Post-flood
status of the Endangered Ganges River Dolphin Platanista gangetica gangetica (Cetartiodactyla: Platanistidae) in
the Koshi River, Nepal
Top
Bahadur Khatri 1, Deep Narayan Shah 2 & Nilamber
Mishra 3
1Conservation and Sustainable Use of Wetlands in Nepal (CSUWN),
Training Section Building, Second floor, Forestry Complex, Babar Mahal,
Kathmandu, Nepal
2Conservation and Sustainable Use of Wetlands in Nepal (CSUWN),
Koshi Tappu Wildlife Reserve, Paschim Kusaha, Sunsari, Nepal. PO Box 20791,
Sundhara, Kathmandu, Nepal
3Department of National Parks and Wildlife Conservation, Koshi
Tappu Wildlife Reserve, Paschim Kusaha, Sunsari, Nepal
Email: 1 tbkhatri@wetlands.org.np, 2 shahdeepnarayan@yahoo.com
(corresponding author), 3 nmishra@yahoo.com
Date of publication (online): 26
December 2010
Date of publication (print): 26
December 2010
ISSN 0974-7907 (online) | 0974-7893
(print)
Editor: Gill Braulik
Manuscript details:
Ms # o2496
Received 29 June 2010
Final received 10 November 2010
Finally accepted 30 November 2010
Citation: Khatri, T.B., D.N. Shah & N. Mishra (2010). Post-flood status of the Endangered Ganges River Dolphin Platanista gangetica gangetica (Cetartiodactyla: Platanistidae) in the Koshi River, Nepal. Journal of Threatened Taxa 2(13): 1365-1371.
Copyright: © Top Bahadur
Khatri, Deep Narayan Shah & Nilamber Mishra 2010. Creative Commons
Attribution 3.0 Unported License. JoTT allows unrestricted use of this article
in any medium for non-profit purposes, reproduction and distribution by
providing adequate credit to the authors and the source of publication.
Author
Details: Author Details: Top Bahadur Khatri’s research interests are in resource
management, park-people interface, community stewardship and wetland
conservation in Asia. He has been
implementing various integrated conservation and development projects in and
around the protected areas of Nepal for over two decades. In addition, he is
associated with a number of professional and scientific organizations.
Deep Narayan Shah’s research interests are in aquatic
biology, ecology and wetland conservation in Asia. He has been conducting research in different wetlands
of Nepal and is associated with several national and international scientific
organizations.
Nilamber Mishra’s research interests are in the
ecology and conservation of the large mammals of South Asia. He is currently the Conservation Officer (Warden)
of Koshi Tappu Wildlife Reserve.
Author
Contribution: DNS conducted the field study and wrote up the paper. TBK and NM
contributed by writing the paper as well as conducted field study.
Acknowledgements: We thank Dr. Gopal Sharma, Scientist ‘B’, Zoological Survey of India for
constructive comments on an earlier version of the manuscript. Special thanks are due to Ram Devi T. Shah
(Aquatic Ecologist, Hindu Kush Himalayan Benthological Society) for participation
in the fieldwork during November, helpful comments in the draft version of the
manuscript and assistance with the maps preparation.
Abstract: The breach of the eastern
embankment of the Koshi Barrage at Paschim Kusaha Village of Sunsari District
on 18 August 2008, created havoc for wildlife and their habitats, as well as
people’s livelihood and welfare. The
Koshi River flowed through the breach for five months. Following the breach, a population assessment survey of the Endangered Ganges
River Dolphin Platanista gangetica
gangetica was made between March and November 2009 in the Koshi River main
channel starting from Chatara to 2km south of Koshi Barrage to ascertain their
status. A direct count survey was
conducted by two teams of researchers simultaneously searching for animals by
boat from Chatara to the Koshi Barrage including the Triyuga River and on foot
along the river banks downstream of Koshi Barrage and along the Mariya
River. Standard protocols were followed
to record the number of sighted dolphins. A total of 11 dolphins were recorded in the entire 49-km river stretch
with an encounter rate of 0.23 dolphins per km. The current result showed an encouraging population of dolphins in the
Koshi Tappu Wildlife Reserve and its buffer zone but the threats for
conservation still remain challenging. Close monitoring of dolphins and their habitats involving local
communities are required for long term conservation of the river dolphins in
Nepal.
