Animal Info - Ganges River Dolphin

(Other Names: Blind Dolphin, Delfín del Ganges, Ganges-Delphin, Ganges Dolphin, Ganges Susu, Gangetic Dolphin, Hihu, Plataniste du Gange, Shushuk, Side-swimming Dolphin, Sousou, Susu)

Platanista gangetica gangetica (P. gangetica)

Status: Endangered


Contents

1. Profile (Picture)
2. Tidbits
3. Status and Trends (IUCN Status, Countries Where Currently Found, Taxonomy, Population Estimates, History of Distribution, Threats and Reasons for Decline)
4. Data on Biology and Ecology (Size and Weight, Habitat, Age to Maturity, Gestation Period, Birth Season, Birth Rate, Early Development, Maximum Age, Diet, Behavior, Social Organization, Density and Range)
5. References


Profile

Pictures: Ganges River Dolphin #1 (9 Kb JPEG) (Mohan 2000); Ganges River Dolphin #2 (5 Kb JPEG) (Cetacea); Ganges River Dolphin #3 (67 Kb JPEG) (Terrambiente)

The Ganges River dolphin has a long beak, a stocky body, and large flippers. Its eye lacks a lens, and the dolphin is sometimes referred to as being blind, although its eyes do seem to function as a direction-finding device. The Ganges River dolphin measures 1.5 - 2.5 m (4.9 - 8.2 ft) in length and weighs up to 90 kg (200 lb). It occurs only in fresh water, in Bangladesh and India, where the rivers flow slowly through the plains, as well as in Nepal, where the dolphin can be found in relatively clear water and rapids. The Ganges River dolphin lives not only in the main channels, but also, during the flood season, in seasonal tributaries and flooded lowlands. 

The Ganges River dolphin feeds on several species of fish, invertebrates, and possibly turtles and birds. It does much of its feeding at or near the bottom. The waters that it inhabits are extremely murky.  Probably for this reason, the dolphin's sight has degenerated.  To find food, it probably uses echolocation and also probes with its sensitive snout and flipper for prey in the bottom mud. Reports from the 19th century speak of ‘large schools’ of Ganges River dolphins to be seen near most large towns on the Ganges River. However, in more recent times, this dolphin has usually been found to occur in small groups or alone. 

The Ganges River dolphin was formerly distributed throughout the Ganges-Brahmaputra river system of Bangladesh, India and Nepal, and possibly Bhutan. Although it still has a fairly extensive range, its distribution has contracted, and its abundance has declined dramatically in some areas. Currently it is found in the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Bangladesh and India. A few individuals survive in Nepal in the Karnali River and possibly the Sapta Kosi River.  The linear extent of its distribution in the Ganges mainstem appears to have diminished by some 100 km (62 mi) since the 19th century, and even larger amounts of tributary habitat have been lost due to reduction in water flow below irrigation barrages.  Its habitat is severely fragmented, and additional barrages continue to be built. Further reductions in the extent of occurrence and area of occupancy of this dolphin are expected. It is almost certainly declining in numbers and will continue to do so as habitat degradation shows no sign of abating. 


Tidbits

*** The Ganges River dolphin lives in one of the world's most densely populated areas - almost a tenth of the world's population lives within the Ganges River drainage area (Cetacea).

*** It has been recently found that fish oils can be used in the place of Ganges River dolphin oil for the preparation of bait. Popularization of fish oil as bait may reduce the poaching of dolphins for its oil, which causes the mortality of hundreds of dolphins every year. (Sinha 2002)


Status and Trends

IUCN Status:

Countries Where the Ganges River Dolphin Is Currently Found:

2006: Occurs in Bangladesh, India and Nepal (Ganges-Brahmaputra-Megna and Karnaphuli-Sangu river systems). May occur in Bhutan. (IUCN 2006)

Taxonomy:

The Indus and Ganges River dolphin populations, previously treated as separate species, have recently been reduced to subspecies of a single species.  The new species is named the "Ganges River dolphin" (Platanista gangetica), with two subspecies - the Ganges River dolphin (Platanista gangetica gangetica) and the Indus River dolphin (P. g. minor).  Under this new assignment of scientific names, the newly named species as well as the two subspecies retain the listing of "Endangered" by the IUCN.  (IUCN 2003a, Reeves 2004)

Population Estimates:

[Note: Figures given are for wild populations only.]

