Ganges River Dolphin Platanista Gangetica Research Articles

Status, distribution, threats, and conservation of the Ganges River Dolphin Platanista gangetica (Mammalia: Artiodactyla: Cetacea) in Nepal

The Ganges River Dolphin Platanista gangetica has been classified as Endangered in the IUCN Red List of Threatened Species. The IUCN changed its status from ‘Vulnerable’ to ‘Endangered’ in 1996 as the species population was declining in its entire distribution range. It is, however, classified as ‘Critically Endangered’ in Nepal. Historically, the freshwater cetacean has been documented in the Karnali, Koshi, Narayani, and Mahakali basins. With their population and distribution range in decline, the Ganges River Dolphin (GRD) is no longer found in the Mahakali River system, which demarcates and traverses the Western border of India and Nepal. This study examines the status and distribution of the GRD in the river systems of Nepal during the monsoon of 2016. The national dolphin population survey was conducted in the three largest river basins in Nepal—Karnali, Narayani, and Koshi. Each of the three basins represent the extreme upstream limit of the GRD distribution in Ganges River basin. The national population survey included both a boat-based survey and shore-based synchronized counting in each of the three river systems. Fifty-two (Best-High-Low: 52-61-50) dolphins were counted during the entire nationwide survey, conducted in July–August, 2016. Researchers gathered social-data from locals residing alongside the observed basin, giving priority to artisanal fishers and those subsisting to some degree from the rivers known to host the river dolphin. A questionnaire survey of ninety-two residents from riparian villages adjacent to the GRD hotspots sheds light on the local perspectives towards dolphin conservation coupled with an assessment of their socio-economic status; artisanal fishing practices; and their awareness of dolphin conservation. According to the survey, notable threats to dolphin conservation are prey depletion; non-availability of suitable habitat; habitat fragmentation and a low level of awareness. Based on the counting outcomes and social survey, recommendations have been put forward for the conservation of this species.

Fishing for the facts: river dolphin bycatch in a small‐scale freshwater fishery in Bangladesh

AbstractFisheries bycatch is a primary driver of cetacean declines, especially for threatened freshwater cetaceans. However, information on the factors influencing cetacean susceptibility to bycatch in small‐scale fisheries is limited, impeding development of evidence‐based conservation strategies. We conducted 663 interviews with fishers from southern Bangladesh to investigate the influence of net and set characteristics on seasonal bycatch rates of Ganges River dolphins Platanista gangetica gangetica and assess the sustainability of annual mortality levels. Between October 2010–October 2011, 170 bycatch events (and a minimum of 14 mortalities) were reported, 89% of which occurred in gillnets. The probability of bycatch increased as water depth declined, and as net mesh size increased. While the number of recorded bycatch incidents was higher in gillnets, risk of mortality was greater in set bagnets. Our mortality estimate indicates that fisheries‐related bycatch currently exceeds the sustainable limit recommended by the International Whaling Commission by 3.5 times. Numerous regulations have been developed to improve the productivity of commercially important fisheries, and if regulations were effectively enforced, these may also reduce river dolphin bycatch.

Irrigation demands aggravate fishing threats to river dolphins in Nepal

Riverine species are adapted to natural habitat changes caused by seasonal flood-pulses. However, abrupt river channel changes following flooding events intersect with social systems of land and water management (e.g. agriculture, fisheries) and in turn generate significant consequences for conservation of endangered aquatic species. We investigated tradeoffs between changing river habitat availability and exposure to fishing intensity for a small population of Ganges River dolphins Platanista gangetica gangetica in the Karnali basin of Nepal. A major natural flooding event in the Karnali basin in 2010 caused the river channel to shift from the Geruwa (flows through a protected area where fishing is restricted) to the Karnali channel (high fishing activity, agriculture-dominated), where dolphins moved in response. Based on our survey data (2009–2015) and long-term hydrological trends in the basin, we found that irrigation diversions since 2012 had aggravated fishing impacts on dolphins, suggesting that their new habitat had become an ‘ecological trap’. Regression models showed that at low river depths, fishing intensity negatively affected dolphin abundance, but at higher depths no effect of fishing was observed. Two records of dolphin bycatch in gillnets confirmed this, as both events corresponded with periods of sudden increase in water abstraction for irrigation. Overall, dolphin distribution shifted downstream and the population declined from 11 in 2012 to 6 in 2015. Effective protection of this river dolphin population from extinction will require the Government of Nepal to prioritize ecologically adequate river flow regimes for implementing efficient irrigation schemes and adaptive fisheries regulations in the Karnali basin.