Keywords:Conservation, Ganges River Dolphin, human pressure, Koshi River, Nepal, status.
For figures, images &
tables -- click here
INTRODUCTION
River dolphins occurring in Asia and South America are amongst the world’s most threatened mammal species (Kreb & Budiono 2005) largely due to increasing human intervention into freshwater ecosystems. The freshwater dolphins inhabit some of the largest river systems in both Asia and South America. The Ganges River Dolphin Platanista gangetica gangetica, or Susu, is a freshwater dolphin distributed throughout the Ganga, Brahmaputra and Meghna river systems in India and Bangladesh, with very small numbers present in Nepal (Smith et al. 1994). Although the aggregate range-wide abundance of Ganges River Dolphins were estimated by Jones (1982) as 4000-5000 individuals and more recently by Mohan et al. (1997) as fewer than 2000, these were only guesses (Smith et al. 2004). Population assessments conducted within isolated portions of the huge network of riverine and deltaic dolphin habitats have been based on counts. Few rigorous estimates of absolute abundance, with estimates of precision, are available for the Ganges River Dolphin anywhere in its range (Smith et al. 2004). Sinha et al. (2000) documented 22 to 32 animals during May 1994 in the Koshi River in Indian territory from the Koshi Barrage to 60km downstream. Subsequently, Sinha & Sharma (2003) during March 2001 reported 87 animals downstream from Koshi Barrage to the confluence with the Ganga at Kursela in India. The studies conducted in the Nepal section of the Koshi River by Shrestha (1989) found a population of eight dolphins between the Koshi Barrage and Barahachetra. Smith et al. (1994), found only three dolphins between the Koshi Barrage and the confluence of the Arun and Sun Koshi rivers and two dolphins downstream of the Koshi Barrage during March-April, 1993. Chaudhary (2007) found no dolphins upstream of the Koshi Barrage in the river section between the barrage and Chatara, but reported a population of 10 to 15 dolphins within 2km downstream of the barrage during October 2006 and January 2007. The survey data implies that the number of dolphins in the Koshi River is variable.
The Koshi River (Fig. 1) is a trans-boundary river that originates
in Tibet (Autonomous Region of China) and flows through Nepal and then
India. It is one of the largest
tributaries of the Ganges. It has seven
Himalayan tributaries: Sun Koshi, Tama Koshi, Dudh Koshi, Indrawati, Likhu,
Arun and Tamur, and is popularly known as SaptaKoshi in Nepal and Koshi in
India. The Koshi River is one of the
extreme upstream limits of Ganges River Dolphin distribution. Koshi Tappu Wildlife Reserve (Fig. 2) is
located 6km upstream of the Koshi Barrage on the floodplain of this river. It was gazetted
in 1976 to preserve habitat for the only remaining population of Wild Water
Buffalo, Arna Bubalus arnee. The threatened Gharial crocodile and Gangetic Dolphin also occur in
the reserve. In Nepal, the river dolphin is protected by Section 10 of the National
Parks and Wildlife Conservation Act 1973 and it is among 27 protected mammals
in Schedule I (His Majesty Government of Nepal/HMGN 1973). In 1987, Koshi Tappu was declared a Ramsar
site, a wetland of international significance. In 2004, the Government of Nepal declared a 173.5km2 buffer
zone surrounding the Reserve. The average annual flow of
Koshi River at Chatara is about 1,600m3/s and the peak flood
generally occurs in June to July (average flood discharge 11,400m3/s)
when the monsoon rain dominates the river flow regime. About 80% of the total annual rainfall occurs
during the monsoon season. The extreme
flow in the Koshi River at Chatara station was 25,879m3/s in 1968
followed by 24,241m3/s in 1954 and then about 24,000m3/s
in 1980 (UNESCO 2009). The breach of the
Koshi embankment occurred during the summer flood in 2008. The mean flood discharge at Chatara during
August 2008 was 5,120m3/sec and peak flood on 18 August 2008 was
only about 4,250m3/s when the breach occurred (UNESCO 2009). The river not only shapes the physical
features of the region, but also modifies the ecosystem of the area and has a
profound impact on the socio-economic characteristics of the local communities’
resident in the buffer zone. The river
is characterized by: (i) alluvial braided channels, (ii) relatively high
velocity, (iii) large seasonal and annual variations in stream flow and
sediment transport, and (iv) mixed use riparian areas, with small settlements of
subsistence farmers and fishermen and forested jungle and grassland (Smith et
al. 1994) contained within Koshi Tappu Wildlife Reserve.
