Overview

Brief Summary

Biology

Ganges river dolphins are usually solitary creatures (9). The eye lacks a lens and therefore functions solely as a means of detecting the direction of light. In the muddy waters of their habitat, good eyesight is not needed, and echolocation is used to detect food and navigate (5). Individuals tend to swim with one flipper trailing along the substrate (4), and will root around with their beak to disturb and detect the shrimp and fish upon which they feed (5).   Births may take place year round but appear to be concentrated between December to January, and March to May (9). After around one year, juveniles are weaned and they reach sexual maturity at about ten years of age (5). During the monsoon, dolphins tend to migrate to tributaries of the main river systems (9). Occasionally, individuals swim along with their beak emerging from the water (7), and they may 'breach', jumping partly or completely clear of the water and landing on the side of the body (7).
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Description

The Ganges river dolphin was recognised as a separate species in the 1970s (4), although some controversy remains surrounding its relationship with the Indus river dolphin (P. minor) (9). It has a fairly stocky body with a long beak that thickens at the tip (7); females tend to be larger than males (9). The flippers are large and the dorsal fin is undeveloped, being more of a triangular ridge than a fin (4). The forehead rises steeply and the eyes are very small (4). The skin is a light grey-brown and becomes paler on the belly, often with a tinge of pink (4). The local name 'susu' is said to refer to the noise this dolphin makes when it breathes (7).
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Distribution

Ganges,Brahmaputra, Karnaphuli and Indus river systems
  • UNESCO-IOC Register of Marine Organisms
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Range Description

Ganges-Brahmaputra-Megna (GBM) and Karnaphuli-Sangu (KS) river systems, from the deltas upstream to where rocky barriers, shallow water, fast currents, dams, or barrages (low, gated, diversion dams) prevent upstream movement. The GBM and KS systems are disjunct and therefore so are their respective dolphin populations, although there may be occasional demographic interaction during the high water season if the freshwater plumes of the two river systems meet. There is likely further population separation within the two systems, some of it "natural" but much more of it secondary caused by the presence of physical barriers constructed within the last 100 years. (Follow link below to see a distribution map).

The Ganges River Dolphin was considered by some researchers to be a distinct species for several decades (1970s–1990s) and was listed as such in the 1996 Red List. Its range is disjunct with that of the other subspecies, the Indus River Dolphin, Platanista gangetica minor, and therefore the two have been assessed and listed, and should be managed, separately.

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.
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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; follow link below).

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.
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Geographic Range

Limited to southern Asia, Platanista gangetica inhabits the Ganges and Indus rivers and the many associated tributaries and connected lakes. This species is restricted to freshwater. There are two subspecies: Platanista gangetica gangetica, found in Eastern India, Nepal and Bangladesh in the Ganges, Meghna, Karnaphuli, Bramaputra, and Hooghly river systems, and Platanista gangetica minor, found in Pakistan in the Indus River system.

Biogeographic Regions: oriental (Native )

  • Nowak, R. 2003. Ganges and Indus Dolphins, or Susus. Pp. 128-130 in Walker's Marine Mammals of the World, Vol. 2, 1st Edition. Baltimore, MD: The Johns Hopkins Univesity Press.
  • Nowak, R. 1999. Walker's Mammals of the World, Vol. 2, 6 Edition. Baltimore: The Johns Hopkins University Press.
  • Moreno, P. 2003. Ganges and Indus Dolphins. Pp. 13-17 in M Hutchins, D Kleiman, V Geist, J Murphy, D Thoney, eds. Grzimek's Animal Life Encyclopedia, Vol. 15, 2 Edition. Farmington Hills: Gale Group.
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Range

This species inhabits parts of the Ganges, Meghna and Brahmaputra river systems in India, Bangladesh, Nepal and Bhutan (4).
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Physical Description

Morphology

Physical Description

The two subspecies of Ganges River dolphins are virtually identical in physical appearance. They are readily identified by their elongated snout, which can reach lengths of 20% of total body length. Upon sexual maturity, females develop slightly longer snouts than males. This characteristic is useful in identifying sexually mature individuals. The beak is relatively flat and becomes widest at the tip. They bend slightly upward and can reach a length of 21 cm. On both the top and lower parts of the jaw they have long, sharp teeth, which are visible even when the mouth is closed. On the upper jaw, there are between 26 and 39 teeth on each side and on the lower jaw 26 to 35 teeth on each side. The lower teeth are typically longer than the teeth on the upper jaw. With age, the teeth eventually are worn down and become flat. Unlike other dolphins, Platanista gangetica lack snout hairs.

