mcbem-2014-01-submission-wwf-en
mcbem-2014-01-submission-wwf-en
mcbem-2014-01-submission-wwf-en
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Table A2. The five functional hearing groups for noise exposure criteria based on Southall et al. (2007).<br />
Group<br />
Low-frequ<strong>en</strong>cy cetaceans<br />
Mid-frequ<strong>en</strong>cy cetaceans<br />
High- frequ<strong>en</strong>cy cetaceans<br />
Pinnipeds in air<br />
Pinnipeds in water<br />
Examples<br />
bale<strong>en</strong> whales- e.g., gray, fin, and blue<br />
whales<br />
toothed whales and dolphins – e.g., sperm,<br />
killer and beluga whales, Pacific white-sided<br />
dolphins<br />
porpoises – e.g., Dall’s and harbour<br />
porpoises<br />
all seals, sea lions and fur seals e.g.,<br />
Harbour seals, Steller sea lions<br />
all seals, sea lions and fur seals e.g.,<br />
Harbour seals, Steller sea lions<br />
It is critically important to appreciate that the lower the frequ<strong>en</strong>cy of the sound, the further the sound<br />
will travel. In water, a 100 Hz signal can travel over 1000 km with relatively little loss of sound <strong>en</strong>ergy.<br />
Most of the <strong>en</strong>ergy in shipping noise, and in bale<strong>en</strong> whale communication signals, lies in frequ<strong>en</strong>cies<br />
below 1000 Hz. In many approaches to analysing sounds, the <strong>en</strong>ergy is measured within differ<strong>en</strong>t<br />
frequ<strong>en</strong>cy bands. The bandwidth used most oft<strong>en</strong> in bioacoustics is 1/3 of an octave, where an octave<br />
repres<strong>en</strong>ts a doubling of frequ<strong>en</strong>cy (Table A3). The European Union has chos<strong>en</strong> the 63 Hz and 125 Hz<br />
1/3 octave bands as the focus of their long term underwater noise monitoring program.<br />
How do we describe sounds quantitatively?<br />
There are a number of units that are used to describe sound, but unlike volume or l<strong>en</strong>gth measurem<strong>en</strong>ts<br />
that have absolute values, measures of sounds are relative. The decibel (dB) is now the most commonly<br />
used unit wh<strong>en</strong> considering the biological impacts of sound, and it is simply a unit in a logarithmic scale<br />
that describes sound int<strong>en</strong>sity level or pressure level relative to a fixed refer<strong>en</strong>ce int<strong>en</strong>sity or pressure.<br />
For every 3 dB increase, the sound <strong>en</strong>ergy doubles. In air, the refer<strong>en</strong>ce int<strong>en</strong>sity is 20 micropascals<br />
(µPa) or .0002 microbars, which is considered to be the g<strong>en</strong>eral lower limit of audibility to the human<br />
ear. However, the refer<strong>en</strong>ce int<strong>en</strong>sity for sound in water is 1 micropascal (µPa). Therefore sound<br />
pressure levels in air are not the same as sound pressure levels in water. Wh<strong>en</strong> evaluating sound<br />
measurem<strong>en</strong>ts, the refer<strong>en</strong>ce int<strong>en</strong>sity should always be clearly stated. In water, the refer<strong>en</strong>ce int<strong>en</strong>sity<br />
is typically expressed as dB re 1 µPa @ 1 m.<br />
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