Capture-recapture estimates of Antarctic blue whale abundance and population growth rate

Abstract

Photo-identifications of Antarctic blue whales (Balaenoptera musculus intermedia) collected from 2003/2004 to 2018/2019 were used in a capture–recapture analysis to estimate abundance and population growth rate for the circumpolar Antarctic. Two capture–recapture models, POPAN and Pradel, were applied to these data. Estimates of annual abundance and their variances from the left and right side photo data were inferred using multimodel averaging, weighted by corrected Akaike information criterion (AICc), of 26 model configurations with prespecified survival rates from .75 to 1.0. These estimates based on the left and right side databases were then combined using inverse-variance averaging into single estimates for each year. The POPAN superpopulation estimate (total number of individuals present during the sampling period) was 3,506 whales, 95% confidence interval (CI) [2,107, 5,832]. The estimated abundance from the final year of the study in 2018/2019 was 1,817 whales, 95% CI [714, 4,624]. The abundance estimates in this study may be biased downwards due to capture heterogeneity as a result of unequal spatial sampling. Population growth rate estimates were 11% from Pradel and 10% from POPAN. These rates were within the confidence interval estimated by a previous study for Antarctic blue whale population growth rate.