Temporal patterns in the acoustic presence of baleen whale species in a presumed breeding area off Namibia

Abstract

The eastern Atlantic Ocean is considered to provide important breeding and wintering habitats for several migratory cetacean species. The spatio-temporal distributions and migratory behaviors of cetaceans off southern Africa are nevertheless still poorly understood. This study investigated the temporal patterns of acoustic occurrence of baleen whales in a presumed baleen whale breeding area off Namibia using passive acoustic recordings collected between November 2011 and May 2013. Our results show seasonal acoustic presence of humpback whales Megaptera novaeangliae, fin whales Balaenoptera physalus and Antarctic minke whales B. bonaerensis from November to January and from June to August. Their acoustic absence from February to May possibly indicates that most animals migrated to other areas (presumably in higher latitudes) in austral summer to feed. By contrast, Antarctic blue whales B. musculus intermedia were acoustically present throughout the recording period, indicating that part of the population remains at lower latitudes year-round. Our findings support the presumed ecological importance of the oceanic area off Namibia, providing (part of) a suitable cetacean wintering and, possibly, breeding range or migratory corridor. Furthermore, the occurrence of Antarctic blue and minke whales off Namibia, concurrent with their reported acoustic presence in high-latitude feeding areas, adds to growing evidence that baleen whale migration is not obligate but much more dynamic than has long been assumed.