Estimating survival and capture probability of fur seal pups using multi-state mark-recapture models

Abstract

We use a multistate mark–recapture model incorporating information on body mass, sex, time of capture, and natal colony to estimate the probabilities of survival, capture, and mass-state transition of New Zealand fur seal (Arctocephalus forsteri) pups from 3 sites (colonies) on Otago Peninsula, South Island, New Zealand. Apparent survival for a mean sampling interval of 47 days was high (≥0.850) after correcting for tag loss, and there was evidence that there were differences between sexes and among sites even after controlling for mass at capture. Survival did not differ among body-mass classes. Heavier pups had lower capture probabilities; however, differences in mass adequately explained any potential differences in capture probability due to sex. State-transition probabilities among mass classes also differed with time of capture, and between sexes and among sites. Although bias in estimates of survival probability is minimal when survival is high, heterogeneity in capture probabilities among different classes of individuals can bias estimates of pup growth rate and sex ratio. We recommend measuring mass of individuals and incorporating this and perhaps other pertinent information into multistate mark–recapture models when attempting to estimate survival and to determine the effect of capture probability on estimates of other life-history parameters.