Léa Bouffaut, Martin Landrø, and John R. Potter (NTNU) have published the paper “Source level and vocalizing depth estimation of two blue whale subspecies in the western Indian Ocean from single sensor observations” in the Journal of the Acoustical Society of America (JASA).
The source level (SL) and vocalizing source depth (SD) of individuals from two blue whale (BW) subspecies, an Antarctic blue whale (Balaenoptera musculus intermedia; ABW) and a Madagascar pygmy blue whale (Balaenoptera musculus brevicauda; MPBW) are estimated from a single bottom-mounted hydrophone in the west- ern Indian Ocean. Stereotyped units (male) are automatically detected and the range is estimated from the time delay between the direct and lowest-order multiply-reflected acoustic paths (multipath-ranging). Allowing for geometric spreading and the Lloyd’s mirror effect (range-, depth-, and frequency-dependent) SL and SD are estimated by minimizing the SL variance over a series of units from the same individual over time (and hence also range). The average estimated SL of 188.5 +/- 2.1 dB re 1microPa measured between [25–30] Hz for the ABW and 176.8 +/- 1.8 dB re. 1microPa measured between [22–27] Hz for the MPBW agree with values published for other geographical areas. Units were vocalized at estimated depths of 25.0 +/- 3.7 and 32.7 +/- 5.7 m for the ABW Unit A and C and, approximately 20 m for the MPBW. The measurements show that these BW calls series are stereotyped in frequency, amplitude, and depth.