Towards an estimate of the Southeastern Pacific humpback whale stock

Abstract

Between 1991 and 1997 a photo-identification study of Southeastern Pacific humpback whales was carried out on the central coast of Ecuador (1°26’S, 80°50’W), South America. During this period, a total of 219 whales were identified and catalogued by the colouration pattern on the ventral side of their flukes. Naturally marked whales were used to estimate the population through the Petersen’s mark-recapture method as modified by Bailey. With data from the final two seasons (1996-1997), the resultant estimate was 1,922 (95% CI = 77-3,767) whales. Pooling data from the first six years resulted in an estimate of 2,683 (95% CI = 397-4,969) whales. Sources of bias relate to violations of the assumptions of closure and equal catchability conditions. The low inter-yearly resighting rate and a high rate of new discoveries in the last season indicate that only a fraction of the population has so far been identified. Despite the broad confidence interval, these data provide an indication of the current number of whales.