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Ganges River Dolphin: An Overview of Biology, Ecology, and Conservation Status in India


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Ganges River dolphin, Platanista gangetica gangetica, is one of the three obligatory freshwater dolphins in the world and is distributed in the Ganges-Brahmaputra-Meghna and Sangu-Karnaphuli River systems in India, Nepal, and Bangladesh. This species is facing considerable threats to its survival, and its population has dwindled from 4000 to 5000 in the early 1980s to 3500 in 2014 in the distribution range. This article reviews current status of the sub-species, habitat use, and the potential threats that the dolphins face for their survival (details of taxonomic status and genetics, evolutionary adaptations and anatomical peculiarities, physical adaptation, primitive characteristics, biology, behavior, surfacing behavior and dive times, mating and birth, and life span/age have been placed as Electronic Supplementary Materials). Recommendations have been made for the protection and developing strategies for the conservation of this Endangered and endemic sub-species.
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1 23
A Journal of the Human Environment
ISSN 0044-7447
DOI 10.1007/s13280-014-0534-7
Ganges River Dolphin: An Overview of
Biology, Ecology, and Conservation Status
in India
Ravindra K.Sinha & Kurunthachalam
1 23
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Ganges River Dolphin: An Overview of Biology, Ecology,
and Conservation Status in India
Ravindra K. Sinha, Kurunthachalam Kannan
Received: 4 October 2013 / Revised: 16 January 2014 / Accepted: 2 May 2014
Abstract Ganges River dolphin, Platanista gangetica
gangetica, is one of the three obligatory freshwater dol-
phins in the world and is distributed in the Ganges–Brah-
maputra–Meghna and Sangu–Karnaphuli River systems in
India, Nepal, and Bangladesh. This species is facing con-
siderable threats to its survival, and its population has
dwindled from 4000 to 5000 in the early 1980s to 3500 in
2014 in the distribution range. This article reviews current
status of the sub-species, habitat use, and the potential
threats that the dolphins face for their survival (details of
taxonomic status and genetics, evolutionary adaptations
and anatomical peculiarities, physical adaptation, primitive
characteristics, biology, behavior, surfacing behavior and
dive times, mating and birth, and life span/age have been
placed as Electronic Supplementary Materials). Recom-
mendations have been made for the protection and devel-
oping strategies for the conservation of this Endangered
and endemic sub-species.
Keywords Ganges River dolphin Conservation
Population Endangered species
Ganges River dolphins, commonly known as susu, Pla-
tanista gangetica gangetica, are distributed throughout the
Ganges–Brahmaputra–Meghna and Karnaphuli–Sangu
river systems of Nepal, India, Bangladesh, and potentially
Bhutan (Mohan et al. 1997; Sinha et al. 2000; Smith et al.
2001). There is no credible estimate of the range-wide
numbers, but the subspecies was listed as ‘‘endangered’’ on
the 1996 International Union for Conservation of Nature
(IUCN) Red List, due to a reduction in its historical dis-
tribution range and projected declines in population size
due to increasing threats (IUCN 1996).
Although the Ganges dolphin is mentioned in mytho-
logical and historical literature, its occurrence in the
Hooghly River, the tidal zone of the Ganges, was first
documented in 1801 by William Roxburgh, Superintendent
of the Botanical Garden, Calcutta (Roxburgh 1801).
Anderson (1879) provided the first description of the dis-
tribution range, morphology, and anatomy of the dolphin,
although he did not discuss the dolphin’s population status
or ecology. Approximately 100 years later, however, a few
papers reported some details on the population status of the
Ganges dolphin as of the 1980s (Jones 1982; Mohan 1989).
Nevertheless, these reports were not based on continuous
or systematic surveys, and the population status was most
likely a rough estimate. Overall, information on ecology
and conservation status of river dolphins in India is spa-
tially and temporally patchy.
Our research team at Patna University (Patna) has con-
ducted several surveys in discrete segments of the Ganges
River from 1991 to 1996, under the Dolphin Conservation
Project sponsored by the Ganga Project Directorate, Min-
istry of Environment and Forests, Government of India
(Sinha 1996,1997; Sinha et al. 2000; Sinha and Sharma
2003a,b). During 1990–1994, other researchers have
conducted dolphin surveys at several sections of the Gan-
ges River and its tributaries (Behera 1995; Smith et al.
1994; Behera and Rao 1999). Continuous surveys were
conducted in the Ganges River in a stretch of over 1900 km
from Haridwar, at the foothills of the Himalayas, to Far-
akka near the India–Bangladesh border in 1996–1998
(Sinha 1999; Sinha et al. 2000) with support of
Electronic supplementary material The online version of this
article (doi:10.1007/s13280-014-0534-7) contains supplementary
material, which is available to authorized users.
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DOI 10.1007/s13280-014-0534-7
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Biodiversity Support Program (BSP), a consortium of
World Wildlife Fund, the Nature Conservancy, and the
World Resources Institute. From the results of surveys
conducted in 1982–1985, Singh and Sharma (1985) esti-
mated that 45 dolphins were present in approximately
305 km segment of the River Chambal between Batesura
and the confluence of the Yamuna River. With support
from the National River Conservation Directorate (earlier
the Ganga Project Directorate under the Ministry of
Environment and Forests, Government of India), Patna
University undertook intensive studies from 2001 to 2007
in a 500-km stretch of the Ganges in the state of Bihar,
where over 50 % of the total population of the Ganges
River dolphin in India (currently over 3,000) survive
(Sinha et al. 2010a). During the same period, other
researchers conducted continuous surveys in the Brah-
maputra River, a large river of the Ganges river system in
India, in the state of Assam (Biswas and Boruah 2000;
Wakid 2005,2009). A map of the Ganges basin and major
locations mentioned in this article is presented in Fig. 1.A
summary of the various survey efforts to study the distri-
bution and status of the Ganges River dolphin in various
sections of the Ganges River is listed in Tables 1,2, and 3.
We also documented various threats to which the
Ganges dolphins were exposed, including directed and
incidental killings by the fishermen to extract oil from
their blubber for use as bait in the oil fishery in the
dolphins’ distribution range (Sinha 2002). The dolphin oil
is used as an attractant to catch two economically
important fish—Clupisoma garua and Eutropiichthyes
vacha (Sinha 2002). In addition, we collected dolphin
carcasses from the Ganges and its tributaries in the 1980s
and 1990s, tissues of which were analyzed for toxic
pollutants, including heavy metals; organochlorines,
including polychlorinated biphenyls (PCBs) and pesticides
(e.g., DDT and HCH); organotin compounds; and per-
fluorinated chemicals (PFCs) (Kannan et al. 1993,1994,
1997; Senthilkumar et al. 1999; Yeung et al. 2009). One
of the projects (Project No. 23), recommended by the
IUCN/SSC Cetacean Specialist Group Action Plan, was to
develop an alternative to dolphin oil for use as a fish lure
(Perrin 1988). As a part of this investigation, oil from fish
scraps was developed as an alternative to dolphin oil
(Sinha 2002). Other threats including the effects of dams
and barrages on Ganges dolphins were studied by Sinha
(2000) and Smith et al. (2000). Similar to that in India,
status and threats that the Ganges dolphins face in Nepal
and Bangladesh have been reported earlier (Kasuya 1972;
Kasuya and Haque 1972; Smith 1993; Smith et al. 1998,
Fig. 1 The Ganges River basin in India
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Our constant efforts to study the susu led to decla-
ration of the Ganges dolphin as the ‘‘National Aquatic
Animal of India’’ on October 5, 2009. Despite this
designation, the species is facing severe threats of
extinction throughout its distributional range, and there
are many aspects of the animal’s biology and ecology
that remain obscure. Under these circumstances,
renewed efforts are needed to generate consistent
information about the species’ ecological requirements
throughout its distribution range, and its response to
anthropogenic and natural disturbances, as the basis for
the design and implementation of relevant conservation
strategies. This review is based on the results from
several of the surveys and studies listed above,
including some unpublished data from the lead author
and information gathered from local people and orga-
nizations in India. We have made an attempt to
describe the current state of knowledge on the Ganges
dolphin in India, and narrated the future scope of work
to address the challenges ahead in the conservation of
this species.
The range of distribution of Platanista in the Ganges River
was, between longitudes 77°E and 89°E, from mouth of the
river in Bay of Bengal to as far up as the river was navi-
gable near the foothill of Himalayas (Anderson 1879)
(Fig. 2). Anderson (1879) stated that, in the Brahmaputra
River, Platanista was present ‘‘throughout all the main
rivers, as far eastwards as longitude 95°E by latitude
27°300N, frequenting all its larger tributaries.’’ Outside the
Ganges–Brahmaputra–Meghna river systems, susus were
present in the Karnaphuli River (Anderson 1879) and
possibly the Sangu River in eastern Bangladesh (Haque
Currently, the Ganges dolphin (Platanista gangetica
gangetica) is an endangered sub-species of the South Asian
river dolphin (Platanista gangetica), which is distributed in
the Ganges–Brahmaputra–Meghna river systems in India,
Nepal, and Bangladesh and the Sangu–Karnaphuli Rivers
in Bangladesh from the deltas upstream to where they were
blocked by rocky barriers, shallow waters, dams, and
Table 1 Population status and distribution of Ganges river dolphin in the main stem of the Ganges River in India
River Segment No. of Dolphin Year Reference Remarks
Ganga Between Haridwar and Middle
Ganga Barrage at Bijnor
(approx. 100 km)
0 December
Sinha et al. (2000) The current upstream limit of the range of
Ganges dolphins in the Ganges main
stem appears to be below the Bijnor
Ganga Between Bijnor and Narora
Barrages (approx. 166 km)
22/56 1993-95/
Behera (1995)/Pers.
comm. S. Behera
The isolated dolphin population between
the two barrages appears to be
Ganga Between Narora and Kanpur
(358 km)
0 1997 Sinha (1999) Very low water in this stretch
Ganga Between Kanpur and
Allahabad (approx.252 km)
98 2012 Pers. comm.
