The Indus River dolphin (scientific name: Platanista minor) is fresh water cetacean closely related to the Ganges River dolphin (Platanista gangetica). These two endangered dolphins were long regarded as a single species and some regard them as two subspecies rather than distinct and separate species. Though Platanista minor and Platanista gangetica barely differ morphologically except for slight differences in tail lengths, the two species are distinguishable by their ranges. Platanista minor occurs only in the Indus River system, while Platanista gangetica inhabits only the Ganges River system.
The close connection of these species is likely explained by the fact that "until the late Pliocene, the present-day Indus, Ganges and Brahmaputra (except for the upper reach, the Yarlung Zangpo Jiang) Rivers constituted a single westward-flowing river called the Indobrahm (Hora 1950, 1953). Even up until historical times there was probably sporadic faunal exchange between the Indus and Ganges drainages by way of head-stream capture on the low Indo-Gangetic plains, between the Sutlej (Indus) and Yamuna (Ganges) Rivers (Dey 1968)."
|Indus river dolphin. Source: Associated Press|
|Size comparison of an average human against the Finless porpoise. Source: Chris Huh|
Gross morphological features are: endothermic metabolism and bilateral symmetry. Indus River dolphins are roughly the same colour as the river, gray or brown, though they sometimes are lighter on their undersides. Their beaks are distinctively swollen at the tip and quite long, reaching 20% of the length of their bodies, with large, visible teeth.
In contrast to their veaks, dorsal fins are rather small and reduced compared to other river dolphins. Large flippers and flukes, combined with long and remarkably flexible necks, probably help the dolphins navigate effectively. Platanista minor has external ears located below their eyes, but their eyes are very small and probably can only see shadowy, unclear images.
Though P. minor and P. gangetica scarcely differ physically except for slight differences in tail lengths, the two species are clearly diagnostic by their ranges. P. minor solely in the Indus River system, while P. gangetica is found only within the Ganges River basin. Clear sexual dimorphism is displayed with females being larger than males. (Moreno, 2004)
Key overview behaviors are: natatorial; motile; solitary; and social. The Indus River dolphin is described as chiefly solitary, although the has occasionally been observed in groups consisting of as many as 30 individuals. In general, however, Indus River dolphins travel in groups of no more than three.
These dolphins are equipped to swim on their sides in very shallow water if necessary, yet except for juveniles, P. minor rarely exhibits the stereotypical dolphin aerial leaping behavior. On the other hand, like other dolphins, these marine mammals are highly vocal and perceive their environment through echolocation. These sounds are principally used to navigate while swimming, with a very small percentage used for communication. (Moreno, 2004; Pilleri, 1974)
Little data is available about the home range of the Indus River dolphin. The Ganges River dolphin, however, has been reported at densitites of 0.70-1.36 dolphins per kilometer. Perhaps the Indus River dolphin also requires about a square kilometer of space each, though data is still absent to determine how far they travel. Most of what is known about spatial movement is that they appear to migrate seasonally along the river. (Smith et al., 2001)
Voice and Sound Production
Indus River dolphins have extremely poor eyesight, perhaps since vision is nearly useless to navigate the heavily silted rivers in which they live. They instead rely on echolocation to sense and map their environment. Indeed, one of the common names for Platanista minor is Blind river dolphin. Their external ears may help receive echolocation signals, which are intermittent pulses rather than continuous whistles. Though Indus River dolphins are very vocal, they use sounds for communication only about five percent of the time that they vocalise. (Moreno, 2004) While the species communication channels are solely acoustic, their perception channels are tactile, echolocation and chemical.
There is virtually no data available regarding the lifespan of the Indus River dolphin. Members of the species likely have a significantly long lifespan, since individuals are relatively large and require ten years to reach sexual maturity. However, recent poor water quality and reduced habitat may affect the current longevity of these animals in the wild. At least a few Indus River dolphins have been kept in captivity; however, longevity data is unavailable. (Herman, 1980; Reeves and Chaudhry, 1998)
Key reproductive features are: Iteroparous; year-around breeding; gonochoric/gonochoristic/dioecious (sexes separate); sexual; viviparous. Though scattered assemblies exist of captive populations of Platanista minor, little is known about the mating behaviour of any of the members of the Platanistidae family. (Herman, 1980; Moreno, 2004) These dolphins probably do not mate seasonally, since calves are born at different times throughout the year. However, in a captive population of two females and a male in Switzerland, the male reportedly chased the females in the spring. There is a very long gestation period of eight to eleven months.
Though not emphasised in the literature, this species probably gives birth to only a single offspring at a time, since newborns are about a meter long when they are born, which is nearly half the length of an adult female. (Moreno, 2004) Since calves nurse up to a year after birth, Indus River dolphin offspring are probably very costly in terms of maternal energy and time consumption. (Moreno, 2004)
The Indus River dolphin probably does not breed more than once every two years, due to the protracted gestation and nursing periods. Beyond the nursing data, little information is available about parental investment in Platanista minor; however, it is deemed likely that parental nurturing involves considerable time and energy on their offspring.
