Blue whale calling in the Rottnest trench-2000, Western ... - ANP

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Figure 10: Distribution of the frequencies of the spectral peak for each component type, as determined by averaging the frequency content over each component duration (FFT's taken with a 0.0763 Hz resolution two averages per component, distribution shown with a 0.2 Hz bin width). Figure 11: Frequency spectra of high S/N ratio components for each component type, over the frequency band 10- 100 Hz. 14
Figure 12: Spectrogram of two blue whale components (type I over 8-57 s and a type II over 61-86 s). The type I component displays sidebands associated with amplitude modulation of the carrier tone. 3.1.2) Received component levels For the same sequence of type I, II and III components (a call), each component consistently had different received levels. Based on matched components within the same call which had no other complicating sources (ie. overlapping clicks or other blue whale calls) and using the mean squared pressure over the component duration to compare received component levels, then: • the type II component was 3-10 dB higher in received level than the type I component (4 matched components) • and the type II component was 0.4-3 dB higher than the type III component (seven matched components). This implies differences in source levels for each component. The nature of received calls emphasised this, for very long range calls, or those with low signal to noise ratios, it was always the type II component which showed up best. For the deep water moored hydrophone (bluey logger at 450 m depth) low SNR signals displayed the 20-26 Hz type II fundamental and harmonics. For the drifted hydrophone (at 55 m depth) it was often the 60-80 Hz harmonic of the type II component which showed up best in spectrograms, with the 19-26 Hz tones often lost. There was considerable variability of the received level through a component. Examples of this for the type II component are shown in Figure 13, where the magnitude of the Hilbert transform of several components have been overlaid. This analysis displays the positive component envelope, assuming it to be symmetric about the zero pressure axis. The envelope of the lowest level component displayed showed a bi-model peak in received level. This was common for many received signals. The highest level component displayed showed a large increase in received level towards the end of the component. Although some of this variability is under the control of the animal, (of the order of seconds) much of it is believed a function of sound propagation peculiarities for tones (of the order of the entire component length) and is discussed further in section 3.3. 15
Page 1 and 2: Centre for Marine Science and Techn
Page 3 and 4: Contents Abstract..................
Page 5 and 6: Along the Western Australian coast
Page 7 and 8: Figure 2: Location of the Rottnest
Page 9 and 10: Figure 4: Examples of temperate (th
Page 11 and 12: The first call component, referred
Page 13: Figure 9: Bandpass filtered wavefor
Page 17 and 18: For the final censusing technique a
Page 19 and 20: the medium sand thickness was linea
Page 21 and 22: interference patterns produced by t
Page 23 and 24: coast. Calling depths of 22-34 m, a
Page 25 and 26: of the same frequency, different ph
Page 27 and 28: Figure 23: Distribution of 'possibl
Page 29 and 30: Figure 26: Predicted ranges for the
Page 31 and 32: 31 and Figure 32. These also displa
Page 33 and 34: signals were received with a wide r
Page 35 and 36: each time point tested. All calcula
Page 37 and 38: Figure 37: Arrangement of kernel (a
Page 39 and 40: 16:00) using combinations of mean c
Page 41 and 42: Figure 40: (top) Number of callers
Page 43 and 44: 2. and the type II component call s
Page 45 and 46: Figure 43: Number of callers averag
Page 47 and 48: Figure 47: Time averaged spectra (1
Page 49: Figure 51: Time averaged spectra (1
Page 52 and 53: each block then gave the total numb
Page 54 and 55: 5) References Bannister, J.L. (1993

Blue whale calling in the Rottnest trench-2000, Western ... - ANP

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