S. Behera
Ganga Allahabad to Buxar (approx.
425 km)
204 (Downstream
1997 Sinha (1999)
Ganga Buxar to Maniharighat
(500 km)
808 (Upstream
2006 Sinha et al. (2010a) The river has more water in this stretch as
all the four major tributaries from Nepal
discharge into the Ganges and create
more hydro-geomorphological
Ganga Maniharighat to Farakka
(approx. 70 km)
115 (Downstream
1998 Sinha (1999)
Ganga Farakka Feeder Canal
(38.2 km)
21 (Downstream
1996 Sinha et al. (2000) Farakka Barrage diverts regulated Ganges
water to the River Bhagirathi through
this canal
Bhagirathi Jangipur to Triveni Ghat
(320 km)
119 (Downstream
1995 Sinha (1997) Dolphin population is relatively low as
the river receives regulated water with
low silt resulting in low hydrogeological
Hoogly Triveni to Sagar Island
(190 km)
97 (Downstream
2008 Pers. comm. Gopal
This tidal zone has high river traffic and
large vessels
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barrages. The river dolphins prefer areas that create eddy
countercurrents, such as small islands, sand bars, river
bends, and convergent tributaries. In the monsoon season,
Ganges dolphins migrate locally to tributaries and then
return to larger river channels in the dry, winter season
(Smith 1993; Sinha et al. 2000; Sinha and Sharma 2003a,
b) The dolphins have been reported to move along the coast
of the Bay of Bengal when monsoons flush freshwater out
along the southeastern coast of India (Moreno 2003).
Kasuya and Haque (1972) recorded susus as far as Di-
oghat on the Narayani River, Nepal, 250 m above sea level
and approximately 100 km farther upstream than Anderson
recorded in 1879. Shreshtha (1989) reported dolphins in the
four main river systems of Nepal: the Mahakali, Karnali,
Narayani, and Kosi Rivers. Susus ascend the Meghna river
systems in Bangladesh at least to Sunamganj (Jones 1982).
Nine susus were also sighted in the Barak River in 2006 at
Silchar in Assam (pers. comm. Pawlen Singha. Email: in India (Barak River is
called Meghna River in Bangladesh). Jones (1982) stated
that the broad plume of freshwater created by the Ganges
outflow in the Bay of Bengal may facilitate the dispersal of
susus to rivers outside the Ganges–Brahmaputra–Meghna
systems. In 2006, one susu entered the Burhabalang River
Table 2 Population status and distribution of Ganges river dolphin in various tributaries of the Ganges River in India
River Segment No. of
Year Reference Remarks
Yamuna From confluence of Chambal river to
Yamuna-Ganga confluence at
Allahabad (250 km)
31 2012 Pers. comm. S. Behera
Girwa India/Nepal border to Girijapuri Barrage
(approx. 20 km)
39 2012 Pers. comm. S. Behera This is a protected area, Katarniaghat
Gharial Sanctuary
Ghaghara Girijapuri Barrage to Deorighat (505 km) 295 2006 WWF-Nepal (2006)
Rapti 15–20 km 8 2012 Pers. comm. S. Behera
Saryu 22 km 16 2012 Pers. comm. S. Behera
Chambal Rajghat to Panchnada (approx. 550 km) 85 2012 Pers. comm. S. Behera
Sone From Uttar Pradesh/Bihar border to its
confluence with Ganges about 35 km
upstream Patna in the state of Bihar
(approx. 300 km)
0 2001 Sinha and Sharma (2003b) Not enough water to sustain dolphin in
this stretch
Sone Between Bicchi in Madhya Pradesh to
Banjari (130 km)
10 1998 Sinha et al. (2000) These dolphins were sighted in some
deep pools in Madhya Pradesh
Sarda Sarda Barage to Palia (approx. 100 km) 0 1994 Sinha and Sharma (2003a) Not enough water to sustain dolphin in
this stretch
Kosi Between Kosi Barrage to Kursela
(approx. 200 km)
85 2001 Sinha and Sharma (2003b)
Gandak Gandak Barrage to Gandak-Ganges
confluence at Patna (approx. 320 km)
257 2010 Choudhary et al. (2012)
Ken Confluence with Yamuna to Sindhan
Kalan village (30 km)
8 1998 Sinha et al. (2000)
Betwa Confluence with Yamuna to Orai (84 km) 6 1998 Sinha et al. 2000
Sind Confluence with Yamuna to 110 km
5 1998 Sinha et al. 2000
Rupnarayan Gadiara to Mankur (42 km), West Bengal 18 2006 WWF-Nepal (2006)
Table 3 Population status and distribution of Ganges river dolphin in the Brahmaputra River and its tributaries
River Segment No. of Dolphin Year Reference
Brahmaputra Arunachal Pradesh/Assam to India/Bangladesh border (856 km) 583 2012 Pers. comm. Wakid
Subhansiri Katai Sapori to its confluence with the Brahmaputra at Jamuguri (94 km) 35 2012 Pers. comm. Wakid
Kulsi From Gharamara to its confluence with the Brahmaputra at Nagarbera (76 km) 17 2012 Pers. comm. Wakid
123 ÓRoyal Swedish Academy of Sciences 2014
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in the state of Orissa, which discharges into the Bay of
Bengal almost 300 km southwest of the mouth of the
Ganges (Pers. comm. S. K. Behera). This river has never
been connected with the Ganges system.
In the recent years, the dolphin’s range in substantial
portions of the Ganges system, especially in upstream
areas, has diminished. For example, a continuous survey
in low-water season in December 1996 showed that no
dolphins were sighted in the 100-km stretch of the Ganges
River between Bhimgoda Barrage at Haridwar and Middle
Ganga Barrage at Bijnor, at the upstream limit of their
historical range in the river (Sinha et al. 2000). Since
December 1996, dolphin sighting was not reported in the
River Ganges upstream Middle Ganga Barrage at Bijnor.
After 1967, dolphins have not been reported in the
Yamuna River above the Chambal River confluence near
Etawa to Tajewala near the foothills of the Himalayas
(736 km) during the dry season (October–June) (Sinha
et al. 2000). Historically, dolphins were found year-round
in the Yamuna River at Delhi (Anderson 1879), 512-km
upstream of the Chambal confluence. Ganges dolphins
apparently have been extirpated from a 163-km stretch of
the Sarda River (also called the Mahakali River in Nepal)
between Lower Sarda Barrage at Sardanagar in Uttar
Pradesh state and Upper Sarda Barrage (also called Ban-
basa Barrage) at Tanakpur along the India-Nepal border in
Uttarakhand state during the dry season (Sinha and
Sharma 2003a) (Fig. 1); in a 300 linear-km segment of the
Sone River, above and below the Indrapuri Barrage
(during the dry season, October–June); and upstream of
the Ganges confluence (Sinha and Sharma 2003b). We did
not find any dolphins crossing the Lower Sarda Barrage
both during the flood season (July–September) as well as
lean season in the month of March–April when the gates
of the barrage were opened. Additionally, no dolphins
were observed in the section of the Mahakali River (called
River Sarda in India) that flows through Nepal (Smith
et al. 1994).
It is challenging to assess whether the extirpations were
due to population fragmentation or habitat degradation
caused by construction of dams and barrages. Physio-
graphic and hydrologic complexities play an important role
in making rivers suitable for inhabitation of dolphins,
whereas dams and barrages degrade dolphin habitats, as
they reduce physiographic and hydrologic complexity
(Reeves and Leatherwood 1994).
Statistically robust and standardized density and population
estimates are necessary to determine the conservation status
and to monitor trends of the river dolphin population
worldwide (Reeves and Leatherwood 1994;IWC2000;
Smith and Reeves 2000). In the absence of a robust method,
direct counts in discrete sections of rivers generally have
been conducted (Smith and Reeves 2000). Capture-recapture
analysis of photo-identified animals is commonly used to
estimate the abundance of cetaceans (Hammond 2009). This
method relies upon capturing images of uniquely marked
animals; the proportion of identified individuals recaptured
during subsequent sampling events is then used to estimate
the population abundance (Borchers et al. 2002). This
method has substantial limitations for the survey of Pla-
tanista spp.; however, because (1) these animals are extre-
mely difficult to photograph, as they surface alone,
Fig. 2 Distribution map of Platanista gangetica in the 1870s (Anderson 1879) and 2009; red highlight on the left panel indicates the historical
distribution range
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unpredictably, for about one second or less, and they seldom
approach boats or vessels; and (2) they lack a prominent
dorsal fin, and the individuals rarely possess any readily
identifying marks or features (Braulik et al. 2012a). In an
earlier survey, not a single individual could be identified
from 1,200 photographs of Ganges dolphins taken during
that time (Smith and Reeves 2000). During 2012 surveys in
the Ganges River, we took about one thousand photographs
of susu, of which three individual dolphins had identifying
features: The upper jaw and lower jaw of two individuals
were broken, and there was a deep cut in the dorsal fin of the
third. Tropical rivers, such as the Ganges, are often turbid, as
they carry heavy loads of silt, and, therefore, underwater
photography is almost impossible.
