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

June 2014
AMBIO A Journal of the Human Environment 43(8)

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Patna University

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.

Population status and distribution of Ganges river dolphin in various tributaries of the Ganges River in India

…

Estimated population of the Ganges River dolphins in the early 2000s

…

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

…

Figures - uploaded by Ravindra Kumar Sinha

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Content may be subject to copyright.

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AMBIO

A Journal of the Human Environment

ISSN 0044-7447

AMBIO

DOI 10.1007/s13280-014-0534-7

Ganges River Dolphin: An Overview of

Biology, Ecology, and Conservation Status

in India

Ravindra K.Sinha & Kurunthachalam

Kannan

1 23

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REVIEW

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

INTRODUCTION

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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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,

2001,2006,2010).

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.

DISTRIBUTION

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

1976).

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

1996

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

Barrage

Ganga Between Bijnor and Narora

Barrages (approx. 166 km)

22/56 1993-95/

2010

Behera (1995)/Pers.

comm. S. Behera

The isolated dolphin population between

the two barrages appears to be

increasing

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

Survey)

1997 Sinha (1999)

Ganga Buxar to Maniharighat

(500 km)

808 (Upstream

Survey)

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

complexities

Ganga Maniharighat to Farakka

(approx. 70 km)

115 (Downstream

Survey)

1998 Sinha (1999)

Ganga Farakka Feeder Canal

(38.2 km)

21 (Downstream

Survey)

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

Survey)

1995 Sinha (1997) Dolphin population is relatively low as

the river receives regulated water with

low silt resulting in low hydrogeological

complexities

Hoogly Triveni to Sagar Island

(190 km)

97 (Downstream

Survey)

2008 Pers. comm. Gopal

Sharma)

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:

thpawlensingha@gmail.com) 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

Dolphin

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

upstream

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

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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).

ABUNDANCE

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

Dolphins

Source

Ganges River Main Stem and

tributaries

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.

POPULATION DENSITY

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

Conﬁdence

intervals

Average group

size of dolphins

Std. Error

of group size

Range of

group size

Encounter rate

(dolphin/km)

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;

Can

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).

DISPERSAL

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).

HABITAT USE

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.

GANGES DOLPHIN AS A BIOINDICATOR SPECIES

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.

THREATS

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,

2010b;Sinha2002).

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

1102/km

, 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.

EFFECTS OF DAMS AND BARRAGES

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

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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.

CHEMICAL POLLUTION

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.

DIRECTED AND INCIDENTAL CATCHES

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.

CONSERVATION AND CHALLENGES AHEAD

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

efforts.

RECOMMENDATIONS FOR 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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AUTHOR BIOGRAPHIES

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,

India.

e-mail: rksinha.pu@gmail.com

AMBIO

ÓRoyal Swedish Academy of Sciences 2014

www.kva.se/en 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.

e-mail: kkannan@wadsworth.org

AMBIO

123 ÓRoyal Swedish Academy of Sciences 2014

www.kva.se/en

Author's personal copy

Ganges River Dolphin (Platanista gangetica gangetica): An Indicator of Ecosystem Health in the River Basins

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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.

The effect of physiographic and hydrologic complexities and their alterations on the distribution of obligate freshwater dolphins

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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.

Modeling Ganges river dolphin distribution and prioritizing areas for efficient conservation planning- a range-wide assessment

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Mar 2023
ECOL MODEL

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.

Lockdown impact on dolphins as an aquatic health indicator and maintenance of sustainable Gangetic ecosystem: An overview

Article

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Jun 2023

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.

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Article

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Sep 2023

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.

Towards a successful River Dolphin conservation plan in India: A scientometric mapping of past research and current needs_26_1

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Aug 2023
AQUAT ECOSYST HEALTH

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.

Public Evaluation of the Effects of River Restoration Projects on Social Benefits

Chapter

Aug 2023

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

Territory and status of dolphins in Nepalese rivers: A Review_26_1

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Aug 2023
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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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Aug 2023
AQUAT ECOSYST HEALTH

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.

Towards automated long-term acoustic monitoring of endangered river dolphins: a case study in the Brazilian Amazon floodplains

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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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Faunal diversity of the river Sarda, Uttar Pradesh, India

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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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Article

Full-text available

Dec 1997

Ravindra Kumar Sinha

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.

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Chapter

Nov 2020

Biology and conservation of freshwater cetaceans in Asia

Article

Jan 2000

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Article

Jan 2008
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Jan 2005

On a resident population of the Ganges river dolphin Platanista gangetica in the Kulsi river (Assam) a tributary of Brahmaputra

Article

Jan 1998

Mark-recapture

Article

Dec 2009

Philip S. Hammond

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.

Estimating Animal Abundance: Closed Populations

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Sep 2003

Lyman Mcdonald

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

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