Dolphins are the most uncontroversial of popular motifs of contemporary times, promoted on television and Hollywood movies alike as symbols of wholesome fun, innocence and gentle intelligence. The exposure, however, is biased towards marine dolphins. Freshwater dolphins, in dire need of public sympathy and protection, have gone largely neglected. Most people are not even aware of the fact that that some species of dolphins (or cetaceans) are found in habitat other than seas and oceans. In fact, four of a total of about 40 species of cetaceans inhabit rivers; three of these are found in Asia, and, of them, two belong to South Asia.
The South Asian freshwater dolphins are the Platanista gangetica minor (bhulan, sometimes also referred to as susu) in the Indus river of Pakistan and the Platanista gangetica (susu) of the Ganga-Brahmaputra system in India, Nepal and Bangladesh. The lipotes vexillifer (baiji) is confined to the Yangtze of China, and the fourth specie, inia geoffrensis (boto), belongs to the Amazon.
While there is no conclusive fossil record, estimates are that the Gangetic dolphin has been around for about 20 million years. It was not until 1801 though, that the susu was first scientifically documented and christened Platanista gangetica by William Roxburgh, a Scottish botanist who was at the time the superintendent of the Calcutta Botanical Garden. The dolphin that was thus identified lives in the highly turbid waters of the Ganga, Brahmaputra, Meghna and Karnaphuli rivers and their tributaries. It inhabits these rivers from the estuarine area to as far upstream as is navigable by them, depth and the evenness of the riverbed being crucial determinants. The Gangetic dolphin is found in Nepal too where the rivers are comparatively clear.
The Ganga dolphin has a sturdy and flexible body, large flippers and a low triangular dorsal fin. In the Ganga, on average, the maximum length that an adult female dolphin may attain is 2.5 metres while the male attains a maximum length of 2.1 metres. After a gestation period of 10 to 11 months, a fully developed calf is born that is usually about 70 cm long. Adult dolphins are light grey in colour whereas the calves are dark chocolate brown. The jaws of an adult are lined with over 130 prehensile teeth meant for capturing small fish usually not more than 10 cm long; the lower jaw is longer than the upper one.
The susu has a narrow gullet and cannot masticate its food, as a result of which it can prey on only small fish. When the dolphin breaks the water surface to breathe through its blowhole (a nasal opening on the head) at intervals that can last from 10 seconds to several minutes, it produces a typical sound that is the basis of its various local names. The Sanskrit word for the river dolphin is shishumachli but this gentle creature is more usually called sous, susa, sunsar, sus, susu, soonse, souns, susuk, hiho or huh among other things. In parts of Nepal, the dolphin is called the suongsu.
Since the Ganga river dolphin lives in muddy water, it is difficult to study the animal and little is known about its behaviour. It is known, though, that susu are solitary creature, seldom found in groups.
Most toothed whales are thought to be able to interrogate their environment with sound. By bouncing sounds off an underwater target and analysing the signal they get back, a dolphin is able to accurately locate an object, determine whether and where it is moving, differentiate between object densities, say fat from bone, and tell whether the target is dead or alive. If alive and potential food, a dolphin may be able to stun it, and sometimes kill it, with a high-density beam of sound.
Perhaps the most remarkable thing about the susu is that notwithstanding the absence of crystalline lens from its eyes, which helps in forming images, and the absence of which renders the susu blind, it occupies the top level of the food chain in the Ganga river system. One hypothesis holds that the susu lost its vision due to its environment. Vision would not be of much use in the muddy waters of the Ganga, its habitat, so over the evolutionary course the susu lost its vision. Instead, the Gangetic dolphin seems to be a sophisticated user of ‘echolocation’, that is, emitting sounds and locating underwater targets by analysing the bounced reverberations.
