Platanista gangetica ssp. minor
|Scientific Name:||Platanista gangetica ssp. minor Owen, 1853|
Platanista minor Owen, 1853
|Red List Category & Criteria:||Endangered A2abcde; B1ab(i,ii,iii,iv); C1 ver 3.1|
|Assessor(s):||Braulik, G.T., Smith, B.D. & Chaudhry, S.|
|Reviewer(s):||Reeves, R. & Taylor, B.L.|
This subspecies meets several of the criteria for listing as Endangered, as follows:
Only very limited data are available on the life history of Platanista sp. (reviewed by Brownell 1984). Age at first reproduction is likely between 6–10 years and maximum longevity may be close to 30. Therefore, generation time is probably more than 10 but possibly less than 20 years, so three generations into the past would be to 1944–1974 and two generations would be 1964–1984.
Subcriterion A2 applies because a population size reduction of more than 50% since 1944 (the longest estimated time of three generations) is inferred and suspected, given that almost all of the critical barrage construction associated with the large-scale decline in the area of occupancy has occurred since that time. Moreover, the reduction and its causes have not ceased (habitat quality is expected to deteriorate further and mortality from canal entrapment continues), are not fully understood, and may not be reversible. The basis could rest on any or all of (a) to (e) with the case strongest for (c).
The linear extent of occurrence of the subspecies is approximately 1,000 km of the Indus River (Reeves et al. 1991, Braulik 2003). Analysis of satellite images indicates that during the dry season the average width of the Indus River is 900 m, meaning that the extent of occurrence for the Indus Dolphin is approximately 900 km², clearly below the 5000 km² threshold for listing as EN under Criterion B1 (Braulik 2004). The area of occupancy of this subspecies is 690 linear km, or 620 km², falling just outside the 500 km² threshold for criterion B2.
The metapopulation presently occurs at no more than five locations (defined as segments of river between two barrages), thereby meeting subcriterion 'a' of B1. Prior to 1990 there were occasional reports of dolphins in the lower Chenab and Sutlej Rivers, but these reports have ceased, implying that the remnant subpopulations in those tributaries have now been extirpated. Subpopulations above Chashma Barrage and below Sukkur Barrage have been reduced in size so that they are almost certainly too small to persist in the long term. Meanwhile, the demand for river water for agricultural, industrial, and urban use continues to escalate, which implies a continuing decline in suitable habitat, and in the number of subpopulations, extent of occurrence, and number of mature individuals, thereby also meeting subcriterion 'b' of B1.
Although the best estimate of about 1,000 individuals made by Braulik (2003) for the total population size may be negatively biased due to availability (i.e., dolphins were submerged when in the field of view of observers) or perception (observers were looking elsewhere or were inattentive), the number is far below the Criterion C threshold of 2,500 mature individuals. Evidence that the Indus population meets this criterion becomes even more compelling when the measures taken by Braulik (2003) to minimize and evaluate sighting biases are considered (see above). Given the rapid escalation in demand for water from the Indus and the likely associated degradation and loss of habitat for the subspecies, it is reasonable and precautionary to estimate that a 20% or greater reduction in population size is likely to occur in the next two generations (20–40 years). The subspecies therefore also qualifies for listing as EN according to Criterion C1.
|Previously published Red List assessments:|
|Range Description:||This subspecies 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) (see Figure 1 in the Supplementary Material). |
The Indus River Dolphin was considered by some researchers as a distinct species for several decades (1970s–1990s) and was listed as such in the 1996 Red List. Its range is disjunct with that of the other subspecies, Ganges River Dolphin, Platanista gangetica gangetica, and therefore the two have been assessed and listed, and should be managed, separately.
The map shows where the species may occur. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states.
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Direct-count surveys of the largest subpopulations have been conducted regularly by the Sindh and Punjab Wildlife Departments since the early 1980's, but described methods do not provide a basis for evaluating bias, estimating precision, or detecting trends in abundance (Reeves and Chaudhry 1998). Dolphin counts between Guddu and Sukkur Barrages show an apparent increase from 139 dolphins recorded in 1974 (Pilleri and Zbinden 1973–74), to 290 in 1979 (Pilleri and Bhatti 1980), and 458 dolphins in 1996 (Mirza and Khurshid 1996). If this increase was real and not an artifact of variable sighting biases, it could be explained by recovery of the subpopulation after implementation of a hunting ban in 1974 (see Conservation Actions below) or by permanent immigration from upstream subpopulations (see Major Threats below). A comprehensive review of previous survey data is presented in Reeves and Chaudhry (1998) and Reeves et al. (1991). |
The most recent and comprehensive assessment of the Indus Dolphin population was a survey of their entire range conducted in March and April 2001 that resulted in a minimum abundance estimate of 965 dolphins (based on the sum of best estimates of group size of all sightings). High and low estimates of group size were also recorded. The sum of high estimates was 1,171 and the sum of the low estimates 843. This survey also documented a pronounced increase in the abundance and encounter rate of dolphins as the survey vessel proceeded downstream. The largest subpopulation is located in the Sindh Dolphin Reserve between the Guddu and Sukkur Barrages, at the downstream end of the range. Best estimates of 602 total dolphins and 3.6 dolphins/linear km were recorded for this section, 259 dolphins and 0.74 dolphins/linear km for the section between Guddu and Taunsa, and 84 dolphins and 0.28 dolphins/linear km for the furthest upstream section between Taunsa and Chashma. Two dolphins were seen upstream of Chashma Barrage and 18 downstream of Sukkur Barrage.
The minimum abundance estimate of 965 dolphins for the subspecies is likely to be close to the actual population size due to measures taken in the field to increase sighting efficiency. Essentially all potential dolphin habitat was surveyed in the Indus mainstem, including secondary channels and braids off the main channel, from a non-motorized vessel (mean survey speed = 5 km/hr), which maximized detection opportunities. Double-concurrent counts were also conducted from a second vessel traveling behind the primary survey vessel. Sightings were considered unique if they were greater than 750 m distant from another group according to the GPS positions. Preliminary analyses indicate that the primary survey vessel missed less than 10% of dolphin groups, and no groups of more than 3 individuals (mean group size recorded was 2.0; SD = 1.6; range 1–11) (Braulik 2004). The probability of double counting dolphins due to their movement from surveyed to unsurveyed areas overnight was considered to be balanced by the probability that an equal number of dolphins were missed altogether due to their movements in the opposite direction.
The linear extent of occurrence of the subspecies has declined from approximately 3,400 km of Indus mainstem and its tributaries in the 1870s (see Anderson 1879) to approximately 1,000 linear km of the mainstem today (Braulik 2004). An estimated 99% of the dolphin population occurs in only 690 linear km, which corresponds to an 80% reduction in the area of occupancy (Anderson 1879, Reeves et al. 1991, Braulik 2003, Braulik 2004). During the 1970s and 1980s there were occasional reports of dolphin occurrence between barrages in the lower reaches of the Indus tributaries (Reeves et al. 1991). No recent surveys have been conducted in those areas. However, due to an increase in upstream water abstraction and a decline in dry season flows, it is unlikely that any dolphins remain in these reaches.
|Current Population Trend:||Unknown|
|Habitat and Ecology:||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.|
|Movement patterns:||Full Migrant|
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).
|Conservation Actions:||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).|
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|Citation:||Braulik, G.T., Smith, B.D. & Chaudhry, S. 2012. Platanista gangetica ssp. minor. The IUCN Red List of Threatened Species 2012: e.T41757A17628296.Downloaded on 13 December 2017.|
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