History of Distribution:

The Ganges River dolphin was formerly distributed throughout the Ganges-Brahmaputra river system of Bangladesh, India and Nepal, and possibly Bhutan, below an elevation of about 250 m (820'). Although it still has a fairly extensive range, its distribution has contracted, and its abundance has declined dramatically in some areas. Currently it is found in the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Bangladesh and India. A few individuals survive in Nepal in the Karnali River and possibly the Sapta Kosi River.  The linear extent of its distribution in the Ganges mainstem appears to have diminished by some 100 km (62 mi) since the 19th century, and even larger amounts of tributary habitat have been lost due to reduction in water flow below irrigation barrages.  Its habitat is severely fragmented, and additional barrages continue to be built. Further reductions in the extent of occurrence and area of occupancy of this dolphin are expected. It is estimated to be declining in numbers and will continue to do so as habitat degradation shows no sign of abating. The current population size has been reduced by an unknown amount compared to historical levels, but it is still thought to be large enough to be viable in the long-term if adequate conservation measures are taken soon. (IWC 2000, Culik 2003c, Reeves et al. 2003, IUCN 2006)

Distribution Map #1S (23 Kb JPEG) (WCMC/CMS) (smaller map)
Distribution Map #1L (69 Kb JPEG) (WCMC/CMS) (larger map)
Distribution Map #2 (55 Kb JPEG) (IUCN 2006) 

Threats and Reasons for Decline:

Construction of 50 or more dams and barrages within the Ganges River dolphin’s historic range has drastically altered its habitat and fragmented the population. More such structures are planned or are under consideration. Approximately 3500 km (2200 mi) of embankments have been constructed along the main channel of the Ganges and its tributaries. Embankments interrupt access to spawning habitat for floodplain-dependent fishes and eliminate eddy counter-currents where the dolphins spend much of their time. Dredging and the removal of stones, sand, and woody debris also compromise the ecological integrity of the riverine environments, especially in small tributaries. Concentrations of toxic chemicals such as organochlorine and butyltin  in the tissues of Ganges River dolphins are high enough to cause concern about adverse effects. Incidental mortality in fishing gear, especially gillnets, is a severe problem for the Ganges River dolphin throughout most of its range. (Reeves et al. 2003)

Deliberate killing of Ganges River dolphins for meat and oil is believed to have declined in most areas, but it still occurs in some locations. The demand for these products means that there is little incentive for fishermen to reduce the bycatch or to release dolphins that are still alive when found in nets. (Reeves et al. 2003)


Data on Biology and Ecology

Size and Weight:

The Ganges River dolphin measures 1.5 - 2.5 m (4.9 - 8.2 ft) in length and weighs up to 90 kg (200 lb).

Habitat:

The Ganges River dolphin occurs only in fresh water in  Bangladesh and India, where the rivers flow slowly through the plains, as well as in Nepal, where the dolphin can be found in relatively clear water and rapids.   In both areas, there is a preference for deep waters, especially deep counter-current eddy pools below channel convergences and sharp meanders and above and below mid-channel islands, bridge pilings, and other engineering structures that cause scouring. The Ganges River dolphin lives not only in the main channels, but also, during the flood season, in seasonal tributaries and flooded lowlands.  It has been found in water between 8 and 33 deg C (46 - 91 deg F). Brackish waters are a major component of the total range, but the Ganges River dolphin is not generally known to occur in salinities greater than 10 ppt, although it has been recorded in waters as saline as 23 ppt. (Klinowska 1991, Sinha 2000, Sinha et al. 2000, Smith et al. 2001, Culik 2003c, IUCN 2006)

The Ganges River dolphin lives in the Indo-Burma Biodiversity Hotspot (Cons. Intl.).

Age to Maturity:

Males become sexually mature at 1.7 m (5.6') or less, at an age of about 10 years.  The smallest sexually mature female so far reported was 2.0 m (6.6'). (Klinowska 1991) Age at first reproduction for females is probably 6 - 10 years (IUCN 2006).

Gestation Period:

Approximately 1 year.

Birth Season:

Calving apparently can occur at any time of the year, but there may be peaks during December - January and March - May. (Culik 2003c)

Birth Rate:

A single young is born.

