Chapter 3 STATUS OF TIGERS IN THE SUNDARBAN BIOSPHERE RESERVE: SESSION 2015-2016

Authors

Debmalya Roy Chowdhury, Sunit Kumar Das and Ratul Saha

Editorial Team

Anindita Bidisha Chatterjee and Ratul Saha

Citation

Roy Chowdhury, D., Das, S.K. and Saha, R. (2018). Status of Tigers

in the Sundarban Biosphere Reserve: Session 2015-2016. World Wide

Fund for Nature─India, New Delhi.

Cover Photo

Shuvarthi Guha

Maps

Abhijit Choudhury

Edition, January, 2018

© WWF-India, 2018

STATUS OF TIGERS IN THE SUNDARBAN BIOSPHERE RESERVE: SESSION 2015-2016

STATUS OF TIGERS IN SUNDARBAN BIOSPHERE RESERVE: SESSION 2015-2016

ii

CONTENTS

TIGER POPULATION DYNAMICS OF SUNDARBAN BIOSPHERE RESERVE – SESSION: 2012-2016 IV

3.1 ACKNOWLEDGEMENTS

3.2 BACKGROUND 01

3.3 RESULTS FROM EARLIER EXERCISES 03

3.4 METHODS 04 3.4.1 Planning: Analysis of tides 04

3.4.2 Reconnaissance survey 04

3.4.3 Field Sampling 04

3.4.4 Data Analysis 05

3.5 RESULTS 07 3.5.1 Age and Sex of Captured Tigers 08

3.5.2 Tiger Population Estimates ( ) 13

3.5.3 Annual Population Turnover Rate 14

3.5.4 Tiger Density Estimates ( ) 15

3.6 DISCUSSION AND WAY FORWARD 18

REFERENCES 20

ANNEXURE 1 22

ANNEXURE 2 44

ACKNOWLEDGEMENTS This exercise is supported by WWF-Sweden.

We are grateful to PCCF and Chief Wildlife Warden, West Bengal; the Sundarban Biosphere Reserve Director, the Field Director; Sundarban Tiger Reserve and Divisional Forest Officer, 24 Parganas (South) Forest Division for their collaboration and logistical support.

We would like to thank all the rage and beat level staff of Sundarban Tiger Reserve and 24 Parganas (South) Forest Division in carrying out the study successfully.

We would also like to thank the boat crew of MB Sundari; Sridam Gayen, Ishwar Chandra Shaw, Amol Mondal and Nikhil Borkondaj for their excellent services and on-board hospitality.

We are grateful to Dr. Pranav Chanchani and Mr. Rishi Kumar Sharma for reviewing the report at very short notice. Their comments have strengthened this report.

Last but not the least, we are grateful to Mr. Ravi Singh, SG & CEO, WWF-India; Dr. Sejal Worah, Programme Director, WWF-India; and Dr. Dipankar Ghose, Director, Species and Landscapes Programme, WWF-India for their inputs.


TIGER POPULATION DYNAMICS OF SUNDARBAN BIOSPHERE RESERVE SESSION: 2012-2016

24 Parganas (South) Forest Division: A total sampling effort [Ramganga (20 locations

x 30 days), Raidighi (21 locations x 34 days) and Herobhanga (2 locations x 34 days)] in

2012-2013, photo-captured 21 adult tigers. The next survey in 2014-2015 (73 locations x

41 days), carried out in the entire area photo-captured 17 adult tigers and 4 cubs. A total

of 10 individuals were common between these two years and 7 new adult individuals were

identified. A total sampling effort (50 locations x 40 days) in 2015-2016, photo-captured

24 adult tigers, 2 sub adults and one cub. Among these 24 adult tigers, 18 individuals

were common when compared with 2014-2015 and 6 new adult individuals were identified.

A total of 3 tiger individuals found in 2014-2015 were not photo-captured in 2015-2016.

National Park (East) Range: A total sampling effort (56 locations X 49 days) in 2012-

2013 photo-captured 20 adult tigers. The next survey (60 locations x 39 days) that was

carried out during 2013-2014 photo-captured 18 adult tigers. A total of 13 individuals

were common between these two years and 5 new adult individuals were identified. A total

sampling effort (60 locations x 19 days) during 2015-2016 photo-captured 14 adult tigers.

Among these 14 adult tigers, 7 individuals were common with those photo-captured in

2014-2015 and 2 individuals were common when compared with the findings of 2012-2013.

A total of 5 new adult individuals were identified. A total of 11 tiger individuals found in

2014-2015 were not photo-captured in 2015-2016.

National Park (West) Range: A total of 21 adult individuals along with two cubs

were reported by the Forest Department during 2012-2013. The next survey (60 locations x

38 days) carried out during 2015-2016 photo-captured 19 adult tigers and 3 cubs.

Sajnekhali Wildlife Sanctuary: A total sampling effort (56 locations x 46 days) during

2012-2013 photo-captured 14 adult tigers. Out of these 14 adult individuals, one male was

rescued and is now in Jharkhali rescue centre. The next survey (60 locations x 30 days),

carried out during 2015-2016, photo-captured 9 adult tigers and 2 sub adults. Among

these 9 adult tigers, 5 individuals were common with those found in 2014-2015 and 4 new

adult individuals were identified. A total of 8 tiger individuals, which were found in 2012-

2013, were not photo-captured in 2015-2016.

Basirhat Range: A total sampling effort (56 locations X 31 days) during 2012-2013 photo-

captured 13 adult tigers. The next survey (63 locations x 53 days) was carried out during

2014-2015 and photo-captured 14 adult tigers and 3 cubs. Out of these three cubs, two

were found dead just after the exercise. A total of 7 individuals were common between these

two years and 7 new adult individuals were identified. A total sampling effort (44 locations x

40 days) during 2015-2016 photo-captured 11 adult tigers. Among these 11 adult tigers, 7

individuals were common with those found in 2014-2015 and 4 new adult individuals were

identified. A total of 7 tiger individuals, which were found in 2014-2015, were not photo-

captured in 2015-2016.

