Estimating Annual Pup Production in Grey Seal Breeding Colonies

Estimating pup production from aerial survey data is the best way of estimating grey seal population size. We have developed a parsimonious model to describe fecundity, pup mortality and loss, pup moulting and departure during the breeding season. To deal with possible misclassification we combined this with a model of the observation process. We have Monte-Carlo Markov-Chain techniques to fit both models. This computer-intensive approach affords considerable flexibility and future expandability to the process model, enables us to support the model with independent information on its parameters in the form of priors, get feedback by directly estimating these parameters in the form of posteriors, and explicitly deal with uncertainty in parameters and predictions. We present preliminary results from an application of this approach to simulated data. This validation exercise demonstrates that despite containing 30 parameters, the model can be fitted successfully to relatively sparse data. The results quantify pup production and provide insights about the demographic processes taking place during the breeding season. We discuss extentions of this methodology and its application to real data from grey seals and other seal species.