Proposal for a common simple and widely applicable model for right whale population assessments
A simple model is presented whose aim is to be applicable across a number of right whale populations, in particular so as to provide results that can be compared across these populations. For this reason, the model is designed to require only very limited data, specifically a time series of comparable annual calf counts without too many missing values. Right whales are assumed to calve at either three- or five-year intervals, with the associated proportions changing over time. Similarly, the value of the parameter (X) reflecting the product of the proportion of births that are female and the first-year survival rate may change over time. An initial application to calf count data for the South African right whale population suggests that such data do not contain sufficient information for annual variations in both the X parameter and in the annual proportion of calving intervals that are three years to be estimated. Fixing X and estimating annual changes in the proportion of three-year calving intervals only appears to provide the best performing approach.