1

3.1 BACKGROUND

The Sundarbans, one of the richest ecosystems and the largest tract of estuarine

mangrove forests in the world, supports one of the largest population of wild tigers

worldwide (Jhala et al. 2011, Aziz et al., 2013). The Sundarbans ecosystem is subjected

to tidal fluctuations and consequent variable salinity, resulting in this unique com-

munity structure (Aziz et al., 2013, Roy et al., 2016). This ecosystem provides a both

unique and challenging setting for tiger conservation; because the species’ habitat in the

Sundarbans is spread across innumerable mangrove islands, large portions of which are

subject to inundation under sea water with tidal fluctuations. For effective management

and long-term conservation, it is essential to: understand how tigers and their prey are

distributed in this dynamic ecosystem, model their population trends over time and

assess the influence of ecological and anthropogenic factors on demography and habitat

use.

Robust science-based estimates of population parameters are required to periodically

assess population status and make relevant linkages with management. Over the past

two decades, camera-trap sampling combined with Mark-recapture analyses have

increasingly been used to estimate demographic parameters of wild tigers (Karanth,

1995). In addition, studies continued at the same site(s) over multiple years are very

useful for understanding and managing populations of large carnivores. Such multi-

year studies can yield estimates of rates of change in abundance (O’Connell et al., 2011).

As the marked individuals are tracked through time, biologists can investigate the suite

of factors that drive changes in abundance such as rates of survival, recruitment and

dispersal.

This report uses data collected between 2015 and 2016 to: estimate tiger populations in

the Indian Sundarbans (Fig 1), and describe turnover in the population by comparing

these data with tiger-capture histories from previous years.

2


Fig 1: Map of Sundarban Biosphere Reserve, and the study area (shaded)

3

3.2 RESULTS FROM EARLIER EXERCISES

During the period January 2012 - April 2013, to estimate tiger numbers, WWF-India

and the Sundarban Biosphere Reserve Directorate collaboratively carried out camera

trapping sampling in the Sundarban Biosphere Reserve to establish a population base-

line for the Sundarbans. In 24 Parganas (South) Forest Division, the exercise was car-

ried out from January 2012 to March 2012. Twenty unique individuals were identified

from this division and range wise density was calculated. Tiger density was estimated

to be 3.8 (±SE1.5)/100 sq. km. and 5.2 (±SE1.7)/100 sq. km. for Raidighi Range. In Na-

tional Park (East) range, the exercise was carried out from November 2012 – January

2013. 21 unique individuals were identified from this range. Tiger density was estimated

to be 3.69(±SE0.82)/100 sq. km. In Sajnekhali Wildlife Sanctuary, the exercise was

carried out from January – March 2013. 13 unique individuals were identified from

this range. Tiger density was estimated to be 2.36 (±SE 0.64)/100 sq. km. In Basirhat

Range, the exercise was carried out from March 2013 to April 2013. Thirteen unique

individuals were identified from this range. Tiger density was estimated to be 2.57 (±SE

0.76)/100 sq. km.

In session 2013-2014, camera traps were installed in Ramganga Range of 24 Parganas

(South) Forest Division and in National Park (East) Range of the Sundarban Tiger

Reserve. The same dataset was used in the All India Tiger Census. Five unique individu-

als were identified from Ramganga Range. The estimated tiger density was 1.57 (±SE

0.74) individuals/100 sq. km for Ramganga Range. Twenty unique individuals were

identified from National Park (East) Range. The estimated tiger density was 3.77 (±SE

1.03) individuals/100 sq. km for National Park (East) Range. Camera traps could only

be deployed in 20 locations in Basirhat Range for a short period of time due to rough

weather conditions. The data from this exercise was not taken into account.

In 2014-2015, camera traps were again placed in Basirhat Range of the Sundarban

Tiger Reserve and in the entire tiger habitat of 24 Parganas (South) Forest Division

comprising three ranges (Ramganga, Raidighi and Herobhanga Range). Seventeen

unique individuals along with four cubs were identified from 24 Parganas (South) For-

est Division. The estimated tiger density was 3.42 (±SE 0.74) individuals/100 sq. km

for 24 Parganas (South) Forest Division. Sixteen unique individuals along with three

cubs were identified from Basirhat Range. The estimated tiger density was 3.33 (±SE

0.09) individuals/100 sq. km for Basirhat Range.

A need was felt among the stakeholders to monitor the tiger population of the entire

tiger habitat in the Indian Sundarbans using camera traps within a season in a single

calendar year. Keeping this in mind, the Sundarban Biosphere Reserve Directorate in

active collaboration with WWF-India decided to monitor the tiger population of the

entire tiger habitat in the Indian Sundarbans using camera traps in a season within a

single calendar year (2015-2016). This endeavour will help to formulate effective tiger

conservation strategies.

4


3.3 METHODS

The standard method of camera-trap sampling coupled with Capture-Recapture analy-

sis (Karanth et al. 2002, Otis et al. 1978, Pollock et al. 1990) was followed to collect and

analyse data. Methods were customized and standardized for the Sundarban island

system, which is characterized by dense mangrove islands with no trails/roads. The

margins of these islands are also subject to tidal-flooding (Das et al., 2012, Roy et al.,

2016, and Roy Chowdhury et al., 2018).

3.3.1 PLANNING: ANALYSIS OF TIDES

As the Sundarbans ecosystem is subjected to tides twice a day with varying tide levels,

there is a high risk of the camera traps being inundated. The first step was to analyse the

tidal fluctuation from the data available from tide tables (Survey of India, 2016).

