from upstream subpopulations. No credible time series of estimates is available for the Ganges subspecies, but downward trends are plainly evident for a number of upstream tributaries.
Marked declines have occurred in the extent of occurrence for both subspecies – in the case of Indus dolphins, from approximately 3,400 km of the main channel and its tributaries in the 1870s to approximately 1,000 linear km of the main channel today. An estimated 99% of the Indus dolphin population occurs in only 690 linear km, corresponding to an 80% reduction in the area of occupancy for that subspecies. In the case of Ganges dolphins, the picture is less clearcut, but substantial portions of the range, particularly in upstream areas, have been lost. For example, in the northern Ganges tributaries, at least three of six subpopulations that were isolated by barrages have disappeared, and in a recent dry-season survey of the Son River, no dolphins were found. Kaptai Dam in southeastern Bangladesh (built in 1961) resulted in the elimination of extensive habitat in the upper Karnaphuli River.
More specific information on the subspecies is provided below:
Platanista gangetica gangetica
Although the aggregate range-wide abundance of Ganges River dolphins was estimated by Jones (1982) as 4,000–5,000 individuals and more recently by Mohan et al. (1997) as fewer than 2,000, these were only guesses. Population assessments have been based on 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 estimates of precision, are available. Available counts and estimates are summarized in Table 1 (see Supplementary Material).
Highest "densities" of Ganges River dolphins (defined as animals per linear river kilometer) have been observed in the Ganges mainstem between Maniharighat and Buxar (1.5/km) (Sinha, unpublished) - and within this segment particularly in the Vikramshila Gangetic Dolphin Sanctuary (2.8/km) (Smith, unpublished) and just downstream between Kahalgaon and Manihari Ghat (near Katihar) (3.4/km) (Sinha, unpublished) - and the lower Sangu River, Bangladesh (1.4/km) (Smith et al. 2001). A few Ganges River dolphins were still present during the mid 1990s as far downstream in the Hoogly River as Kakdwip (Sinha 1997). In the Sundarbans of Bangladesh a minimum of 134 Ganges River dolphins were counted resulting in a "density" estimate of 0.09 individuals/km, with Irrawaddy dolphins Orcaella brevirostris replacing Platanista in higher salinity waters of the southern and western portions (Smith, unpublished). No information is available on the status of Ganges River dolphins in the Indian Sundarbans, except for historical reports of occurrence (Anderson 1879, Jones 1982).
Roughly accounting for duplicate counts or estimates in Table 1 (see Supplementary Material), the total of about 1,200–1,800 animals provides a reasonable lower range for the total metapopulation abundance. However, considering that areas with potentially large numbers of animals have not been accounted for at all (e.g., Indian portion of the Sundarbans Delta) and that at least some of the counts and estimates are known to be negatively biased (e.g., see Smith et al. 2001), the true number could be several times as high.
Numerical Declines: Although no credible time series of abundance estimates are available for most of the subspecies' range, the numbers shown in Table 1 (see Supplementary Material) imply downward trends in a number of upstream tributaries (see also Range Declines below).
Range Declines: The range of the subspecies has declined progressively since the nineteenth century when it was mapped by Anderson (1879). No dolphins have been reported in recent years between the Madhya Ganga Barrage at Bijnor and the Bhimgoda Barrage near Haridwar, at the upstream limit of their historical range in the Ganges (Sinha et al. 2000). This suggests a roughly 100 km decline in their range in the Ganges River since the late 1800s. In recent years, dolphins have not been reported in the Yamuna River above the Chambal River confluence during the dry season because upstream channels have become too shallow and polluted to support dolphins, but the segment may still be occupied during the monsoon (Sinha et al. 2000). Historically, they were found year-round in the Yamuna River approximately 400 km upstream to Delhi (Anderson 1879).
Elsewhere in the Ganges mainstem, four extant subpopulations are isolated by barrages, including Farakka Barrage located approximately at the center of the subspecies' overall range. In the northern Ganges tributaries, of the six subpopulations that were isolated above or between barrages, three have been extirpated (in the Gandak River above the Gandak Barrage and in the Sarda River above the upper and lower Sarda barrages) (Sinha et al. 2000) and one reduced to insignificant numbers (in the Kosi River above the Kosi Barrage) (Smith et al. 1994). Ganges River dolphins have apparently been extirpated from the Son River (at least during the dry season) based on a survey covering ca. 300 km upstream of the Ganges confluence, above and below the Indrapuri Barrage (Sinha and Sharma 2003).