Distribution and Movements
Indus River dolphins are found only in the Indus River in Pakistan. Platanista minor previously ranged throughout the river system, but the dolphins are now only found in the waters above the Kotri Barrage and below the Chasma, Trimmu, Sidhnai, and Islam Barrages. These human-created barriers, in addition to changes in rainfall patterns, have greatly limited the dolphins’ distribution. (Hamilton et al., 2001; Mann et al., 2000; Moreno, 2004). Distribution of the Indus River Dolphin. Source:IUCN Red List: South Asian River Dolphin
The IUCN Red List provides additional details: [The Indus River dolphin] is endemic to the rivers of the lower Indus basin in Pakistan. Historically it occurred in the Indus mainstem and the Sutlej, Beas, Ravi, Chenab, and Jhelum tributaries. It ranged from the Indus delta upstream to the Himalayan foothills where rocky barriers or shallow water prevented further upstream movement. Development of the vast Indus Basin Irrigation System has severely fragmented the dolphin population within a network of barrages (low, gated, diversion dams) and water diversion has dramatically reduced the extent of dolphin habitat. Current occupancy is effectively limited to three subpopulations in the Indus mainstem located between the Chashma and Taunsa, Taunsa and Guddu, and Guddu and Sukkur Barrages. A few individuals still remain above Chashma Barrage and below Sukkur Barrage (Braulik 2003, Reeves and Chaudhry 1998, Reeves 1998)
Platanista minor currently occurs only in the freshwater Indus River. However, some paleontologists believe that river dolphins might have evolved from marine-dwelling relatives that eventually moved to estuaries and then rivers as seawater levels rose and fell during the Miocene. Though this species prefers water deeper than three meters, Indus River dolphins have special adaptations such as swimming on their sides that enable them to exist in shallower waters as well. The temperature of the water ranges from 8 to 33 degrees Celsius. (Hamilton et al., 2001; Mann et al., 2000; Moreno, 2004) The totality of aquatic biomes utilised are cheifly benthic zones of rivers and streams including brackish waters.
The IUCN Red List adds:
Indus River dolphins generally occur in the deepest river channel and are less common in secondary channels and small braids (Bhatti and Pilleri 1982, Braulik 2003). Reported habitat preferences include channel constrictions, confluences, and deep, low-velocity water (Kasuya and Nishiwaki 1975, Khan and Niazi 1989, Braulik 2004). During the low-water season (October to April), barrages divert almost all river water such that dolphin habitat downstream of Sukkur Barrage and in some tributary segments has been eliminated. As water levels drop in the winter, dolphins are concentrated in the remaining deep areas, including the head ponds upstream of barrages.
Indus River dolphins use their echolocation abilities combined with their densely toothed, long snouts to forage for many bottom-dwelling animals including fish and invertebrates. Platanista minor has been known to consume certain species of Siluriformes, Clupeiformes, Cyprinidae, Gobiidae, mahseers, Malacostraca, and Bivalvia. Captive individuals reportedly consume approximately one kilogram of food each day. (Moreno, 2004) Other animal prey include a variety of mollusks, aquatic crustaceans and miscellaneous aquatic invertebrates
Indus River dolphins each consume approximately one kilogram of benthic fish and invertebrates daily, it is not clear how strongly they impact any of their prey populations. (Moreno, 2004) Platanista minor has few if any natural predators, however, they are often hunted by local people. (Moreno, 2004)
Economic Importance for Humans
There are no known adverse affects of Platanista minor on humans, though no one knows what might happen to the river ecosystem if these highly-endangered animals eventually become extinct. At the very least, however, Pakistan will lose part of its biodiversity forever if the country does not take steps to protect this unique dolphin. (Moreno, 2004; Reeves and Chaudhry, 1998)
Threats and Conservation Status
The IUCN Red List reports:
The entire current range of the Indus subspecies was surveyed in 2001 and resulted in an estimates of 843 to 1171 individuals, with a most likely population value of 965. The largest subpopulation, containing more than 60% of the total, is located in the Sindh Dolphin Reserve between the Guddu and Sukkur Barrages, at the downstream end of the subspecies’ range. The next largest, with about 27% of the total for the subspecies, is immediately upstream in the Guddu-Taunsa segment of the Indus.
. . . Dolphin counts in the Guddu-Sukkur segment of the Indus showed an apparently increasing trend from 1974 to 1996. If this increase was real and not an artifact of variable sighting biases, it could be explained by recovery after implementation of a hunting ban in 1974 or by permanent immigration from upstream subpopulations.