A high-resolution image of the study areas was procured and processed for its use in the

reconnaissance survey and thereafter. The study areas were divided into grids of four

sq. km each thus systematically dividing the area. This helped the team plan the recon-

naissance survey better and decide on the sites and minimum distance between camera

trap stations.

3.3.2 RECONNAISSANCE SURVEY

Reconnaissance surveys were carried out in different grids for potential camera trap

locations. Geo-coordinates of the survey and suitable sites were recorded using a

handheld Global Positioning System receiver (Garmin 72 H). These tracks and points

were laid over a gridded high-resolution image in the Geographic Information System

environment using MapInfo 8.5.

Most of the trapping grids were standardized across the years. For the newly sampled

areas and grids with no tiger capture for years, the trapping grids were selected based

on the following criteria: (i) tiger pugmarks, (ii) comparatively high elevation areas un-

likely to get submerged even during high tides, and (iii) exclusion of sample grids with

excessive human disturbance to minimize losses of camera traps and data.

3.3.3 FIELD SAMPLING

Sampling was carried out on 30 occasions (days; from midnight to midnight) commenc-

ing from 4th December, 2015 and ending on 2nd January, 2016 in Sajnekhali Wildlife

Sanctuary; 38 occasions (days) commencing from 8th January, 2016 and ending on

14th February, 2016 in National Park (West) Range; 38 occasions commencing from

19th January, 2016 and ending on 25th February, 2016 in National Park (East) Range;

40 occasions, commencing from 3rd March, 2016 and ending on 11th April, 2016 in

Basirhat Range; and on 40 occasions commencing from 10th March, 2016 and ending

on 18th April, 2016 in 24 Parganas (South) Forest Division. Due to limited resources in

5

terms of camera traps and manpower, the total area was sampled in blocks (ranges).

The analysis was also carried out separately for different ranges, to avoid violating the

assumption of population closure. The different ranges are separated by large river

channels and not frequently crossed by tigers over shorter time spans (Jhala et al., 2011,

Naha et al., 2016).

Cameras with heat-motion sensors were deployed to capture tigers and other fauna.

The distance between adjacent camera trap stations in the grid was ≥1 km. At each sta-

tion, two camera units were deployed between 40 and 50 cm. height from the ground in

such a way that both flanks of the animal were captured. The camera delay was mini-

mised to ensure photo captures of tigresses with cubs in case such an event occurred.

To maximise both tiger captures as well as recaptures, an olfactory lure was applied at

all sites. All the camera trap stations were monitored periodically to check the status of

camera traps, and if required, the height of the camera trap was changed or compara-

tively high elevation sites within the same grid were selected. This was done due to the

presence of a high water mark in the sampling session, which could inundate camera

trap units in the particular site. To ensure recaptures of unique individuals the olfactory

lure was reapplied during periodic checking of camera traps to download data.

Identification of tigers was done visually with the images from camera traps, based on

unique pelage stripe patterns and also with the help of Extract Compare V1.08 software

(Hiby 2009).

3.3.4 DATA ANALYSIS

Data was analysed using closed-population capture-recapture models (Huggins pa-

rameterization). We compared different models to test the effects of behaviour, time,

individual heterogeneity and variation in capture probability owing to lure-application

tiger captures. The lure effect was incorporated while designing the matrix ─ to assess

whether the probability of a tiger being photo-captured diminished as a function of

time, subsequent to lure application. Therefore, the effect of attractants on estimates

of population parameters were also taken into account. (Roy Chowdhury et al., 2018).

Population estimation ( ) was conducted using several parameters and AICc values for

different models were compared (Akaike 1973, Burnham and Anderson 1998). Model

averaging was computed in case of all the blocks as AICc weight for most of the models

lie between 0 and 1. For rare and elusive carnivores, the capture probability seldom

goes beyond 0.3. This estimate, coupled with a longer sampling duration, poses a

problem when coming up with robust estimates of population parameters. Keeping this

in mind, capture probability for every individual at least once (p*) over the sampling

period was calculated from the overall capture probability. p* can be calculated as

p* = 1 – (1-p)n, where p is the overall capture probability and n is the number of sam-

pling occasions (Gerber et al., 2014).

To establish demographically closed population, closure test was performed using the

CloseTest software for each block. The trapping area was calculated based on the inte-

gration region, which is calculated based on a finite space, defined by the placement of

trapping stations and animal movement (Borchers and Efford 2008, Royle and Young

2008).

6


Density1 estimation for tigers in the study area was performed using minimum bound-

ing polygon, with habitat masking2 by using DENSITY (5.0) and Arc GIS (9.3) software.

Data analysis for each block was carried out using maximum likelihood SECR analysis

using the DENSITY program.

A binomial point process model with a 15-km buffer around the camera trap array were

assumed. Detection models were fitted by maximising the likelihood to estimate the

density and other parameters. Analysis was carried out for different buffer sizes and it

was found that a 15-km buffer for SECR density estimation was likely a large enough

area to capture the movements of tigers whose territories may only partially overlap the

camera trap grids.

To accurately describe the region of integration (state space) over which animal activity

centres are distributed, SECR requires that habitat and non-habitat areas be delineated

using forest boundary GIS files. For these analyses, a habitat mask was created wherein

only forested areas (habitat) were included within the area state space S, while non-

habitat areas, basically the large and wider river channels separating the ranges, were

masked out for this unique landscape. Effective camera trapped areas for each block

was calculated using the same concept. Various alternate parameterizations of detection

parameters (g0 and σ) were included in the model set.

1 To estimate tiger density ( ), we used Spatial Explicit Capture Recapture analyses in a likelihood

framework (ML-SECR), using Density 5.0 (Efford 2004). SECR treats animal home range centres

as being distributed across the study area (defined by a spatial point process). The locations of these

activity centres are unknown, but are estimated by modelling the movement of animals around their

activity centres, assuming that this process can be described as a half-normal detection function

(probability of capture decreases as an animal moves away from the activity centre). The detection

process is described by the parameters g0 and σ, which are estimated (Borchers and Efford 2008).