Status of ganges dolphin, Platanista gangetica gangetica (Roxburgh, 1801) in the river Buriganga, Dhaka

Population abundance and density of the Ganges River Dolphin Platanista gangetica gangetica (Roxburgh, 1801) was studied in the Buriganga River from December 2012 to November 2013.The survey was conducted twice a month. The dolphins were counted directly and applied in transect length of 10.5 km within 15 km stretches of the river. A total of 34 sightings of dolphins were recorded both in individuals and groups. We encountered the dolphins at the rate of 0.48 dolphins per km in the Buriganga River. Highest best-high-low estimate of 12-14-10 individuals were recorded in November 2013. The mean density was 0.38 (SD ±0.37) dolphins/km² with the highest density of dolphin observed also in the month of November, which was 1.14 dolphin/km². Pollution and water traffic were observed to be the major threats to the dolphins.Bangladesh J. Zool. 43(1): 109-120, 2015

The Endangered Ganges River dolphin Platanista gangetica gangetica in Nepal: abundance, habitat and conservation threats

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 29:59-68 (2015) - DOI: https://doi.org/10.3354/esr00702 The Endangered Ganges River dolphin Platanista gangetica gangetica in Nepal: abundance, habitat and conservation threats Shambhu Paudel1,2,*, Prabhat Pal2, Michael V. Cove3, Shant Raj Jnawali4, Grant Abel5, John L. Koprowski6, Rishi Ranabhat7 1Kathmandu Forestry College, PO Box 8973, Kathmandu, Nepal 2The Himalaya, Kathmandu, Nepal 3Department of Applied Ecology, North Carolina State University, Raleigh, North Carolina 27695, USA 4Hariyo Ban Program, World Wildlife Fund (WWF-Nepal), Kathmandu, Nepal 5Ocean Park Corporation, Hong Kong 6Wildlife and Fisheries Science, School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona 85721, USA 7Department of National Parks and Wildlife Conservation, Kathmandu, Nepal *Corresponding author: oasis.excurrent@gmail.com ABSTRACT: Conservation of the last remaining Ganges River dolphins Platanista gangetica gangetica in Nepal will require robust population estimates and better information on suitable habitat characteristics. To gain a better understanding of these parameters, we conducted boat-based surveys in the 3 major river systems (Karnali, Sapta Koshi, and Narayani) of Nepal. We recorded covariates at high spatial resolution and utilized these data to inform occurrence and abundance models. We allowed for detection bias by applying occupancy and N-mixture models that account for imperfect and heterogeneous detection. Occupancy results indicate that dolphin site use varies among the different river systems, across 2 seasons, and increases with river depth. River effects received nearly 100% of the model support and had the strongest influence on dolphin occurrence and abundance. The seasonal influence on dolphin occurrence in the systems (Σωi = 0.997) revealed that occupancy probabilities were heightened during the pre-monsoon season. Deep pool habitat was also identified as a predictor of dolphin habitat use, which accounted for 41.02% of all dolphin sightings occurring in this habitat. Although estimates vary depending on season, we estimate that there are between 37 and 42 (95% CI: 28 to 52) Ganges River dolphins distributed in the rivers of Nepal. Results suggest that seasonality and each specific river affect dolphins and their habitat in Nepal; we strongly recommend site and season-specific conservation actions. Further research on the integration of additional and alternative abundance techniques, behavioral studies, and pursuit of a conservation genetics approach are all important steps in the management of this endangered species. KEY WORDS: Ganges River dolphin · Endangered species · Abundance · Habitat · Distribution · Nepal Full text in pdf format PreviousNextCite this article as: Paudel S, Pal P, Cove MV, Jnawali SR, Abel G, Koprowski JL, Ranabhat R (2015) The Endangered Ganges River dolphin Platanista gangetica gangetica in Nepal: abundance, habitat and conservation threats. Endang Species Res 29:59-68. https://doi.org/10.3354/esr00702 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 29, No. 1. Online publication date: November 25, 2015 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2015 Inter-Research.