. . . Marked declines have occurred in the extent of occurrence . . . from approximately 3,400 km of the main channel and its tributaries in the 1870s to approximately 1,000 linear km of the main channel today. An estimated 99% of the Indus dolphin population occurs in only 690 linear km, corresponding to an 80% reduction in the area of occupancy for that subspecies.
The most significant threat to dolphins in the Indus has been the construction of at least 25 dams and barrages that have severely fragmented the population and reduced the amount of available habitat (Smith and Reeves 2000). Upstream subpopulations may lose individuals downstream if dolphins move through barrage gates when they are open in the wet season. Individuals are unlikely to move upstream through a barrage because of strong downstream hydraulic forces at the gates. While there have been no direct observations of dolphins moving through a barrage, they often swim through regulator gates into irrigation canals, which, although smaller, present a similar obstacle (Braulik 2002). Evidence for permanent downstream emigration includes that each subsequent downstream subpopulation is larger than the one above (see Range and Population above), despite the reduced linear extent and availability of water in downstream segments. Encounter rates in the farthest downstream subpopulation (between Guddu and Sukkur Barrages) are very high (3.60 dolphins/linear km), approaching three times those recorded in similar surveys elsewhere for Platanista dolphins (Braulik 2003). The possible large increase in the dolphin subpopulation between Guddu and Sukkur Barrages (described above) may be due to reproduction and reduced mortality alone, or may be augmented by downstream emigration. Even a low emigration rate could dramatically affect the persistence of upstream subpopulations (Reeves et al. 1991, Reeves and Smith 1999).
Since the mid 1990s, there have been increasing reports of dolphins trapped in irrigation canals near Sukkur Barrage. Dolphins have survived for several months in the canals until they are drained in January for annual de-silting and maintenance. Between January 2000 and December 2002, 34 dolphins were reported trapped in these canals. Twenty-four were successfully rescued and returned to the Indus River, while the remainder died (Bhaagat 1999, Braulik 2002, WWF-Pakistan unpublished data).
One of the direst threats to the survival of the Indus River Dolphin is probably the escalating demand for water. Pakistan is a largely desert nation, with a rapidly growing human population and fast developing industrial and agricultural sectors that demand increasing amounts of water. Several years of extreme drought have depleted aquifers that would normally be expected to augment river flows in the dry season.
Pollution may be affecting the viability of the subspecies, especially considering the decline in flushing and dilution due to reduced flows. The Indus River corridor is not highly developed and above the Panjnad River confluence, the habitat is likely to be relatively unpolluted. However, more than 75% of the dolphin population occurs downstream of the confluence with the Panjnad River, which receives a large pollution load from the industrialized cities of the Punjab. There are almost no facilities for treatment of municipal waste in Pakistan and few controls on industrial effluent. Massive fish kills have reportedly become common from industrial pollution in urban areas and from pesticides used on irrigated crops grown along the riverbanks (Reeves and Chaudhry 1998). The pressures on river water supply and continued untreated discharge of pollutants imply that there will be a continuing decline in the amount and quality of dolphin habitat.
Deliberate killing for meat and oil was a traditional and widespread practice until at least the early 1970s (Pilleri and Zbinden 1973–74). Hunting is now banned although poaching occasionally occurs. Similar to all cetaceans, this subspecies is vulnerable to entanglement in fishing gear and vessel collisions. However, the areas of the Indus River where dolphins are extant are not heavily fished or utilized by vessels and these factors may not be major threats at present. Incidents of accidental killing and observations of dolphin carcasses and products are documented in Reeves et al. (1991) and Reeves and Chaudhry (1998).
Platanista minor is a species of critical concern, and a combination of human-created barriers such as dams and barrages, hunting, and a limited natural range have resulted in a dangerously-low total population of only several hundred individuals. These dolphins are classified as endangered, and have been so since the 1970's. Their extremely low population size may also restrict their gene pool, thus they might soon have many problems associated with low genetic variation within a population. (Moreno, 2004; Reeves and Chaudhry, 1998)
In 1972, dolphins were protected under the Wildlife Act of Sindh and in 1974 the government of Sindh declared the Indus River between the Sukkur and Guddu Barrages a dolphin reserve. The government of Punjab prohibited deliberate killing of dolphins in the Punjab Wildlife Protection Act in 1974 and established the Taunsa Wildlife Sanctuary and Chashma Wildlife Sanctuary in 1983 and 1984, respectively (Reeves et al. 1991, Reeves and Chaudhry 1998, Chaudhry and Khalid 1989). Enforcement of regulations prohibiting dolphin hunting appears to have arrested the rapid population declines reported by Pilleri and Zbinden (1973–74) for these river segments. A programme sponsored by the United Nations Development Programme (UNDP) to rescue dolphins trapped in irrigation canals and return them to the Indus mainstem has had some success in reducing mortality (Braulik 2002, Bhaagat 2002).
The species is classified as endangered according to the IUCN Red List as well as the USA Federal List. The species is set forth in CITES: Appendix I.
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