Alternative population estimates of humpback whales (Megaptera novaeangliae) in Hawaiian waters

Abstract

Based on a census of photographically identified humpback whales in Hawaiian waters during the years 1977 to 1981, J. D. Darling and H. Morowitz (1986. Can. J. Zool. 64: 105–111) estimate that the number of individuals visiting this breeding ground is 1000 during a single winter and 2100 across five winters. Confidence limits are not reported for either estimate, however, and the authors do not consider fully the potential biases of their capture–recapture analyses. A test of the frequency of capture model used for the within-year analysis showed, in some cases, a poor fit between the theoretical distribution and the reported data, thus indicating that the resulting population estimates may also be incorrect. Alternative estimates of across-years abundance were calculated using data from an independent study of humpback whales in Hawaiian waters conducted during the years 1980 to 1983. From the resighting records of the 519 whales identified during this period, Petersen and Jolly–Seber models provide estimates ranging from 635 to 1536 individuals for contiguous sampling years. These estimates are difficult to reconcile with the larger across-years estimate of Darling and Morowitz and suggest that further study is needed to accurately assess the status of this endangered population.