The primary challenge to the application of line or strip
transect methods of population survey in the Indus, Ganges,
and Brahmaputra Rivers is that the rivers are very shallow,
and survey vessels are restricted to traveling up or down the
thalweg (the line that follows the deepest part of the river)
along a single curving transect that periodically approaches
alternate banks as the river meanders. A thalweg transect
survey unavoidably samples unrepresentative habitats as it
passes through areas with higher densities; in addition, the
animals are unlikely to be uniformly distributed in the sur-
veyed strips (Braulik et al. 2012b). Transects that run from
bank to bank, perpendicular to the flow, are used for line
transect surveys of cetaceans in the Amazon River (Vidal
et al. 1997; Martin and da Silva 2004), but in the compara-
tively shallow, sand-bedded, South Asian rivers, navigational
constraints preclude this approach. A single transect parallel
to and a standard distance from the river banks also has been
used for strip transect surveys in the Amazon (Vidal et al.
1997; Martin and da Silva 2004) and for adapted line transect
surveys on the Yangtze River (Zhao et al. 2008), but this is
not possible on South Asian rivers, as the channel width
changes rapidly and vessels cannot maintain a standard dis-
tance from the banks due to shallow depths (Braulik et al.
2012b). In the Ganges and tributaries, we followed the direct
count method suggested by Smith and Reeves (2000).
A total of approximately 3,526 dolphins were sighted in
their distribution range in India, Nepal, and Bangladesh
during the recent surveys, details of which are shown in
Table 4. However, various researchers have not followed
consistent and robust methods. Many tributaries north of
the Ganges River, such as Mahananda, Mechi, Bagmati,
Kamala, Balan, Burhi Gandak, are yet to be surveyed, of
which Mahananda and Bagmati are large rivers.
In the recent past, a local activist, Mr. Bhoj Raj
Shreshtha, founded a Dolphin Conservation Center in the
Kailali District of western Nepal. Mr. Shreshtha has suc-
cessfully motivated villagers in the area to keep records of
dolphin sightings, especially during the flood period of
July to September, when a good number of dolphins
ascend into the smaller tributaries of the Karnali River.
The number of dolphins sighted in the river was claimed to
be over fifty, but the sighting records are not based on a
‘scientific method.’’ Nevertheless, these data have been
collected from an area that is not traditionally monitored,
and further efforts, which include the help of local orga-
nizations, are needed to comprehensively assess the status
of dolphins.
An estimate of the abundance of Ganges dolphins was
generated in 2004, 2005, 2006, and 2012 by both upstream
and downstream vessel-driven direct counts by the same
team of experts in the same stretch (500–525 km) of the
Ganges River in the middle segment of the river in the state
of Bihar (Sinha et al. 2010a;Sinha2013). This segment of
the Ganges supports maximum density of the dolphins, as all
of the four major rivers of Nepal discharge into the Ganges
in this stretch, which results in more water and the creation
of suitable habitats for the dolphins. The surveys were
conducted between Buxar and Maniharighat (500 km) in
2004–2006. In 2012, a survey was conducted in a 525-km
stretch in the Ganges between Chausa (15 km upstream of
Buxar, where the Karmanasa River joins the Ganges from
south and forms the political boundary of Uttar Pradesh and
Bihar states) and Sahibganj, located about 10 km down-
stream of Maniharighat on the opposite bank of the Ganges.
Table 4 Estimated population of the Ganges River dolphins in the early 2000s
Location Number of
Ganges River Main Stem and
2381 Sinha (1997), Sinha et al. (2000,2010a,b), Sinha (1999), Sinha and Sharma (2003a,b);
Behera, S. K. pers. comm. January 2014
Brahmaputra and tributaries 635 Wakid, A. pers. comm. January 2014
Ganges River system and Sundarbans
area in Bangladesh
460 Smith et al. (2006,2009); Alam and Sarker (2012)
Karnali River and tributaries—River
Mohana and Pathariya; and River
Koshi in Nepal
[50 Smith et al. (1994), pers. comm. Bhojraj Shreshtha;
and pers. comm. Kevin Denlay Dec. 2013
Total 3526
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A summary of the findings with confidence intervals and
Standard Error is presented in Table 5. The population
growth rate is an important measure for the assessment of
the health and survival of dolphins, but such information is
not currently available. Thus, further studies should focus on
assessing the growth rate of the Ganges dolphin population.
The frequency of dolphin sightings remains high in the
middle and lower reaches of the main stem of the Ganges,
as the river has more hydro-physiographic complexity and
greater hydraulic refuge as induced by minor geomorphic
features. The river is productive due to the seasonal flood
pulse that brings adequate nutrients and has reduced
velocity due to its low gradient (1300:1) (Sinha and Prasad
2012). A mean encounter rate of 1.8 dolphins/linear km
was reported for the Vikramshila Gangetic Dolphin sanc-
tuary (Choudhary et al. 2006) in the middle of the Ganges
River. In November 2012, our team recorded an average
density of 2.3 dolphins/linear km in the sanctuary and 1.6
dolphins/linear km in the 525-km stretch of the middle
Ganges between Sahibganj and Chausa.
The encounter rates of dolphins reported in other surveys
are shown in Table 5. It should be noted that the encounter
rate is dependent on the speed of the vessel. In the upstream
survey, the encounter rate was 1.3–1.6 dolphins/linear km,
and the vessel speed was 6.3–6.8 km/h. In the downstream
survey, the encounter rate was 0.9–1.4 dolphins/linear km,
with a vessel speed of 10.2–12 km/h. Thus, the speed of the
vessel has a direct bearing on the encounter rate of the dol-
phin. In 2001, the encounter rate recorded for the Guddu–
Sukkur subpopulation was almost five times greater than that
of any other river dolphin subpopulation (Braulik 2006).
This encounter rate (averaging 3.60 dolphin/km, peaking at
5.05 dolphin/km) was several times greater than that recor-
ded for the Ganges dolphin in the rivers of India and Ban-
gladesh. The high density of the Guddu–Sukkur
subpopulation is probably due to a ban on hunting since the
1970s (Braulik 2006). More dolphins are sighted in the main
channel as compared to the larger secondary channels or
braids (Braulik 2006; Basir et al. 2010).
The spatial and temporal habitat selection of dolphins is a
complex and dynamic function of requirements for food,
mates, avoidance of predators and competitors, and the
ability to move between habitat patches (Davis et al. 2002;
Schofield 2003). Fluvial habitat within river networks is often
described as a mosaic of habitat patches of different sizes that
are formed principally by hydro-geomorphic forces (Crook
et al. 2001; Thorp et al. 2006). Consequently, fluvial aquatic
species are variably distributed, and variations in hydrology
and geomorphology play a critical role in determining species
Table 5 Summary of Ganges dolphin sightings in the Ganges River (upstream survey) between Maniharighat and Buxar during 2004–2006, and between Sahibganj and Chausa (15 km
upstream Buxar) in November–December 2012
Parameter Distance
traveled (km)
Average vessel
speed (km/h)
Total no.
of sightings
Best estimate
of dolphins
Average group
size of dolphins
Std. Error
of group size
Range of
group size
Encounter rate
Period of survey
March 2004 (u/s) 505.7 6.8 358 777 765–816 2.2 0.088 1–11 1.5
March 2004 (d/s) 499.4 10.9 314 696 687–730 2.2 0.079 1–10 1.4
November 2005(u/s) 507.4 6.3 425 664 578–750 1.6 0.039 1–7 1.3
November 2005(d/s) 494.8 11.2 349 517 465–576 1.5 0.037 1–4 1.0
December 2006 (u/s) 517.1 6.3 557 808 729–931 1.5 0.030 1–4 1.6
December 2006 (d/s) 501.0 10.2 405 559 486–668 1.4 0.032 1–7 1.1
October–November 2012 (u/s) 526.7 6.5 813 813 736–838 2.1 0.077 1–15 1.6
October–November 2012 (d/s) 519.3 12.0 439 439 415–476 2.2 0.100 1–11 0.9
u/s Upstream Survey (against the river current)
d/s Downstream Survey (along the river current)
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distribution (Stazner and Higler 1986; Poff and Allan 1995;
Power et al. 1995; Poff et al. 1997). The distribution of prey is
likely to be one of the most important factors that influences
the distribution ofriver dolphins; however, habitat selection is
frequently assessed in terms of physical habitat characteris-
tics, as these are the primary determinants of prey distribution
and are more easily measured (Gregr and Trites 2001;
ˇadas et al. 2002; Davis et al. 2002; Bearzi et al. 2008).
Most riverine fish prefer specific types of habitat, and water
depth is widely considered the most important variable that
drives their distribution (Baird and Beaseley 2005; Sarkar and
Bain 2007). For example, small or young fish often prefer
shallow and slow water, whereas larger or older fish prefer
deeper areas, often with faster flows (Sarkar and Bain 2007).
Research has indicated that dolphins move downstream in the
winter season when river discharge is low and that, as the
flood waters rise in the monsoon season, dolphins move into
upstream waters that comprise smaller tributaries (Anderson
1879; Kasuya and Haque 1972; Shreshtha 1989; Sinha and
Sharma 2003a; Kelkar et al. 2010). Given the large variation
in river discharge and velocity, a seasonal movement is
probable. During the flood season, many dolphins enter into
the smaller tributaries, and most return to the main channel of
the large rivers after the flood. However, some individuals
stay back in pools of the tributaries during the dry season
(Pelletier and Pelletier 1980), which makes them vulnerable
and subject to being killed by local fishermen. On two occa-
sions in 2001 and in 2013, such dolphins were successfully
rescued and translocated to the nearby large rivers in West
Bengal and Bihar, respectively, by our team in Patna.
Between 2002 and 2012, no dolphin was found or reported
stayed back in small tributaries which required to be rescued
and translocated. Efforts to rescue such individuals are
important to conserve the dolphin population, and resources/
infrastructure should be made available for this purpose.
Susus have been reported to have lived for several years in a
lake near Kaziranga, Assam (Pilleri 1970).
