Abstract:
Marker-loss is a common feature of mark–recapture studies and important as
it may bias parameter estimation. A slight alteration in tag-site of double tagged
southern elephant seals (Mirounga leonina), marked at Marion Island from 1983 to
2005 in an ongoing mark–recapture program, had important consequences for tagloss.
We calculated age-specific tag-retention rates and cumulative tag-retention
probabilities using a maximum likelihood model selection approach in the software
application TAG LOSS 3.2.0. Under the tag-loss independence assumption, double
tag-loss of inner interdigital webbing tags (IIT; 17 cohorts) remained below 1%
in the first 5 yr and increased monotonically as seals aged, with higher tag-loss
in males. Lifetime cumulative IIT tag-loss was 11.9% for females and 18.4% for
males, and equivalent for all cohorts. Changing the tag-site to the outer interdigital
webbing (OIT; 6 cohorts) resulted in increased and cohort-dependent tag-loss,
although the variation (mean ± 95% CI) in cumulative tag-loss probabilities never
exceeded 5.3% between cohorts at similar age. Although different studies may
homogenize techniques, we advocate the importance of data set-specific assessment
of tag-loss rates to ensure greatest confidence in population parameters obtained
from mark–recapture experiments. Permanent marking should be implemented
where feasible.