Between 1958 and 1964, a barrage was constructed on the Koshi River in Nepal, about 15km upstream of the international border with India with the eastern and western embankments bounding the river floodplain (UNESCO 2009). The construction of the barrage has changed the pattern of deposition and braiding of the river i.e., decreased braiding activity in downstream of the barrage and increasing sedimentation in the upstream of the barrage. The Koshi River, which was earlier shifting its course gradually, changed its course dramatically during the monsoon of 2008 when it made a 2km breach in an embankment in Kusaha Village (Fig. 2) into a settlement area. This sudden shift in the course of Koshi River caused a dramatic change in the physical landscape and has caused subsequent effects on human settlements. During the flood, three marooned dolphins were found to be trapped in Sripur Village near the Nepal-India border; two of them were rescued and released later into the Koshi River near Paschim Kusaha Village (Image 1) by the Koshi Tappu Wildlife Reserve personal while the other died. The reconstruction of the embankment and diversion of the water flow into its old channel through the barrage was completed in January 2009. The Koshi River course was connected directly to the Ganga River for five months. Given the large changes in the Koshi River in 2008, a population survey of the Endangered Ganges River Dolphin (Image 2) was conducted to ascertain its current status.
MATERIALS AND METHODS
We conducted three surveys of the Ganges River Dolphin on 25-28
March 2009, 21-24 May 2009 and 17-20 November 2009. This season was selected because the river
discharge is at its minimum and dolphins remain concentrated in a narrower
channel and are therefore easier to observe and count. Moreover, to avoid the seasonal migration of
dolphins during the high water level, the survey was conducted in these seasons
(pre-and post-monsoon), as it provides best conditions for population
assessment.
The survey design principles followed those used in previous studies
conducted by different authors (Shrestha 1989; Smith et al. 1994; Chaudhary 2007). Based on local consultations and information
from the Reserve staff, all potential sites frequented by dolphins were
sketched and mapped on a topographic sheet. A survey was then conducted in the entire river stretch from Chatara to
2km downstream of Koshi barrage including the Triyuga and Mariya rivers
(tributaries of the Koshi) to document the distribution of dolphins. Special attention was paid in the identified
potential dolphin habitats in the Koshi River.
The survey was carried out by boat from Chatara to the Koshi Barrage
including the Triyuga River and on foot along the river banks downstream of
Koshi Barrage and along the Mariya River. The Koshi River was divided into six sections namely Chatara to Rajabas
(A), Rajabas to Prakashpur (B), Prakashpur to Cofferdam (C), Cofferdam to
Haripur (D), Haripur to Koshi Barrage (E) and south of Koshi Barrage (F). Surveys were conducted by two teams of
researchers working in different areas, simultaneously. One team surveyed the Koshi Barrage area including
Mariya and Triyuga rivers while the other team made a survey from Chatara to
Koshi Barrage. The teams remained in
mobile phone contact to coordinate searching effort and avoid double counting
the same animal. Each team was led by a
researcher (Deep Narayan Shah and Nilamber Mishra) who had prior experience on
dolphin surveys. The survey boat followed a single transect, following the deepest channel
and moving from one bank to another. The
speed of the boat was maintained at 5-7km/h in a downstream direction. Six observers recorded sighting of dolphins
with four forward observers, two rear observers and a data recorder in each
team. The areas of favourable dolphin microhabitats
such as confluences, meandering, downstream of sandbars, Koshi Barrage areas
etc. were given greater attention. We
used a direct count method (Smith et. al. 1994; Sinha & Sharma 2003) to
estimate the population. When dolphins
were sighted we remained in the area for approximately 30 minutes before
recording a best estimate of the number of animals. Further standardized
point counts were done at the confluence of Triyuga River and at the downstream
of Koshi Barrage. The sighting locations were recorded by a Garmin GPS, and
the time of the record was documented. Dolphin encounter rate was calculated by dividing the number of dolphins
sighted by the total length of the surveyed river stretch measured by GPS.