Several researchers have noted extremely patchy distribu-
tions of river dolphins in rivers of South Asia, with a
preference for confluences (Jerdon 1874; Kasuya and
Haque 1972; Haque et al. 1997; Sinha 1997; Sinha et al.
2000; Basir et al. 2010). Nearly all reports, however, are
qualitative. A few studies reported that preferred habitats in
rivers include downstream of shallow and narrow areas
(Kasuya and Haque 1972), in narrow and deep sections of
rivers (Pilleri 1970), in deep locations where the current is
weak (Pilleri and Zbinden 1973–74; Bairagi et al. 1997), in
deep water pools off the mouths of irrigation canals (Basir
et al. 2010), near villages and ferry crossings (Pilleri and
Bhatti 1982; Sinha 1997), downstream of bridge pilings
(Sinha 1997; Smith et al. 2001; Choudhary et al. 2006),
downstream of sand bars and sharp meanders, near bathing
ghats, cremation ghats (Sinha 1997), and in channels with
muddy and rocky substrates (Kelkar et al. 2010). The river
dolphins preferentially congregate in such locations that
are preferred by local fishermen, and the sites with dolphins
had a higher biomass of small fish than did areas in which
their presence was not recorded (Kelkar et al. 2010). We
understand that, in areas of human activities such as
bathing and washing ghats, ferry ghats, and cremation
ghats, people tend to throw into the water some edible
items that could attract fish and, ultimately, dolphins.
It is clear that South Asian river dolphins are patchily
distributed according to characteristics of their habitat, but
there have been few studies that have statistically tested
which types of habitat are preferred in different seasons or
locations. The three most comprehensive studies are as fol-
lows: (1) Smith (1993) conducteda study in the Karnali River
in Nepal, which is the extreme upstream limit of the Ganges
dolphin distribution. Primary and marginal habitats were
identified, and it was concluded that dolphins consistently
used the same areas characterized by high prey availability
and low water flow velocity. River dolphins were assumed to
exploit the ‘‘hydraulic refuge’’ provided by counter-current
eddies in deep pools. (2) A study by Smith et al. (2009), in the
extreme downstream, limits in the Sundarbans delta man-
grove forest, river dolphins showed a consistent preference of
water of approximately 12-m deep, from a possible range of
0–40 m, irrespective of seasons. Generalized additive models
showed that the dolphin distribution was dependent on water
with low salinity, high turbidity, and moderate depth during
both low and high flows, with a preference for wide sinuous
channels with at least two small confluences or one large
confluence in the tidalzone in the Sundarbans. (3) A studyby
Braulik et al. (2012a) foundthat dolphins selected locations in
the Indus River with significantly greater mean depth, cross-
sectional area, and hydraulic radius, and significantly nar-
rower river width and a lower degree of braiding. Dolphins
with higher frequency at river constrictions and river con-
fluences were also recorded. Channel cross-sectional area
was the most important factor that affected dolphin presence
and abundance. The greatest influence on presence and
abundance of dolphin is exerted by area of water depth below
one meter. Indus dolphins avoided channels with a small
cross-sectional area (\700 m
There is no quantitative information on which aspects of
the riverine habitat that are important to the Ganges dol-
phin in India, where the river has vast floodplains and many
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confluences and meanders, and is highly braided, with
many deep pools, hydraulic refuges, and hydro-geomorphic
complexities. River dolphins are expected to be most vul-
nerable during the low-water season, when the habitat is
limited, and it is, therefore, important to determine which
habitats are preferentially used at this time, so that con-
servation efforts can be focused in those locations.
Rivers are at risk from multiple stressors, including changes in
water quantity and quality, habitat modification, over-exploi-
tation of resources, climate change, pollution, and invasive
species. The current impacts of these stressors on rivers are
dramatically increasing (Alcamo et al. 2005; Foley et al. 2005).
Currently, 65 % of global river discharge is considered to be
under moderate to high threat, and the water security of 80 % of
the human population is at high risk (Vorosmarty et al. 2010).
In addition, biodiversity in freshwater ecosystems is in rapid
decline, and this reduction in freshwater system is considered
even more threatened than are marine ecosystems (Revenga
et al. 2000;Vorosmartyetal.2010).
Degradation of the freshwater ecosystem is sometimes
measured using a suite of ecological indicators, such as
macro-invertebrates, fishes, and macrophytes. Carefully
selected indicators can provide warning signals of cryptic but
significant changes to ecosystems (Karr 1999; Noss 1999).
Top predators, such as mammalian carnivores, sea birds, and
raptors, are among the widely used indicator species (Fur-
ness and Camphuysen 1997; Sergio et al. 2005,2006,2008;
Piatt et al. 2007). Top predators tend to be concentrated in
important biodiversity hotspots (Worm et al. 2003; Sergio
et al. 2005,2006). The reduction or disappearance of top
predators is related to significant ecosystem transformations,
including impacts on several trophic levels and changes in
energy flows, over-exploitation of resources, and changes in
the behavior of prey or food chain structure (Soule et al.
2005; Heithans et al. 2008; Braum and Worm 2009).
Moreover, their presence or absence can indicate the extent
of the footprint of human pressures.
River dolphins are top predators that inhabit some of the
largest tropical river basins in Asia and South America and
may be ideal candidates for ecological indicators. Gomez-
Salazar et al. (2012) investigated the relationships between
measures of ecosystem degradation and river dolphins as
potential ecological indicators. They tested three ecological
indicators of freshwater ecosystem degradation using river
dolphins: (i) density of river dolphins, (ii) mean group size
of dolphins, and (iii) dolphin sighting rates. A strong
negative relationship between measures of habitat degra-
dation and river dolphin density estimates was found in
selected locations of the Amazon and Orinoco Rivers. It
was suggested that river dolphins are flagship and sentinel
species for monitoring the conservation status of large
tropical rivers in South America. The contents of micro-
pollutants, such as organochlorines, organotin compounds,
and perfluorinated chemicals in the Ganges dolphin tissues
(Kannan et al. 1993,1994,1997; Senthilkumar et al. 1999;
Yeung et al. 2009), which were otherwise below detectable
levels in the river water or in other invertebrates and fishes,
suggest that dolphins are sentinels of toxic chemical pol-
lution in the river. Low dolphin populations in the river’s
upstream dams and barrages on the India–Nepal border and
in other areas indicate ecosystem degradation. Thus, Gan-
ges dolphins’ low population in some locations can be
related to environmental degradation in the Ganges basin.
Several cetacean subpopulations are under siege from vari-
ous stressors, such as climate change; chemical, pathogen,
and noise pollution; ship traffic; and fishery bycatches; and
the Ganges dolphin population is no exception. Freshwater
cetaceans have declined dramatically in numbers and range,
especially in Asia (Reeves et al. 2000; Smith and Jefferson
2002). The Yangtze River dolphin is already extinct (Turvey
et al. 2007). The threats are diverse, longstanding, and very
difficult to assess or manage.
All of the existing river dolphins are endangered, mainly
due to human activities an d multiple threats, including direct or
incidental catch; hydroelectric power plants; construction of
dams, barrages, and embankments; strikes by vessels; chemi-
cal pollution from the discharge of domestic effluents, from the
agriculture, industry, mining, and health sector; noise pollution
due to underwater explosions and vessels; and deforestation,
which lead to heavy siltation and competing demands of
freshwater for irrigation, especially in the Indian subcontinent.
All freshwater cetaceans require adequate water flow and
water quality within their range; these are the basic elements of
a suitable habitat and are needed by the animals to support their
physical health, mobility, and ability to forage efficiently and
to find prey. River dolphins face intense competition with
humans for resources such as fish and freshwater. The Ganges
dolphins share their lowland riverine habitat with hundreds of
millions of people, which results in high mortality rates from
hunting, entanglement in fishing gear or entrapment in irriga-
tion canals, population fragmentation by dams and barrages,
and severe habitat depletion by water extraction, and degra-
dation by pollution and altered flow regimes (Sinha et al. 2000,
The future of the South Asian river dolphins is inti-
mately tied to the region’s water security. South Asia has
approximately 25 % of the world’s human population but
only 4.5 % of its renewable water resources (Babel and
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Wahid 2008). As per Indian Census 2011, the average
population density in the Ganga Basin in India is 581/km
and, in Bihar state (located in the Ganges basin), it is
, compared to the world’s average population
density of 13.3/km
. Thus, the Ganges basin is one of the
most densely populated regions in the world, and the loss
of freshwater biodiversity is inevitable and the prospects
for the South Asian river dolphins uncertain.
Construction of at least 50 dams and barrages within the
known or suspected historical range of the Ganges dolphin
(Smith et al. 2000) has dramatically affected its habitat,
abundance, and population structure during the last
45–50 years. Dams and barrages (low-gated diversion dams)
restrict the movement of dolphins, rendering them isolated
into separate sub-populations. A subpopulation is defined by
the IUCN as ‘‘geographically or otherwise distinct groups in
the population between which there is little demographic or
genetic exchange (typically one successful migrant indi-
vidual or gamete per year or less)’’ (IUCN 2001).
The Farakka Barrage (24.7891°N, 87.8878°E; located
on the Ganges River 400 km downstream of Patna and
400 km upstream of Calcutta near the India–Bangladesh
border; Fig. 3) has affected the dolphin population in the
Ganges, as the barrage has not only created a physical
barrier for movement of the dolphin but also the reach of
the river has been changed from a lotic to a lentic eco-
system (Sinha 2000). Due to the increased sedimentation
rate, more than 75 % of the ‘head pond’’ has been filled,
and a huge sand bar (3 km 90.3 km) was formed in 2004
(Sinha 2013). Sediments are trapped behind dams and
barrages and reduce the volume of suspended matter
transported downstream, lessening the potential for bars
and sand islands to form in the lower reaches of the river.
