Population composition of humpback whales, Megaptera novaeangliae, on Silver Bank, 1984

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Abstract
Between 14 February and 19 March 1984, 19 d were spent observing humpback whales, Megaptera novaeangliae, on Silver Bank. In total, 317 whales were individually indentified from photographs of ventral fluke patterns. Comparison of these photographs with the North Atlantic humpback whale catalogue revealed that 97 of the whales had previously been observed in other areas. Matches were made with all of the major known high-latitude feeding grounds: Greenland [Denmark] (6), Newfoundland-Labrador [Canada] (43), the Gulf of St. Lawrence (7), and the Gulf of Maine (12). Matches were also made with habitats in the winter range of this population: Bermuda (1), Silver bank in other years (26), Puerto Rico (18), Virgin Bank (1), and Anguilla Bank (1). Analysis of matches suggests that whales form the various high-latitude feeding stocks mix randomly on Silver Bank. Seven surface-active groups contained whales from different high-latitude feeding stocks, providing the strongest evidence to date for genetic mixing among these stocks. The behavior and composition of surface-active groups are discussed. Overall, the number of whales, calves, and surface-active groups observed during this study confirms the apparently singular importance of Silver Bank to the breeding ecology of western North Atlantic humpback whales.