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
\nwintering habitats for several migratory cetacean species. The spatio-temporal distributions and
\nmigratory behaviors of cetaceans off southern Africa are nevertheless still poorly understood. This
\nstudy investigated the temporal patterns of acoustic occurrence of baleen whales in a presumed
\nbaleen whale breeding area off Namibia using passive acoustic recordings collected between November
\n2011 and May 2013. Our results show seasonal acoustic presence of humpback whales
\nMegaptera novaeangliae, fin whales Balaenoptera physalus and Antarctic minke whales B.
\nbonaerensis from November to January and from June to August. Their acoustic absence from
\nFebruary to May possibly indicates that most animals migrated to other areas (presumably in
\nhigher latitudes) in austral summer to feed. By contrast, Antarctic blue whales B. musculus intermedia
\nwere acoustically present throughout the recording period, indicating that part of the population
\nremains at lower latitudes year-round. Our findings support the presumed ecological importance
\nof the oceanic area off Namibia, providing (part of) a suitable cetacean wintering and,
\npossibly, breeding range or migratory corridor. Furthermore, the occurrence of Antarctic blue and
\nminke whales off Namibia, concurrent with their reported acoustic presence in high-latitude feeding
\nareas, adds to growing evidence that baleen whale migration is not obligate but much more dynamic
\nthan has long been assumed.