Barrages reduce or eliminate the ‘‘freshet effect,’’ which, in
many wild rivers, renew the floodplains and contributes to
meandering (Reeves and Leatherwood 1994).
The Bhagirathi River receives regulated flow with a low
sediment load from the Farakka Barrage through a 38.2-km
long feeder canal. The water with the low sediment load
has reduced the physiographic and hydrologic complexity
in the Bhagirathi River up to Katwa (155 km). The reduced
complexity has led to a very low dolphin population (0.3
Fig. 3 A sand bar (3 km 90.3 km) in the head pond of Farakka Barrage along the Ganges River in December 2004
123 ÓRoyal Swedish Academy of Sciences 2014
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dolphin/linear km) compared to the other, lower segments
of the Ganges and Bhagirathi Rivers, which have about
0.5–1 dolphin/linear km (Sinha 1997). A small tributary,
Ajay River, with heavy loads of silt from the highlands of
Jharkhand, discharges into the Bhagirathi River from the
west at Katwa. The Bhagirathi River has more hydro-
physiographic complexity downstream of Katwa, which is
evident from the presence of more dolphins and avian
fauna (Sinha 1997). Dams and barrages have a number of
potential problems, including downstream effects on prey
caused by changes in flow rate and sediment transport
(Reeves and Leatherwood 1994).
Embankments cause sediment deposits in the riverbed
instead of in floodplains, thereby eliminating or reducing the
extent of the eddy-counter currents, where dolphins are gen-
erally found (Smith et al. 1998). The embankments also restrict
access of riverine fishes to the floodplain habitat critical to their
reproduction and growth (Boyce 1990). Approximately
3,500 km of embankments have been constructed along the
Ganges main stem and the Gandak, Burhi Gandak, Bagmati,
Kamala, Yamuna, Punpun, and Sone tributaries (Mishra
1999). Dolphins were apparently extirpated from at least
35 km of the Punpun tributary of the Ganges after embank-
ments were constructed in 1975 (Sinha et al. 2000). Other
sources of habitat degradation in the distribution range include
heavy siltation in river beds, due to loss of green cover in the
catchments area, and change in land use pattern (e.g., crop
farming in floodplains); water abstraction from surface pumps,
especially in the Ganges system, where the mean dry-season
water depth has declined dramatically in recent years; dredg-
ing; and removal of stones (Shreshtha 1989), sand (Mohan
et al. 1998), and wood debris (Smith 1993).
A large number of completed and ongoing hydroelectric
projects on the Ganges and in tributaries in the Himalayas are
further expected to aggravate the problem of flow decline in
the middle and lower reaches of the Ganges, where dolphins
survive (Sinha et al. 2010b). The cumulative effects of these
activities compromise the ecological integrity of the riverine
ecosystems, especially the small tributaries where the suitable
habitat is limited and disproportionately vulnerable to local
disturbance. Declining flows in the rivers have received little
attention for a long time. The newly established National
Ganga River Basin Authority by the Indian government in
2009, an apex body under the chairmanship of the Prime
Minister of India, has the mandate of ‘Aviral Dhara Nirmal
Dhara’(uninterrupted quality flow). Such efforts may help
restore the riverine environment.
The riverine ecosystem is in close proximity to human activ-
ities and, therefore, is an ultimate sink for the discharge of
sewage and industrial wastewater that emanates from human
activities. The Ganges River basin is the most densely popu-
lated basin in the world and is heavily polluted by fertilizers,
pesticides, industrial chemicals, and domestic effluents.
Exposure of dolphins to toxic chemicals can affect their
reproduction and survival. In the Ganges River food chain, the
dolphins, as an apex predator, have been shown to accumulate
high levels of persistent and toxic chemicals in their tissues.
Several studies conducted by our research group have reported
elevated levels of DDT in the blubber of Ganges dolphins
(Kannan et al. 1994; Senthilkumar et al. 1999)(Table6).
Notable levels of immunotoxic chemicals, such as butyltins
and perfluorinated chemicals, have been found in the tissues of
Gangesdolphins (Kannan et al. 1997,2005; Yeung et al. 2009).
Heavy metals, including cadmium and lead, have been mea-
sured in the livers of Ganges dolphins (Kannan et al. 1993).
Although levels of the some of the toxicants were rel-
atively low, based on the analysis of the metabolic index
(see details in Kannan et al. 1994), it was found that
Ganges dolphins have a low capacity to metabolize some
toxic pollutants. The proximity to intense pollution sources
and low capacity to metabolize pollutants make the Ganges
dolphins vulnerable to the effects of chemical pollution.
Several studies have shown that some freshwater aquatic
mammals, such as mink and river otter, are very sensitive
to the effects of chemical pollution (Kannan et al. 2000).
Thus, studies are needed to assess the impact of pollutants
on the health of river dolphins. In addition to the con-
taminants studied thus far, other emerging contaminants
that arise from sewage pollution and diseases in river
dolphins should be examined in future studies. Our study
on mercury pollution in water, sediment, benthic macro-
invertebrates, and fishes of the Ganges River at Varanasi
found higher levels of mercury (0.0–91.7 ppm) in fishes
than those of fishes collected from the western coast at
Mumbai (0.03–0.82 ppm) (Sinha et al. 2007). Recent
studies have reported elevated levels of arsenic in the
Ganges river basin (Nickson et al. 2007; Kumar et al.
2010). Mercury and other industrial pollutants that arise
from the discharges of wastes from several industries need
to be studied in different segments of the Ganges.
Deliberate killing of the Ganges dolphins is believed to have
declined in most areas but still occurs at least occasionally in
the Ganges near Patna (Sinha 2002) and in the upper reaches
of the Brahamaputra River in Assam (Mohan et al. 1997) for
their meat and oil, which is used as a fish attractant. Mortality
from fishing gears, especially monofilament nylon gillnets, is
a severe problem for the Ganges dolphins throughout their
range (Sinha 2002). Dolphins are particularly vulnerable,
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because their preferred habitat is often in the same location as
the fishing grounds. A specific problem is that, because
dolphin oil is highly valued as a fish attractant, fishermen
have a strong incentive to kill any dolphin found alive in their
nets and even to set their nets strategically in the hope of
capturing dolphins, which is termed ‘‘assisted incidental
capture’’ (Sinha 2002). Meaningful quantitative data on the
magnitude of catches, either deliberate or incidental, are
unavailable and unlikely to become available in the absence
of organized fishing in the river system.
Although the Ganges dolphin was given legal protection
in India under the Wildlife (Protection) Act of 1972, the law
was not effective until the end of the 20th century. The
efficacy of the Act became noticeable after the proceedings
of the Patna High Court (CWJC No. 5628 of 2001). Field
trials have shown that fish scrap oil is an efficient substitute
for dolphin oil as a fish attractant (Sinha 2002). We con-
ducted several extension programs, with the help of Wildlife
Trust of India (Sinha 2004), a non-governmental organiza-
tion, to popularize the use of fish scrap oil as an alternative to
dolphin oil. Many groups of fishermen from Assam visited
our laboratory at Patna University during the last 10 years,
and the most recent was in 2012, to get training on how to
obtain oil from fish scraps and its use in the oil fishery. Some
fishermen, however, continue to use dolphin oil. In
November 2012, we encountered a couple of fishermen who
were using dolphin meat and oil at Sultanganj near the
Vikramshila Gangetic Dolphin Sanctuary in Bihar and
another fisherman at Barh in the Patna District. After these
observations, we organized an interactive meeting on Janu-
ary 25, 2013, with fisherman who use dolphin meat and oil in
their village near Sultanganj to create awareness, educate,
and motivate the fishermen to save the dolphin. State gov-
ernment officials also participated in the meeting. Such
meetings and the extension program to popularize the fish
scrap oil will help to save the Ganges dolphin.
India has been a pioneer in conserving wildlife. The world’s
first recorded wildlife conservation measures were enacted
in India during the third century BC. One of the greatest
Indian emperors, Ashoka the Great, who reigned from 274 to
232 BC, stressed the sanctity of an animal’s life. Some of his
decrees engraved in stone have survived until today in the
Pillar Edict V. The Ganges dolphin (called Ganga-puputaka
in ancient days) was included in the list of animals declared
inviolable by the emperor (Sinha 1996).
The Government of India provides legal protection to the
Ganges River dolphin (Fig. 4) by includi ng it in Schedule I of
the Wildlife (Protection) Act, 1972 since the Act was enacted
in 1972. Killing and poaching of any animal included in
Schedule I of the Act are cognizable offenses, and the
offender may be fined up to $500 US and/or receive a 7-year
imprisonment. The efficacy of this act, however, was not
evident until the 1990s, when we started intensive and
extensive awareness campaigns among the general public.
Help rendered by the mass media, both print and electronic,
was valuable in educating people of different social strata.
