Ecological and anthropogenic covariates ... - GANGAPEDIA

The sampling protocol was followed in order to meet the basic assumptions of
capture-recapture models, as follows:
1) All individuals have an equal probability of being captured:
Although crocodilian population surveys are affected by biases against smaller size
classes, I ensured that all zones within the study area, which included the river stretch,
mid-channel islands, sand-bars, rocky outcrops and adjacent banks, were observed
with equal effort. I used powerful optics (a Bushnell EXCURSION FLP 20 - 60x -
80mm Spotting Scope and 16 x 50 Porro-Prism Binoculars) to ensure that were no
‘holes’ where an individual could have zero capture probability.
2) Capture does not affect subsequent recapture:
This technique did not involve physical capture and restraint of gharial; and data
collection through stationary bank observations were being carried out from
concealed locations to minimize disturbance and observer influence. Moreover, a time
period of at least three weeks between subsequent occasions was considered sufficient
to aid recovery from any possible stress or disturbance arising from the study.
3) Marks are not lost:
The tail of the gharial is laterally compressed, and on its sides, it has black markings
on a base of light to dark brown. Proximally, the tail has a double crest of projecting
scutes and, distally, a single crest. Individual identification of gharial were made,
primarily, by comparing natural permanent blotches and markings on the lateral
scutes on the tail, and by using additional cues like size classes, injuries and scars.
These markings are not known to change and are individually unique.
4) Marked and unmarked individuals have the same probability of survival:
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