Summary
Long term acoustic records of underwater sound can be used to assess the timing of migrations, peak periods of relative abundance, and seasonality and overlap of different species’ presence over large spatial scales. Long-term acoustic data was collected over large portions of the Southern Ocean between Australia and the Antarctic continent. A three year hydro-acoustic record (<~100 Hz) from the Comprehensive Nuclear-Test Ban Treaty Organization (CTBTO) was obtained from lower latitude waters off Western Australia between January 2004 and February 2007. Bottom mounted autonomous recording packages (ARPs) were deployed off eastern Antarctica (between 115-75° E) in the waters near Casey station from February 2004 through February 2005, and near Prydz Bay and the southern Kerguelen Plateau from February 2005 through February 2007. The ARPs recorded low frequency (<250Hz) sound continuously over this period. Three additional acoustic loggers (recording <2000Hz) were deployed roughly along a line of longitude (141°E) between Tasmania and the Antarctic continent between October 2006 and February 2007. Power spectral density (PSD) analyses of the frequency bands of blue (Antarctic and pygmy) and fin whale calls was carried out. The peak acoustic presence of pygmy blue whales that occurred at the more northerly recording sites was consistently earlier (March-May) than peak Antarctic blue whale acoustic presence (May-August) at these sites. At the northerly CTBTO site, fin whale and Antarctic blue whale acoustic seasonal presence appeared nearly identical. Fin whale acoustic presence in the Antarctic data appeared to be over a much shorter time (April-June) than Antarctic blue whales, which maintained some acoustic presence nearly year round, but had seasonal peaks between March and July/August. In addition, two previously identified types of pygmy blue whale calls (West Australia and Madagascar) were detected representing, as far as we are aware, the furthest south these sounds have been recorded.