MEPS 426:277-287 (2011)  -  DOI: https://doi.org/10.3354/meps08984

ABSTRACT: Data on distribution and behaviour of mother–calf pairs of humpback whales Megaptera novaeangliae obtained during the breeding season (June to October) off Ecuador were analysed. The study was carried out between 2001 and 2009 aboard whale-watching boats. A total of 187 groups containing mother–calf pairs were recorded: 124 pairs alone (MC), 44 with an escort whale (MCE) and 18 with 2 or more whales (MC + n). Five environmental variables were used to assess mother–calf distribution with a principal component analysis (PCA). Two variables, depth and time of day, were sufficient to explain heterogeneity. Average depths increased significantly with group size from MC to MC + n groups (p < 0.001), showing that mother–calf social condition would be a function of the depth at which they moved. MC groups were distributed in shallower waters during afternoon hours (p = 0.035), indicating a preference for shelter areas when sea conditions worsened. The proportion of the 3 female–calf group classes remained fairly constant during the season. In 2 MCE groups, the same escort accompanied the pair after 1 and 4 d, indicating some level of stability and/or guarding behaviour. Twenty resightings of 14 different mother–calf groups were recorded, 90% of resightings occurred within 10 d, showing low site fidelity. In coastal waters, a lower proportion of mother–calf pairs was associated with competitive groups than in other breeding areas located in oceanic archipelagos. This is probably because whales breeding in continental shores do not have to enter oceanic waters when moving between sites within the breeding area. Coastal distribution exposes mother–calf pairs to a greater extent than other age classes to anthropogenic activities in coastal waters, which must be taken into account when considering coastal management.

KEY WORDS: Humpback whales · Breeding behaviour · Spatial distribution · Conservation · Southeastern Pacific