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 recent surveys have found no evidence that the subspecies survives there (Smith et al. 2001). Thus, the dam's construction is likely to have caused a substantial reduction in the subspecies’ range in southeastern Bangladesh, but in the absence of any historical information on occurrence in the upper Karnaphuli no quantitative estimate of range reduction is possible.
No surveys have been conducted in the Damodar River system but a single dolphin was rescued after becoming stranded in a deep pool after flow was diverted during the dry season by an upstream barrage. The downstream effects of at least ten dams and barrages constructed in its mainstem and tributaries has probably severely reduced and fragmented dolphin habitat (Smith et al. 2000).
Platanista gangetica minor
Direct-count surveys of the largest subpopulations have been conducted regularly by the Sindh and Punjab Wildlife Departments since the early 1980's, but described methods do not provide a basis for evaluating bias, estimating precision, or detecting trends in abundance (Reeves and Chaudhry 1998). Dolphin counts between Guddu and Sukkur Barrages show an apparent increase from 139 dolphins recorded in 1974 (Pilleri and Zbinden 1973–74), to 290 in 1979 (Pilleri and Bhatti 1980), and 458 dolphins in 1996 (Mirza and Khurshid 1996). If this increase was real and not an artifact of variable sighting biases, it could be explained by recovery of the subpopulation after implementation of a hunting ban in 1974 (see Conservation Actions below) or by permanent immigration from upstream subpopulations (see Major Threats below). A comprehensive review of previous survey data is presented in Reeves and Chaudhry (1998) and Reeves et al. (1991).
The most recent and comprehensive assessment of the Indus Dolphin population was a survey of their entire range conducted in March and April 2001 that resulted in a minimum abundance estimate of 965 dolphins (based on the sum of best estimates of group size of all sightings). High and low estimates of group size were also recorded. The sum of high estimates was 1,171 and the sum of the low estimates 843. This survey also documented a pronounced increase in the abundance and encounter rate of dolphins as the survey vessel proceeded downstream. The largest subpopulation is located in the Sindh Dolphin Reserve between the Guddu and Sukkur Barrages, at the downstream end of the range. Best estimates of 602 total dolphins and 3.6 dolphins/linear km were recorded for this section, 259 dolphins and 0.74 dolphins/linear km for the section between Guddu and Taunsa, and 84 dolphins and 0.28 dolphins/linear km for the furthest upstream section between Taunsa and Chashma. Two dolphins were seen upstream of Chashma Barrage and 18 downstream of Sukkur Barrage.
The minimum abundance estimate of 965 dolphins for the subspecies is likely to be close to the actual population size due to measures taken in the field to increase sighting efficiency. Essentially all potential dolphin habitat was surveyed in the Indus mainstem, including secondary channels and braids off the main channel, from a non-motorized vessel (mean survey speed = 5 km/hr), which maximized detection opportunities. Double-concurrent counts were also conducted from a second vessel traveling behind the primary survey vessel. Sightings were considered unique if they were greater than 750 m distant from another group according to the GPS positions. Preliminary analyses indicate that the primary survey vessel missed less than 10% of dolphin groups, and no groups of more than three individuals (mean group size recorded was 2.0; SD = 1.6; range 1–11) (Braulik 2004). The probability of double counting dolphins due to their movement from surveyed to unsurveyed areas overnight was considered to be balanced by the probability that an equal number of dolphins were missed altogether due to their movements in the opposite direction.
The linear extent of occurrence of the subspecies has declined from approximately 3,400 km of Indus mainstem and its tributaries in the 1870s (see Anderson 1879) to approximately 1,000 linear km of the mainstem today (Braulik 2004). An estimated 99% of the dolphin population occurs in only 690 linear km, which corresponds to an 80% reduction in the area of occupancy (Anderson 1879, Reeves et al. 1991, Braulik 2003, Braulik 2004). During the 1970s and 1980s there were occasional reports of dolphin occurrence between barrages in the lower reaches of the Indus tributaries (Reeves et al. 1991). No recent surveys have been conducted in those areas. However, due to an increase in upstream water abstraction and a decline in dry season flows, it is unlikely that any dolphins remain in these reaches.
