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Brian D. Smith - One of the best experts on this subject based on the ideXlab platform.
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Ganges River Dolphins Using a Combined Visual- Acoustic Survey
2020Co-Authors: Nadia I Richman, Samuel T. Turvey, Tomonari Akamatsu, Benazir Ahmed, Emile Mahabub, Brian D. Smith, James M Gibbons, Julia P. G. JonesAbstract:Abstract Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability. We used a combined visual-acoustic survey to estimate detectability of Ganges River dolphins (Platanista Gangetica Gangetica) in four waterways of southern Bangladesh. The combined visual-acoustic survey resulted in consistently higher detectability than a single observer-team visual survey, thereby improving power to detect trends. Visual detectability was particularly low for dolphins close to meanders where these habitat features temporarily block the view of the preceding river surface. This systematic bias in detectability during visual-only surveys may lead researchers to underestimate the importance of heavily meandering river reaches. Although the benefits of acoustic surveys are increasingly recognised for marine cetaceans, they have not been widely used for monitoring abundance of freshwater cetaceans due to perceived costs and technical skill requirements. We show that acoustic surveys are in fact a relatively costeffective approach for surveying freshwater cetaceans, once it is acknowledged that methods that do not account for imperfect detectability are of limited value for monitoring
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To See or Not to See: Investigating Detectability of Ganges River Dolphins Using a Combined Visual- Acoustic Survey
2016Co-Authors: Nadia I Richman, Samuel T. Turvey, Tomonari Akamatsu, Benazir Ahmed, Emile Mahabub, Brian D. Smith, James M Gibbons, Julia P. G. JonesAbstract:Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability. We used a combined visual-acoustic survey to estimate detectability of Ganges River dolphins (Platanista Gangetica Gangetica) in four waterways of southern Bangladesh. The combined visual-acoustic survey resulted in consistently higher detectability than a single observer-team visual survey, thereby improving power to detect trends. Visual detectability was particularly low for dolphins close to meanders where these habitat features temporarily block the view of the preceding river surface. This systematic bias in detectability during visual-only surveys may lead researchers to underestimate the importance of heavily meandering river reaches. Although the benefits of acoustic surveys are increasingly recognised for marine cetaceans, they have not been widely used for monitoring abundance of freshwater cetaceans due to perceived costs and technical skill requirements. We show that acoustic surveys are in fact a relatively cost-effective approach for surveying freshwater cetaceans, once it is acknowledged that methods that do not account fo
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To see or not to see: investigating detectability of Ganges River dolphins using a combined visual-acoustic survey.
PloS one, 2014Co-Authors: Nadia Richman, James Gibbons, Samuel T. Turvey, Tomonari Akamatsu, Benazir Ahmed, Emile Mahabub, Brian D. Smith, Julia P. G. JonesAbstract:Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability. We used a combined visual-acoustic survey to estimate detectability of Ganges River dolphins (Platanista Gangetica Gangetica) in four waterways of southern Bangladesh. The combined visual-acoustic survey resulted in consistently higher detectability than a single observer-team visual survey, thereby improving power to detect trends. Visual detectability was particularly low for dolphins close to meanders where these habitat features temporarily block the view of the preceding river surface. This systematic bias in detectability during visual-only surveys may lead researchers to underestimate the importance of heavily meandering river reaches. Although the benefits of acoustic surveys are increasingly recognised for marine cetaceans, they have not been widely used for monitoring abundance of freshwater cetaceans due to perceived costs and technical skill requirements. We show that acoustic surveys are in fact a relatively cost-effective approach for surveying freshwater cetaceans, once it is acknowledged that methods that do not account for imperfect detectability are of limited value for monitoring.
