Temporal pattern of humpback whale (Megaptera novaeangliae) group structure around Abrolhos Archipelago breeding region, Bahia, Brazil

Abstract

To characterize temporal patterns of humpback group structure around Abrolhos Archipelago, Brazil, seven years (1998–2004) of data obtained from July through November were analysed. During one-hour scans, observers determined group composition within 9.3 km around a land-based station. A total of 930 scans, comprising 4288 groups were analysed. Seven group categories were identified and their frequencies were 14.6% of 1AD (lone whale), 25.2% of DYAD (two adult whales), 7.3% of TRIO (three adult whales), 5.2 of TRIO+ (more than three adults), 24.9% of MOC (mother and calf), 19.6% of MOCE (mother, calf and one escort), and 3.1% of MOCE+ (mother, calf and more than one escort). Proportions of whale-group categories did not change between morning and afternoon, nor among years. However, as the season progressed, groups with calves increased while groups without calves decreased. This progression may be explained by the segregated migration patterns of humpback whales and also by changes in the social status of individuals. The Abrolhos Reef provides protection from the prevailing winds, which may explain the higher proportion of groups with calves in the area.