The IUCN categorized the Ganges dolphin as endan-
gered in 1996 (IUCN 1996). The species was included in
Appendix I of the Convention on the International Trade on
Endangered Species of Flora and Fauna (CITES) and in
Appendix II of the Convention on Migratory Species. The
government of India declared the Ganges dolphin the
National Aquatic Animal of India on October 5, 2009, and
formal notification was issued on May 10, 2010. Thus,
Table 6 Reported concentrations (ng/g wet wt) of DDT, HCH, polychlorinated biphenyls (PCBs) in the blubber and butyltins and perfluo-
rooctanesulfonate (PFOS) in the liver of Ganges river dolphins from India
Date of collection Sex Length (cm) Tissue Lipid (%) PCBs DDTs HCHs Butyltins* PFOS*
24 January 1988 M 70.4 Blubber 34 360 4700 190 2000
6 October 1991 M 104 Blubber 31 410 9100 470 380
21 July 1991 F 115 Blubber 41 620 12000 430 250
27 March 1992 F 233 Blubber 74 420 13000 610 61
11 February 1993 F 250 Blubber 51 1500 31000 860 NA
27 June 1994 M 84 Blubber 53 13000 64000 1100 NA
3 November 1994 M 123 Blubber 77 2560 63000 1100 NA
29 November 1994 M 117 Blubber 70 2100 30000 1900 NA
5 November 1996 F 133 Blubber 71 1100 21000 1900 NA
1993-2007 (n =15) 10 M&5F 68-248 Liver NA NA NA NA NA 28 (0.74–74)**
For details see Kannan et al. (1993,1994,1997); Senthilkumar et al. (1999); Yeung et al. (2009)
*Refers to concentrations in liver (for sum of mono-, di- and tri-butyltins and PFOS)
**values in parentheses indicate range; NA =Not analyzed
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India became the first country to adopt the river dolphin as
its National Aquatic Animal.
A separate Conservation Action Plan (CAP) for the
Ganges river dolphin has been prepared for the Government
of India (Sinha et al. 2010b). The CAP includes protection
and restoration of habitats, community participation,
capacity building, conducting of periodic status surveys and
monitoring, establishing protected areas, providing educa-
tion awareness, minimizing incidental catches, rescue and
rehabilitation, and initiating researches on identified thrust
areas besides, identifying agencies for implementation of the
Action Plan. A National Dolphin Research Center is to be
established at Patna shortly as an institutional support for the
long-term conservation of the dolphin. With the help of
activists, NGOs, university researchers, government
departments/officials, and other stakeholders, especially
fishermen, various action plans are being implemented. The
State Government of Bihar designated October 5 as ‘‘Dol-
phin Day’’ and is celebrating the ‘‘Dolphin Day’’ every year
on October 5 since 2012, as a means to help create awareness
among the general public in addition to annual monitoring of
government activities to save and conserve the dolphins.
One of the important tasks for researchers is the
development of a robust scientific method for population
estimation to provide a basis for determining which areas
should be given the highest conservation priority. Fur-
ther, age-wise habitat use during different seasons must
be studied as a means to help prioritize the conservation
The baiji’s extinction clearly demonstrates that, without
appropriate and timely actions, the future of the remaining
freshwater cetaceans is precarious. All freshwater ceta-
ceans require adequate water flow and water quality within
their range; these are the basic elements of a suitable
habitat and are needed by the animals to support their
physical health, mobility, and ability to forage efficiently.
The long-term viability of freshwater cetacean popula-
tions requires management of entire ecosystems and
watersheds, i.e., an ecosystem approach for the conserva-
tion and management of rivers and river dolphins. Water-
shed management, especially in upstream sections, is
required to reduce sedimentation from agriculture, forestry,
and land conversion; to limit water removal and dramatic
changes in flow regimes by dams and barrages; to ensure
adequate water and sustain essential geomorphic features
in cetacean habitat; and to reduce toxic effluents and
chemical pollution from agriculture, industry, industrial
transport, and human settlements.
Organochlorine and butyltin concentrations in samples
from the tissues of Ganges dolphins were high enough to
cause concern about their effects. Further, several unstud-
ied pollutants that arise from the disposal of sewage are
expected to compromise the health of dolphins. Pollutant
loads can be expected to increase with industrialization,
and the spread of intensive agricultural practices is facili-
tated by water diversion. River dolphins may be
Fig. 4 Platanista gangetica gangetica surfacing in the River Ganges (Photo by Fernando Trujillo)
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particularly vulnerable to industrial pollution, because their
habitats in counter-current pools downstream of conflu-
ences and sharp meanders often place them in proximity to
point sources in major urban areas in India. Further, the
capacity of rivers to dilute pollutants has been drastically
reduced in many areas because of upstream water
abstraction, diversion, and impoundment. This problem is
destined to worsen as more development takes place along
the river. It is of utmost importance to maintain pollution-
free, uninterrupted flow in the rivers to address these
issues. Particularly in river systems where there is great
demand for fresh water for human use, critical minimum
flow and the maintenance of natural flow variability are of
overarching importance.
It is important to determine which habitats are prefer-
entially used by dolphins during the low-water season so
that conservation efforts can be focused in these locations.
In the dry season, channel constrictions, confluences, and
channels with high cross-sectional areas are all high-use
dolphin habitats that could benefit from management as
discrete dolphin conservation zones. The monitoring of
river dolphin populations and habitats on a regular basis, as
has been performed for tigers and elephants, is very much
required. Involvement of fishermen in dolphin conservation
efforts will encourage them to have a sense of ‘‘owner-
ship.’’ Further, a study is needed on the implications of
climate change on freshwater cetaceans that include con-
sideration of habitat resilience.
It is important to collect as much scientific information
as possible on behaviors and other ecological requirements
of the dolphin in the Ganges River. We recommend
building a microcosm in the Ganges River at Patna for
captive breeding and rescue efforts. For this, a big enclo-
sure (2–3 km 9100 m 95 m) could be created, using
smooth metal poles and wire mesh (30 cm 930 cm) along
the left bank of the river at Patna, where enough water flow
is available year-round. This will ensure availability of
enough water flow and prey through the enclosure. A
couple of male and female dolphins can be kept in the
enclosure to study their behaviors and the possibilities of
‘breeding’’ in natural habitat.
Having declared the river dolphin, Platanista gangetica
gangetica, the National Aquatic Animal, the Indian gov-
ernment should complement this commendable action by
setting up a national network of protected/conserved areas
for river dolphins and associated aquatic fauna and con-
sidering initiating a National River Dolphin Project along
the lines of Project Tiger, Project Elephant, Project Snow
Leopard, and Project Rhino. In doing so, the project should
identify the dolphins’ present pattern of distribution and
status in the context of their historical distribution
throughout the Ganges and Brahmaputra systems, Indus
tributaries, and coastal waters of India (including
Sundarbans). Given that fishery interactions are the pri-
mary cause of river dolphin mortality, the Inland Fisheries
Act needs to be reviewed and amended so that rules and
regulations are in place, making fisheries sustainable, and
reducing risks to dolphins and other aquatic wildlife.
We need to consider the development of community-
based river dolphin conservation areas, where sustainable
fisheries and dolphin conservation measures are promoted
in an integrated manner, with possible model planning,
design, and implementation of ecotourism projects focused
on dolphin watching, with appropriate safeguards against
disturbance (harassment). Such projects should incorporate
education and awareness efforts and should be promoted as
a preferable alternative to dolphinariums. We also need to
design and implement a national awareness campaign on
river dolphins through innovative media programs and the
establishment of interpretation and information centers in
dolphin conservation/protected areas.
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Ravindra K. Sinha PhD, is a Professor of Zoology at Patna Uni-
versity, Patna, India. His research interests include Conservation of
the Ganges River dolphin, River Ecology, Pollution Biology, Bio-
monitoring, and Limnology. He has conducted several field surveys
on river dolphins in India and Nepal for over 25 years.
Address: Department of Zoology, Patna University, Patna 800 005,
ÓRoyal Swedish Academy of Sciences 2014 123
Author's personal copy
Kurunthachalam Kannan (&) PhD, is a Research Scientist at
Wadsworth Center, New York State Department of Health and a
Professor of Department of Environmental Health Sciences, State
University of New York at Albany, New York, USA. His research
interests include understanding of environmental distribution, fate,
and toxic effects of organic pollutants. His research has focused on
the effects of toxic environmental chemicals on marine mammals and
other aquatic wildlife.
Address: Wadsworth Center, New York State Department of Health
and Department of Environmental Health Sciences, State University
of New York at Albany, Empire State Plaza, P.O. Box 509, Albany,
NY 12201-0509, USA.
123 ÓRoyal Swedish Academy of Sciences 2014
Author's personal copy
... River dolphins are apex predators found in many of the largest tropical river basins in Asia and South America and are considered excellent candidates for ecological indicators [15]. Gomez-Salazar et al., [16] studied the relationship between indices of ecosystem degradation and river dolphins as ecological indicators. ...
... The Gangetic river dolphin has been given legal protection by the Government of India as it is included in Schedule I of the Wildlife (Protection) Act, 1972. Killing or poaching any species listed in Schedule I of the Act is a cognizable offense punishable by a maximum fine of US$500 and/or up to 7 years in prison [15]. The highest level of protection for the species is provided by Bangladesh's Wildlife (Conservation and Protection) Act, 2012, and Nepal's National Parks and Wildlife Conservation Act 2029 (1973), as well as the Aquatic Animals Protection Act 1960, Nepal [21]. ...
... Since 2012, the Bihar state government has celebrated "Dolphin Day" on 5 October in an effort to raise public awareness and track government efforts to save and conserve dolphins on an annual basis [15]. Additionally, a concrete action plan for the Ganges River Dolphin was approved at the 13 th Convention on Migratory Species (2020) in Gandhinagar, India, which aims to promote conservation and research activities on dolphins in transboundary areas. ...
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Along with turtles, crocodiles, and a few different species of sharks, the Ganges river dolphin (Platanista gangetica gangetica) is one of the oldest animals on the planet. The Ganges and Brahmaputra river basins in India, Nepal, and Bangladesh are home to this species. It generally lives in countercurrent systems of the main river channel and feeds mostly on fish. The Gangetic river dolphin is considered important because it acts as an indicator of the health of the overall river ecosystem. It was designated as the National Aquatic Animal of India on 5 October 2009. This species is now extinct in most of the areas where it once existed, due to serious threats from water development projects, pollution, poaching, and deaths from accidental entanglement in fishing gear. Currently, their population is estimated to be less than 2000 individuals. The Ganges river dolphin comes under Schedule I of the Wildlife Protection Act (1972). They are classified as Endangered in the IUCN Red List and included in CITES Appendix I. The Wildlife Institute of India launched an initiative called "Development of a Conservation Action Plan for Dolphins" in 2016 with the intention of saving these endangered dolphins.