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clicking in shallow rivers short range echolocation of irrawaddy and ganges river dolphins in a shallow acoustically complex habitat
PLOS ONE, 2013Co-Authors: Frants H Jensen, Brian D. Smith, Alice Rocco, Rubaiyat M Mansur, Vincent M Janik, Peter T MadsenAbstract:Toothed whales (Cetacea, odontoceti) use biosonar to navigate their environment and to find and catch prey. All studied toothed whale species have evolved highly directional, high-amplitude ultrasonic clicks suited for long-range echolocation of prey in open water. Little is known about the biosonar signals of toothed whale species inhabiting freshwater habitats such as endangered river dolphins. To address the evolutionary pressures shaping the echolocation signal parameters of non-marine toothed whales, we investigated the biosonar source parameters of Ganges river dolphins (Platanista Gangetica Gangetica) and Irrawaddy dolphins (Orcaella brevirostris) within the river systems of the Sundarban mangrove forest. Both Ganges and Irrawaddy dolphins produced echolocation clicks with a high repetition rate and low source level compared to marine species. Irrawaddy dolphins, inhabiting coastal and riverine habitats, produced a mean source level of 195 dB (max 203 dB) re 1 µPapp whereas Ganges river dolphins, living exclusively upriver, produced a mean source level of 184 dB (max 191) re 1 µPapp. These source levels are 1–2 orders of magnitude lower than those of similar sized marine delphinids and may reflect an adaptation to a shallow, acoustically complex freshwater habitat with high reverberation and acoustic clutter. The centroid frequency of Ganges river dolphin clicks are an octave lower than predicted from scaling, but with an estimated beamwidth comparable to that of porpoises. The unique bony maxillary crests found in the Platanista forehead may help achieve a higher directionality than expected using clicks nearly an octave lower than similar sized odontocetes.
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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
Aquatic Conservation-marine and Freshwater Ecosystems, 2009Co-Authors: Brian D. Smith, Gill T Braulik, Samantha Strindberg, R Mansur, M A A Diyan, Benazir AhmedAbstract:1. 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. 2. 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. 3. 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. 4. 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.
Shambhu Paudel - One of the best experts on this subject based on the ideXlab platform.
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in stream habitat availability for river dolphins in response to flow use of ecological integrity to manage river flows
PLOS ONE, 2021Co-Authors: Shambhu Paudel, John L Koprowski, Usha Thakuri, Ajay KarkiAbstract:Population decline and extinction risk of river dolphins are primarily associated with flow alteration. Previous studies predominantly highlighted maintenance of adequate flow for low water seasons when habitats contract and the risk of local extinction escalates. Although river dolphins are sensitive to reduction in river flow, no studies quantify the relationships between flow and ecology of river dolphins to mitigate the potential adverse impacts of flow alteration. We quantify the relationships between flow and the ecology of river cetaceans concerning Ganges River dolphins (GRD; Platanista Gangetica Gangetica) usable area availability (AWS) for the low water season at wider flows (50-575 m3/s) at finer spatial and temporal scales. This study reveals that distribution of area usable to GRD is highly regulated by the adequate flow and river attributes (velocity and depth) interactions that likely offer energetically efficient modes of locomotion to GRD, suggesting the hydro-physical environment as a major determinant of river dolphin distribution and abundance. Flow and AWS relationships indicate that the flow during the dry season negatively contributed to AWS, whereas that of pre-monsoon maximized the AWS, suggesting that modifying flow regimes does alter in-stream habitats at varying spatial scales and may influence life-history strategies. Substantial fragmentation in suitable pool availability and loss of longitudinal connectivity exhibited by dry season flow suggested a higher risk of adverse biological effects during the dry season, which may reduce population viability by reducing survivorship and reproduction failure. Owing to river dolphins' dependence on the attribute of freshwater flow, they can be expected to be more affected by flow regulations as interactive effects. Considering the seasonal effects and changes in the availability of usable areas by flow alteration, adopting effective habitat retention plans by water-based development projects appears critical to avoid further ecological risks in aquatic species conservation. Identifying priority riverscapes for river cetaceans and prioritizing investment opportunities is an essential first step towards effective riverine cetacean conservation.
