Estimation of demographic parameters for NZ sea lions breeding on the Auckland Islands – 1997/98–2008/09
Introduction
This report provides an update on the estimation of demographic parameters for New Zealand sea lions breeding on the Auckland Islands from data collected up to the 2008/09 field season. Published 2010.Download the publication
Summary
Similar methodology to last year was used to analyse the updated data, although additional models were considered that included annual variation in demographic parameters.
Results indicate that survival probabilities were relatively low between the 2007/08 and 2008/09 breeding seasons compared to previous years (survival probability lower by approximately 0.05). Breeding probabilities in 2008/09 were also relatively low for females that had bred in the previous year.
As the age profile of the tagged population is changing though time, it is cautioned that some apparent temporal effects may be due to changes in the age distribution, or vice-versa.
A model-based method for estimating population size was applied to the data and suggested that the number of female New Zealand sea lions may have reduced in 2008/09 by approximately 700 individuals to between 4100-5200. These estimates may be sensitive to the specific model used, however, and it is recommended that field methods be trialled that will enable direct estimates of population size.