Though it was discovered as long ago as 1942 that dolphins are able to use sound for navigation and finding prey, and there have been many experiments since then, to this day we know very little about their echolocation system. We do know, however, that most dolphin species emit a single and narrow ‘beam’ of echolocation clicks, which gives them an acoustical picture of the terrain; the bottlenose dolphin, for example, has a beam of about nine degrees, a thin pencil-beam of sound. Platanista gangetica, though thought to be a more primitive species, emits a 65 degrees beam with two beams of clicks, which gives it two pictures. One beam gives the dolphins fuzzy ‘big pictures’ of the river channel environment while the other beam is reflected by an extraordinary projection of the back of the upper jaw, giving the dolphins a more detailed view of what is directly in front of their open mouths.
The first beam is most useful for navigating complex river channels, and ‘looking’ for fish, while the second beam works best for actually capturing fish. Part of the evolution of these creatures might have been a narrowing of the beam width, which would give them greater penetrative power for the same amount of energy. The concentration of energy in narrow-beam dolphins has become so intense that the prey becomes affected by it even as it is located, resulting in an entirely novel way of catching food. Dr Georgio Pilleri, of the Institute of Brain Anatomy at Berne, observed that the susu continuously emits trains of high frequency (15 to 150 kHz) echolocation clicks which are interrupted only by short pauses of 1 to 60 seconds.
The hydrological regime of a river has a direct bearing on the movement of the dolphins. There is constant daily local migration usually in search of food but in addition, there is also seasonal migration. The search for food leads the Gangetic dolphin to floodplains in the monsoon where most fish migrate in order to spawn and the prey is plentiful. Water levels also dictate migration patters. That is why in the dry months between October and April, the tributaries have barely any dolphins in them. A migration to the main river channels takes place, and a reverse flow occurs after the monsoon. However, barrages and dams on rivers have in many cases disrupted this pattern.
Of all the river dolphins, the baiji, as also the finless porpoise with which it shares the waters of the Yangtze, is the most critically endangered. It teeters on the brink of extinction with not more than a few score still alive. Compared to this, the susu population seems robust. In the Ganga, the major susu habitat, a total of 730 dolphins have been sighted in recent years between Bijnor, near the foothills of the Himalaya, and Farakka, near the Indo-Bangladesh border. A survey team sighted 152 dolphins in the river Bhagirathi-Hoogli between Farakka and Calcutta in 1995. About 400 dolphins have been sighted in the Brahmaputra, which is the other major susu habitat in the Subcontinent. It is estimated on the basis of various surveys that about 2000 dolphins survive in the Ganga system today. However, if not protected now, it is likely that the Gangetic dolphin will face the same fate as its cousin in China. Indeed, the Gangetic dolphin is in a precarious situation today, its survival threatened by a fast receding habitat that is increasingly fragmented.
About half of India’s susu population is found in the waters of the Ganga and its tributaries within the state of Bihar. The latest survey, conducted by the Environmental Biology Laboratory of Patna University in 2000-01, counted 68 dolphins in a 60 km stretch between the Ganga-Punpun confluence at Fatuha (about 20 km downstream from Patna) and the Ganga-Ghaghara confluence at Doriganj (40 km upstream from Patna). One of the areas frequented by the susu, in fact, is the confluence of the Gandak and the Ganga, right by Patna University’s riverside campus where the laboratory is located and where this writer works.
In the Vikramshila Gangetic Dolphin Sanctuary between Sultanganj and Kahalgaon in Bihar, the only one of its kind in India, a total of 114 dolphins were sighted during a survey in 2000. In March 2001, 85 dolphins were sighted in the river Kosi between the Kosi Barrage at the India-Nepal border and the confluence with the Ganga at Kursela. Besides these major concentrations, dolphins have also been sighted in other tributaries of the Ganga.
While there are as yet significant numbers of susu in the main stem of the Ganga as it flows through Bihar, the dolphin’s status in the Ganga tributaries of Nepal is a matter of great concern. Mostly, it is the barrages built across the tributaries in India to feed irrigation canals that affects the susu population. These barrages block the migratory passage of dolphins, which empties the rivers of the susu upstream in Nepal.
The Karnali river in Nepal (called Ghaghara in India) is the furthest upstream that the dolphins are found in the Ganga system, the species not being seen in the tributaries further to the west. In 1976, the Girija Barrage was constructed across the Karnali river, about 20 km into India. There are now about 30 dolphins upstream of the barrage, a majority of them in Indian territory, and the Karnali’s flow in Nepal is thought to host less than 10 dolphins. What seems to have significantly endangered the dolphins of the Karnali-Ghaghara, besides the impact of the barrage, is the loss of prey to over-fishing by humans.