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in stream habitat availability for river dolphins in response to flow use of ecological integrity to manage river flows
bioRxiv, 2020Co-Authors: Shambhu Paudel, John L Koprowski, Usha Thakuri, Ajay KarkiAbstract:Abstract Population decline and extinction risk of riverine cetaceans are primarily associated with flow alteration. Previous studies predominantly highlighted maintenance of adequate flow for low water seasons when habitats contract and the risk of local extinction escalates. Although riverine cetaceans are sensitive to reduction in river flow, no studies quantify the relationships between flow and ecology of riverine cetaceans to mitigate the potential adverse impacts of flow alteration. We quantify the relationships between flow and the ecology of river cetaceans with reference to Ganges River dolphins (GRD; Platanista Gangetica Gangetica) usable area availability (AWS) for the low water season at wider flows (50-575 m3/s) at finer spatial and temporal scales. This study reveals that distribution of usable area to GRD highly regulated by the adequate flow level as the interaction of appropriate velocity and depth at particular geomorphic that likely offer energetically efficient modes of locomotion to increase surfacing behavior efficiency, suggesting the hydro-physical environment as a major determinant of river cetaceans distribution and abundance. Flow and AWS relationships indicate that the flow during dry season negatively contributed to AWS, whereas that of pre-monsoon maximized the AWS, suggesting that modifying flow regimes does alter in-stream habitats at varying spatial scales and may influence life-history strategies. Substantial fragmentation in suitable pool availability and loss of longitudinal connectivity exhibited by dry season flow suggested a higher risk of adverse biological effects during the dry season, which may reduce population viability by reducing survivorship and reproduction failure. Owing to riverine cetaceans’ dependence on the attribute of freshwater flow, they can be expected to be more affected by flow regulations as interactive effects. Considering the seasonal effects and changes in the availability of usable areas by flow alteration, adopting effective habitat retention plans by water-based development projects appears critical to avoid further ecological risks in aquatic species conservation. Identifying priority riverscapes for river cetaceans and prioritizing investment opportunities is an essential first step towards effective riverine cetacean conservation.
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factors affecting the persistence of endangered ganges river dolphins Platanista Gangetica Gangetica
Ecology and Evolution, 2020Co-Authors: Shambhu Paudel, John L KoprowskiAbstract:The Ganges-Brahmaputra-Meghna and Karnaphuli (GBMK) River Basin in Nepal, India, and Bangladesh is among the world's most biodiverse river basins. However, human-induced habitat modification processes threaten the ecological structure of this river basin. Among the GBMK's diverse flora and fauna of this freshwater ecosystem, the endemic Ganges River dolphin (Platanista Gangetica Gangetica; GRD) is one of the most charismatic species in this freshwater ecosystem. Though a >50% population size reduction has occurred since 1957, researchers and decision-makers often overlook the persistence (or evolutionary potential) of this species in the highly fragmented GBMK. We define the evolutionary potential as the ability of species/populations to adapt in a changing environment by maintaining their genetic diversity. Here, we review how evolutionary trap mechanisms affect the dynamics and viability of the GRD (hereafter Ganges dolphin) populations after rapid declines in their population size and distribution. We detected six potential trap mechanisms that might affect the Ganges dolphin populations discretely or in combination: (a) habitat modification; (b) occurrence of finite and geographically restricted local populations; (c) ratio of effective to estimate population size; (d) increasing risk of inbreeding depression in genetically isolated groups; (e) at-risk behavioral attributes; and (f) direct fisheries-dolphin interactions. Because evolutionary traps appear most significant during low water season, they adversely affect demographic parameters, which reduce evolutionary potential. These traps have already caused local extirpation events; therefore, we recommend translocation among populations, including restoring and preserving essential habitats as immediate conservation strategies. Integrative evolutionary potential information based on demographic, genetic, and environmental data is still lacking. Thus, we identify gaps in the knowledge and suggest integrative approaches to understand the future of Ganges dolphins in South Asian waterways.
