Occurrence, population composition, and habitat use of humpback whales in Samana Bay, Dominican Republic

Abstract

A study of humpback whales (Megaptera novaeangliae) was conducted between 1988 and 1991 in Samana Bay, Dominican Republic. Humpbacks were observed as early as the earliest survey (3 January) and as late as the latest (16 March). Local abundance varied from 0 whales per hour to a maximum of 3.2 whales per hour (mean = 1.70, SD = 0.79), and densities calculated from track surveys ranged from 0.09 to 0.82 whales per square nautical mile (mean = 0.31). Abundance generally peaked in February, but variation was observed both within a season and between years. Almost all whales were observed in the eastern part of the bay, towards or at its mouth. In all, 397 individuals were photographically identified during the study period. Of these, 18 were observed in more than 1 year (17 in 2 years, 1 in 3 years). A total of 15.8% of identified individuals were observed on more than 1 day in a year (maximum 5 days), with mothers representing 33.3% of all resightings. Observed occupancies of resighted animals ranged from 1 to 33 days (mean = 6.3 days, SD = 7.14). The mean group size was 1.95 (range = 1–15, SD = 1.30, n = 652 groups). Ninety-nine groups contained a calf, and all groups larger than three (n = 45) were competitive in nature. Comparisons of fluke photographs with the North Atlantic Humpback Whale Catalogue revealed 141 matches of 118 individuals to other areas. Of these, 76 were to high-latitude feeding grounds (including the Gulf of Maine, Newfoundland, Labrador, the Gulf of St. Lawrence, and west Greenland), while the remaining 65 were to other areas of the West Indies (Silver Bank, Navidad Bank, Puerto Rico, Virgin Bank, or Anguilla Bank) or to Bermuda. We suggest that Samana Bay is one of the most important winter habitats in the West Indies for humpback whales from all over the western North Atlantic, although whaling records suggest that the abundance of whales in this area may be a relatively recent phenomenon. Sightings of other marine mammal species in Samana Bay are summarized.