The spatially-explicit estimates of density ( ) can be interpreted as the intensity of the point process

at each of n potential activity centres which form a grid across habitat areas within the integration

region (trapping grid + buffer area), in which the super population is distributed.

2 As per the radio telemetry data from the Sundarbans (Jhala et al., 2011), tigers rarely cross channels

wider than 1 km in width within a short span of time. Therefore, channels wider than 1 km and forest

fringe villages were masked in a GIS platform and classified as ‘non-habitat’. All mangrove patches

and channels <1km wide were classified as ‘habitat’.

7

3.4 RESULTS

Table 1: Data metrics showing total effort and capture summaries during the study period in the Sundarban Biosphere Reserve

Forest

Division/

Range

Total area

(sq. km)

Total grids

of 4

sq. km

each

Camera

trap

grids

Trap

Night

Effort

Trapping

area [sq. km]

(Extent of

trapping

grid)

Session

date

(start)

Session

date (end) Total camera-

Tiger Individuals Identified

trap stations

with

tiger

captures

*Previ-

ously

encoun-

tered

New Total

24 Parganas

(South) For- est Division

454 116 50 2000 200 10.03.2016 18.04.2016 37 18 8 26

National Park (East)

Range

850 155 60 1140 240 19.01.2016 25.02.2016 23 9 5 14

National Park (West) Range

890 138 60 2280 240 08.01.2016 14.02.2016 38 - 19 19

Sajnekhali Wildlife

Sanctuary

430 103 60 1800 240 04.12.2015 02.01.2016 27 5 6 11

Basirhat Range

466 94 44 1760 176 03.03.2016 11.04.2016 16 7 4 11

Grand Total 81*

* Out of these 81 individuals 4 individuals were sub adults (less than 2 years old) and were omitted from analysis. No individual was found

common between the ranges. A new individual means it has never been encountered in previous camera trapping sessions.

Table 2: Demography of tiger individuals in the Sundarbans

Sl. No.

Areaw Tiger Individuals

Male Female Sex ID not

possible Cub& Sub

adults* Total Adult

Individuals

1 24 Parganas (South) Forest Division 9 15 0 3 24

2 National Park (East) Range 2 12 0 0 14

3 National Park (West) Range 4 13 2 3 19

4 Sajnekhali Wildlife Sanctuary 1 6 2 2 11

5 Basirhat Range 3 6 2 0 11

Total 19 52 6 8

Grand Total 77

*A tiger individual is considered as a cub or sub adult if less than two years old (pre-dispersal juveniles).

8


Fig 2: Map showing locations (grids) with tiger capture individuals in 24 Parganas (South) Forest Division

3.4.1 AGE AND SEX OF CAPTURED

TIGERS

Most of the sampling blocks (ranges) are

separated by large and wide river channels.

No individual was found common between

the ranges although some crossed from one

range to another over the study period. Cap-

ture of 4 cubs and 4 sub adults (less than two

years old) were not incorporated into density

estimation, following the recommendation

of Karanth and Nichols (2002). Sub adults

and cubs were classified after comparing the

dataset across sessions. Because we did not

have left and right flank pictures for all tigers,

unique individuals were identified using all

available pictures of both flanks and the right

flank, while omitting left flank only pictures.

24 Parganas (South) Forest

Division

A total sampling effort of 2000 trap days

(50 camera trap stations, each operating on

40 occasions) at 24 Parganas (South) For-

est Division yielded 265 photographs (both

flanks combined) of tigers. A total of 37 out

of 50 camera trap stations recorded the

photographs. There were no tiger captures on

22.5% occasions. A total of 27 unique tigers

were identified. Out of these 27 individuals, 3

individuals─ SB110 (Sub Adult Male), SB111

(Sub Adult Male) and SB118 (a cub) were not

used for analysis as all of them were less than

two years old.

The capture history file used for data analysis

had 86 records of tiger captures of 24 tigers.

This included fifteen captures of SB90,

thirteen captures of SB83, seven captures of

SB92, six captures of SB10, four captures of

SB7, SB13, SB18 and SB114, three captures of

SB14, SB91 and SB94, two captures of SB20,

SB93, SB112, SB113, SB115, SB116 and SB117

and single captures of SB3, SB9, SB15, SB96,

SB97 and SB98 (Table 1, Fig 2 and Annexure

1).

9

National Park (East) Range

A total sampling effort of 1140 trap days (60 camera trap stations, each operating for 19

occasions) at National Park (East) Range yielded 130 photographs (both flanks com-

bined) of tigers. A total of 23 out of 60 camera trap stations recorded the photographs.

There were no tiger captures on 46.7% occasions. A total of 14 tigers were individually

identified. The capture history file used in data analysis had 35 records. This included

six captures of SB21, five captures of SB44, four captures of SB123, three captures of

SB38 and SB120, two captures of SB35, SB40, SB86, SB87 and SB119 and single cap-

tures of S24, SB84, SB121 and SB122 (Table 1, Fig 3 and Annexure 1).

Fig 3: Map showing movement of tiger individuals in National Park (East) Range

10


National Park (West) Range

A total sampling effort of 2280 trap days (60 camera trap stations, each operating for

38 occasions) at National Park (West) Range yielded 319 photographs (both flanks)

of tigers. A total of 38 out of 60 camera trap stations recorded the photographs. There

were no tiger captures on 10.5% occasions. A total of 22 tigers were individually identi-

Fig 4: Map showing movement of tiger individuals in National Park (West) Range

11

fied. Out of these 22 individuals, 3 were cubs (SB153, SB154 and SB155) and not used

for analysis as all of them were less than one year old. The capture history file used for

data analysis had 93 captures and recaptures. This included thirteen captures of SB134

and SB140, eleven captures of SB139, eight captures of SB141, seven captures of SB138,

six captures of SB135 and SB142, five captures of SB144 and SB152, four captures of

SB137 and SB 143, three captures of SB 148, two captures of SB 136 and single captures

of SB145, SB146, SB147, SB149, SB 150 and SB151 (Table 1, Fig 4 and Annexure 1).