Well designed for aquatic life, Ganges River dolphins have long flippers that can be up to 18% of total body length. The tail fluke is quite large as well, reaching 46 cm or roughly a quarter of total body length. The dorsal fin resembles a fleshy hump on its back and is usually just a few centimeters in height. They are usually a grey to brown color, but may also have pink bellies and dark grey backs. Dorsal color is generally darker than ventral color.

The skull is highly asymmetrical and has a distinctly steep forehead and a longitudinal ridge. These river dolphins are unique in having long necks with unfused vertebrae. This makes them able to turn their heads from side to side with great flexibility. Ganges River dolphins are sometimes referred to as "blind river dolphins" since their eyes are extremely tiny and lack a lens. These animals are not reliant on vision as a primary sensory system, but the eye is thought to function as a light detector. Slightly larger than the eye and positioned just below it are the external ears. The blowhole is longitudinally positioned, which is unique in comparison to the horizontally positioned blowholes in most other toothed whales. Ganges River dolphins characteristically have several folds of skin that form a wattle. The exact function or purpose of this ornamentation is unknown.

Upon sexual maturity, females tend to be larger than males in overall body size and snout length. Unofficial records have adult females measuring 400 cm, but the average adult rarely exceeds 300 cm in length. At birth, young average 70 cm in length. Typical adult weights are between 51 and 89 kg.

Range mass: 51 to 89 kg.

Range length: 200 to 400 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: female larger; ornamentation

  • Wilson, D., D. Reeder. 2005. Mammal Species of the World: A Taxonomic and Geographic Reference, Vol. 1, 1 Edition. Baltimore: The Johns Hopkins University Press.
  • Reeves, R., R. Brownell Jr.. 1989. Susu. Pp. 69-99 in S Ridgway, S Harrison, eds. Handbook of Marine Mammals, Vol. 4, 1 Edition. London: Academic Press.
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
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 (Smithet 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 10ppt, although they have been recorded in waters as saline as 23ppt (Smith and Braulik, unpublished data).

Systems
  • Freshwater
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Habitat and Ecology

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.

Systems
  • Freshwater
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Ganges River dolphins occupy freshwater river systems in southern Asia. They inhabit the Ganges and Indus River systems and their many tributaries, streams, and connecting lakes. They are found in tributaries that run through the hills and lowlands in Nepal (roughly 250 meters above sea level) and sometimes in flood plains and areas of rivers with heavy currents. These river dolphins prefer areas that create eddy countercurrents, such as small islands, river bends, and convergent tributaries. Since these animals occupy a vast area of river systems, they can tolerate a wide variance of temperatures; some as cold 8 degrees Celsius to warm waters above 33 degrees Celsius (46.4F to 91.4F). They inhabit depths from 3 to 9 meters and must surface every few minutes for air. In the monsoon season, Ganges River dolphins locally migrate to tributaries and then back to larger river channels in the dry, winter season. They also move along the coast of the Bay of Bengal when monsoons flush freshwater out along the southeastern coast of India.

Range elevation: 0 to 250 m.

Range depth: 0 to 9 m.

Average depth: 3 m.

Habitat Regions: tropical ; freshwater

Aquatic Biomes: lakes and ponds; rivers and streams; coastal ; brackish water

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A preference is shown for faster flowing, clear rivers in Nepal, but on the Indian Plains this species prefers slow-moving stretches of the Ganges (4).
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Trophic Strategy

Food Habits

Ganges River dolphins are top predators in their river ecosystems. Side swimming and a flexible neck allow them to search river bottoms to stir up hiding prey. Their formidable speed and ability to swim in shallow water allows them to chase and herd schools of fish. They feed on a variety of aquatic animals. Their physical appearance demonstrates how well equipped they are to catch fish and crustaceans. They are strictly carnivorous, although some vegetation has been found in their stomachs, most likely as a result of messy foraging in the river bed or left over plant remains inside the fish the dolphins have consumed. Their teeth and long snouts are designed to catch and hold fish. They have been observed shaking prey in their jaws and manipulating it to be swallowed head first so that the scales on the fish do not move against the animals throat. As these dolphins do not use vision as a sensory system to catch prey, they rely on echolocation to find food hidden in the mud and river bottom. Once prey are located, they grab it with their long snouts.

In the Indus river, catfish (Wallago attu, Sperata aor) and carp (Gibelion catla) make up a majority of the Ganges River dolphin's diet. Other fish, such as a gobies (Glossogobius callidus), herring (Setipinna phasa), and freshwater sharks (Heteropneustes fossilis) are frequently taken. In addition to freshwater fish, crustaceans such as prawn (Palaemon and Penaeus) and mollusks, such as Indonia coerulea, are eaten.

