Tiger population estimation using camera trapping methods in the Sundarbans of Bangladesh

--Md. Jahidul Kabir Divisional Forest Officer Wildlife Managment and Natur Conservation Division, Khulna

19. Zahidul Kabir

Wild tigers are not only a symbol of all that is splendid, mystical and powerful about nature but they are also a beacon of biodiversity linking together the forests they inhabit (BFD 2012).  The loss of tiger would carry a great catastrophe to the ecosystem of the tiger range countries. In Bangladesh, the Sundarbans is the last stronghold of the Bengal tiger (Panthera tigris tigris). There is a trend of wildlife poaching in the world which also prevails in the Sundarbans.  Due to many other factors the number of wildlife including tigers is declining in its habitat round the globe and this is alarming that the number of tiger has been declined from one tenth of million to only 3000 to 3200 in the wild. If this tendency of declining continues the future of tiger is nowhere. However, with species extinction rates increasing throughout the globe, it has become important to not only determine the species composition in a given area, but to attempt to gain an understanding of the population dynamics: how many individuals are living in the area of interest (population size) and is the population increasing or decreasing over time (population trend) (Ancrenaz et al. 2012).

In the Bangladesh several methods were tried to estimate tiger population in the Sundarbans. Two methods were followed in the assessment of tiger number viz. interview with forest officers/local people and pugmark method. The pugmark was used in 2004 where the adult tiger number was 419 (BFD, 2012). However, tiger abundance survey was done using the pugmark sighting on the river banks (popularly known as Khal Survey) and it was being followed in 2007, 2009, 2010, 2011 and 2012.  This method cannot produce the number of tiger in their habitat. Though various methods were being used to estimate the tiger population, there are debates in using those methods (BFD, 2012).

There are several methods for determining tiger population in the world but above all, the camera trapping is been proved a very effective method in the tiger range countries. However, Bangladesh Forest Department (BFD) with the financial assistance from IDA funded Strengthening Regional Cooperation for Wildlife Protection Project (SRCWP) is conducting this study first time to estimate the tiger number in Bangladesh Sundarbans.

Objective and expected output:

The prime objectives of the proposed camera trapping are

w         To estimate and monitor the size of tiger population and density in the Bangladesh Sundarbans

w         To know about the relative abundance of tiger using Khal survey and line transect methods

The expected results of the study are

w         Tiger density per 100 square kilometer

w         Recent tiger population abundance in the Sundarbans

Methodology

Training

Training on Camera Trapping for tiger estimation in the Sundarbans has been imparted to the forest staffs by the Wildlife Institute of India during the period May 03, 2013 to May 06, 2013.  In that training a one-day indoor training and three-day field training was provided by Dr. Y.V. Jhala and Dr. Qamar Qureshi of India and the whole work is done with the technical support of Wildlife Institute of India (WII).

Equipment

Trap Camera: Cudde Back Attack digital infrared cameras with thermal and motion detector sensors that fired instantaneously when triggered. Associated materials such as SD Card, D-Size Battery, GPS, GPS Battery, Range Finder, Earthen Pot, Nylon Net, Rope, Wooden stick, Sting Bomb,     g rid Map, Data Sheet etc.

Study Period

The study of tiger population estimation will be conducted within two years in the selected three blocks of the Satkhira, Sarankhola and Khulna Ranges of Bangladesh Sundarbans. First year field survey has completed by the Wildlife Management and Nature Conservation Division (WMNCD), Khulna in the month of 1st November 2013 to 10th April 2014 in  collaboration with two territorial divisions.

Study Area

Three blocks have been selected for this study during a preliminary field visit of WII researchers and senior officers in May, 2013. The blocks are i) South-Eastern Block which covers the Sundarbans East Wildlife Sanctuary ii) Central block and iii) North Western Block (see map below). The Sundarbans is divided into 5 sq km grids and a total of 271 grid points which cover 1,355 sq km area under this study.

i)          South-Eastern Block: This block falls into Sarankhola Range of SE Forest Division and consists of Compartment number 3, 4, 5, 6 and part of 7. It has got 71 grids which covers a total area 355 square kilometer. The study of this block has been completed during 1st November 2013 to 25th January 2014.

ii) Central Block: This block falls into Khulna Range of SW Forest Division and consists of compartment number 41 and 42. This has 128 grids and covers an area of 640 square kilometer. Each of the grids will be covered under camera traps (Figure-ii). This block will be done into three sessions where 43 pairs of camera will be placed in each session. Moreover during the exercise some more grid station will be determined to represent the area. This block will be covered in the financial year 2014-15.

iii) North-Eastern Block:  This block includes compartment no 46, 47 and 50B of Satkhira Range and covers an area of 360 square kilometer. This has 72 camera stations and has completed field survey in two sessions during 1st February to 10th April 2014.

First step is the reconnaissance survey where suitable trap station is being identified and GPS locations of the possible places are noted down. The GPS locations of those points are plotted in the grid maps with the help of ArcGIS software for geo-rectification. Second step is the camera setting where the selected trap stations are being cleared properly to avoid unnecessary photographs. Two cameras at each trap station are then placed approximately opposite to each other maintaining a distance of 15 to 20 feet at a height of 1 to 1.5 ft above the ground and tied with standing straight tree or pole. Nylon nets and branches of trees are being placed on the camera side to get clear pictures of both the flanks. Attractants (Olfactory cues) made by fresh eggs, meat and hot water are being used to allure tigers to the trap stations.

Camera Checking

After successful setting of the camera in the whole study areas, the next step is to check the cameras at a certain period of intervals. Cameras are being checked at every 3rd day and SD cards were replaced at every 6th day for checking whether any tiger individuals came or not. During camera checking we used to check attractants, battery efficiency, fresh water and camera setting. We deployed cameras for 35-40 days in each session depending upon capture-recapture rate.

Data Analysis

Tiger pictures collected during field study used for individual identification with windows media gallery manually as well as with matching software. We have prepared a capture history and capture matrix with the collected data for each block. Mark Capture Recapture software will be used for determining absolute density of tigers in each block.

Conclusion

Population estimation of tiger is a difficult task as they are nocturnal, solitary, elusive and cryptic in nature. However, estimation of tiger density and population size is urgently needed with a statistically robust approach to formulate management plans for Sundarbans. Though camera trapping method is more scientific and reliable but it is not possible to conduct this study throughout the Sundarbans within a statistical framework. Wildlife Institute of India and Bangladesh Forest Department are working together to model tiger densities across the Sundarbans by using double sampling approach of calibrating tiger sign indices with camera trap densities. The upcoming model might solve our quarries regarding tiger densities in Sundarbans.