Here is the second part of an article published by Shri Vinod Rishi in
The paradigm shift in the approach for monitoring tigers – NTCA’s holistic approach
In a Technical Note the newly constituted National Tiger Conservation Authority (NTCA) made a mention of the criticism faced by the pugmark based census methodology and the limitations, both in design and application, of the alternative proposal to estimate
tiger densities from individually identified tigers using camera traps as the reason for adopting their new approach.
In this approach NTCA applied a hierarchical model and statistical framework for monitoring tigers and other animals. The entire tiger range in India was converted to 6 Landscape Complexes covering 17 Tiger States; each Landscape Complex used Forest Beats or
equivalent areas covering 15-20 sq km of wildlife habitat as the smallest sampling units. Habitat occupancy by tigers was surveyed in all units, and the units were categorized in terms of tiger sign abundance classes – high, medium, low and no density class
– at Forest Beat sampling unit level and at 100 km2 area resolution level. Population densities for tigers were estimated in 5 – 13 replicates of the size of 100-200 km2 in each of the tiger sign abundance classes in which the Landscape Complex had been stratified.
Mark-Recapture sampling method was used to find out tiger densities. Extrapolation of densities was carried out from the results obtained in each sub-sample level to the area covered by its corresponding tiger sign abundance class at landscape level. It was
then followed by conversion of densities/indices into numbers. Computer programs specially designed for the purpose were used for the analysis of the data. A large manpower of trained researchers supervised the collection of field data, which was then verified
by international and national experts (Jhala, Y.V., et al., 2005a, 2005b, 2008).
The results obtained by paradigm shift
The results of the holistic approach were declared in 2008. The estimated all India tiger population is reported to be between 1,165 and 1,657, with a mid value of 1,411 tigers in India. For public consumption the mid value is reported as the population of
tigers in India. It is the latest report on the status of India’s tigers. (Jhala, Y.V., et al., 2008).
Reliability of results from current approach for monitoring and conservation of tigers
A. National Level Monitoring:
The scope for use of the results in monitoring and conservation of tigers has been reduced by the following factors:
1) The figure of 1,411 tigers is the arithmetical mid-value of a statistical range, and not the actual number of tigers. The statistical estimate with a minimum value of 1,165 and a maximum of 1,657 spans a margin of 492 numbers, which is almost 40% of the
minimum value. Somewhere within this margin lies the actual population of tigers in India. With almost 500 numbers to choose from the estimate, a large population falls in the indeterminate grey area. The lack of reasonable precision in the result makes the
reported status of tigers in India too vague to be of any utility in the monitoring and conservation of tigers.
2) The extended period of time over which the field data was collected in 2005-2006 does not permit one to define a temporal reference point for comparison with later date estimates. Small populations of tigers can disappear in an extended time frame. There
was no fixed date(s) common to all places from where the data was collected. Because of the absence of any common temporal reference point, the data does not lend itself for comparison with any other data for monitoring the status of tigers in India.
3) The results do not give the structure of tiger populations: the work has not provided any information on the age, sex and breeding status of the tigers; and the methodology is not designed to provide information on juveniles, cubs and transient tigers.
4) Even with field data collected under the supervision of a large and highly qualified manpower, and its verification carried out by national and international experts (Jhala et al., 2008), serious flaws have appeared in the tiger occupancy estimates. The
methodology could not generate reliable tiger habitat occupancy maps and other related records.
a. For instance, the map for northern West Bengal shows tiger occupancy in Gorumara National Park, and in fragments of Buxa tiger reserve and other forest areas that have had no record of resident tigers over the past more than five years; also, the map
shows absence of tigers in tiger occupied areas like Mahananda Wildlife Sanctuary and the northern part of Buxa tiger reserve where one was recently photographed.
b. The sampling based statistical estimation of the extent of area under tiger occupation is erroneous for Sunderbans and many other tiger habitats. Therefore, the extrapolation of densities calculated from such erroneous base-line data cannot give accurate
-to be continued