... Deep pools are known to facilitate longer dives and hence yield the highest usable area for dolphins (Paudel et al., 2021). A combination of deep and shallow river segments also supports activities such as resting, feeding, and reproduction (Mosquera-Guerra et al., 2020;Sinha & Kannan, 2014). ...
... While the decline in the freshwater dolphin population has been attributed to hydrologic alteration by water-based infrastructures such as dams, there is also clear evidence of increase in population of dolphins in certain segments of rivers affected by such hydraulic structures. For instance, the Bijnor-Narora stretch of the Upper Ganges, the Upper Ganges Ramsar Site, and the Katarniaghat Wildlife Sanctuary in Uttar Pradesh, India, have witnessed increases in Ganges dolphin population mostly due to increase in water depth in the rivers (Kreb et al., 2010;Sinha & Kannan, 2014). An increase in sinuosity in certain sections of the Ganges river after the construction of Bijnor barrage has led to additional hydraulic refuge for dolphins (Sonkar & Gaurav, 2020). ...
... The habitat preference of dolphins noted in earlier studies is based on observations, which are mainly qualitative in nature. For instance, the preference for confluences by dolphins has been noted by many studies (Bashir et al., 2010;Sinha & Kannan, 2014). This study provides a quantitative account of such habitat preferences. ...
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Physiographic and hydrologic complexities play major role in determining the habitat suitability for river dolphins. However, dams and other water development structures alter hydrologic regimes that degrade habitat conditions. For the three extant species of obligate freshwater dolphins, namely: Amazon dolphin (Inia geoffrensis), Ganges dolphin (Platanista gangetica), and Indus dolphin (Platanista minor), the threat is high as dams and water-based infrastructure dotted throughout their distribution range impact dolphin populations by restricting their movement. But there is also evidence of localized increase in dolphin population in certain segments of habitats affected by such hydrologic alterations. Hence, the impacts of hydrologic alterations on dolphin distribution are not as binary as it seems. We aimed to ascertain the role of hydrologic and physiographic complexities in determining the distribution of the dolphins in their geographic ranges using density plot analysis and also to understand how hydrologic alterations in the rivers affect their distribution using a combination of density plot analysis and review of literature. The influence of some of the study variables such as distance to confluence and sinuosity was similar across species-for instance, all three dolphin species preferred slightly sinuous river segments and habitats near confluences. However, varying influences across species were observed for some other variables such as river order and river discharge. We assessed 147 cases of impacts of hydrological alterations on dolphin distribution by categorizing the reported impacts in nine broad types out of which habitat fragmentation accounted for the majority of the impacts (35%) followed by habitat reduction (24%). These endangered species of freshwater megafauna will experience further intensified pressures as more large-scale hydrologic modifications such as damming and diversion of rivers are underway. In this context, basin-scale water-based infrastructural development planning should take into consideration the salient ecological requirements of these species to ensure their long-term survival.
... The Ganges river dolphin Platanista gangetica is one of the two Endangered South Asian river dolphin species that inhabits the perennial floodplains of the Ganges-Brahmaputra-Meghna river basin of India, Nepal and Bangladesh, and the Karnaphuli-Sangu river basin of Bangladesh (together being referred henceforth as GBMKS basins) including several associated tributaries Sinha and Kannan, 2014;Braulik et al., 2021;Kelkar et al., 2022). Exposed to a multitude of environmental stresses and anthropogenic perturbations, the species has witnessed a population decline of more than 50% coupled with 18% reduction in its distribution range over the past few decades (Kelkar et al., 2022;Braulik et al., 2021). ...
... The GBMKS basins have one of the highest human footprint in the world, mainly in the form of artisanal fisheries Kelkar et al., 2010;Sinha and Kannan, 2014), which makes it difficult to maintain the balance between local economic needs and dolphin conservation (Kelkar et al., 2010;Paudel et al., 2016). Dolphin-fisheries interactions thereby pose significant conservation concerns in the GBMKS basins through direct competition for certain fish size-classes, habitat and diel activity overlap, prey-fish depletion, by-catches, intentional killing for oil and meat, and boat-traffic Sinha, 2002;Sinha 2006;Read, 2008;Kelkar et al., 2010;Sinha et al., 2010;Paudel et al., 2016;Kelkar et al., 2018). ...
... Dolphin-fisheries interactions thereby pose significant conservation concerns in the GBMKS basins through direct competition for certain fish size-classes, habitat and diel activity overlap, prey-fish depletion, by-catches, intentional killing for oil and meat, and boat-traffic Sinha, 2002;Sinha 2006;Read, 2008;Kelkar et al., 2010;Sinha et al., 2010;Paudel et al., 2016;Kelkar et al., 2018). However, Ganges dolphins have for long persisted in human-dominated river systems and have shown affinity to sites of frequent human use (Sinha and Kannan, 2014). So far many studies have described dolphin-fisheries interactions along with their effects and associated risks (Read, 2008;Kelkar et al., 2010;Khanal et al., 2016;Paudel et al., 2016). ...
The Endangered Ganges river dolphin is a flagship species that inhabits the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems. Exposed to a multitude of environmental stresses and anthropogenic perturbations, the species has experienced severe population decline and shrinking of potential habitat in much of its distribution range. A range-wide mapping of its potential habitat and assessment of factors associated with species occurrence therefore bears immense relevance for conservation planning. We used an ensemble of species distribution models (SDM) using occurrence data to investigate dolphin distribution in relation to hydrological, climatic, physiographic, land cover and anthropogenic variables across the species entire range. We followed a systematic prioritization approach to identify highly suitable habitat patches (potential hotspots) for dolphins that require immediate protection. We identified nearly 7945 sq. km of river area as highly suitable for dolphins as habitat refugia for the species, more than 93% of which are outside the protected area regime, thus demanding immediate conservation attention. This study is a step towards delivering evidence required for spatial risk assessments and conservation planning wherein the habitat suitability maps will help in developing better management plans and strategies, and the predicted three tier classification of suitable habitats will facilitate decision making and prioritization of river segments for inclusion in the protected area network. We recommend that the inferences drawn from our study must be implemented on priority to ensure species conservation in the riverscape. Besides, our study provides huge scope for fine scale assessment and validation of the predicted suitable areas for model improvement.
... Here the impact of such human ecological footprints is difficult to monitor as they are not accessible to all and most importantly, they do not belong to the jurisdiction of any nation. But the Gangetic dolphin species, being at the apex of the food chain can ensure the health of the entire river environment as well as the conservation of its aquatic lives (Sinha et al., 2014) naturally. This is reflected in its safe migration through the Ganges using the specially shaped streamlined body structure and the SONAR communication system. ...
... Additionally, persistent organic pollutants from commercial sectors, including pesticides like DDT, along with municipal liquid waste into the Ganges, cause mainly physical, chemical and microbial contamination of its water (Hossain, et al., 2020). Its impact ranges from the dolphin's habitat degradation (Sinha et al., 2014) to direct physical poisoning, resulting in the damage of its reproductive and immune systems along with other aquatic mammals which may lead to their increased mortality (Nabi et al., 2022). ...
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A healthy ecosystem is a subject matter of interest because of its rich biodiversity. But natural climatic changes, as well as various man-made anthropogenic factors, not only emit greenhouse gases into the atmosphere resulting in global warming but influence various ecosystems of the earth. The aquatic ecosystem is one such example where the dolphin, with its complex behaviour, is recognized as one of the most intelligent members. The natural hydrodynamic body system speeds up underwater and the SONAR system communication technology helps dolphins to work as an efficient aquatic health indicator. But human activities, including aquatic poaching and fishing, creating underwater noise pollution and undesirable infrastructures and producing debris from their generated wastes obstruct the proper functioning of these systems and ultimately contribute to their habitat loss. So, dolphins’ ( Gangetic ones in India) disappearance from their comfortable living zone was inevitable and observed in the past few decades as they migrated to areas with more favourable conditions. The available information related to the rejuvenation in the qualities of the Gangetic water and the restoration of the dolphin’s habitat during COVID pandemic confirmed the absence of the negative impact of human activities on the Gangetic ecosystem. Hence, identification of the important steps to be implemented by the concerned authorities in post-COVID situation and their maintenance by the common people is necessary to balance such important aquatic biodiversity in the long run, keeping the country’s developmental activities operational. This review article is an endeavour towards that direction.
... The Ganga river basin includes a vast network of irrigation canals that draw water from the surrounding rivers (Reeves et al., 2000;Sinha et al., 2010;2014). When the barrage gates close, water is diverted into these irrigation canals. ...
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The Ganges river dolphin (Platanista gangetica) is an endangered freshwater species found in the rivers of India, Nepal and Bangladesh. The development of dams and barrages have severely affected this habitat as dolphins move into irrigation canals where they are at risk of injury or death due to a range of factors, such as rapidly receding waters, heat stroke, drowning and human interference. Between 2013–20, the TSA Foundation India and the Environment, Forest and Climate Change Department, Uttar Pradesh, rescued 24 dolphins in 18 entrapment events. While 19 dolphins were rescued, five died during capture or transportation. Here we describe our capture and transportation methods to raise awareness of the issue and improve survival rates in future entrapment events.
... The study by Day et al. (2019) 193 suggested maintaining ecological flows, downscaling of vessel traffic, and propeller modifications can 194 reduce cavitation noise and help mitigate noise impacts on Ganges River dolphins. 195 196Research status and needs197 198The Ganges River dolphin is suggested to be one of the reliable indicator species to understand the health 199 of the Ganga River ecosystem(Sinha and Kannan, 2014). A sustained research program on this species 200 ...
