Ganges dolphin [1] [2] [3] [4] [5] , or susuk [1] ( lat. Platanista gangetica ) - aquatic mammal of the toothed whale suborder, a representative of the group of river dolphins .
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International Red Book IUCN 3.1 Endangered : 41758 |
In the 1970s the single species Platanista gangetica was divided into 2 species: the Ganges and Indian dolphins ( Latin Platanista minor ), after it became clear that the Indus and Ganges populations had not crossed for several hundred years. However, in the 1998 taxonomic classification (Rice), both species were again combined on the basis that the morphological differences between them are insignificant.
General Description
This dolphin deviates most sharply from other species of dolphins. The length of his body is 2–2.6 m, weight - 70–90 kg; females are larger than males. The color is solid dark gray, sometimes almost black, brightening on the belly, with a pinkish tinge.
The body is full. Cervical interception is pronounced. The pectoral fins are large, wide, chopped off. Instead of the dorsal fin there is a low triangular hump. Caudal fin about 46 cm wide. The pectoral and caudal fins are large compared to the body.
Breathing longitudinally, slit-like, and not lunate, like most dolphins. The head is small. The beak is long, 18-20 cm, narrow, noticeably thickens towards the end; adapted to the search for food in the bottom soil. The frontal ledge is steep. Teeth 29-30 pairs above and 29-33 pairs below; front teeth sharply enlarged. The teeth are visible even when the mouth is closed. The eyes are tiny. Due to the habitat in murky water, susuk's eyes lost their lens , their optic nerve degraded, and the mucous membrane began to perform a tactile function. Susuk is almost blind, although it is still able to capture the intensity and direction of light. Guides and hunts with the help of developed echolocation . When breathing, the dolphin makes a characteristic sound “susuk”, which served as the occasion for its name.
Distribution and abundance
The Ganges dolphin lives in the basins of the Ganges and Brahmaputra ( India , Nepal , Bhutan , Bangladesh ), Hoogli ( India ), Meghna and Karnaphuli (Bangladesh), as well as in the river basin. Indus ( Pakistan ). The most studied Indian subspecies. Historically, its range has stretched from the delta to the foot of the Himalayas , where rapids and shallow water impeded further distribution. In the XIX century. the range of the dolphin in the Indus was 4-5 times higher than the modern one; in particular, dolphins were found in the tributaries of Sutledge , Ravi, Chinab, and Jhelam. The linear extent of the range in the 1870s . amounted to about 3400 km along the Indus and tributaries, then at present it is 900 km, and 99% of the population is concentrated throughout only 690 km. Now the population in the river. Indus is divided into 3-5 subpopulations between the dams of Chashma and Towns, Towns and Guddu, Guddu and Sukkur. The population density according to 2001 was:
- 3.6 individuals / km in the Sinda nature reserve between the Guddu and Sukkur dams (602 individuals),
- 0.74 individuals / km between the Guddu and Towns dams (259 individuals),
- 0.28 individuals / km between the dams of Towns and Chashma (84 individuals)
2 dolphins were seen above the Chashma Dam and 18 below the Sukkur Dam.
- The greater number of dolphins in the lower Indus is probably due to one-way migration, when dolphins freely pass through open gates of dams during the rainy season. However, a strong current prevents them from returning up the river. In the same way, dolphins pass through the control gates of irrigation canals. As a result, the number of dolphins in the lower (and most polluted) sections of the river increases, while in the upper reaches it decreases. Dolphins also fall into traps in irrigation canals and die during their planned drainage. From January 2000 to December 2002 , 34 dolphins were rescued from canals near the Sukkur Dam [6] .
According to paleontology, river dolphins apparently evolved from marine mammals, which gradually migrated to the estuary and then to the fresh water of the rivers during the Miocene . At the end of the Pliocene , when the modern Indus, Ganges, and the lower reaches of the Brahmaputra represented the united Indobrahma River, flowing to the west, the susuk freely settled along its length. Even in historical times, river fauna exchanges were possible between the Indus ( Sutledge ) and Ganga ( Yamuna ) basins during strong river spills [6] .
Lifestyle
The Ganges dolphin lives in slowly flowing muddy rivers and their tributaries; sometimes goes into irrigation canals. Maintains mainly in the upper reaches. It goes down to the mouth only in the rainy season, but never leaves the sea. It occurs at water temperatures from 8 to 33 ° C. It keeps at day depth (more than 3 m) during the day, hunts in shallow water at night (up to 20-30 cm). It remains under water for up to 2 minutes, usually 35-40 seconds. Often swims on its side, especially in shallow water. Usually slow, but capable of high-speed jerks. With the exception of young individuals, acrobatic abilities are not usual for dolphins.
Searches for food, mainly digging with beak and pectoral fins in the bottom soil. It feeds on fish ( catfish , carps , gobies) and various invertebrates (crustaceans, mollusks). The amount of food eaten daily is about 1 kg (in captivity). The ability to echolocation is very developed; With it, a dolphin is able to detect a wire with a diameter of 1 mm. The study showed that 81% of the sounds (clicks) emitted by dolphins are related to echolocation and only 5% to communication. Dolphins keep alone, occasionally in groups of 3-10 individuals (maximum 30). They usually accumulate at the confluence of rivers and tributaries, that is, at fodder places, as well as at the mouths of canals, in areas with a weak current, near villages and crossings. Moved in groups of no more than 3 individuals. According to observations, the population density of dolphins is 0.7-1.36 individuals / km. Perhaps an adult requires at least 1 km of space.