Sajnekhali Wildlife Sanctuary

A total sampling effort of 1800 trap days (60 camera trap stations, each operating for

30 occasions) at Sajnekhali Wildlife Sanctuary yielded 69 photographs (both flanks)

of tigers. A total of 27 out of 60 camera trap stations recorded the photographs. There

were no tiger captures on 36.7% occasions. A total of 11 tigers were individually identi-

fied. Out of these 11 individuals, 2 individuals ─ SB132 (Sub Adult Female), and SB133

(Sub Adult Female) were not used for analysis as all of them were less than two years

old.

The capture history file used for data analysis had 37 captures and recaptures. This

included ten captures of SB48, seven captures of SB57, six captures of SB124, five

captures of SB64, three captures of SB 129, two captures of SB49 and SB 131, and single

captures of SB50 and SB130 (Table 1, Fig 5 and Annexure 1).

Fig 5: Map showing movement of tiger individuals in Sajnekhali Wildlife Sanctuary

12


Basirhat Range

A total sampling effort of 1760 trap days (44 traps station for each operation on 40 oc-

casions) at Basirhat Range yielded 75 photographs (both flanks) of tigers. A total of 16

out of 44 camera trap stations recorded the photographs. There were no tiger captures

on 50% occasions. A total of 11 tigers were individually identified. The capture history

file used for data analysis had 31 captures and recaptures. This included six captures of

SB61, four captures of SB124, SB125 and SB126, two captures of SB69, SB72, SB104,

SB105, SB106 and SB 127 and single capture of SB101 (Table 1, Fig 6 and Annexure 1)

Fig 6: Map showing movement of tiger individuals in Basirhat Range

13

3.4.2. TIGER POPULATION ESTIMATES ( )

Because multiple models had comparable support (model weights) we computed

model-averaged estimates of abundance (Burnham and Anderson, 2002). The popula-

tion was estimated to be 25.02 ± 1.22 ( ± SE) individuals (Table 3 and Annexure 1).

The model-averaged estimate for tigers in the National Park (East) Range and National

Park (West) Range were 15.42 ± 1.93 ( ± SE) and 19.26 ± 0.61 ( ± SE) individuals

respectively (Table 3 and Annexure 1). The model-averaged estimate of population size

was 9.15 ± 0.43 ( ± SE) individuals for Sajnekhali Wildlife Sanctuary, and for Basirhat

Range the estimate was 12.09 ± 1.38 ( ± SE) individuals (Table 3 and Annexure 1).

Table of model results and associated AIC scores are reported in Annexure 3.

Table 3: Selected model and tiger population in the study areas.

Note: = Population size; SE= Standard Error; Mt+1= Number of animals captured; LCL= Lower Confidence Limit; UCL= Upper Confidence Limit; p= Capture probability of new individual tiger at each sampling occasion; p*= Capture probability for an individual at least once over the sampling period in the study area.

Model

Mt+1

SE

LCL

UCF p (SE) of

model M o

p*

24 Parganas (South) Forest Division [at 95% Confidence Interval]

Model-averaged

estimates

24

25.03

1.22

22.63

27.42

0.08 (0.01)

0.96

National Park (East) Range [at 95% Confidence Interval]

Model-averaged

estimates

14

15.42

1.93

11.63

19.21

0.1 (0.02)

0.86

National Park (West) Range [at 95% Confidence Interval]

Model-averaged

estimates

19

19.26

0.61

18.06

20.47

0.11 (0.01)

0.99

Sajnekhali Wildlife Sanctuary [at 95% Confidence Interval]

Model-averaged

estimates

9

9.15

0.43

8.30

10

0.13 (0.02)

0.98

Basirhat Range [at 95% Confidence Interval]

Model-averaged

estimates

11

12.09

1.38

9.37

14.8

0.05 (0.01)

0.87

14


3.4.3. ANNUAL POPULATION TURNOVER RATE

Individual turnover rate of a population is an important indicator of its dynamics over

time. High turnover rate can imply that the population is unstable and local extinc-

tion and colonization might also be in action. Turnover3 is estimated by calculating the

rate of change of individuals in terms of influx (new captures) and outflow (no capture

of previously recorded individuals) with respect to the entire population. Only adult

individuals were considered from the comparable dataset of three years for 24 Parganas

(South) Forest Division and Basirhat Range (Fig. 7a, 7b, and 7c).

Fig 7a: Overall annual turnover rate of tigers over the study period (2013 – 2016)

1.00

0.80

0.60

0.40

0.20

0.00 24 Parganas (South) Forest Division Basirhat Range

Area

Fig 7b: Annual turnover rate of male tigers over the study period (2013 – 2016)

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10


Area

Fig 7c: Annual turnover rate of female tigers over the study period (2013 – 2016)

1.00

0.80

0.60

0.40

0.20


Area

3 Turnover rate = (Influx+Outflow)/Total Population (N)

Male Turnover Rate 2014-2015

2015-2016

0.64 0.67 0.60

0.33

Overall Turnover Rate

2014-2015

2015-2016

0.52

0.43 0.39

0.21

Female Turnover Rate

2014-2015

2015-2016

0.67

0.50 0.44

0.21

Tu

rno

ver

Ra

te

Tu

rno

ver

Ra

te

Tu

rno

ver

Ra

te

15

3.4.4. TIGER DENSITY ESTIMATES ( )

Estimated tiger density in 24 Parganas (South) Forest Division, National Park (East)

Range, National Park (West) Range, Sajnekhali Wildlife Sanctuary and Basirhat Ranges

were 5.46 ± 1.27 individuals/100 sq. km2, 2.09 ± 0.66 individuals/100 sq. km2, 3.07 ±

0.8 individuals/100 sq. km2, 1.79 ± 0.63 individuals/100 sq. km2, 3.56 ± 1.35 individu-

als/100 sq. km2 respectively (Fig 8, 9, 10, 11, 12 and Table 4).