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The Ganges Dolphin needs uninterrupted water sources in order to both communicate and to locate its food. Ever-increasing activities in the rivers, especially from motorized vessels, are likely to add noise to the soundscape used by this animal and may affect its ability to locate its prey or to sense its environment. Although efforts have been made to improve the quality and flow of the water passing through the Ganga River system, a coordinated effort among policymakers, local implementing authorities, researchers, and funding agencies is needed to achieve the desired goal of restoring the habitat of dolphins, stopping their accidental deaths, increasing their number by captive breeding, and reinstating the biodiversity of aquatic organisms that are passively or actively linked to them. While passive restoration plans such as improving water quality, increasing water volume, and habitat reclamation may work well, the developmental needs along the river exert constant pressure on these plans. These plans may not be effective without the strict enforcement of guidelines, an understanding of the requirements of the plans by all the stakeholders, and the awareness of the population living along the rivers. Therefore, conservation efforts, along with ongoing passive restoration processes aimed at improving the dolphin's living ecosystem by providing enough quality water cover and prey, should focus on increasing the population of these animals by propagating them in captivity through biological or biotechnological means, the success of which needs strong scientific research backing. A scientometric analysis of 20 years (2001-2020) on this animal shows that scientific studies are confined to the ecology of the animals and very little is known either of their biology or their genetics. During the study period, India occupied fourth spot in number of publications on river dolphins, with the Indian Institute of Technology as leading institute. Advance biology techniques may allow us to breed the animal in captivity and even clone the animal. However, the research towards this requires creating the necessary basic infrastructure, funding, and policy support, and developing human resources for research and management.
River systems worldwide are severely degraded due to diverse threats. River restoration aiming to reverse negative impacts has become a priority strategy for enhancing social benefits and river ecosystems in urban development. River restoration projects provide multiple ecosystem services to human beings, and social benefits derived from cultural services have been underestimated and have attracted increasing interest from researchers and policymakers. The purpose of this research is to investigate the public evaluation of the impacts of river restoration projects on social benefits. Two restored river sites in Hong Kong were selected as the case sites. The questionnaire survey was implemented to collect the public evaluation of the social benefits derived from the cultural services of the restored projects, and their visiting patterns and feelings. Regarding the evaluation of the cultural services, the public thought the restored rivers contribute to public health, quality of life, and recreation activities. Additionally, the respondents thought there is a substantial improvement in the aesthetics of the environment. Many people are supportive of similar projects in future implementation. The results summarized from the 158 responses show that local citizens frequently visit the restored river sites for diverse motivations. People generally feel good about air condition and sounds at the restored sites. Most people are in a good mood when staying at the restored sites, indicating that river restoration contributes to the public’s healthy living. A large proportion of people think there are no negative impacts of projects though some people are concerned about insects, guano, and animal disease. Generally, the public holds a positive view of the projects. The research finding enables policymakers to understand the public’s opinions on the river restoration projects and increase their confidence in implementing more similar projects in the urban environment.KeywordsRiver restoration projectsPublic evaluationSocial benefitsCultural services
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Nepal is endowed with vast water resources in form of glaciers, lakes, streams and rivers. All the rivers in Nepal are connected to the Ganges River system of India. The major rivers are reliable sources of water and provide habitats for aquatic animals, opportunities for hydropower, and irrigation development in downstream regions. The major rivers of Nepal include the Koshi, Gandaki (Narayani), Karnali, and Mahakali which all drain from north to south. These rivers support abundant wildlife species as well as a number of fishes, amphibians and reptiles. Most relevant to this paper is the Ganges River Dolphin (Platanista gangetica gangetica Roxburgh, 1801). The Ganges River Dolphin preys on fish, mollusks and other aquatic animals. Being a migratory species, the dolphins move from larger rivers to their tributaries, seasonally. This paper is intended to review work on the status of Ganges River Dolphin in Nepalese rivers based on secondary data obtained from different published surveys targeting the dolphin populations. The records show the Karnali River has the largest population, followed by the Koshi and Narayani rivers, with no record of dolphins occupying the Mahakali River in recent years. Recent surveys estimate about 100 dolphins living in Nepal, with 80 estimated in the Karnali River. Different anthropogenic activities including construction work, intensive fishing, pollution and the lack of conservation planning for dolphins have resulted in a decline in number from historic levels. The presence of this aquatic mammal is considered as an indicator of the overall health of the river system. The COVID-19 pandemic and lock down might have caused increased dolphin sightings. Additionally, high pre-monsoon precipitation in recent years have caused higher water levels in smaller rivers, possibly causing the dolphins to return earlier than usual to the major river systems. They were recorded to be present in the Mohana and other small tributaries of the Karnali River as early as first week of June.
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Nepal is a land-linked country relatively small in area. However, it is home to several rivers, and these rivers are undoubtedly beautiful additions to the mountainous nation's splendid scenic landscape. Most of Nepal's surface water drains through the three major rivers are Saptakoshi, Narayani, and Karnali. Mechi and Mahakali Rivers and their tributaries mark the international boundaries between Nepal and India. All of these originate either from the Himalayas or from the Tibet Plateau and are perennial. However, dams and other water development projects, intensive fishing, pollution, and extensive human disturbances have decreased the abundance of the Ganges River Dolphin, which is now restricted only to the Koshi and Karnali River systems and in an isolated form. The first Integrated Dolphin Census of Nepal, conducted in 2016, recorded 52 dolphins throughout the country. Of the 52 dolphins, 43 were sighted in the Mohana of Karnali and its tributaries. No dolphins have been recorded recently for the Mahakali river, and sightings in the Narayani river, are occasional. The population of the River Dolphins is declining at an alarming rate. Therefore, it is important to regularly assess the status and trends of their populations and design strategies for their conservation and sustainable use.
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Using passive acoustic monitoring (PAM) and convolutional neural networks (CNN), we monitored the movements of the two endangered Amazon River dolphin species, the boto (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis) from main rivers to floodplain habitats (várzea) in the Mamirauá Reserve (Amazonas, Brazil). We detected dolphin presence in four main areas based on the classification of their echolocation clicks. Using the same method, we automatically detected boat passages to estimate a possible interaction between boat and dolphin presence. Performance of the CNN classifier was high with an average precision of 0.95 and 0.92 for echolocation clicks and boats, respectively. Peaks of acoustic activity were detected synchronously at the river entrance and channel, corresponding to dolphins seasonally entering the várzea. Additionally, the river dolphins were regularly detected inside the flooded forest, suggesting a wide dispersion of their populations inside this large area, traditionally understudied and particularly important for boto females and calves. Boats overlapped with dolphin presence 9% of the time. PAM and recent advances in classification methods bring a new insight of the river dolphins’ use of várzea habitats, which will contribute to conservation strategies of these species.
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A continuous both upstream and downstream boat survey was conducted in the River Sarda between Sardanagar and Palia (175-200 km) in the month of March, 1994 to assess the status of faunal diversity of the river during low water season. The river segment meanders frequently and lies between two barrages: Banbassa Barrage at Tanakpur at India-Nepal border, and Sarda Barrage at Sardanagar in Lakhimpur-Khiri District of Uttar Pradesh. A total of 33 species of zooplankton including 21 rotifers, 7 cladocerans and 5 copepods; 12 benthic macroinvertebrates, belonging to 6 insects, one oligochaetes, 3 gastropods and 2 pelecypods were recorded during the survey. Besides, 55 species of fishes, a very rich and diversified turtle fauna (8 species). 44 species of avifauna were recorded during the survey. The gharials, crocodiles, others and dolphins could not be sighted, however, locals reported sightings of gharials and dolphins during flood. Indiscriminate poaching of turtles including the rare species, Chitra indica by the locals was encountered during the survey.
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The Ganges river dolphin, Platanista gangetica is a freshwater dolphin, commonly known as susu and is distributed in Ganga-Brahamputra-Meghna and Karnaphuli river systems in India, Nepal and Bangladesh. It is found in the freshwater and estuarine zones but never enters sea. It is one of the four freshwater cetacean species found in the world. Over-exploitation and habitat destruction are the major factors for rapid decline in dolphin population. Construction of Farakka Barrage in mid-1970s has genetically isolated the susu population. For the first time dolphin count in Feeder Canal, Bhagirathi and Hooghly rivers, and downstream Farakka Barrage was undertaken in low water season of 1995. Actual count as suggested by Cetacean Specialist Group of IUCN/SSC was done between Farakka and Calcutta. A best count of 152 dolphins was obtained. Habitat preferences of susus and impact of pollution and other human activities were studied. Based on the study, current status of dolphin in Bhagirathi and Hooghly rivers has been discussed and conservation measures suggested.
The capture, marking, release, and recapture of individual animals can be used to study movement patterns, the size and structure of populations, survival and recruitment rates. It is thus an important method for marine mammal researchers interested in ecology, life history, conservation, and management. Mark–recapture analysis is widely used in ecology to estimate abundance and survival rates. The basic data required are a set of capture histories of individually identified animals. A capture history is simply a string of 1s and 0s representing whether an animal was (1) or was not (0) captured in a series of sampling occasions. A sampling occasion is a finite period of time during which data are collected, e.g., a survey day, but in studies of marine mammals sampling occasions are often taken to be longer, e.g., a season. Mark–recapture analyses make a number of assumptions, the violation of which may lead to biased estimates of survival and, especially, abundance. Although it is straightforward to apply mark–recapture analysis to capture history data, great care must be taken to consider the effects of failing to meet these assumptions. Although analytical models exist that allow some assumptions to be relaxed, there is no substitute for a well-designed field study.