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characterization of the artisanal fishing communities in nepal and potential implications for the conservation and management of ganges river dolphin Platanista Gangetica Gangetica
PeerJ, 2016Co-Authors: Shambhu Paudel, Juan C Levesque, Camilo Saavedra, Cristina Pita, Prabhat PalAbstract:The Ganges River dolphin (Platanista Gangetica Gangetica) (GRD) is classified as one of the most endangered of all cetaceans in the world and the second scarcest freshwater cetacean. The population is estimated to be less than 2,000 individuals. In Nepal's Narayani, Sapta Koshi, and Karnali river systems, survival of GRD continues to be threatened by various anthropogenic activities, such as dam construction and interactions with artisanal fisheries. A basic description of the geographic scope, economics, and types of gear used in these fisheries would help managers understand the fishery-dolphin interaction conflict and assist with developing potential solutions. The main goal was to provide new information on the artisanal fishing communities in Nepal. The specific objectives were to identify, compile, and investigate the demographics, economics, fishing characteristics, and perception of fishermen about GRD conservation in the Narayani, Sapta Koshi, and Karnali rivers so conservation managers can develop and implement a potential solution to the GRD-fishery interaction problem in Nepal. Based on 169 interviews, 79% of Nepalese fishermen indicated fishing was their primary form of income. Fishermen reported fishing effort was greater in summer than winter; greatest in the afternoon (14:30 hrs ± 0:27) and during low water level conditions; and gear was set 4.8 ± 0.2 days/week. Fishermen reported using eight different types of monofilament nets (gillnets and cast nets). Sixty percent used gillnets less than 10 m long, and nearly 30% preferred gillnets between 10 and 100 m long; a few used gillnets longer than 100 m. Most fishermen reported they believed education, awareness, and changing occupations were important for GRD conservation, but they indicated that alternative occupational options were currently limited in Nepal. Nepalese fishermen acknowledged that fisheries posed a risk to GRD, but they believed water pollution, and dam/irrigation developments were the greatest threats.
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the endangered ganges river dolphin Platanista Gangetica Gangetica in nepal abundance habitat and conservation threats
Endangered Species Research, 2015Co-Authors: Shambhu Paudel, Prabhat Pal, John L Koprowski, Michael V Cove, Shant Raj Jnawali, Grant Abel, Rishi RanabhatAbstract: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 boatbased 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.
Gill T Braulik - One of the best experts on this subject based on the ideXlab platform.
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an evaluation of age estimation using teeth from south asian river dolphins platanistidae
Nammco Scientific Publications, 2014Co-Authors: Christina Lockyer, Gill T BraulikAbstract:The South Asian river dolphins ( Platanista Gangetica minor and P. g. Gangetica ) are endangered, geographically isolated, freshwater cetaceans. Accurate age estimation of individuals is an important aspect of population biology as it is used for calculating parameters such as age at maturity and reproduction, longevity, and growth and survival rates. However this has never been comprehensively studied for this endangered cetacean family. A sample of 41 teeth from 29 skulls stored in museum collections was available. We compared two different aging methods to select the most appropriate. This involved decalcification and freeze-sectioning of teeth at variable thicknesses (10–25 micron), and staining with 1) Toluidine Blue, or 2) Ehrlichs Acid Haematoxylin. Stains were then compared for readability of Growth Layer Groups (GLG). The optimum section was found at 20 micron using Erhlichs Acid Haematoxylin. Both dentinal and cemental GLG were readable and comparable, but cemental GLG were generally easier to interpret because they were better defined. Ages varied from newborn / young of year (with none or only a neonatal line present) to a maximum age of 30 GLG. There is currently no validation available for GLG deposition rate, but it is likely annual because of the extreme seasonal changes in the river habitat.
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habitat fragmentation and species extirpation in freshwater ecosystems causes of range decline of the indus river dolphin Platanista Gangetica minor
PLOS ONE, 2014Co-Authors: Gill T Braulik, Masood Arshad, Uzma Noureen, Simon NorthridgeAbstract:Habitat fragmentation of freshwater ecosystems is increasing rapidly, however the understanding of extinction debt and species decline in riverine habitat fragments lags behind that in other ecosystems. The mighty rivers that drain the Himalaya - the Ganges, Brahmaputra, Indus, Mekong and Yangtze - are amongst the world’s most biodiverse freshwater ecosystems. Many hundreds of dams have been constructed, are under construction, or are planned on these rivers and large hydrological changes and losses of biodiversity have occurred and are expected to continue. This study examines the causes of range decline of the Indus dolphin, which inhabits one of the world’s most modified rivers, to demonstrate how we may expect other vertebrate populations to respond as planned dams and water developments come into operation. The historical range of the Indus dolphin has been fragmented into 17 river sections by diversion dams; dolphin sighting and interview surveys show that river dolphins have been extirpated from ten river sections, they persist in 6, and are of unknown status in one section. Seven potential factors influencing the temporal and spatial pattern of decline were considered in three regression model sets. Low dry-season river discharge, due to water abstraction at irrigation barrages, was the principal factor that explained the dolphin’s range decline, influencing 1) the spatial pattern of persistence, 2) the temporal pattern of subpopulation extirpation, and 3) the speed of extirpation after habitat fragmentation. Dolphins were more likely to persist in the core of the former range because water diversions are concentrated near the range periphery. Habitat fragmentation and degradation of the habitat were inextricably intertwined and in combination caused the catastrophic decline of the Indus dolphin.