Table 4: Density estimation of tigers in the study area

Variables 24 Parganas

(South) Forest

Division

National Park

(East) Range National Park

(West) Range Sajnekhali Wildlife

Sanctuary Basirhat Range

model specifica- tions and

estimates

SE model specifica- tions and

estimates


estimates


estimates


estimates

SE

No. of Occasions4

40 - 19 - 38 - 30 - 40 -

Camera Trap

Stations 50 - 60 - 60 - 60 - 44 -

Trap Night Effort5

2000 - 1140 - 2280 - 1800 - 1760 -

Integration Region

546.62 sq. km

- 523.67 sq. km.

- 580.34 sq. km.

- 413.42 sq. km.

- 403.83 sq. km.

-

Detection

Model Half normal - Half

normal - Half normal - Half normal - Half

normal -

Selected

Model

g0 [.]σ [h ] 2

- g0 [.]σ [.] - g0 [.]σ [h2] - g0 [.]σ [.] - g0 [.]σ [.] -

Density / 100

km2

MLSECR

5.46 1.27 2.09 0.66 3.07 0.8 1.79 0.63 3.56 1.35

g 0

0.03 0.005 0.009 0.003 0.02 0.003 0.02 0.004 0.03 0.013

o (meters) 2173.03 236.49 5864.7 1014.38 3033.36 306.64 3791.32 491.35 1488.34 280.02

Note: SE= Standard Error; g0= the probability of capture when the distance between the animal’s activity centre and the trap is zero; Sigma= distance between animal’s activity centre and trap; MLSECR= Maximum Likelihood Spatial

4 Occasion is the sampling day of a sampling period. 5 Trap Night Effort: It is usually measured by the number of camera traps multiplied by the sampling days.

16


Fig 8: Map showing camera traps and Minimum

Bounding Polygon at 24 Parganas (South) Forest

Division. Camera trapped area 546.62 sq. km.


Bounding Polygon at National Park (West) Range.

Camera trapped area 580.34 sq. km.


Bounding Polygon at National Park (East) Range.



Bounding Polygon at Sajnekhali Wildlife Sanctuary.


17


Bounding Polygon at Basirhat Range. Camera

trapped area 403.83 sq. km.

18


3.5 DISCUSSION AND WAY FORWARD

Estimation of population size and distribution pattern is an integral component

of monitoring population status, demographic trends and management efficacy.

Systematic monitoring of tiger population in the Indian Sundarbans over a period of

4 years suggests that the population may not be stable as portrayed by the capture

history of individuals. The overall female:male ratio in the study area for the current

study (2.73:1) is strongly female biased, as has been reported in some other areas

(e.g. Chitwan). The capture pattern indicates that spatial overlap is minimal among

the males whereas between females as well as males and females it is comparatively

higher, which is consistent with the territorial behaviour of tigers. Density estimates

have remained relatively stable over the years. It is worth noting that in spite of being

reserve forests (with greater human use), both 24 Parganas (South) Forest Division and

Basirhat Range support a higher density of tigers than the adjacent National Park.

A large section of the 24 Parganas (South) Forest Division (556 sq. km.) has been

declared as the West Sundarbans Wildlife Sanctuary, based on the findings of the

camera trap study conducted in 2012. It also has led to the necessity of evaluating

the current management practices for effective tiger conservation. This is where

Conservation Assured | Tiger Standards (CA|TS) comes in. CA|TS is a set of criteria

which allows tiger sites to check if their management will lead to successful tiger

conservation. CA|TS is organised under seven pillars and 17 elements of critical

management activity. WWF-India facilitated the process of implementing CA|TS which

will strengthen effective tiger conservation in the long run in the area.

Areas like 24 Parganas (South) Forest Division appear to have immense potential to

harbour a healthy tiger population as the area has comparatively higher density of

tigers in spite of being a reserve forest. A wide array of factors is likely to contribute to

this. For example, change in weather, lunar-tidal cycle, coverage of vegetation, plant

type, water availability, human presence and prey-base activity impact the activity

of the tiger in this unique landscape as discussed in previously published literature

(Roy Chowdhury et al., 2018). Dataset from consecutive years shows that a significant

number of new individuals are being added to the population along with no capture

of some previously captured individuals for both 24 Parganas (South) Forest Division

and Basirhat Range. These kinds of observations warrant attention in the present

conservation scenario to identify factors like anthropogenic impacts, dispersal of

individuals and natural deaths.

1. It would be more useful if the all the ranges in the entire SBR are sampled

simultaneously with more sampling effort, by increasing the number of camera

trap locations and days for a robust estimate. The surveys should also be

coordinated to be done simultaneously with the Bangladesh portion of the

Sundarbans to arrive at a robust estimate of the tiger population in the entire

Sundarbans system. The Bangladesh Sundarbans is larger in expanse than the

19

Sundarbans of India, and co-ordinated monitoring will provide important insights

about tiger space use and movement across management and administrative

boundaries.

2. Dynamics of this isolated population needs to be examined by estimating survival

rate, growth rate, and recruitment; using an open population framework6 as the

population exhibits higher turnover rate. This parameter will provide a broad idea

about what might be happening to the population.