The direct count of the fisherman was done each
day in each section of the Koshi River from Chatara to downstream of Koshi
Barrage during the dolphin survey. They
were identified either with fish nets or other fishing activities using fishing
boats. They were also recognized with
the fishing license issued by Koshi Tappu Wildlife Reserve administration.
A key-informants interview survey among 50 people was conducted in
the vicinity of the Koshi River to generate and substantiate information about
the presence and abundance of dolphins in the area and about its population
trend. It was conducted in an informal
way with open-ended questions with the local people. Qualitative information on the occurrence and
distribution of dolphins was obtained from the Koshi Tappu Wildlife Reserve
naturalists, biologists, buffer zone committees and line agencies, using semi-structured
interviews. Structured interviews were
mainly employed for knowledgeable local fishermen who spend most of their time
on the Koshi River.
In order to identify the current threats and challenges to the
existing population, a focus group discussion was conducted with the user
groups and user committees of the Reserve buffer zone. Information on recent sightings was reviewed
and measures that could be taken to minimize the threats at the local level
were discussed and documented.
RESULTS
An estimated
total of 11 dolphins, five upstream and six just downstream to Koshi Barrage were recorded in the entire 49km survey area
with an encounter rate of 0.23 dolphins per km in the Koshi River system within
the territory of Nepal. The present study
identified the Koshi Barrage area as the hotspot as the highest number of
dolphins was sighted at this location despite a high level of human
disturbance.
Dolphins were
distributed (Table 1) in the upstream of Koshi Barrage i.e., in Prakashpur,
Cofferdam, Haripur, the confluence of Triyuga River and downstream of Koshi
Barrage (Fig. 3). Downstream of the
barrage dolphins were seen to be concentrated just close to the Koshi Barrage
in the Nepalese territory. Dolphins were
mostly observed solitarily or in small groups but as many as two to six
individuals occurred in the main channel of the Koshi River. They were mostly seen to use the counter
current pools just below the river convergences (Triyuga and Koshi), below mid
Channel Islands (Haripur area), sharp meanders (Rajabas, Prakashpur) and
downstream of Koshi Barrage. No dolphins
were recorded in the Mariya and Triyuga rivers. Locals reported sightings of dolphin activity in Chatara area in the past
but animals have not been sighted there since the construction of the Chatara
irrigation canal in 1975.
We recorded in average a total of 215 fishermen per day in the Koshi River
during the survey, of which 50% were concentrated in the barrage area. We
encountered a minimum (2.15 fishermen/km) in the stretch from Rajabas to
Haripur and the greatest number (10.7 fishermen/km) in the stretch from Haripur
to 2km downstream of Koshi Barrage.
DISCUSSION
Our survey indicates that the Koshi Barrage
area is the most important stretch of the Koshi River in terms of dolphin
abundance. We encountered the dolphins
at the rate of 0.23 dolphins per km. The
present encounter rate in Koshi River is similar to the findings in Brahmaputra
River (Wakid 2009) and is comparatively lower than other major habitats of the
Gangetic Dolphin. In the
Karnaphuli-Sangu river complex and the lower Sangu of Bangladesh, the encounter
rate was 0.76 and 1.36 dolphins per km respectively (Smith et al. 2001). In the Vikramshila Gangetic Dolphin
Sanctuary, located in the middle reaches of Ganges mainstream, the encounter
rate was 0.81 dolphins per km (Sinha et al. 2000). However, this survey was conducted at the
upstream limit of the dolphin distribution and a lower encounter rate than in
the center of the distributional range is to be expected.