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore )

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Associations

Ecosystem Roles

Ganges River dolphins are top predators in their river ecosystems. They are important in controlling and maintaining healthy fish and crustacean populations, their primary sources of food. Unfortunately, these river dolphins are experiencing the adverse effects of human environmental impacts and are highly endangered.

While little is known about parasites that use Platanista gangetica as a host, there are reports of Cyclorchis campula, Echinochasumus andersoni, Anisakis simplex, and Contracaecum lobulatum parasitizing these dolphins.

Commensal/Parasitic Species:

  • Cyclorchis campula
  • Echinochasumus andersoni
  • Anisakis simplex
  • Contracaecum lobulatum

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Predation

Other than humans, there are no known natural predators of Ganges River dolphins. Humans have exploited these animals for oil, meat, and as bait for catching catfish. Otherwise, they are typically considered the top predator in their river ecosystems.

Known Predators:

Anti-predator Adaptations: cryptic

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Life History and Behavior

Behavior

Communication and Perception

Ganges River dolphins have poor vision. They lack lenses in their eyes, making it impossible for them to resolve images, they are likely to only be able to detect the presence or absence of light. Ganges River dolphins have highly developed sonar systems. They use pulse sounds not whistles to navigate. This allows them to perceive objects, specifically prey, in murky water. Over a 24-hour period there is almost always a constant emission of sound, 87% of these sounds are clicks for echolocation, the remaining sounds are sounds used in communication. There have not been enough studies to determine what the significance is of these communicative sounds.

Communication Channels: tactile ; acoustic

Perception Channels: visual ; acoustic ; ultrasound ; echolocation

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Life Expectancy

Lifespan/Longevity

Very little is known about the lifespan and longevity of Ganges River dolphins. Few specimens have been observed for the entirety of their lives, but a handful of estimates exist. The oldest male on record lived to be 28 years of age, while the oldest female reached 17.5 years of age. Based on crude estimates, dolphins reaching 18 to 22 years of age may not be uncommon. Few successful efforts have brought Platanista gangetica individuals into captivity for study.

Range lifespan

Status: wild:
28 (high) years.

Average lifespan

Status: wild:
18-22 years.

Average lifespan

Sex: male

Status: wild:
28.0 years.

Average lifespan

Status: wild:
28.0 years.

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Lifespan, longevity, and ageing

Observations: Some dolphins may still be growing after the age of 26. Maximum longevity is unknown even though there are records of animals kept in captivity.
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Reproduction

Not much is known about mating systems in Ganges River dolphins. Further studies must be done to provide information regarding their mating behavior. They breed year round. Difficulty studying these species can in part be attributed to environmental conditions in their habitat due to the monsoon season. In addition the political and socioeconomic state of the area where these dolphins are found is not conducive to research.

Breeding in Platanista gangetica occurs year round, as does birthing. Most births are from October to March, with a peak in December and January, preceding the beginning of the dry season. Gestation is typically about 10 months but can be from 8 to 12 months. Ganges river dolphins bear a single offspring from 70 to 90 cm long. Weaning can begin as early as 2 months or as late as 12 months, typical time to weaning is at 9 months old. Once offspring have been weaned, they disperse and become independent. Males and females typically reach sexual maturity at 10 years of age, although growth continues into their 20's.

Breeding interval: Breeding interval in Ganges River dolphins are not known.

Breeding season: Breeding occurs at all times of the year, although most breeding occurs from October to March.

Range number of offspring: 1 to 1.

Range gestation period: 8 to 12 months.

Range weaning age: 2 to 12 months.

Average weaning age: 8 months.

Average time to independence: 12 months.

Average age at sexual or reproductive maturity (female): 10 years.

Average age at sexual or reproductive maturity (male): 10 years.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average number of offspring: 1.

Average age at sexual or reproductive maturity (male)

Sex: male:
3652 days.

Average age at sexual or reproductive maturity (female)

Sex: female:
3652 days.