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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
Aquatic Conservation-marine and Freshwater Ecosystems, 2009Co-Authors: Brian D. Smith, Gill T Braulik, Samantha Strindberg, R Mansur, M A A Diyan, Benazir AhmedAbstract:1. 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. 2. 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. 3. 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. 4. 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.
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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
Marine Mammal Science, 2006Co-Authors: Brian D. Smith, Benazir Ahmed, Gill T Braulik, Samantha Strindberg, Rubaiyat M MansurAbstract:Independent 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.
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status of the ganges river dolphin or shushuk Platanista Gangetica in kaptai lake and the southern rivers of bangladesh
Oryx, 2001Co-Authors: Brian D. Smith, Benazir Ahmed, Muhammad Edrise Ali, Gill T BraulikAbstract:Surveys for shushuks Platanista Gangetica were conducted during January to April 1999 in Kaptai Lake and the southern rivers of Bangladesh. A popula- tion of at least 125 dolphins was recorded in the Karnaphuli and Sangu rivers and connecting canal. The overall encounter rate was 0.76 dolphins per km. Density was highest in the lower reaches of the Sangu, where we recorded 1.36 dolphins per km. These rates are fairly high when compared with other areas of shushuk distribution. Dolphin movements in the Sikal- baha-Chandkhali Canal were consistent with it being used as a corridor for migration and dispersal between the Karnaphuli and Sangu. Shushuks were also sighted in marine waters of the Karnaphuli and Sangu river mouths, adding credibility to the hypothesis that dolphins move along the coast between the Ganges- Brahmaputra-Meghna and Karnaphuli-Sangu systems, perhaps during the monsoon when freshwater plumes extend into the Bay of Bengal. No dolphins were observed in Kaptai Lake, a dam-created reservoir of the upper Karnaphuli, despite reports of occasional sightings by local fishermen. No shushuks were ob- served in the Bagkhali and Matamuhuri rivers, possibly because of seasonal-closure dams present near the mouths of both rivers. The main threats to dolphin survival in the Karnaphuli-Sangu system are probably accidental entanglement in monofilament gillnets, bio- accumulation of persistent contaminants and possibly collisions with motorized vessels and a decline in prey as a result of over fishing. The most significant conser- vation measure that could be taken would be to establish a protected area for dolphins in the Sangu River below the Dohazari Bridge.
S. P. Biswas - One of the best experts on this subject based on the ideXlab platform.
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the status of the ganges river dolphin Platanista Gangetica Gangetica in the river barak assam india
Journal of the Bombay Natural History Society, 2013Co-Authors: Th P Singha, B K Dutta, S. P. BiswasAbstract: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.
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A grave danger for the Ganges dolphin (Platanista Gangetica Roxburgh) in the Subansiri River due to a large hydroelectric project
The Environmentalist, 2012Co-Authors: Debojit Baruah, Lakhi P. Hazarika, Bikramaditya Bakalial, Sabita Borah, Ranjit Dutta, S. P. BiswasAbstract:The Ganges River dolphin ( Platanista Gangetica Roxburgh) of Subansiri River may be in great danger of extinction due to the construction of the 2,000-MW Lower Subansiri Hydroelectric Project, which started in 2006. A recent survey indicates that there are now 29 Ganges dolphins, up from 21 in 2006. It is feared that drastic changes would occur in the downstream hydrology and ecology of the Subansiri River after the installation of the project, scheduled for 2012. The water discharge during a major part of the day in dry months would come down to a meager 6 cumecs from the present average of 450 cumecs (1 cumec is shorthand for cubic meter per second; also cms, or m^3/s (m^3s^–1). Riverine mega fauna like the dolphin would be worst hit by this extremely low discharge. Dumping of an extra amount of sediment from different construction phases has already increased sediment load in the Subansiri downstream and degraded some earlier pockets of dolphin up to 20 km below the dam site. There is reason to believe that high sediment influx might have silted up some of the deeper pools downstream, a preferred habitat of dolphins, forcing them to congregate close to the confluence of the Subansiri.
