Capture-recapture estimates of abundance of Antarctic blue whales
Paula A. Olson, Douglas Kinzey, Michael C. Double, Koji Matsuoka, Ken Findlay
Photo-identification data of Antarctic blue whales from 2003/2004 to 2018/2019 were used in a capture-recapture analysis to produce estimates of super-population abundance, from which derived estimates of annual abundances were obtained, for the circumpolar Antarctic. Photographs were collected during IWC, IWC-SORP, ICR, and SAABWS cruises and also made available by opportunistic contributors. Separate capture-recapture estimates were made using photos taken of the left and right sides of the whales. Two values of annual survival rates, 0.90 and 0.96, were supplied as model inputs. The estimates for the separate sides were similar but the assigned survival values had a larger impact on the population estimates. The circumpolar superpopulation estimates for the 0.90 survival rate were 3,912 (95% CI 1,891 to 7,930) Antarctic blue whales (left side photographs) and 4,296 (95% CI 2,095 to 9,085) (right side photographs) for the 16 year period of the study. For the 0.96 survival rate these estimates were 4,130 (95% CI 1,935 to 9,122) (left side) and 4,624 (95% CI 2,109 to 10,491) (right side). As more data become available in the future, it should be possible to estimate survival from photo-ID capture-recapture modeling in addition to the other estimated parameters.