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

A localised aggregation of blue whales. which may be pygmy blue whales (B. m. brevicauda), occurs in southern Australian coastal waters (between I39°45'E-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.

Ecological linkages in the Bonney Upwelling blue whale feeding area

This research has described linkages between the cold-water Bonney Upwelling of south-east Australia, associated primary and secondary biological production, and the presence of feeding blue whales Balaenoptera musculus. This is a previously undescribed, seasonally predictable blue whale feeding area, where whales prey on abundant swarms of krill Nyctiphanes australis.

Blue whale habitat selection and within-season distribution in a regional upwelling system off southern Australia

Blue whales Balaenoptera musculus aggregate to feed in a regional upwelling system during November–May between the Great Australian Bight (GAB) and Bass Strait. We analysed sightings from aerial surveys over 6 upwelling seasons (2001–02 to 2006–07) to assess within-season patterns of blue whale habitat selection, distribution, and relative abundance. Habitat variables were modelled using a general linear model (GLM) that ranked sea surface temperature (SST) and sea surface chlorophyll (SSC) of equal importance, followed by depth, distance to shore, SSC gradient, distance to shelf break, and SST gradient. Further discrimination by hierarchical partitioning indicated that SST accounted for 84.4% of variation in blue whale presence explained by the model, and that probability of sightings increased with increasing SST. The large study area was resolved into 3 zones showing diversity of habitat from the shallow narrow shelf and associated surface upwelling of the central zone, to the relatively deep upper slope waters, broad shelf and variable upwelling of the western zone, and the intermediate features of the eastern zone. Density kernel estimation showed a trend in distribution from the west during November–December, spreading south-eastward along the shelf throughout the central and eastern zones during January–April, with the central zone most consistently utilised. Encounter rates in central and eastern zones peaked in February, coinciding with peak upwelling intensity and primary productivity. Blue whales avoided inshore upwelling centres, selecting SST ~1°C cooler than remotely sensed ambient SST. Whales selected significantly higher SSC in the central and eastern zones than the western zone, where relative abundance was extremely variable. Most animals departed from the feeding ground by late April.