AN OCEAN-BASIN-WIDE MARK-RECAPTURE STUDY OF THE NORTH ATLANTIC HUMPBACK WHALE (MEGAPTERA NOVAEANGLIAE)

Although much is known about the humpback whale, Megaptera novaeangliae, regional studies have been unable to answer several questions that are central to the conservation and management of this endangered species. To resolve uncertainties about population size, as well as the spatial and genetic structure of the humpback whale population in the North Atlantic, we conducted a two-year ocean-basin-wide photographic and biopsy study in 1992-1993. Photographic and skin-biopsy sampling was conducted of animals in feeding and breeding areas throughout most of the range of this species in the North Atlantic, from the West Indies breeding grounds through all known feeding areas as far north as arctic Norway. A standardized sampling protocol was designed to maximize sample sizes while attempting to ensure equal probability of sampling, so that estimates of abundance would be as accurate and as precise 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 microsatellite loci, and mitochondrial control region sequence. The photographs and microsatellite loci were used to identify 2,998 and 2,015 individual whales, respectively. Previously published results from this study have addressed spatial distribution, migration, and genetic relationships. Here, we present new estimates of total abundance in this ocean using photographic data, as well as overall and sex-specific estimates using biopsy data. We identify several potential sampling biases using only breeding-area samples and report a consistent mark-recapture estimate of oceanwide abundance derived from photographic identification, using both breeding and feeding-area data, of 10,600 (95% confidence interval 9,300-12,100). We also report a comparable, but less precise, biopsy-based estimate of 10,400 (95% confidence interval of 8,000-13,600). These estimates are significantly larger and more precise than estimates made for the 1980s, potentially reflecting population growth. In contrast, significantly lower and less consistent estimates were obtained using between-feeding-area or between-breeding-area sampling. Reasons for the lower estimates using the results of sampling in the same areas in subsequent years are discussed. Overall, the results of this ocean-basin-wide study demonstrate that an oceanwide approach to population assessment of baleen whales is practicable and results in a more comprehensive understanding of population abundance and biology than can be gained from smaller-scale efforts.     

SPATIAL AND SEASONAL DISTRIBUTION OF THE HUMPBACK WHALE, MEGAPTERA NOVAEANGLIAE, IN THE MEXICAN PACIFIC

From observations of the spatial distribution of humpback whales in the Mexican Pacific between 1981 and 1986, it is possible to recognize four subregions: 1) the southern coast of Baja California; 2) the northern Gulf of California, including the Midriff Islands; 3) the mainland coast of Mexico, including the Isla Isabel and Islas Tres Marias and 4) the Revillagigedo Archipelago. The seasonal distribution of whales near the Mexican mainland and the Revillagigedo Archipelago extends from November to May and is similar to that of other winter breeding grounds, including the Hawaiian Islands. Along the southern coast of Baja California, whales have been observed from September to April, possibly indicating a shorter migratory route. In the northern Gulf of California, however, humpback whales have been reported throughout the year and are occasionally observed feeding during both summer and winter months. The degree of individual movement between the four subregions is still unknown. The number of individual humpback whales identified photographically in recent years suggests that there ate more whales in the Mexican Pacific than previously reported.     

TEMPORAL VARIABILITY IN FEATURES USED TO PHOTO-IDENTIFY HUMPBACK WHALES (MEGAPTERA NOVAEANGLIAE)

Photographs of 99 humpback whales of known age were analyzed to assess the temporal variability and recognizability of individually distinctive fluke and dorsal fin features used for photo-identification. Stable features tended to be morphological in nature (dorsal fin shape and edges, the trailing edge of the fluke, and the raised bumps on the caudal peduncle termed "knobs"). Transitory features typically were superficial marks (scarring, scratching, and pigmentation). The variability of several features was found to be age-dependent as well. Young animals sometimes experienced substantial change to their fluke coloration patterns, though this feature stabilized with age. Dorsal fin edges and fluke serration peaks tended to undergo more change in males than in females, with most changes occurring following sexual maturation. Peduncle knobs were the most stable feature, with no documented change in any age interval. Given the extreme stability (and hence recognizability) of dorsal fin shape and peduncle knobs, we suggest that photographs combining the dorsal fin and the caudal peduncle provide the most consistent way to reidentify humpback whales, particularly calves following weaning.     

POPULATION CHARACTERISTICS AND MIGRATION OF SUMMER AND LATE-SEASON HUMPBACK WHALES (MEGAPTERA NOVAEANGLIAE) IN SOUTHEASTERN ALASKA

A total of 326 humpback whales (Megaptera novaeangliae) were individually identified in southeastern Alaska during five summer seasons (July to September) and four late seasons (November to February) spanning the years 1979 to 1983. Peak numbers of whales were found late in August or early in September. Whales arrived 1–2 wk later in 1982 than in 1981. Whales sighted in both the summer and late seasons of 1981 and 1982 remained about 3.7 mo and one whale remained for at least 4.9 mo. Humpback whales from southeastern Alaska wintered in Hawaiian or Mexican waters, but generally did not travel to other feeding regions. The most rapid migratory transit between Hawaii and southeastern Alaska was 79 d. Based on mark-recapture analyses of the photographic data, we estimate a population of 270–372 whales in the southeastern Alaska feeding herd.