The main form of parental care in Platanista gangetica, besides gestation, is provisioning in the form of lactation until weaning. Offspring are weaned no later than 1 year old. Once weaning occurs both male and female offspring disperse. Platanista gangetica are solitary animals so, upon leaving, the offspring is entirely on its own.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)

  • Nowak, R. 2003. Ganges and Indus Dolphins, or Susus. Pp. 128-130 in Walker's Marine Mammals of the World, Vol. 2, 1st Edition. Baltimore, MD: The Johns Hopkins Univesity Press.
  • Jefferson, T., M. Webber, R. Pitman. 2008. Marine Mammals of the World: A Comprehensive Guide to their Identification. San Diego, CA: Academic Press.
  • Reeves, R., B. Stewart, P. Clapham, J. Powell. 2002. Sea Mammals of the World. New York: Chanticleer Press, Inc..
  • MacDonald, D., S. Norris. 2001. The New Encyclopedia of Mammals, Vol. 1, 1st Edition. New York: Oxford University Press.
  • Moreno, P. 2003. Ganges and Indus Dolphins. Pp. 13-17 in M Hutchins, D Kleiman, V Geist, J Murphy, D Thoney, eds. Grzimek's Animal Life Encyclopedia, Vol. 15, 2 Edition. Farmington Hills: Gale Group.
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
A2abcde+3bcde+4abcde

Version
3.1

Year Assessed
2012

Assessor/s
Smith, B.D., Braulik, G.T. & Sinha, R.

Reviewer/s
Reeves, R. & Taylor, B.L.

Contributor/s

Justification
Determining the status of this subspecies is especially problematical because of the lack of rigorous quantitative data (current or historical) on numbers, mortality, extent of occurrence, and area of occupancy. However, the diversity and scale of threats – recent, ongoing, and projected – are such that precautionary reasoning is even more appropriate than is usually the case.

Criterion A. Only very limited data are available on the life history of Platanista sp. (reviewed by Brownell 1984). 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).

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 can be applied because a population size reduction of more than 50% since some time between 1944–74 is plausible (note that most of the dam and barrage construction has occurred since the late 1950s), and it is certainly true that the reduction and its causes have not ceased (more barrages are planned and under construction — e.g., Kanpur Barrage on the Ganges mainstem; mortality from hunting and net entanglement continue unabated despite protection laws), are not fully understood, and may not be reversible. The basis could rest on any or all of (a) to (e) under A1.

Subcriterion A3 and subcriterion A4 can also be applied because a population size reduction of more than 50% could plausibly be projected over the next 30–60 years, or inferred, projected, or suspected over a period of 30–60 years including both the past and the future, with the causes uncertain, continuing, and possibly irreversible, again in either instance based on any or all of (a) to (e). Evidence for subcriterion 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 (see above), as well as at least 19 other barrages and 17 high dams constructed in the GBM system 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 Ganges-Brahmaputra inter-link canal and dam project is constructed (scheduled to be completed in 2016). The cumulative effects of these projects indicate a probable population size reduction of more than 50% from 1956–2016.

Criterion B. It has not been possible to estimate the extent of occurrence or area of occupancy for this subspecies because its potential total range is vast but severely fragmented, and there is great uncertainty about the continued occurrence of dolphins in many parts of the potential range. In any event, although it would easily qualify under subcriteria B1b and B2b, it would not qualify under either B1ac or B2ac and therefore would not qualify as EN under this criterion even if its extent of occurrence or area of occupancy were within one or both of the stated thresholds.

Criterion C. The substantial investment made to date in surveys has failed to explicitly account for more than about 1,500 animals (Table 1). Although it is possible that the total population size is less than 2,500 mature individuals, current information from field surveys does not allow for this criterion to be credibly applied to the subspecies. If future population assessments ultimately indicate that the population meets the
Criterion D. The population size is definitely 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.

It is concluded that the subspecies qualifies as EN under criteria A2abcde+3bcde+4abcde, with available evidence strongest for criterion A4c.

The Karnaphuli-Sangu subpopulation should possibly be listed separately as it may qualify for Critically Endangered status.

History
  • 2004
    Endangered
  • 1996
    Endangered
    (Baillie and Groombridge 1996)
  • 1996
    Endangered
  • 1996
    Endangered
  • 1994
    Vulnerable
    (Groombridge 1994)
  • 1990
    Vulnerable
    (IUCN 1990)
  • 1988
    Vulnerable
    (IUCN Conservation Monitoring Centre 1988)
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IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
A2abcde

Version
3.1

Year Assessed
2012

Assessor/s
Smith, B.D. & Braulik, G.T.

Reviewer/s
Reeves, R. & Taylor, B.L.

Contributor/s

Justification
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.