The Status of the Ganges River Dolphin Platanista gangetica gangetica in the River Barak, Assam, India

The Ganges River Dolphin Platanista gangetica gangetica , once common in the River Barak in southern Assam, is now rarely sighted. Currently, the dolphins in winter (December-February) congregate in a 14 km stretch of the Barak centring on two sites. During the rainy season (mainly June-August), they frequent tributaries and flooded paddy fields. The population in the 135 km stretch of the Barak, before its bifurcation near the Indo-Bangladesh border, was estimated at 14, 12, 10, 9, 9, 8, and 8 in 1999, 2001, 2003, 2005, 2006, 2007, and 2008, respectively. About 60%, 31%, and 9% of the population was made up of adults, subadults and calves respectively. Information on 29 dolphin mortalities in the Barak comprised 28% adults, 34% subadults and 38% calves. Fishing activities were responsible for 90% of the mortalities; 37% of deaths of calves were due to entanglement in gill-nets. Direct and indirect hunting, uses of dolphin oil as fish attractant and medicine, habitat loss and degradation, depletion of prey fish, water development projects, lack of people's awareness, and poor law enforcement threaten the dolphins. Among others, notification of Barak Dolphin Sanctuary and strict enforcement of laws are required to conserve the dolphins in the Barak.

River dolphin distribution in regulated river systems: implications for dry‐season flow regimes in the Gangetic basin

ABSTRACT River flow regulation and fragmentation is a global threat to freshwater biodiversity, ecosystem processes, and associated human activities. Large dams in the Ganges river basin of the Indian subcontinent have severely altered natural flow regimes, particularly in the low‐flow dry season. Altered flows could have negative impacts on endangered species such as the Ganges river dolphin Platanista gangetica. Habitat use by river dolphins was investigated in relation to river channel depth and morphology, over 332 km of the flow‐regulated Gandak River in India. Dolphin distribution patterns were compared across multiple spatial scales in the Gandak, Kosi, Chambal, Sone Rivers and the upper and lower sections of the Ganges main stem. Dolphin presence was recorded in 40% of segments in the Gandak river, with a best count of 257 (range 250–267) and average individual encounter rates at 0.75 dolphins km‐1 (SD 0.89). Bayesian zero-inflated spatial models showed that river dolphin abundance was positively influenced by river depth, presence of meanders and corresponded closely with gillnet fishing. Minimum mid‐channel depth requirements were estimated at 5.2 m for dolphin adults and between 2.2 and 2.4 m for mother–calf pairs. Adult dolphins showed highly similar habitat preferences across regulated or unregulated rivers, for depths >5 m, and meandering channels. Dry‐season habitat availability was reduced as the degree of flow regulation increased across rivers, mainly owing to loss of lateral and longitudinal channel connectivity. Overall encounter rates were reduced from >3 km‐1 in less regulated stretches, to <0.3 km‐1 in regulated rivers. Clustering of dolphins in deep pools increased along the gradient of river flow reduction, with dolphins almost absent from intervening segments because of low flow rates. These results indicate the importance of maintaining adequate dry‐season flows to ensure river habitat availability and connectivity for dolphins. Copyright © 2012 John Wiley & Sons, Ltd.

Post-flood status of the Endangered Ganges River Dolphin Platanista gangetica gangetica (Cetartiodactyla: Platanistidae) in the Koshi River, Nepal

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. 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. 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.

Socio-economic factors threatening the survival of Ganges River Dolphin Platanista gangetica gangetica in the upper Ganges River, India

The present study was conducted along the upper Ganges River between Narora barrages and Anupshahar from January to June 2007. Community interviews were conducted in order to assess the socio-economic profile of the fishermen community, their level of dependence on the river and their attitude towards the conservation of Ganges River Dolphin Platanista gangetica gangetica. The estimated literacy rate from interviews was 45%, and average annual income per household was 27,000 INR (Indian National Rupee). The respondents were found to be well aware of the river biodiversity and believed excessive water extraction and pollution to be the responsible for any perceived decline in the dolphin population. About 55% of the fishermen were found to fish for commercial purposes, and a majority of them (71%) used nylon gill-nets. A majority (94%) of respondents that had boats of their own fished in the middle of the river, an activity often conducted in groups. 12% of respondents reported to have encountered dolphin carcasses. Excessive fishing and dolphin poaching were found to be interrelated; if fishing can be more effectively managed poaching may automatically decline. 41% of the fishermen interviewed were found to be willing to stop fishing providing adequate alternative livelihoods are provided by the government.