|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 floods cause 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.|
More specific information on the subspecies is provided below:
Platanista gangetica gangetica
Ganges River dolphins are generally concentrated in counter-current pools below channel convergences and sharp meanders (Kasuya and Haque 1972, Smith 1993, Smith et al. 1998) and above and below mid-channel islands, bridge pilings, and other engineering structures that cause scouring (Smith, unpublished data). Their fidelity to counter-current pools is probably greatest in fast-flowing channels (Smith et al. 1998). Annual monsoon-driven floods cause great variability in the dolphins’ access to large parts of their range. Isolation in seasonal lakes sometimes occurs (especially in the Brahmaputra basin), as does "escapement" from the river channels into artificial water bodies such as canals and reservoirs. Deltaic (brackish) waters are a major component of the total range, but Ganges River dolphins are not generally known to occur in salinities greater than 10 ppt, although they have been recorded in waters as saline as 23 ppt (Smith and Braulik, unpublished data).
Platanista gangetica minor
Indus River dolphins generally occur in the deepest river channel and are less common in secondary channels and small braids (Bhatti and Pilleri 1982, Braulik 2003). Reported habitat preferences include channel constrictions, confluences, and deep, low-velocity water (Kasuya and Nishiwaki 1975, Khan and Niazi 1989, Braulik 2004). 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. As water levels drop in the winter, dolphins are concentrated in the remaining deep areas, including the head ponds upstream of barrages.
|Movement patterns:||Full Migrant|
|Use and Trade:||It is hunted locally for food, and to extract oil which is used as a fish attractant.|
Water development projects have dramatically affected the habitat, abundance, and population structure of this species throughout its range. In addition to fragmenting populations, 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 interbasin transfers, will continue to be driven principally by the escalating demands from agriculture, industry, and municipalities; by strategic considerations; and by the need to control flooding.
Pollutant loads in South Asian rivers can be expected to increase with industrialization and the spread of intensive agricultural practices facilitated by water diversion. The capacity of these rivers to dilute pollutants (e.g., arsenic, DDT) and salts 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.
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.
Mortality in fishing gear, especially gillnets, is a severe problem for Ganges dolphins throughout most of their range. They are particularly vulnerable because their preferred habitat is often in the same location as the fishing grounds. A specific problem in parts of India and Bangladesh is that, because dolphin oil is highly valued as a fish attractant, fishermen have a strong incentive to kill any animals found alive in their nets and even to set their nets strategically in the hope of capturing dolphins.
More specific information on the subspecies is provided below:
Platanista gangetica gangetica
Water Development Projects
Construction of at least 50 dams and dams within the known or suspected historical range of the subspecies (Smith et al. 2000) has dramatically affected its habitat, abundance, and population structure. The subspecies exists as a metapopulation, with numerous subpopulations isolated to varying degrees by mostly manmade but also natural barriers, as outlined in the preceding section.
In addition to fragmenting dolphin populations, dams and barrages degrade downstream habitat and create reservoirs (known as head ponds (or pondage in India) in the case of barrages) with high sedimentation and altered assemblages of fish and invertebrate species. For example, luxuriant growth of macrophytes and excessive siltation have eliminated suitable habitat immediately above Farakka Barrage (Sinha 2000). Moreover, the insufficiency of water released downstream of this barrage has eliminated dry-season habitat for more than 300 km, or until the Ganges (Padma)-Brahmaputra confluence (Smith et al. 1998). It has also allowed salt water to intrude an additional 160 km into the Sundarbans Delta (Rahman 1986), further decreasing the amount of suitable habitat for this obligate freshwater dolphin (Reeves et al. 1993).
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, Smith et al. 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 (Smith et al. 1994).
Since the 1980s, momentum has been growing within India to proceed with large-scale inter-basin water transfer projects, which will involve additional dam construction and diversion of water from rivers inhabited by dolphins. Although no final decision has been taken to proceed with construction, feasibility studies are to be completed in December 2005 and detailed project reports in 2006. It was anticipated in 2004 that, if built, the entire project would be finished by 2016. During the May 2004 national elections in India all political parties supported the construction of inter-basin water transfer projects and promised to accelerate the construction process. Several key categories of potential threat are: (a) further fragmentation of the dolphin metapopulation, (b) reduction or elimination of habitat simply in terms of dry-season flow, (c) "escapement" of dolphins into canals where they are unlikely to be able to get back into rivers and are therefore doomed, (d) cascading effects from interrupted migrations of prey 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, etc, and (g) downstream effects on the ecology of the delta (e.g., saline encroachment, loss of sediment).