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endangered river dolphin Platanista Gangetica Gangetica roxburgh 1801 and their threatened habitat in the river barak
Assam University Journal of Science and Technology, 2010Co-Authors: Th P Singha, B K Dutta, S. P. BiswasAbstract:Gangetic river dolphin Platanista Gangetica Gangetica Roxburgh 1801 is a globally endangered cetacean found in the River Barak. During dry season when depth of water reaches minimum in the river, only certain sections and spots act as dolphin habitat and dolphins congregate there. Till 1970s during dry months dolphins congregated almost at all dahrs, meanders, ferryghats and near mid-stream islands of the River Barak. But now these animals congregate centring on only two spots of the river. Highlighting the threats faced by the dolphins and their crucial dry season habitat in the River Barak, the present paper portrays the demography of the dolphin, the geomorphologic, hydrological, physico-chemical conditions of their congregation spots vis-a-vis other parts of the river, availability of prey-fish in these areas and finally puts forward measures for mitigating the threats.
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Ecology of the River dolphin (Platanista Gangetica) in the upper Brahmaputra
Hydrobiologia, 2000Co-Authors: S. P. Biswas, S. BoruahAbstract:There are nearly 200 species of aquatic vertebrates, almost exclusively fishes, in the Brahmaputra River System. This faunal composition includes not only a wide variety of food-fishes, but also about 50 varieties of aquarium fishes. The most spectacular animal in the Brahmaputra is undoubtedly the river dolphin, Platanista Gangetica. The population of many species, particularly of the dolphin, is in steady decline. River dolphins, mostly juveniles, often entangle themselves in gill and drift nets, while feeding on trapped fishes. Proper implementation of Indian Fisheries Act, especially a total ban on destructive nets and on killing of brooders and juveniles by explosives and poisoning should be strictly implemented. Poor communication facilities in remote riverbank areas and lack of funds are two important reasons for the slow progress of the conservation of river dolphin and this endangered species is now on the verge of extinction. The anthropogenic activities and their impact on the habitat of river dolphin are discussed.
John L Koprowski - One of the best experts on this subject based on the ideXlab platform.
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in stream habitat availability for river dolphins in response to flow use of ecological integrity to manage river flows
PLOS ONE, 2021Co-Authors: Shambhu Paudel, John L Koprowski, Usha Thakuri, Ajay KarkiAbstract:Population decline and extinction risk of river dolphins are primarily associated with flow alteration. Previous studies predominantly highlighted maintenance of adequate flow for low water seasons when habitats contract and the risk of local extinction escalates. Although river dolphins are sensitive to reduction in river flow, no studies quantify the relationships between flow and ecology of river dolphins to mitigate the potential adverse impacts of flow alteration. We quantify the relationships between flow and the ecology of river cetaceans concerning Ganges River dolphins (GRD; Platanista Gangetica Gangetica) usable area availability (AWS) for the low water season at wider flows (50-575 m3/s) at finer spatial and temporal scales. This study reveals that distribution of area usable to GRD is highly regulated by the adequate flow and river attributes (velocity and depth) interactions that likely offer energetically efficient modes of locomotion to GRD, suggesting the hydro-physical environment as a major determinant of river dolphin distribution and abundance. Flow and AWS relationships indicate that the flow during the dry season negatively contributed to AWS, whereas that of pre-monsoon maximized the AWS, suggesting that modifying flow regimes does alter in-stream habitats at varying spatial scales and may influence life-history strategies. Substantial fragmentation in suitable pool availability and loss of longitudinal connectivity exhibited by dry season flow suggested a higher risk of adverse biological effects during the dry season, which may reduce population viability by reducing survivorship and reproduction failure. Owing to river dolphins' dependence on the attribute of freshwater flow, they can be expected to be more affected by flow regulations as interactive effects. Considering the seasonal effects and changes in the availability of usable areas by flow alteration, adopting effective habitat retention plans by water-based development projects appears critical to avoid further ecological risks in aquatic species conservation. Identifying priority riverscapes for river cetaceans and prioritizing investment opportunities is an essential first step towards effective riverine cetacean conservation.
