Vocal characteristics of pygmy blue whales and their change over time
Locations of the HA01 CTBT station (black triangle) and two IMOS acoustic observatories (black squares) used for studying vocalization characteristics of pygmy blue whales.
Spectrograms of pygmy blue whale songs consisting of repeating three-sound themes (top panel) and two-sound themes (bottom panel). Spectrogram parameters: 1024-point FFT, 1024-point Hanning window with 95% overlap.
Spectrograms of downsweep signals of pygmy blue whales calls recorded in Geographe Bay (top panel) and off Cape Leeuwin (bottom panel) in Western Australia. Spectrogram parameters: 256-point FFT, 128-point Hanning window with 95% overlap.
Located positions of two vocalizing whales (small dots) making regular tonal calls (top panel) and sporadic downsweep calls (bottom panel) recorded in 2002 and 2003 respectively; the relative location of the HA01 hydrophones (black circles); location ambiguity zones (shadowed areas in the top panel); and error ellipses of location at 95% confidence level (dashed ellipses). The arrow in the top panel shows the general travel direction of the singing whale with the mean speed .
Acoustic transmission losses averaged in two frequency bands of 22–25 Hz and 66–75 Hz, modeled for the ocean acoustic environment at the HA01 station and two source depths of 20 m (dashed line) and 30 m (solid line). The dash-and-dot line shows the approximate TL curve based on spherical spreading of acoustic energy with slant range to the source near the sea surface and corrected for the contribution from the surface reflected signal.
Received signal levels measured for seven whales located at different distances from the HA01 hydrophones. The dashed line shows the best fit of the measured level by the approximate TL curve given in Eq. (2).
Received signal levels measured for ten downsweep signals from pygmy blue whales received at different distances from the HA01 hydrophones.
Superposition of two spectrograms of theme sounds 2 and 3 recorded from different whales in 2002 and 2007.
The number of whale calls detected fortnightly at the HA01 station of Cape Leeuwin, in Perth Canyon and off Portland that were used to measure the mean value and standard deviation of call frequency (top panel) and the mean value of the maximum frequency of the third harmonic in sound 2 of the whale song theme measured at these three sites in 2002–2010 (bottom panel). Asterisks represent data from the Cape Leeuwin station, circles, the Perth Canyon, and pluses, the Portland IMOS observatory.
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