History
  • 2008
    Endangered
  • 2004
    Endangered
  • 1990
    Vulnerable
    (IUCN 1990)
  • 1988
    Vulnerable
    (IUCN Conservation Monitoring Centre 1988)
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Ganges River dolphins are among the most endangered of all cetaceans. With rising human populations in Southern Asia, the natural habitat of Ganges River dolphins has been extensively modified and degraded. Agricultural and industrial discharges are polluting the river systems in which these dolphins live and feed. In certain populations, the accumulation of heavy metals and organochlorides is posing serious health risks to the animals. In addition, dangerously high levels of arsenic in the water is a serious health threat to every animal using the water system, including Ganges River dolphins. Human modifications to river systems are also impacting the habitat of the dolphins. Over fifty dams affect populations of Ganges River dolphins, cutting populations off from one another. Dams have caused the gene pools of Ganges River dolphins to shrink, which could pose detrimental effects in future generations. Some engineering efforts are underway to construct channels around dams for aquatic wildlife, including dolphins. Ganges River dolphins are becoming more and more restricted to a smaller range. In Pakistan, a few hundred river dolphins are restricted to roughly 1200 square kilometers of water. Many local peoples regard these dolphins as a source of meat, oil and bait. Hunting has certainly impacted the numbers of dolphins in the Ganges and Indus river systems. Also, Ganges River dolphins are caught and drowned in fishing lines and nets, causing considerable fatalities. Bull sharks that make their way into South Asian river systems are known to attack waders and fishermen and are highly aggressive. Many of these attacks on local peoples are wrongly blamed on Ganges River dolphins. While it is highly unlikely these dolphins would ever attack a human, their similar size and color to bull sharks results in their persecution by local peoples.

US Federal List: endangered

CITES: appendix i

IUCN Red List of Threatened Species: endangered

  • Kannan, K., R. Sinha, S. Tanabe, H. Ichihashi, R. Tatsukawa. 1993. Heavy Metals and Organochloride Residues in Ganges River Dolphins from India. Marine Pollution Bulletin MPNBA, 26: 159-162.
  • Reeves, R., S. Leatherwood. 1994. Dams and River Dolphins: Can They Coexist?. Ambio, 23: 172-175.
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Status

Classified as Endangered (EN - A1acd) by the IUCN Red List 2002 (1). Listed on Appendix I of CITES (2) and Appendix II of the Convention on Migratory Species (CMS or the Bonn Convention) (6). Also listed under ASCOBANS, under the auspices of the CMS (8).
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Population

Population
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 (follow link below).

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 (follow link below), 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 (follow link below) 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).

Population Trend
Decreasing
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Population

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 (follow link below).

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 (follow link below), 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 (follow link below) 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.

Population Trend
Unknown
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Threats

Major Threats
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, Smithet 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).

Toxic Contaminants
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.

Hunting
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.
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Major Threats
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).

Toxic Contaminants
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.

Hunting
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).
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The Ganges drainage area is one of the most densely populated areas in the world, being home to roughly one tenth of the world's human population, and as such suffers enormous demand for its resources (4). A major threat to the Ganges river dolphin has been the extensive damming of rivers for irrigation and electricity generation, which isolates populations and prevents seasonal migration (5). Other threats include chemical pollution, boat traffic, hunting and human disturbance. This species is hunted for oil, fish bait and food by local people; accidental entanglement in fishing nets also occurs (4).
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Management

Conservation Actions

Conservation Actions
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).
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Conservation Actions

Conservation Actions
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).
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Conservation

International trade is prohibited by the listing of the Ganges river dolphin on Appendix I of the Convention on International Trade in Endangered Species (CITES) (2). It is also protected under the Indian Wildlife Act, although these legislations require stricter enforcement (9). Proposed conservation measures include designated dolphin sanctuaries and the creation of additional habitat (9). Further research into the current distribution and abundance of this elusive river-dweller is urgently required in order to implement effective conservation measures (9).
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

There are no known adverse effects of Platanista gangetica on humans.

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Economic Importance for Humans: Positive

Ganges River dolphins have historically been important as a source of oil and meat. The oil is used or as an ingredient in traditional medicines. The oil can be used to lure a specific species of catfish. The meat is used as bait to attract fish. However, dolphin meat does not attract fish any more than other fish scraps, so local fishermen must be educated to use other fish scraps due to the endangered status of Ganges River dolphins. Many top predators, including Platanista gangetica, serve as key indicators of water and environmental quality. In recent decades, due to heightened awareness of human impact on these freshwater ecosystems, many researchers are beginning to understand how extreme the pollution and toxin build up in these river systems has become.

Positive Impacts: food ; body parts are source of valuable material; source of medicine or drug

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Risks

IUCN Red List Category

Endangered (EN)
  • IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
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