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in stream habitat availability for river dolphins in response to flow use of ecological integrity to manage river flows
bioRxiv, 2020Co-Authors: Shambhu Paudel, John L Koprowski, Usha Thakuri, Ajay KarkiAbstract:Abstract Population decline and extinction risk of riverine cetaceans are primarily associated with flow alteration. Previous studies predominantly highlighted maintenance of adequate flow for low water seasons when habitats contract and the risk of local extinction escalates. Although riverine cetaceans are sensitive to reduction in river flow, no studies quantify the relationships between flow and ecology of riverine cetaceans to mitigate the potential adverse impacts of flow alteration. We quantify the relationships between flow and the ecology of river cetaceans with reference to Ganges River dolphins (GRD; Platanista Gangetica Gangetica) usable area availability (AWS) for the low water season at wider flows (50-575 m3/s) at finer spatial and temporal scales. This study reveals that distribution of usable area to GRD highly regulated by the adequate flow level as the interaction of appropriate velocity and depth at particular geomorphic that likely offer energetically efficient modes of locomotion to increase surfacing behavior efficiency, suggesting the hydro-physical environment as a major determinant of river cetaceans distribution and abundance. Flow and AWS relationships indicate that the flow during dry season negatively contributed to AWS, whereas that of pre-monsoon maximized the AWS, suggesting that modifying flow regimes does alter in-stream habitats at varying spatial scales and may influence life-history strategies. Substantial fragmentation in suitable pool availability and loss of longitudinal connectivity exhibited by dry season flow suggested a higher risk of adverse biological effects during the dry season, which may reduce population viability by reducing survivorship and reproduction failure. Owing to riverine cetaceans’ dependence on the attribute of freshwater flow, they can be expected to be more affected by flow regulations as interactive effects. Considering the seasonal effects and changes in the availability of usable areas by flow alteration, adopting effective habitat retention plans by water-based development projects appears critical to avoid further ecological risks in aquatic species conservation. Identifying priority riverscapes for river cetaceans and prioritizing investment opportunities is an essential first step towards effective riverine cetacean conservation.
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factors affecting the persistence of endangered ganges river dolphins Platanista Gangetica Gangetica
Ecology and Evolution, 2020Co-Authors: Shambhu Paudel, John L KoprowskiAbstract:The Ganges-Brahmaputra-Meghna and Karnaphuli (GBMK) River Basin in Nepal, India, and Bangladesh is among the world's most biodiverse river basins. However, human-induced habitat modification processes threaten the ecological structure of this river basin. Among the GBMK's diverse flora and fauna of this freshwater ecosystem, the endemic Ganges River dolphin (Platanista Gangetica Gangetica; GRD) is one of the most charismatic species in this freshwater ecosystem. Though a >50% population size reduction has occurred since 1957, researchers and decision-makers often overlook the persistence (or evolutionary potential) of this species in the highly fragmented GBMK. We define the evolutionary potential as the ability of species/populations to adapt in a changing environment by maintaining their genetic diversity. Here, we review how evolutionary trap mechanisms affect the dynamics and viability of the GRD (hereafter Ganges dolphin) populations after rapid declines in their population size and distribution. We detected six potential trap mechanisms that might affect the Ganges dolphin populations discretely or in combination: (a) habitat modification; (b) occurrence of finite and geographically restricted local populations; (c) ratio of effective to estimate population size; (d) increasing risk of inbreeding depression in genetically isolated groups; (e) at-risk behavioral attributes; and (f) direct fisheries-dolphin interactions. Because evolutionary traps appear most significant during low water season, they adversely affect demographic parameters, which reduce evolutionary potential. These traps have already caused local extirpation events; therefore, we recommend translocation among populations, including restoring and preserving essential habitats as immediate conservation strategies. Integrative evolutionary potential information based on demographic, genetic, and environmental data is still lacking. Thus, we identify gaps in the knowledge and suggest integrative approaches to understand the future of Ganges dolphins in South Asian waterways.
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the endangered ganges river dolphin Platanista Gangetica Gangetica in nepal abundance habitat and conservation threats
Endangered Species Research, 2015Co-Authors: Shambhu Paudel, Prabhat Pal, John L Koprowski, Michael V Cove, Shant Raj Jnawali, Grant Abel, Rishi RanabhatAbstract: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 boatbased 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.