Stable social associations among humpback whales (Megaptera novaeangliae) in the southern Gulf of Maine

Abstract

Groups of humpack whales (Megaptera novaeangliae) were observed from 1980 to 1987 on their feeding grounds in the southern Gulf of Maine. Although most groups were together for only brief periods, two types of stable association were found: 'continuous' (individual whales associated for at least 7 consecutive days; n = 30) or 'recurring' (individuals associated at least five times in a 6-week period; n = 21). Thirty-seven stable pairs and 3 stable trios involving 56 individual whales were recorded; 11 stable pairs re-associated during more than 1 year. Continuous associations lasted up to 79 days (mean 29.65). Thirty of the 40 associations (75.0%) contained only adults. Females were present in 22 adult associations (73.3%), whereas males were present in only 8 (26.6%). Females sighted with a calf the following year, and therefore pregnant, were members of 6 of the 11 (54.5%) associations that reformed. It is hypothesized that stable associations allow adult females to maximize their net energy gain through cooperative feeding, and may be comprised of closely related animals or individuals with compatible feeding styles.