A blue whale (Balaenoptera musculus) feeding ground in a southern Australian coastal upwelling zone

Résumé

A localised aggregation of blue whales, which may be pygmy blue whales (B. m. brevicauda), occurs in southern Australian coastal waters (between 139°45AE-143°E) during summer and autumn (December-May), where they feed on coastal krill (Nyctiphanes australis), a species which often forms surface swarms. While the abundance of blue whales using this area is unknown, up to 32 blue whales have been sighted in individual aerial surveys. Krill appear to aggregate in response to enhanced productivity resulting from the summer-autumn wind-forced Bonney Coast upwelling along the continental shelf. During the upwelling’s quiescent (winter-spring) period, blue whales appear to be absent from the region. Krill surface swarms have been associated with 48% of 261 blue whale sightings since 1998, with direct evidence of feeding observed in 36% of all sightings. Mean blue whale group size was 1.55 (SD = 0.839), with all size classes represented including calves. This seasonally predictable upwelling system is evidently a regular feeding ground for blue whales, and careful management of human activities is required there.