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

Abstract

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.

Review of Underwater and In-Air Sounds Emitted by Australian and Antarctic Marine Mammals

“…They also migrate annually between higher latitudes in the summer and lower latitudes in the winter and are believed to roam as far north as the northern Indian Ocean and Banda Sea [77]. The Perth Canyon (WA; [78,79]) and the Bonney upwelling (SA; [80]) are two notable feeding aggregations of pygmy blue whales.…”

Horizontal niche partitioning of humpback and fin whales around the West Antarctic Peninsula: evidence from a concurrent whale and krill survey

“…Whale distribution has been linked to oceanographic and bathymetric parameters in many areas of the world (Tynan et al 2005;Laran and Gannier 2008;Gill et al 2011) including Antarctic waters (Friedlaender et al 2006Ribic et al 2008;Ainley et al 2011;Williams et al 2014). For large baleen whales spending the summer months in the Southern Ocean, these parameters most likely serve as proxies for prey distribution, since feeding is the main reason for these species to perform seasonal migrations to Antarctic waters.…”

Evidence for an unrecognised blue whale foraging ground in New Zealand

“…The large distances between the Kahurangi Point upwelling area and the majority of blue whale sightings presented here (50Á150 km) does not weaken this hypothesis. A spatial disconnect between upwelling centres and locations of euphausiid blooms with high rates of blue whale sightings has been documented in studies of blue whales off southern Australia (Gill et al 2011), Channel Islands, California (Croll et al 1998 and Monterey Bay, California (Croll et al 2005). All three of these studies reported increased sightings of foraging blue whales in association with dense concentrations of euphausiids that formed downstream of cold water coastal upwelling systems.…”

“…Systematic aerial surveys, conducted at regular temporal intervals (e.g., monthly) can collect standardised data that will elucidate the spatial (how big) and temporal (how frequent and persistent) scale of blue whale distribution in the region (e.g., Gill et al 2011). The production of high intensity, low frequency and long duration acoustic calls is a common and important aspect of blue whale behaviour worldwide .…”

“…Group size data from the recent blue whale sightings were also examined as an indication of foraging behaviour because blue whales are typically solitary but are known to aggregate on foraging grounds (Sears & Perrin 2009;Gill et al 2011). However, solitary, or pairs of, blue whales do not necessarily denote non-foraging behaviour.…”