Appendices 5-13 - Nautilus Cares - Nautilus Minerals

slowly, or moves independently of any nearby whales (i.e. no deliberate approaches). The
noise is also predicted to be reasonably constant in nature - that is there would normally
be few sharp changes in noise level with time. Watkins (1986) and McCauley et. al.
(1996) have shown that rapidly approaching or rapidly increasing noise may constitute a
threat to whales and that vessel noises which are erratic and involve many sharp changes
in levels over short time scales are more likely to cause adverse behavioural reactions.
Hence it is probable that under normal activities nearby marine mega fauna will be aware
of the mining vessel from hundreds of km, and may approach it to approximately 15 km.
Given the continual and constant nature of the noise it is probable that some resident
animals may quickly habituate, and the noise will not produce any startle or alarm types
of response. Animals resident in the area are also likely to approach the vessel more
closely as they habituate to its presence.
Masking of signals of interest
When a signal (marine animal call) cannot be detected by a listener because of the
presence of noise (potentially the mining vessel noise) then the noise is said to mask the
signal. The masking of signals is a complex function that involves understanding how an
animal hears in the presence of noise, and understanding the character and level of the
masking noise and the signal of interest. Most vertebrates are particularly good at filtering
out noise so as to detect weak signals of interest. Although little is known about the
hearing capabilities of whales, their extensive use of sound and the high and variable
levels of natural background noise in the sea suggest that they have highly adapted
capabilities for detecting signals in noise. For masking to occur the most important factors
are the relative locations of the sender, receiver and masking noise source, the frequency
content and level of the primary signal, the frequency content and level of the masking
signal, and the ambient noise characteristics at the time.
The nature of the mining vessel noise when it is operating in DP mode is that of continual
noise over a wide frequency bandwidth which is intense at the source. This represents the
worst scenario in terms of masking since it implies there are no time brackets free of
masking noise, an animal cannot rely on using a comparatively wide bandwidth signal to
avoid masking since the masking noise is also wide bandwidth, and the noise levels are
high for relatively long ranges around the source. We have not attempted to calculate
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