The waters of São Tomé: a calving ground for West African humpback whales?

Abstract

In the Southern Hemisphere, humpback whales Megaptera novaeangliae feed in Antarctic waters during the austral summer and migrate to their breeding grounds in subtropical and tropical waters during the winter. Historical whaling records suggest that the Archipelago of São Tomé and Príncipe, located in the Gulf of Guinea, serves as a possible breeding ground. In order to investigate the temporal occurrence and group composition of humpback whales around São Tomé Island, annual surveys were conducted during the breeding season between 2002 and 2006. A total of 186 boat-based surveys took place during this period. Data collected during each sighting included geographical positions, group size, group composition and behavioural classifications. Of the 66 groups encountered, mother/calf pairs made up a large proportion (65.15%), followed by solitary individuals (15.15%). Mother/calf pairs were seen in the region into November and resightings of identified animals indicate periods of occupancy that extended over three weeks. Few behaviours typically associated with mating activity were observed. Given the high percentage of mother/calf pairs, sometimes with very young calves, and the low frequency of mating activity, the waters of São Tomé may primarily serve as a calving and nursing or resting area for humpback whales.

Keywords: behaviour, breeding grounds, group composition, South Atlantic

African Journal of Marine Science 2011, 33(1): 91–97