The survey results of dolphin population from 1989 to 2007 in the
Koshi River within the territory of Nepal are variable and are also
incomparable due to different methods and different geographic coverage,
however, we recorded the highest number of dolphins i.e., 11 till date (Table
1). The larger count of dolphins
upstream of Koshi barrage recorded in the current study may be attributed to
the systematic survey and its wider geographic coverage than previous surveys. It may also be due to movement of dolphins
into the area from downstream when there was a direct connection for five
months between the main course of the Koshi River and the Ganges during the
breach of the eastern embankment in Paschim Kusaha Village (12km upstream of
Koshi Barrage) in the year 2008. Also
the higher count could be due to natural growth of this population.
The Reserve authority issued 144 fishing
licenses to buffer zone fishermen in 2009 to promote controlled fishing within
the reserve boundary. We observed that fishing
was intensive in the river segment lying outside the Reserve as well as within
the buffer zone (jurisdiction of KTWR). The intensive fishing during low water levels may have an adverse effect
on dolphin prey availability.
The current result shows an encouraging population of dolphins in
the Koshi River but the threats for conservation still remain challenging. Close monitoring of dolphins and their
habitats involving local communities are required for long term conservation of
the species in the Koshi River. The
Government of Nepal, Ministry of Forest and Soil Conservation has implemented
the project entitled “Conservation and Sustainable Use of Wetlands in Nepal”
since 2008 for the conservation of wetlands and its key species. The project has targeted wetland dependent
communities for their livelihood improvement and reducing their dependency on
the wetlands. The project is also
facilitating Koshi Tappu Wildlife Reserve to issue fishing licenses, to strictly
monitor the mesh size of fishing nets and regulate fishing hours. A well structured community awareness
programme, periodic monitoring, habitat management and livelihood interventions
for the wetland dependent community is in place. Despite these undertakings, the long term
conservation of the river dolphins is still a daunting task due to the numerous
pressures on its habitat. The present
political void of the country has had a profound impact in the law enforcement
regime and it will take a while to bring the situation as before. Additionally, the barrage (a low gated dam of a length of 1150m) has isolated the dolphin population upstream from any possible
genetic interchange with animals inhabiting downstream waters (Smith et al.
1994). Dolphins upstream of the barrage
may occasionally move downstream through the barrage during flood periods,
resulting in a permanent loss of animals to an already small and fragmented
population, however it is also possible that animals may move upstream during
floods. Some migratory human settlements
use poison for fishing in the Koshi River which poses a direct threat to the
dolphins. Plants such as Agave americana, Sapium insinge, Dioscorea sp., Euphorbia sp. are frequently used for fishing in the Koshi River
(Yadav 2002; Chaudhary
2007).
CONCLUSION
Based on the findings of our study, it is
concluded that the status and distribution of the Gangetic Dolphin in Koshi
River within the territory of Nepal is satisfactory. We consider the dolphins inhabiting the Koshi River to be of special
conservation value because of Koshi Tappu Wildlife Reserve that makes them a
valuable economic resource for local eco-tourism development. The Ganges and Indus dolphins have been
declining in range and small populations located upstream have been the first
to disappear, therefore the continued survival of dolphins in the Koshi River
in Nepal is encouraging. This may be the
largest population of river dolphins remaining in Nepal and is therefore of
national significance. However, the area
is heavily affected by human activities mainly from over-fishing with a variety
of traps, nets and poisons that degrade the habitat of the dolphin. Integral to sustainable conservation plans
must be a high priority placed on the economic and social development of
subsistence wetland dependent communities particularly fishermen living within
the Koshi River basin. The protection of
the river downstream of Koshi Barrage needs to be bolstered through an intense
surveillance mechanism in order to keep vigil on the dolphins as well as to
deter any illegal activity taking place within the vicinity.