3. Density and distribution of large carnivores like tigers are principally governed

by the availability and density of prey species. Prey density, in turn, is influenced

by the vegetation structure and the overall ecosystem health. However, in the

Sundarbans, very few studies have used robust methods to monitor prey base

populations (Roy et al., 2016). A novel initiative by WWF-India which can

withstand scientific scrutiny in the Sundarbans aims to look at the micro faunal

assemblage and to establish a baseline for it. Temporal replicates of vegetation

quantification along with soil and water sampling also needs to be carried out to

properly understand the prey habitat associations, since prey distribution governs

predator distribution extensively. Such intensive studies need to be implemented

which will ultimately provide an insight into the health of the ecosystem and in

turn adopt holistic management strategies.

4. Conflict situations both inside and outside forest areas have changed over the years

and so are the offenders who are adopting new technologies to avoid enforcement.

Due to this, the frontline staff such as rangers, forest guards, and beat guards who

are responsible for the day-to-day conservation and management in the field,

need to be trained and empowered in the latest technologies mainly for areas like

24 Parganas (South) Forest Division. Applications like GPS-based patrolling will

ultimately aid in enhanced and effective protection for wildlife.

5. As discussed in an earlier tiger report (Roy Chowdhury et al., 2018), access

to biological resources plays an important role in supporting the livelihood of

fishermen in the Indian Sundarbans. Forest Offence records show that fishing-

related offences are increasing year by year. If GPS-based applications (like Vessel

Monitoring Surveillance) which track and monitor boats anytime and anywhere

are adopted then it would help the Forest Department in enhanced management.

Without these, wildlife management and conservation will suffer a setback.

6 Open population framework – In contrast to closed population, open population framework

takes into account the immigration and emigration, deaths and recruitment of individuals of a

population. This is ideal to estimate population parameters in case of dataset from multiple seasons.

20


REFERENCES

Akaike, H., 1973. Information theory and an extension of the maximum likelihood

principle. In 2nd International Symposium on Information Theory (pp. 267-

281). Akademiai Kiado.

Aziz, A., Barlow, A.C., Greenwood, C.C. and Islam, A., 2013. Prioritizing threats to

improve conservation strategy for the tiger Panthera tigris in the Sundarbans

Reserve Forest of Bangladesh. Oryx, 47(4): 510-518.

Borchers, D. L., & Efford, M. G. 2008. Spatially explicit maximum likelihood methods

for capture–recapture studies. Biometrics, 64(2): 377-385.

Burnham, K.P. and Anderson, D. R. 1998. Model selection and inference: a practical

information theoretic approach. Springer, New York.

Burnham, K.P. and Anderson, D.R. 2002. Model Selection and Inference: A Practical

Information-Theoretic Approach. 2nd Edition, Springer-Verlag, New York.

Das, S.K., Sarkar, P.K., Saha, R., Vyas, P., Danda, A.A., and Vattakavan, J. 2012.

Status of Tigers in Sundarban Biosphere Reserve, 24-Parganas (South) Forest

Division, West Bengal, India. World Wide Fund for Nature – India, New Delhi.

Efford, M. 2004. Density estimation in live-trapping studies. Oikos, 106: 598–610.

Gerber, B.D., Ivan, J.S., and Burnham, K.P. 2014. Estimating the abundance of rare and

elusive carnivores from photographic-sampling data when the population size is

very small. Population Ecology, 56:463-470

Hiby, L., Lovell, P., Patil, N., Kumar, N. S., Gopalaswamy, A. M., and Karanth, K. U.

2009. A tiger cannot change its stripes: using a three-dimensional model to

match images of living tigers and tiger skins. Biology Letters, 5(3): 383-386.

Jhala, Y. V., Qureshi, Q., Gopal, R. and Sinha, P. R. (eds.) 2011. Status of the Tigers,

Co-predators, and Prey in India, 2010. National Tiger Conservation Authority,

Govt. of India, New Delhi, and Wildlife Institute of India, Dehradun. TR

2011/003 pp-302.

Karanth, K.U. 1995. Estimating tiger Panthera tigris populations from camera-trap data

using capture-recapture models. Biological conservation, 71(3): 333-338

Karanth, K. U., N. S. Kumar, and J. D. Nichols. 2002. Field surveys: estimating

absolute densities of tigers using capture–recapture sampling. Pages 139–152

in K. U. Karanth and J. D. Nichols, editors. Monitoring tigers and their prey:

a manual for researchers, managers and conservationists in tropical Asia.

Centre for Wildlife Studies, Bangalore, India.

Karanth, K.U. and Nichols, J.D. eds. 2002. Monitoring Tigers and their prey: A

manual for Researchers, Managers and Conservationists in Tropical Asia.

Centre for Wildlife Studies, Bangalore, India.

21

Naha, D., Jhala, Y.V., Qureshi, Q., Roy, M., Sankar. K. and Gopal, R. 2016. Ranging,

Activity and Habitat Use by Tigers in the Mangrove Forests of the Sundarban.

PLoS ONE 11(4): e0152119

O’Connell, A. F., Nichols, J. D., & Karanth, K. U. (eds.). 2011. Camera traps in animal

ecology: methods and analyses. Springer Science & Business Media.

Otis, D. L., Burnham, K. P., White, G. C. & Anderson, D. R. 1978. Statistical inference

from capture data on closed animal populations, Wildlife Monograph, 62: 1-135.

Pollock, K. H., Nichols, J. D., Brownie, C., & Hines, J. E. 1990. Statistical inference for

capture-recapture experiments. Wildlife monographs, 3-97.

Roy, M., Qureshi, Q., Naha, D., Sankar, K., Gopal, R., & Jhala, Y. V. 2016. Demystifying

the Sundarban tiger: novel application of conventional population estimation

methods in a unique ecosystem. Population Ecology, 58(1): 81-89.

