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Platanista gangeticaGanges river dolphin(Also: susu)

By Jonathan Swinton and Whitney Gomez

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. (Moreno, 2003; Nowak, 1999; Nowak, 2003)

Habitat

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. (; Moreno, 2003)

  • Range elevation
    0 to 250 m
    0.00 to 820.21 ft
  • Range depth
    0 to 9 m
    0.00 to 29.53 ft
  • Average depth
    3 m
    9.84 ft

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. (Moreno, 2003; Nowak, 2003; Reeves and Brownell Jr., 1989; Wilson and Reeder, 2005)

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. (Moreno, 2003; Nowak, 2003; Reeves and Brownell Jr., 1989; Wilson and Reeder, 2005)

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. (Moreno, 2003; Nowak, 2003; Reeves and Brownell Jr., 1989; Wilson and Reeder, 2005)

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. (Moreno, 2003; Nowak, 2003; Reeves and Brownell Jr., 1989; Wilson and Reeder, 2005)

  • Range mass
    51 to 89 kg
    112.33 to 196.04 lb
  • Range length
    200 to 400 cm
    78.74 to 157.48 in

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. (Moreno, 2003; Reeves, et al., 2002)

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. (Jefferson, et al., 2008; Moreno, 2003; Nowak, 2003; Reeves, et al., 2002)

  • 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
  • Average number of offspring
    1
    AnAge
  • 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 (female)
    Sex: female
    3652 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    10 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    3652 days
    AnAge

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. (MacDonald and Norris, 2001)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

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. (Reeves and Brownell Jr., 1989)

Behavior

Ganges River dolphins are solitary animals but they occasionally congregate in groups of 3 to 10 individuals. Groups of up to 30 animals have been reported. Mothers and calves stay together until the infants are weaned. Despite their mostly solitary nature, these river dolphins are found in loose aggregations, especially at tributary junctions where prey congregate. Some consider Ganges River dolphins semi-gregarious. There are some indications of territoriality, as chasing behaviors in males have been observed. Generally, these animals are shy towards humans, even in captivity. Their elusive nature has made them difficult subjects to study. (Moreno, 2003; Nowak, 2003; Perrin, et al., 2002; Reeves and Brownell Jr., 1989)

Ganges River dolphins have a peculiar method of swimming, in that they swim on their sides when submerged. At roughly a 10 degree angle, they swim a few centimeters from the bottom, constantly nodding the head, allowing it to sweep the bottom in search of food. For unknown reasons, most individuals swim on their right sides. Side swimming also positions their eye at an angle appropriate to sensing light, perhaps providing orientation for the animal while diving. Their tails are always positioned higher than the head in side swimming, allowing them to swim in water as shallow as 30 cm. When they surface for air, they level out and swim laterally. In captivity, measured swimming speed reached 5.4 km/hr, but this may not be representative of possible speeds in the wild, where habitats are more open. They have been recorded swimming upwards of 27 km/hr in the wild. Captive animals swim and vocalize continuously over a 24 hour period, with only brief interruptions lasting a few seconds. When swimming intensity relaxed, for example in drifting locomotion, the intensity of vocalizations emitted also relaxed. Dives are typically short, the longest wild dive was 3 minutes. Average dive times in the wild are between 1 minute 10 seconds and 1 minute 40 seconds. Dives in captivity are shorter than wild dive times, with the longest being 1 minute and 35 seconds. In many cetaceans, myoglobin concentrations are generally high to cope with the stress of diving, but due to their relatively shallow river habitats and short dive periods, myoglobin concentrations in heart and muscle tissues are considerably lower.

  • Average territory size
    Unknown km^2

Home Range

Little is known about home range sizes in Platanista gangetica. Aerial and shoreline observations have proven inadequate at determining the given range of an individual. These animals travel extensively throughout river ecosystems, moving from mainland channels to coastlines and tributaries as the seasons change. (Moreno, 2003; Perrin, et al., 2002; Reeves and Brownell Jr., 1989)

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. (MacDonald and Norris, 2001; Moreno, 2003; Nowak, 2003; Reeves and Brownell Jr., 1989)

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. (Reeves and Brownell Jr., 1989)

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 giuris), 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. (Reeves and Brownell Jr., 1989)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

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. (Perrin, et al., 2002)

  • Anti-predator Adaptations
  • cryptic

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. (Moreno, 2003; Reeves and Brownell Jr., 1989)

Commensal/Parasitic Species
  • Cyclorchis campula
  • Echinochasumus andersoni
  • Anisakis simplex
  • Contracaecum lobulatum

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. (MacDonald and Norris, 2001; Moreno, 2003)

Economic Importance for Humans: Negative

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

Conservation Status

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. (Kannan, et al., 1993; Perrin, et al., 2002; Reeves and Leatherwood, 1994)

Contributors

Jonathan Swinton (author), University of Michigan-Ann Arbor, Whitney Gomez (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

Glossary

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

nomadic

generally wanders from place to place, usually within a well-defined range.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

piscivore

an animal that mainly eats fish

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

solitary

lives alone

tactile

uses touch to communicate

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

Jefferson, T., M. Webber, R. Pitman. 2008. Marine Mammals of the World: A Comprehensive Guide to their Identification. San Diego, CA: Academic Press.

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.

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.

Nowak, R. 1999. Walker's Mammals of the World, Vol. 2, 6 Edition. Baltimore: The Johns Hopkins University Press.

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.

Perrin, W., B. Wursig, J. Thewissen. 2002. Encyclopedia of Marine Mammals, Vol. 1, 1 Edition. New York: Academic 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.

Reeves, R., S. Leatherwood. 1994. Dams and River Dolphins: Can They Coexist?. Ambio, 23: 172-175.

Reeves, R., B. Stewart, P. Clapham, J. Powell. 2002. Sea Mammals of the World. New York: Chanticleer Press, Inc..

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.

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