An ocean-basin-wide mark-recapture study of the North Atlantic humpback whale (Megaptera novaeangliae)

Although much is known about the humpback whale, Mesaptera novaeangliae, re gional studies have been unable to answer several questions that are centra l to the conservation and management of this endangered species. To resolve uncertainties about population size, as well as the spatial and genetic st ructure of the humpback whale population in the North Atlantic, we conducte d a two-year ocean-basin-wide photographic and biopsy study in 1992-1993. P hotographic and skin-biopsy sampling was conducted of animals in feeding an d breeding areas throughout most of the range of this species in the North Atlantic, from the West Indies breeding grounds through all known feeding a reas as far north as arctic Norway. A standardized sampling protocol was de signed to maximize sample sizes while attempting to ensure equal probabilit y of sampling, so chat estimates of abundance would be as accurate and as p recise as possible. During 666 d at sea aboard 28 vessels, 4,207 tail fluke photographs and 2,326 skin biopsies were collected. Molecular analyses of all biopsies included determination of sex, genotype using six microsatelli te loci, and mitochondrial control region sequence. The photographs and mic rosatellite loci were used to identify 2,998 and 2,015 individual whales, r espectively. Previously published results from this study have addressed spatial distrib ution, migration, and genetic relationships. Here, we present new estimates of total abundance in this ocean using photographic data, as well as overa ll and sex-specific estimates using biopsy data. We identify several potent ial sampling biases using only breeding-area samples and report a consisten t mark-recapture estimate of oceanwide abundance derived from photographic identification, using both breeding and feeding-area data, of 10,600 (95% c onfidence interval 9,300-12,100). We also report a comparable, but less pre cise, biopsy-based estimate of 10,400 (95% confidence interval of 8,000-13, 600). These estimates are significantly larger and more precise than estima tes made for the 1980s, potentially reflecting population growth. In contra st, significantly lower and less consistent estimates were obtained using b etween-feeding-area or between-breeding-area sampling. Reasons for the lowe r estimates using the results of sampling in the same areas in subsequent y ears are discussed. Overall, the results of this ocean-basin-wide study dem onstrate that an oceanwide approach to population assessment of baleen whal es is practicable and results in a more comprehensive understanding of popu lation abundance and biology than can be gained from smaller-scale efforts.