Roy Chowdhury, D., Das, S.K., Sarkar, P.K. and Saha, R. 2018. Status of Tigers in

Sundarban Biosphere Reserve (2012-2013): National Park (East), Sajnekhali

Wildlife Sanctuary, Basirhat Range, India. World Wide Fund for Nature-India,

New Delhi.

Royle, J. A., & Young, K. V. 2008. A hierarchical model for spatial capture–recapture

data. Ecology 89: 2281–2289.

Survey of India. 2016. Hugli River Tide Tables for Sagar, Gangra, Haldia, Daimond

Harbour, Mayapur and Garden Reach. Geodetic and Research Branch of

Survey of India, Dehradun. 175 p.

22


ANNEXURE 1 Tiger Profile in 24 Parganas (South) Forest Division

SB3L SB3R

SB7L SB7R

SB9L SB9R

23

SB10L SB10R

SB13L SB13R

SB14L SB14R

SB15L SB15R

24


SB18L SB18R

SB20L SB20R

SB83L SB83R

SB90L SB90R

25

SB91L SB91R

SB92L SB92R

SB93L SB93R

SB94L SB94R

26


SB96L SB96R

SB97L SB97R

SB98L SB98R

SB110L SB110R

27

SB111L SB111R

SB112L SB112R

SB113L SB113R

SB114L SB114R

28


SB115L SB115R

SB116L SB116R

SB117L SB117R

29

Tiger Profile in National Park (East) Range

SB21L SB21R

SB24L SB24R

SB35L SB35R

SB38L SB38R

30


SB40L SB40R

SB44L SB44R

SB84L SB84R

SB86L SB86R

31

SB87R

SB119L SB119R

SB120L SB120R

SB121L SB121R

32


SB122R

SB123L SB123R

33

Tiger Profile in National Park (West) Range

SB134L SB134R

SB135L SB135R

SB136L SB136R

SB137L SB137R

34


SB138L SB138R

SB139L SB139R

SB140L SB140R

SB141L SB141R

35

SB142L SB142R

SB143L SB143R

SB144L SB144R

SB145L SB145R

36


SB146L SB146R

SB147L SB147R

SB148L SB148R

SB149R

37

SB150R

SB151R

SB152L SB152R

38


Tiger Profile in Sajnekhali Wildlife Sanctuary

SB48L SB48R

SB49L SB49R

SB50L SB50R

SB130L SB130R

39

SB57L SB57R

SB64L SB64R

SB128L SB128R

SB129L SB129R

40


SB131L SB131R

SB132L SB132R

SB133L SB133R

SB101L SB101R

41

Tiger Profile in Basirhat Range

SB61L SB61R

SB69L SB69R

SB72L SB72R

42


SB104L SB104R

SB105L SB105R

SB106L SB106R

SB124L SB124R

43

SB125L SB125R

SB126L SB126R

SB127R

44


ANNEXURE 2

DETAILED TABLE OF MODEL SELECTION IN PROGRAM MARK FOR EACH OF THE BLOCK OR RANGE IS GIVEN BELOW:

24 Parganas (South) Forest Division:

Model AIC C

AIC Weight C

No. of Parameters Deviance

M h

520.9230 0.60522 3 471.9207

M th_lure

522.5002 0.27506 5 469.4602

M bh

524.1751 0.11905 5 471.1351

M o

536.3677 0.00027 1 491.3864

M t_lure

536.3909 0.00026 2 489.4013

M b

538.3523 0.00010 2 491.3626

M tb_lure

540.1185 0.00004 4 489.0995

National Park (East) Range:

Model AIC C

AIC Weight C


M th_lure

182.7222 0.44647 5 148.9803

M b

184.4576 0.18748 2 156.9009

M t_lure

185.0780 0.13748 2 157.5212

M o

185.8058 0.09554 1 160.2795

M tb_lure

187.8527 0.03433 4 156.1882

M h

189.8823 0.01245 3 160.2795

M bh

190.6428 0.00851 5 156.9009

National Park (West) Range:

Model AIC C

AIC Weight C


M h

496.8370 0.82740 3 457.5946

M bh

500.4825 0.13369 5 457.1898

M th_lure

502.9924 0.03811 5 459.6997

M o

512.6670 0.00030 1 477.4526

M tb_lure

513.5117 0.00020 4 472.2470

M b

513.8125 0.00017 2 476.5869

M t_lure

514.3994 0.00013 2 477.1738

45

Sajnekhali Wildlife Sanctuary:

Model AIC C

AIC Weight C


M h

208.5881 0.31435 3 188.5515

M th_lure

208.6958 0.29787 5 184.5222

M o

209.9909 0.15588 1 194.0296

M t_lure

210.3508 0.13021 2 192.3595

M b

212.0174 0.05659 2 194.0261

M tb_lure

213.6713 0.02475 4 191.5740

M bh

214.0627 0.02035 3 194.0261

Basirhat Range:

Model AIC C

AIC Weight C


M o

202.9417 0.47956 1 183.1835

M b

204.7782 0.19145 2 183.0016

M t_lure

204.9591 0.17489 2 183.1826

M tb_lure

206.6950 0.07342 4 180.8540

M h

206.9876 0.06343 3 183.1835

M bh

210.8890 0.00902 5 183.0016

M th_lure

211.0699 0.00824 5 183.1826

© 1986 Panda Symbol WWF-World Wide Fund For Nature (Formerly World Wildlife Fund)

WWF-India Secretariat

172 B, Lodhi Estate

New Delhi- 110003

Tel: +91 11 4150 4815

STATUS OF TIGERS IN THE SUNDARBAN BIOSPHERE RESERVE: SESSION 2015-2016

Chapter 3 STATUS OF TIGERS IN THE SUNDARBAN BIOSPHERE RESERVE: SESSION 2015-2016 · 2019-03-05 ·...

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