In the case of the Kosi river, at the eastern end of Nepal, it is the massive Kosi Barrage, constructed in 1965 on the border with India that blocks the migration of dolphins and other migratory species. Only three dolphins were sighted in the Kosi on the Nepal side in 1993. In the same year, only one dolphin was sighted in the Narayani-Gandak river in central Nepal. Again, a barrage built at the border point with India in 1968 seems to have decimated the susu population in upstream Narayani. Today, there are probably no dolphins on the river. Barrages on the Mahakali (Sarda in India) at Banbasa on the Indo-Nepal border in 1928, and at Sardanagar in 1974 about 160 km into Indian territory, have similarly resulted in the extinction of dolphins from the Mahakali-Sarda.
As no systematic population survey of dolphins was carried out prior to the one undertaken by the Patna University team in the Ganga and its tributaries, no meaningful comparison with earlier population figures can be made. However, John Anderson, the first superintendent of the Indian Museum at Calcutta, reported in 1879 that even in the month of May, when the water level was low in the Yamuna at Delhi, there used to be a substantial number of dolphins visible in the river. It is unlikely that any susu survive this far upstream on the Ganga system now. Other than a susu carcass which was brought in from the Yamuna to the Delhi Zoo in 1967, there has been no sign of the susu in the Yamuna.
Reports of dolphin killings from different areas are disturbingly regular, and this together with habitat degradation has resulted in a decline in the population throughout the range of distribution. Moreover, a dolphin gives birth to only one calf at a time after a gestation period of about 10 months at an interval of about two to three years. The low natality means that, in any case, the regeneration rate of the dolphin is sluggish. It is clear that, despite the visibility of the susu in the mainstream of the Ganga in Bihar, the Gangetic dolphin is a threatened species.
The clock’s ticking
Is the concern over the susu simply the result of environmental sentimentalism, or does the species have a utilitarian function that can justify its existence? Cynics have been known to ask such questions. The fact is that the Gangetic dolphin does play an important role in a river’s ecology, and in that capacity it is of great assistance to humans and other species who draw sustenance from the water courses. Indeed, the susu is itself a valuable indicator of the health of the river, its presence indicating the availability of fish, besides which it is also a gauge by which to determine the levels of pollutants and toxicity in the water.
The use of organochlorine pesticides by agriculturalists has continually been on the rise in the Gangetic plains, and heavy metals also make their way into the river through untreated industrial and urban waste. Studies have shown alarming levels of these toxins in the body and organs of susu carcasses. Among the organochlorine pesticides, DDT and its metabolites are the most prominent compounds found in the susu, followed by other poisonous chemicals such as hexachloro cyclohexane, aldrin, dieldrin, chlordanes and heptachlor. One can surmise that these chemicals are prevalent in dangerous proportions in the waters of the Gangetic plains, India’s most fertile area and the nub of its agriculture.
Toxic chemicals including Poly Chlorinated Biphenyles (PCBs) and DDT accumulate in the upper micro-layer of the river water and phytoplankton. These toxicants reach the dolphins through the food chain. As a result, a dolphin accumulates a huge quantity of toxic chemicals, especially fat-soluble compounds. Due to bio-magnification, some of these chemical compounds tend to increase at every level of the food chain, and dolphins, being at the apex of the chain, accumulate the highest amounts of these compounds. Such compounds are well known for having adverse effects on vital organs, and on the endocrine system, affecting behaviour, reproduction, fecundity, feeding, nutrition and response to diseases. Organochlorine compounds and heavy metals cross the placenta during pregnancy and are transferred from mother to calf. In such conditions even a newly born calf will have toxic chemicals in its system.
The Gangetic dolphin is not threatened only by pollution, however. Habitat degradation and fragmentation of population are also major causes of concern. Heavier siltation in the rivers due to deforestation and soil erosion in catchment areas, as well as the constriction of flow between embankments in many parts, have decreased the depth of rivers and made it difficult for dolphins to navigate. Barrages restrict the migration of dolphins in upstream and downstream locations, which affects spawning and makes the populations genetically isolated.
