Blue whale calling in the Rottnest trench-2000, Western ... - ANP
Blue whale calling in the Rottnest trench-2000, Western ... - ANP
Blue whale calling in the Rottnest trench-2000, Western ... - ANP
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callers. The aerial surveys sighted up to eight animals per flight <strong>in</strong> <strong>the</strong> <strong>Rottnest</strong> <strong>trench</strong> over <strong>the</strong><br />
study period (Table 5). Given that <strong>the</strong> blue <strong>whale</strong>s have long down times <strong>the</strong>n <strong>the</strong> aerial surveys<br />
are unlikely to have sighted all <strong>the</strong> animals <strong>in</strong> <strong>the</strong> region. Thus <strong>the</strong> mean of <strong>the</strong> maximum<br />
number of <strong>call<strong>in</strong>g</strong> animals per day of 2.24, will represent less than 28% of <strong>the</strong> total number of<br />
blue <strong>whale</strong>s with<strong>in</strong> <strong>the</strong> region (ie. 2.2/8) to give an upper bound to <strong>the</strong> proportion of blue <strong>whale</strong>s<br />
with<strong>in</strong> <strong>the</strong> <strong>Rottnest</strong> <strong>trench</strong> produc<strong>in</strong>g <strong>the</strong> tonal signals.<br />
To give a display of <strong>the</strong> presence of blue <strong>whale</strong>s through time, <strong>the</strong> power spectral density of each<br />
90 s sample from <strong>the</strong> bluey logger (10 m<strong>in</strong>ute sample separation) was determ<strong>in</strong>ed at a 1.22 Hz<br />
resolution us<strong>in</strong>g 219 averages per 90 s (Hann<strong>in</strong>g w<strong>in</strong>dow), and has been displayed with time on<br />
Figure 47 - Figure 51. The presence of blue <strong>whale</strong>s is <strong>in</strong>dicated by <strong>the</strong> band<strong>in</strong>g at 18-25 Hz,<br />
while <strong>the</strong> 20 Hz click<strong>in</strong>g shows up as <strong>the</strong> <strong>in</strong>tense narrow vertical stripes. It can be seen that <strong>the</strong><br />
two call types dom<strong>in</strong>ate <strong>the</strong> sea noise spectra over this period. The bluey logger ran for almost<br />
five weeks. Although <strong>the</strong> degree of <strong>call<strong>in</strong>g</strong> tapered slightly towards April, <strong>the</strong> sea noise spectra<br />
over <strong>the</strong> 18-80 Hz band was still dom<strong>in</strong>ated by blue <strong>whale</strong> <strong>call<strong>in</strong>g</strong> and <strong>the</strong> 20 Hz click<strong>in</strong>g at <strong>the</strong><br />
end of <strong>the</strong> sampl<strong>in</strong>g period, <strong>in</strong>dicat<strong>in</strong>g how profuse <strong>the</strong> <strong>call<strong>in</strong>g</strong> by blue <strong>whale</strong>s and <strong>the</strong> 20 Hz<br />
click<strong>in</strong>g source was, and its significant impact on ambient sea noise levels <strong>in</strong> <strong>the</strong> region.<br />
44