Ecological and anthropogenic covariates ... - GANGAPEDIA

Discussion
One issue that needs to be addressed is the fact that only one side of the gharial is
visible at any one time, and that unless both sides are photographed, an individual’s
identity remains unknown when presented with only the unrecorded side. However,
this can be dealt with by identifying basking sites in advance and positioning oneself
before these animals emerge to bask. Thereafter, the sequence of events that
accompany most basking episodes provide a way to bypass the issue. Gharials emerge
head first onto basking sites, providing an opportunity to ‘capture’ one side and then
re-orient themselves so as to face the river. This allows for the other side to be
captured too.
Other factors that could complicate the implementation of this technique are poor
weather conditions, animals lying at odd angles or congregating in a way such that
individuals are blocking the observers’ view of other individuals, disturbances that
drive basking gharials into the water.
Although the use of natural markings is non-invasive and is advantageous over
applied tags in specific cases, issues relating to uncertainty in the level of
identification, misidentification or misclassification, and unmarkable animals must be
considered (Yoshizaki, 2007). Since conventional methods for analysis of capture–
recapture data do not account for identification errors, special capture-recapture
models that incorporate unmarkable animals (Da Silva et al., 2000, 2003) or models
that incorporate the misidentification mechanism (Yoshizaki, 2007; Yoshizaki et al.
2009) will have to be used.
Capture-Recapture models provide a statistical framework for estimating p (detection
or capture probability) and quantities of biological interest such as population size
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