Early Development:

The young begin eating solid food 1 - 2 months after birth and are weaned within 1 year.

Maximum Age:

The oldest male animal aged so far was about 28 years old (Klinowska 1991).

Diet:

The Ganges River dolphin feeds on several species of fish (e.g. catfish, freshwater shark, mahseers, gobies and carp), invertebrates (e.g. prawns and clams), and possibly turtles and birds. It does much of its feeding at or near the bottom, using echolocation, swimming on one side, and probing the river bottom with its snout and flipper. (Klinowska 1991, Culik 2003c)

Behavior:

The waters that the Ganges River dolphin inhabits are extremely murky.  Probably for this reason, the dolphin's sight has degenerated.  Its eye lacks a lens, and the dolphin is sometimes referred to as being blind, although its eyes do seem to be used for direction-finding. To find food, it probably uses echolocation and also probes with its sensitive snout and flipper for prey in the bottom mud. (Nowak 1999)  

The marked seasonal changes in the distribution and density of the Ganges River dolphin over much of its range are due, at least in large part, to fluctuations in water levels. During the dry season from October - April, many dolphins leave the tributaries of the Ganges - Brahmaputra system and congregate in the main channels, only to return to the tributaries the following rainy season. They may become isolated in pools and river branches during the dry season. (Culik 2003c)

Social Organization:

Reports from the 19th century speak of ‘large schools’ of Ganges River dolphins to be seen near most large towns on the Ganges River. However, in more recent times, this dolphin has usually been found to occur in small groups or alone. One study found that 80 % of the dolphins observed during the dry season in the Meghna and Jamuna Rivers of Bangladesh were solitary individuals. The size of a number of groups surveyed in the Ganges River system averaged 1 - 3, with a range of 1 - 20. Relatively high densities of dolphins are found at sites where rivers join, in areas where the current is relatively weak, off the mouths of irrigation canals, and near villages and ferry routes. (Klinowska 1991, Sinha et al. 2000, Culik 2003c)

Density and Range:

In a 52 sq km (20 sq mi) area of the Karnali River system it was estimated that the density of Ganges River dolphins was 0.23 individuals/sq km (0.60 individuals/sq mi) in September 1982 and 0.38 individuals/sq km (0.98 individuals/sq mi) in January 1983. (Klinowska 1991)

Surveys have resulted in the following estimates of linear densities of Ganges River dolphins (Smith et al. 2001):

  • 0.76 individuals/km (1.2 individuals/mi) (125 dolphins total; entire Karnaphuli-Sangu complex) (Smith et al. 2001)
  • 1.4 individuals/km (2.2 individuals/mi) (59 dolphins total; Sangu below the Dohazari Bridge) (Smith et al. 2001)
  • 0.81 individuals/km (1.3 individuals/mi) (60.3 km (37.4 mi) covered; middle reaches of the Ganges mainstem) (Smith et al. 2001)
  • 0.24 individuals/km (0.39 individuals/mi) (89.6 km (55.6 mi) covered; middle reaches of the Yamuna (Brahmaputra) River) (Smith et al. 2001)
  • 0.30 individuals/km (0.48 individuals/mi) (113.0 km (70.2 mi) covered; Kalni-Kushiyara River) (Smith et al. 2001)
  • 1.5 individuals/km (2.4 individuals/mi) (Ganges River mainstem between Maniharighat and Buxar (within this segment there are two subsegments with densities of 2.8/km (4.5 individuals/mi) and 3.4/km (5.5 individuals/mi))) (IUCN 2006) 
  • 0.09 individuals/km (0.15 individuals/mi) (Sundarbans of Bangladesh) (IUCN 2006) 

References

Ahmed 2000, Burton & Pearson 1987, Cetacea, Cons. Intl., Culik 2003c, IUCN 1994, IUCN 1996, IUCN 2000, IUCN 2002, IUCN 2003a, IUCN 2004, IUCN 2006, IWC 2000, Klinowska 1991, Mohan 2000, Nowak 1999, Nowak & Paradiso 1983, Oryx 1986j, Oryx 1987f, Reeves et al. 2000, Reeves et al. 2003, Reeves 2004, Sinha 2000, Sinha 2002, Sinha et al. 2000, Smith & Reeves 2000, Smith et al. 2001, Terrambiente, WCMC/CMS 


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