Identification and channel characteristics of cetacean hotspots in waterways of the eastern Sundarbans mangrove forest, Bangladesh

AbstractSightings data of two freshwater-dependent cetaceans, the Ganges River dolphin Platanista gangetica gangetica and Irrawaddy dolphin Orcaella brevirostris, were recorded by captains of three nature tourism vessels operating in waterways of the eastern Sundarbans mangrove forest, Bangladesh. These data were used to investigate channel-type preferences and identify cetacean hotspots according to a scoring system based on group, individual and calf encounter rates, the co-occurrence of both species, and encounter rates in neighbouring segments recorded during monsoon, post-monsoon and dry seasons. Six 5-km segments were identified for priority conservation attention from a total of 38 that were surveyed on at least three occasions during each season. An investigation of habitat preferences evaluated 5-km segments that had been surveyed on five or more occasions (n = 69) and assigned them to one of 12 categories defined by channel width, sinuosity and the number of large and small confluences. Significant differences were found between observed and expected frequencies of occurrence in the different segment categories for Ganges River dolphin groups and individuals and for Irrawaddy dolphin individuals. Both Ganges River and Irrawaddy dolphins selected channels with more than two small confluences or at least one large confluence. Understanding the preferred habitat and identifying hotspots of freshwater-dependent cetaceans in the Sundarbans is the first step of a planning process for the potential establishment of a network of protected waterways for these threatened species.

Habitat selection of freshwater‐dependent cetaceans and the potential effects of declining freshwater flows and sea‐level rise in waterways of the Sundarbans mangrove forest, Bangladesh

Abstract Generalized additive models of sighting data for cetaceans collected during two surveys of waterways in the Sundarbans mangrove forest of Bangladesh indicated that Ganges River dolphin Platanista gangetica gangetica distribution was conditionally dependent (P<0.05) on low salinity, high turbidity, and moderate depth during both low and high freshwater flow; and Irrawaddy dolphin Orcaella brevirostris distribution was conditionally dependent (P<0.05) on low salinity during high freshwater flow, high and moderate depths during low and high freshwater flow, respectively; low and high‐low extremes of turbidity during low and high freshwater flow, respectively; and high temperature and increasing numbers of large–small channel confluences during low freshwater flow. According to sighting data collected over a 3‐year period by the captains of three nature tourism vessels, there were significant differences between the actual and expected frequencies of Ganges River dolphin sightings and individuals according to various channel types (chi‐square=64.22, P<0.0001 and chi‐square=134.14, P<0.0001, respectively, df=6) and of Irrawaddy dolphin sightings and individuals (chi‐square=15.28, P=0.0182, and chi‐square=29.42, P<0.0001, respectively, df=6), with shared preferences for wide sinuous channels with at least two small confluences or one large confluence. The dependency exhibited by both species for environmental characteristics associated with abundant freshwater flow, including low salinity and the availability of confluences, make them particularly vulnerable to habitat loss due to upstream water abstraction and sea‐level rise. Although the results of this study may not affect plans for construction in India of large‐scale, inter‐basin water transfer projects that will result in further declines in freshwater flows, or decisions within the international community about CO2 emissions affecting global sea levels, they can be used to prioritize locations where protective measures could be employed to benefit the long‐term conservation of both species. Copyright © 2008 John Wiley & Sons, Ltd.

