Regional and sexual differences in fluke pigmentation of humpback whales (Megaptera novaeangliae) from the North Atlantic Ocean

The relative amount of pigmentation on the flukes of 3812 humpback whales from five feeding and three breeding regions in the western North Atlantic Ocean was ranked subjectively into categories 1 (white) through 5 (black). The distribution of rankings was examined to determine whether differences existed between regions or sexes. Fluke pigmentation differed significantly among whales photographed in the five northern feeding regions (Iceland, southwestern Greenland, Newfoundland (including the Labrador coast), the Gulf of St. Lawrence, and the Gulf of Maine). Whales photographed in the Gulf of Maine were characterized by a significantly higher proportion of dark-colored nukes than whales in all feeding regions except Iceland. Whales photographed near Greenland were characterized by significantly more light-colored flukes than other feeding regions. Fluke pigmentation also varied significantly among whales photographed in the three southern breeding regions (Virgin Bank, Puerto Rico, and the Dominican Republic). The flukes of whales photographed near Virgin Bank differed from those of whales near the Dominican Republic and included a higher proportion of light flukes. Fluke pigmentation of males and females differed significantly in the Gulf of Maine and in the Dominican Republic. Both areas showed higher proportions of dark-fluked females and light-fluked males. Sex bias differences in other regions were not examined because sample sizes were small. Fluke pigmentation of whales photographed only on the summer range did not differ significantly from the pigmentation of those photographed only on the winter range, supporting the belief that all northern feeding aggregations mix on the southern breeding grounds. Regional differences in fluke pigmentation suggest that the western North Atlantic humpback whale population includes a number of relatively isolated subunits, as suggested previously by photoidentification and DNA studies.