Platanista gangetica

South Asian River Dolphin

Platanista gangetica

French: Plataniste / German: Ganges-Delfin / Spanish: Delfin del Ganges

Other common names: Blind River Dolphin, Indian River Dolphin; Ganges River Dolphin, Susu (gangetica); Bhulan, Indus River Dolphin (minor)

Taxonomy. Delphinus gangeticus Lebeck, 1801,

India.

Two subspecies are recognized.

Subspecies and Distribution.

P.g.gangeticaLebeck,1801—Ganges-Brahmaputra-MeghnaandKarnaphuli-SanguriversystemsofSNepal,N&NEIndia,andBangladesh.

P. g. minor Owen, 1853 — Indus River system of SC Pakistan and NW India (Beas River).

Descriptive notes. Total length ¢.170-260 cm, weight c¢.110 kg. The South Asian River Dolphin is a brown or pale gray, stocky dolphin with a very long slender rostrum and exposed teeth. They have small triangular dorsal fins, but very large pectoral flippers and broad tail flukes. The eye is reduced to a tiny slit-like opening in the skinjust above the corner of the mouth. Long, thin, protruding teeth in young individuals wear over time to become flat disks in adults.

Habitat. Distributed through several thousand kilometers of large alluvial rivers of the Indian subcontinent, from the foothills of the Himalaya and Karakoram mountains in the North, to the river deltas in the South. They are almost never found in the ocean. The South Asian River Dolphin is patchily distributed and occurs with highest frequency at confluences of rivers and streams. Deltaic waters, particularly in the Sundarbans in Bangladesh, are also important habitat, and although very occasionally sightings are reported in nearshore marine waters they generally do not occur in salinities greater than 10 ppt.

Food and Feeding. South Asian River Dolphins feed on a large variety of freshwater bottom-dwelling prawns, fish, and crustaceans including catfish (Wallago attu and Sperata aor), carp (Catla catla and Cirrhinus cirrhosus) and freshwater prawns (Macrobrachium rosenbergii and M. malcolmsonii).

Breeding. Females become sexually mature at about eight years of age, and gestation lasts for about one year. Offspring are born during winter or spring and are weaned at about one year of age or before. The breeding cycle is likely two years. Sexual maturity is achieved at around ten years. The oldest individual recorded was a 28year-old male, but it is estimated that animals may live to ¢.35 years.

Activity patterns. South Asian River Dolphins surface rapidly and unpredictably, spending only c.1 second at the surface. Very little is known about the behavior of the South Asian River Dolphin because of their short surface interval and the inability to observe them in the turbid water they inhabit.

Movements, Home range and Social organization. South Asian River Dolphins are believed to shift their distributions with seasonal changes in river discharge; individuals move upstream and into smaller rivers when rivers are swollen during the summer monsoon and move into the mainstream of larger rivers in the dry season when discharge is low. In many places, dams or irrigation barrages now block these seasonal movements. Individuals occur primarily alone or in small groups, but occasionally in aggregations of 20 or more. Individuals and groups often surface in the same location for periods of at least 30 minutes. There is no specific information available on social organization or home range.

Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red List, including both subspecies. Dams and irrigation barrages fragment populations of the South Asian River Dolphin, and its distribution is contracting, especially in the smaller rivers in the northern part of the distributional range. Eleven of 17 subpopulations of the Indus River Dolphin have been extirpated, and only six populations remain, isolated between barrages; three are estimated to have less than 20 individuals each and are probably too small to persist, leaving only three that may be viable in the long-term. The largest population of the Indus River Dolphin is in northern Sindh Province between Guddu and Sukkur barrages. In 2001, this subspecies was estimated to number ¢.1300 individuals and may have been increasing since dolphin hunting ceased in the 1970s. In 2006, the Indus River Dolphin was estimated to number 1550— 1750 individuals. Given its much larger range, the Ganges River Dolphin is likely to be more abundant than the Indus River Dolphin, and there may be several thousand individuals. Significant portions of its range have not been surveyed; however, B. D. Smith and colleagues estimated 255 individuals in the Sundarbans of Bangladesh in 2006. Its major threats are likely population fragmentation, depleted dry-season river flows, and incidental capture in fishing gear. Reduced flows concentrate South Asian River Dolphins, pollutants, and human activities and exacerbate many anthropogenic threats.

Bibliography. Anderson (1879), Arnason et al. (2004), Bashir et al. (2010), Braulik (2006, 2012), Braulik, Bhatti et al. (2012), Braulik, Reichert et al. (2012), Brownell (1984), Cassens et al. (2000), Hamilton et al. (2001), Haque et al. (1977), Harrison (1972), Herald et al. (1969), Home (1818), Jefferson et al. (2008), Kasuya (1972), Kelkar et al. (2010), Kinze (2000), Lebeck (1801), Meredith et al. (2011), Owen (1853), Pilleri (1970), Pilleri, Gihr et al. (1976), Pilleri, Zbinden et al. (1976), Purves & Pilleri (1974), Reeves & Brownell (1989), Reeves et al. (1991), Sinha, Behera & Choudhary (2010), Sinha, Das et al. (1993), Sinha, Smith et al. (2000), Smith (1993), Smith, Braulik, Strindberg, Ahmed & Mansur (2006), Smith, Braulik, Strindberg, Mansur et al. (2009), Ura et al. (2007), Wakid (2009).