Besides, susu populations in their entire distribution range from the Brahmaputra to the Karnali face the threat of monofilament nylon gill nets, which are now commonly used by fishermen. These nets are made of very fine nylon thread that the animal fails to locate with its sonar devices. It therefore often gets trapped in the net, cannot come up for air, and ends up drowning. Up to some decades back, fisher folk used to harpoon susu because they considered the dolphin to be competing for the fish. The fact is that the susu feed only on small fish which have little commercial value, as well as molluscs and insect larvae. Increasing awareness of the provisions of the Wildlife (Protection) Act of India (1972), which protects the susu, has made fishermen give up the harpooning practice, but other causes of morbidity have become increasingly relevant.
The susu has been declared an endangered species by, The World Conservation Union (IUCN) and its inclusion in the wildlife act as a Schedule-I animal, makes possession of any part or product of it an offence. The animal is also included in appendix 1 of the Convention on International Trade of Endangered Species (CITES). However, the good that has come from the legal protection tendered to the susu has been negated by recent developments that make dolphin poaching a lucrative business. Oil extracted from the blubber (the thick layer of fat under the dolphin’s skin) can be used to attract and catch some varieties of catfish. An adult dolphin of more than 100 kg can yield up to 30-35 litres of oil. This oil is sold at the rate of INR 100-300 per kg with the rate varying according to season, availability and the economic status of the customer. Changing food habits contribute their own pressure on the population: while earlier very few communities along the Ganga would eat dolphin meat, now many do. Dolphin meat sells at the rate of INR 25-30 per kg and so even one dolphin can make a fisherman a tidy sum of money.
A river with a good susu population is a healthy river, which translates also into a healthy habitat for humans. The presence of the susu indicates that the level of pollutants is low, that the river’s flow is large, that there are enough fish for the dolphins to prey on, and that the riverine habitat has not been depleted by the diversion of water to irrigation canals, nor violated irrevocably by the intrusion of barrages and dams. There are still some stretches of the Ganga where one gets to experience the frolic of dolphins that our river-faring ancestors would have enjoyed. One such spot is where the Ganga meets the Gandak opposite the Patna University campus. Going out on a boat in mid-morning, one finds the confluence area well populated by susus. Every few seconds one comes up for air, gives a snort, and disappears into the muddy waters. Their smooth grey skins glisten in the sunlight as they emerge and dive quickly, possibly in hot echolocatory pursuit of fish.
As they splash and dunk on the river by Patna city, these dolphins of the Ganga seem unaware of what is almost inevitable – that humans will continue to encroach on their habitat, polluting the river with urban and industrial waste, emptying the river of its flow to quench the thirst of agriculture, and otherwise making the river uninhabitable by the dolphin. Little do the humans know that what they do to the dolphin as a climax species of the Ganga today, they do unto themselves tomorrow. The susu is a symbol of the aquatic heritage of the Subcontinent and it is the responsibility of the people here to let it survive.
The susu in literature and legend
In India, there is enough historical and mythological evidence to confirm that the susu has been a close associate of humans for a long time. In the third century BC, the Maurya emperor Ashok passed a decree through what is known as the ‘fifth pillar edict’ barring the killing or hunting of the “Ganga-puputaka” – the Gangetic dolphin as it was known then. Dolphins are referred to by their Persian name khokk aabi, or water hog, in the Baburnama. Bhattasali, author of Iconography of Buddhist and Brahminical sculptures in Dacca Museum, identifies the susu as the carrier (vahana) of the mythical goddess Ganga. In some villages along the river Ghaghara in Chhapra district, Bihar, India, the riparian community worships the dolphins. They regard them, because they suckle their babies, as “cows of the Ganga”.
According to one belief the dolphins are an incarnation of a royal beauty who drowned in the Ganga. As the legend goes the lady while bathing spotted her father-in-law riding along the bank. Out of sheer embarrassment she tried to veil her face with the rising waves and so went to a watery grave.