Close-Kin Mark-Recapture Without Age Information: Application to Southern Right Whales

Abstract Close-kin mark-recapture (CKMR) has recently emerged as an alternative for some situations where other abundance estimation methods are hard to apply. The age of the sampled individuals is very informative for CKMR. In the current paper we address the situation that age is unobserved, and we derive mathematical formulas for the resulting CKMR machinery. Expressions for the sampling probability for first- and second-order relationships are derived under simplifying assumptions: (1) the sample consists of randomly sampled adults, (2) the population has reached a stable age distribution, (3) adult mortality is age-independent, (4) random reproduction, and (5) mortality and reproduction are not affected by sampling. Finally, we illustrate our method on a dataset consisting of biopsy samples from 161 southern right whales and obtain estimates of population size and population increase rate. The estimates are imprecise and unstable, which is caused by a limited number of genetic markers and identifiability problems with the model. Supplementary materials accompanying this paper appear on-line.