Conservation and biomonitoring in the Vikramshila Gangetic Dolphin Sanctuary, Bihar, India

From March 2001 to December 2003 eight direct count surveys in an upstream direction were conducted for Ganges river dolphins Platanista gangetica gangetica in the Vikramshila Gangetic Dolphin Sanctuary, a c. 60 km long segment of the middle Ganges River in Bihar, India. The mean number of dolphins recorded during upstream surveys was 119.4±SD 31.8 (range 88–174), with an encounter rate of 1.8 dolphins km−1 (range 1.4–2.8). During these surveys a rich diversity of other threatened aquatic wildlife was also documented, including the Indian smooth-coated otter Lutrogale perspicillata, gharial Gavialis gangeticus, a variety of freshwater turtles, and 135 water bird species. An assessment of fisheries documented 76 fish species of which 43% were caught exclusively in monofilament gill nets, a gear known to kill dolphins by entanglement. Eight new records of fishes preyed upon by Ganges river dolphins were identified from the stomach contents of two dolphin carcasses (Setipinna brevifilis, Osteobrama cotio cotio, Puntius sophore, Crosochelius latius, Mystus cavasius, Heteropneustus fossilis, Macrognathus pancalus, Sperata seenghala). These fishes and other species previously recorded in the diet of the dolphins composed 33.3% of the total catch sampled in 2001–2003. Interviews of 108 fishing households revealed that literacy rates were low (29.9%) and almost 50% earned less than USD 411 per year. The most important conservation actions that could be taken are for national and state governments to establish civil control and promote the development of community-based fishing cooperatives. These cooperatives could enjoy ownership rights to certain river segments in exchange for employing sustainable fishing techniques that are less injurious to dolphins.

ABUNDANCE OF IRRAWADDY DOLPHINS (ORCAELLA BREVIROSTRIS) AND GANGES RIVER DOLPHINS (PLATANISTA GANGETICA GANGETICA) ESTIMATED USING CONCURRENT COUNTS MADE BY INDEPENDENT TEAMS IN WATERWAYS OF THE SUNDARBANS MANGROVE FOREST IN BANGLADESH

AbstractIndependent observer teams made concurrent counts of Irrawaddy dolphins Orcaella brevirostris and Ganges River dolphins Platanista gangetica gangetica in mangrove channels of the Sundarbans Delta in Bangladesh. These counts were corrected for missed groups using mark‐recapture models. For Irrawaddy dolphins, a stratified Lincoln‐Petersen model, which incorporated group size and sighting conditions as covariates, and a Huggins conditional likelihood model, which averaged models that individually incorporated group size, sighting conditions, and channel width as covariates, generated abundance estimates of 397 individuals (CV = 10.2%) and 451 individuals (CV = 9.6%), respectively. For Ganges River dolphins, a stratified Lincoln‐Petersen model, which incorporated group size as a covariate, and a Huggins conditional likelihood model, which averaged the same models described above, generated abundance estimates of 196 individuals (CV = 12.7%) and 225 individuals (CV = 12.6%), respectively. Although the estimates for both models were relatively close, the analytical advantages of the Huggins models probably outweigh those of the Lincoln‐Petersen models. However, the latter should be considered appropriate when simplicity is a priority. This study found that waterways of the Sundarbans support significant numbers of Irrawaddy and Ganges River dolphins, especially compared to other areas where the species have been surveyed.

1990 Status and conservation of the Ganges River dolphin Platanista gangetica in the Karnali River, Nepal

Information is given on the population status, distribution and ecology of the Ganges river dolphin, Platanista gangetica, in the Karnali River, Nepal. Seven animals were counted. Sightings were highly habitat-specific. Six habitats were identified and classified as primary or marginal, according to differences in physical characteristics and sighting frequencies within them ( χ 2, p < 0·05, d. f. = 5). Mean sighting frequencies were 0·57 and 0·13 sightings/visit for primary and marginal habitats, respectively. Primary habitats were characterized by an eddy counter-current system in the main river flow caused by a fine sand/silt point bar formed from sediment deposits of a convergent stream branch or tributary. Marginal habitats were characterized by a smaller eddy counter-current system caused by an upstream meander. Mean group size was 1·38 animals. Dolphin movements within primary habitats were found to be nonrandom and aggregate for 25 theodolite tracking sessions ( χ 2, p < 0·05, d. f. = 1–7), concentrated in locations of high prey availability and reduced flow. Human disturbance effects are summarized. Recommendations are given for preservation.