REFERENCES
Chaudhary, S. (2007). Status of, and Threats to, the Ganges River Dolphin (Platanista gangetica) in the Koshi River, Nepal. MSc Thesis. Department of Economics, University of Klagenfurt, Austria, x+38pp.
HMGN (1973). National
Parks and Wildlife Conservation Act, 1973. His Majesty’s Government of Nepal.
Department of National Parks and Wildlife Conservation, Kathmandu, Nepal.
Jones, S. (1982). The present status of the gangetic susu, Platanista gangetica (Roxburgh), with comments on the Indus susu P. minorOwen. FAO Advisory Committee on Marine Resources Research Working Party on Marine Mammals. FAO Fish Series 5(4): 97-115.
Kreb, D. & Budiono (2005). Conservation management of small core areas: key to survival of a critical endangered population of Irrawaddy river dolphins Orcaella brevirostris in Indonesia. Oryx 39(2): 1-11.
Mohan, R.S.L., S.C. Dey, S.P. Bairagi & S. Roy (1997). On a survey of Ganges River Dolphin Platanista gangetica of Brahmaputra River, Assam. Journal of the Bombay Natural History Society 94: 483–495.
Shrestha, T.K. (1989). Biology, status and conservation of the Ganges river dolphin, Platanista gangetica, in Nepal, pp. 70-76. In: Perrin, W.F., R.L. Brownell, Jr., Z. Kaiya & L. Jiankang (eds.).Biology and Conservation of The River Dolphins. Occasional papers of the IUCN Species Survival Commission No. 3, IUCN, Gland, Switzerland.
Sinha, R.K. & G. Sharma (2003). Current status of the Ganges river dolphin in the rivers Koshi and Son. Journal of the Bombay Natural History Society 100(1): 27-37.
Sinha, R.K., B.D. Smith, G. Sharma, K. Prasad, B.C. Chaudhary, K. Sapkota, R.K. Sharma & S.K. Behera (2000). Status and distribution of the Ganges Susu, Platanista gangetica, in the Ganges River system of India and Nepal. pp. 54–61. In: Reeves, R.R., B.D. Smith & T. Kasuya (eds). Biology and Conservation of Freshwater Cetaceans in Asia. IUCN Species Survival Commission Occasional Paper No. 23, IUCN, Gland, Switzerland and Cambridge, UK.
Smith, B.D., R.K. Sinha, U. Regmi & K. Sapkota (1994). Status of Ganges River Dolphins (Platanista gangetica) in the Karnali, Mahakali, Narayani and Koshi rivers of Nepal and India in 1993. Marine Mammal Science10(3): 368-375.
Smith, B.D., A. Benazir, A.M. Edrise & G. Braulik (2001). Status of the Ganges River Dolphin or Shushuk Platanista gangetica in Kaptai Lake and the southern rivers of Bangladesh. Oryx 35: 61–72.
Smith, B.D., G. Braulik & R.K. Sinha (2004). Platanista gangetica ssp. gangetica. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.2. <www.iucnredlist.org>. Downloaded on 18 August 2010.
UNESCO on
behalf of OCHA and UNCT, Nepal (2009). Report of the Rapid Hazard and Risk
Assessment Post-Flood Return Analysis. Nepal, v+104pp.
Wakid, A. (2009). Status and distribution of the endangered Gangetic Dolphin (Platanista gangetica gangetica) in the Brahmaputra River within India in 2005. Current Science 97(8): 1143-1151.
Yadav, S. (2002). Survey of Capture fisheries in the Koshi River Basin. pp. 317-326. In: Peter, T. & S.B. Swar (eds.). Cold Water Fisheries in the Trans-Himalayan Countries. FAO of United Nations Technical paper No. 431, Rome, Italy. <http://www.fao.org/docrep/005/y3994e/y3994e0r.htm>. On-line version dated 21 September 2010.