Reproduction
The biology of reproduction is poorly studied. The mating period is not pronounced, but most births occur in October - March. The largest number of cubs is born in December - January at the beginning of the dry season. The duration of pregnancy is 8-11 months. There is 1 cub in the litter. A newborn has a body length of 45–70 cm and a weight of 7–7.5 kg. At the age of one year, the cub reaches a length of about 116 cm and becomes independent. It reaches puberty between 6 and 10 years. Childbirth probably occurs once every 2 years.
Life expectancy is about 30 years.
Subspecies
Currently, there are 2 subspecies [7] :
- Platanista gangetica gangetica [8] - actually the Ganges dolphin , nominative subspecies;
- Platanista gangetica minor [9] (= Platanista indi [3] [2] , Platanista minor [5] ) - Indian dolphin [10] [2] [11] , or small Ganges dolphin [4] [5] , a subspecies from the river Indus
Conservation Status
Ganges dolphin - a small animal listed in the International Red Book with the status of "endangered species" ( endangered ). He has no natural enemies. It is extracted by people for the sake of meat, which is used as food and fish bait, as well as for fat, which is used for lighting in traditional medicine (in particular, as an aphrodisiac ).
The main danger to the population, however, is man-made pressure on dolphin habitat. River dolphins often get entangled in fishing nets and collide with passing vessels. Irrigation works and water withdrawals for agricultural, industrial and other needs dramatically reduce the water level throughout the dolphin's range, especially in the dry season. Chemical pollution also plays a role in reducing dolphin numbers. Finally, the construction of numerous dams and dams, begun in the 1930s , blocks the flow of rivers, hindering the seasonal migration of the dolphin, changing its habitat and dividing the single population into isolated subpopulations with limited genetic diversity.
The densest dolphin populations are concentrated near Vikramshila's special refuge in India (Vikramshila Gangetic Dolphin Sanctuary), in southern Bangladesh, and in the Pakistani province of Sindh . The smallest number, about 20 individuals, lives in the river. Karnali ( Nepal ). The environmental measures undertaken by the Government of Pakistan allowed to increase the number of Indian subspecies, which in 1974 was estimated at only 450-600 heads. A 2001 survey of the Indian dolphin by WWF Pakistan showed that about 1,171 individuals live in the country; the total number over the entire range may be several thousand. The Indian dolphin is the national symbol of Pakistan, along with the marchor and the Asian lion, and has been protected by laws since 1974 . The Ganges subspecies of the dolphin is less studied, its range and abundance are not exactly known.
The number of Ganges and Indian dolphins, according to environmentalists, will continue to decline due to the degradation of their habitat.
Notes
- ↑ 1 2 Tomilin A.G. Order Cetaceans (Cetacea) // Life of animals . Volume 7. Mammals / ed. V. E. Sokolova . - 2nd ed. - M .: Education, 1989 .-- S. 369-370. - 558 p. - ISBN 5-09-001434-5
- ↑ 1 2 3 Biological Encyclopedic Dictionary / Ch. ed. M.S. Gilyarov ; Editorial: A.A. Baev , G.G. Vinberg, G.A. Zavarzin et al. - M .: Sov. Encyclopedia , 1986.- S. 539.- 831 p. - 100,000 copies.
- ↑ 1 2 Sokolov V.E. Systematics of mammals. Volume 3. Cetaceans, carnivores, pinnipeds, aardvarks, proboscis, damans, sirens, artiodactyls, callopods, artiodactyls. - M .: Higher school, 1979. - S. 19-21. - 528 s.
- ↑ 1 2 Sokolov V.E. The Bilingual Dictionary of Animal Names. Mammals Latin, Russian, English, German, French. / edited by Acad. V. E. Sokolova. - M .: Rus. lang., 1984. - S. 112. - 10,000 copies.
- ↑ 1 2 3 Complete illustrated encyclopedia. "Mammals" Prince. 2 = The New Encyclopedia of Mammals / Ed. D. MacDonald . - M .: Omega, 2007 .-- S. 468. - 3000 copies. - ISBN 978-5-465-01346-8 .
- ↑ 1 2 Platanista gangetica on IUCN
- ↑ Smith BD, Braulik GT 2012. Platanista gangetica . The IUCN Red List of Threatened Species 2012.
- ↑ Smith BD, Braulik GT, Sinha R. 2012. Platanista gangetica ssp. gangetica . The IUCN Red List of Threatened Species 2012.
- ↑ Braulik GT, Smith BD, Chaudhry S. 2012. Platanista gangetica ssp. minor . The IUCN Red List of Threatened Species 2012.
- ↑ Sokolov V.E. Rare and endangered animals. Mammals: Ref. allowance. - M .: Higher school, 1986. - S. 228—229. - 519 p., [24] p. silt - 100,000 copies.
- ↑ Sokolov V.E. Fauna of the world: Mammals: A Handbook. - M .: Agropromizdat , 1990 .-- S. 125. - 254 p. - ISBN 5-10-001036-3