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 (Boyce 1990). Approximately 3,500 km of embankments have been constructed in the Ganges mainstem and 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). Although plans for constructing an extensive system of embankments in the rivers of Bangladesh under the Flood Action Plan (FAP) coordinated by the World Bank (see World Bank 1990) have been drastically scaled-down, several projects are currently planned or being constructed that will have adverse effects on dolphin habitat. These include the Bank Protection and River Training Project (FAP 21/22), Brahmaputra River Bank Priority Works, and Jamalpur Priority Project (FAP 3.1) (Smith et al. 1998). Environmental assessments of these projects have not considered river dolphins, nor have they acknowledged the cumulative impacts of planned embankments, and others built before the FAP, on the fish and crustacean species eaten by river dolphins.
Other sources of habitat degradation in the GBM system include dredging (Smith et al. 1998) and the removal of stones (Shrestha 1989), sand (Mohanet al. 1998), 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. Dolphin habitat is also threatened by water abstraction from surface pumps and tube wells, especially in the Ganges where the mean dry-season water depth has declined dramatically in recent years (Sinha, unpublished). Although the long-term implications of reduced dry-season flows in the Ganges are catastrophic, both for the survival of river dolphins and a major portion of the world’s human population that inhabits the Ganges basin, the cumulative effects of reduced water supplies have received little attention. Meanwhile, new projects to divert dry-season flow, such as Kanpur Barrage in the upper Ganges, continue to be constructed (Smith et al. 2000).
Organochlorine and butyltin concentrations in samples from the tissues of Ganges dolphins were high enough to cause concern about effects (Kannan et al. 1993, 1994, 1997; Senthilkumar et al. 1999). Pollutant loads can be expected to increase with industrialization and the spread of intensive agricultural practices facilitated by water diversion. River dolphins may be particularly vulnerable to industrial pollution because their habitat in counter-current pools downstream of confluences and sharp meanders often places them in close proximity to point sources in major urban areas (e.g., Allahabad, Varanasi, Patna, Calcutta, and Dhaka). Furthermore, the capacity of rivers to dilute pollutants (e.g., arsenic, DDT) and salts has been drastically reduced in many areas because of upstream water abstraction, diversion, and impoundment. Again, this problem is bound to worsen as more development takes place.
Deliberate killing of river dolphins is believed to have declined in most areas but still occurs at least occasionally in the middle Ganges near Patna, India (Smith and Reeves 2000, Sinha 2002), in the Kalni-Kushiyara River of Bangladesh (Smith et al. 1998), and in the upper reaches of the Brahmaputra River in Assam, India (Mohan et al. 1997). Dolphins are killed 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.
Mortality in Fishing Gear
Mortality in fishing gear, especially gillnets, is a severe problem for Ganges River dolphins throughout most of their range (Mohan 1995, Smith and Reeves 2000). They are particularly vulnerable because their preferred habitat is often in the same location as the fishing grounds. In the middle Ganges, although harpooning is now "rare", mortality in fishing nets remains "widespread" (Sinha 2002). A specific problem is that, because dolphin oil is highly valued as a fish attractant, fishermen have a strong incentive to kill any animals found alive in their nets and even to set their nets strategically in the hope of capturing dolphins (described by Sinha 2002 as "assisted incidental capture").
Meaningful quantitative data on the magnitude of catches, either deliberate or incidental, are unavailable and unlikely to become available in the absence of a well-organized, adequately funded, and incorruptible fishery/wildlife management system.
Platanista gangetica minor
The most significant threat to dolphins in the Indus has been the construction of at least 25 dams and barrages that have severely fragmented the population and reduced the amount of available habitat (Smith and Reeves 2000). Upstream subpopulations may lose individuals downstream if dolphins move through barrage gates when they are open in the wet season. Individuals are unlikely to move upstream through a barrage because of strong downstream hydraulic forces at the gates. While there have been no direct observations of dolphins moving through a barrage, they often swim through regulator gates into irrigation canals, which, although smaller, present a similar obstacle (Braulik 2002). Evidence for permanent downstream emigration includes that each subsequent downstream subpopulation is larger than the one above (see Range and Population above), despite the reduced linear extent and availability of water in downstream segments. Encounter rates in the farthest downstream subpopulation (between Guddu and Sukkur Barrages) are very high (3.60 dolphins/linear km), approaching three times those recorded in similar surveys elsewhere for Platanista dolphins (Braulik 2003). The possible large increase in the dolphin subpopulation between Guddu and Sukkur Barrages (described above) may be due to reproduction and reduced mortality alone, or may be augmented by downstream emigration. Even a low emigration rate could dramatically affect the persistence of upstream subpopulations (Reeves et al. 1991, Reeves and Smith 1999).
Since the mid 1990s, there have been increasing reports of dolphins trapped in irrigation canals near Sukkur Barrage. Dolphins have survived for several months in the canals until they are drained in January for annual de-silting and maintenance. Between January 2000 and December 2002, 34 dolphins were reported trapped in these canals. Twenty-four were successfully rescued and returned to the Indus River, while the remainder died (Bhaagat 1999, Braulik 2002, WWF-Pakistan unpublished data).
One of the direst threats to the survival of the Indus River Dolphin is probably the escalating demand for water. Pakistan is a largely desert nation, with a rapidly growing human population and fast developing industrial and agricultural sectors that demand increasing amounts of water. Several years of extreme drought have depleted aquifers that would normally be expected to augment river flows in the dry season.
Pollution may be affecting the viability of the subspecies, especially considering the decline in flushing and dilution due to reduced flows. The Indus River corridor is not highly developed and above the Panjnad River confluence, the habitat is likely to be relatively unpolluted. However, 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 have reportedly become common from industrial pollution in urban areas and from pesticides used on irrigated crops grown along the riverbanks (Reeves and Chaudhry 1998). 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.
Deliberate killing for meat and oil was a traditional and widespread practice until at least the early 1970s (Pilleri and Zbinden 1973–74). Hunting is now banned although poaching occasionally occurs. Similar to all cetaceans, this subspecies is vulnerable to entanglement in fishing gear and vessel collisions. However, the areas of the Indus River where dolphins are extant are not heavily fished or utilized by vessels and these factors may not be major threats at present. Incidents of accidental killing and observations of dolphin carcasses and products are documented in Reeves et al. (1991) and Reeves and Chaudhry (1998).
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. Field trials in India to determine the effectiveness of shark and scrap fish oils as catfish attractant have been judged successful, but it is unclear to what extent fishermen have converted to using them instead of dolphin oil.
It is listed on CITES Appendix I.
More specific information on the subspecies is provided below:
Platanista gangetica gangetica
Ganges River dolphins are legally protected from hunting in all range states. The Vikramshila Gangetic Dolphin Sanctuary, Bihar, India, between Sultanganj and Kahalgaon in the mainstem of the Ganges River was designated as a protected area for dolphins in August 1991 but there is little government support to enforce protective measures. The legal protection in India has been described as "completely ineffective" (Sinha 2002), however, a small measure of progress was the convening of the Regional Seminar on Environmental Laws in the Vikramshila Gangetic Dolphin Sanctuary, Bhagalpur, India in November 2003 (Anon 2002). Also, recent proceedings of the Patna High Court (C.J.W.C. No. 5628 of 2001) directed the state and federals governments to allocate funds for supporting efforts to conserve and monitor dolphins in the Ganges. In a few smaller tributaries, dolphins receive nominal protection by virtue of the fact that small portions of their habitat are within or adjacent to national parks and sanctuaries (e.g., Kaziranga National Park in Assam, India, National Chambal Sanctuary in Madhya Pradesh, India, and Royal Bardia National Park and Katerniya Ghat Gharial Sanctuary, respectively north and south of the Nepal-India border. Although field trials have shown that shark or fish oils would be efficient substitutes for dolphin oil as a fish attractant and some fishermen in the middle Ganges are now using oil made from fish scraps as an alternative, most apparently continue to use dolphin oil by preference or because suitable alternatives are not widely available in either the Ganges or Brahmaputra systems (Mohan and Kunhi 1996, Smith et al. 1998, Bairagi 1999, Sinha 2002).
Platanista gangetica minor
In 1972, 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 (Reeves et al. 1991, Reeves and Chaudhry 1998, Chaudhry and Khalid 1989). 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 programme sponsored by the United Nations Development Programme (UNDP) to rescue dolphins trapped in irrigation canals and return them to the Indus mainstem has had some success in reducing mortality (Braulik 2002, Bhaagat 2002).
|Citation:||Smith, B.D. & Braulik, G.T. 2012. Platanista gangetica. The IUCN Red List of Threatened Species 2012: e.T41758A17355810.Downloaded on 25 June 2017.|