Page 153 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
ship’s echo-sounder or acoustic emissions from a dynamic positioning system would not be
expected to cause widespread disturbance to marine mammals (Scottish Executive, 2007).
For harbour porpoises, the zone of audibility of shipping noise ranges from 1-3km depending
on the frequency of noise emitted by the ship (Thomsen et al., 2006). The Scottish Marine
Wildlife Watching Code advises that the minimum approach distance for vessels to avoid visual
and noise disturbance to dolphins and porpoises is 50m (200-400m for mothers and calves, or
for animals that are clearly actively feeding or in transit). As with fish (Section 5.3.2.3), the key
sources of noise related to construction and device installation are:
ƒ Shipping and machinery;
ƒ Dredging; and
ƒ Pile driving or drilling.
Additionally, cable/pipeline burial requires the use of trenching or jetting machinery in soft
sediments, rock cutting machinery in hard sea-beds, or rock or concrete mattress laying may
be used to protect cables in areas where they cannot be buried.
Of all of the sources of noise noted above, the noise emitted during pile driving is understood to
have the greatest potential effects on marine wildlife (Thomsen et al., 2006). This is due to the
fact that pile driving generates very high sound pressure levels over a relatively broad
frequency range (20Hz to >20kHz). A number of studies have investigated the distances at
which marine mammals may be disturbed as a result of piling particularly associated with
offshore wind farms (Table 23). Based on the findings from these studies it is apparent that,
although hearing injuries from construction are only likely to occur within several hundred
metres of pile driving activity, strong avoidance responses could occur several kilometres from
the piling with masking of vocalization and mild behavioural changes (e.g. change in swimming
direction) occurring as far away as 50km or more from a wind farm development. However, the
levels of noise relates to pile size and most piles used for tidal work will be smaller than those
used for windfarms.
Table 23. Summary of research on the spatial extent of piling noise impacts on
marine mammals
Activity Study Background Information Reference
Pile
driving
Empirical study on
underwater noise levels
during pile-driving at
turbines in NE Scotland
and potential effects on
marine mammals.
Pile-driving noise was measured at distances of
0.1 to 80km (when background noise was no
longer distinguishable above ambient). The
study concluded that for bottlenose dolphins
auditory injury would only have occurred within
100m of the pile-driving and behavioural
disturbance (defined as modifications in
behaviour) could have occurred up to 50km
away.
Bailey et al.
(2010)
Empirical studies of
porpoise behaviour during
construction of offshore
wind farms at Horns Rev
(North Sea) and Nysted
(Baltic).
At the wind farms, acoustic activity of porpoises
decreased shortly after each pile-driving event
and returned to baseline conditions after 3-4h.
This effect was not only observed in the direct
vicinity of the construction site but also at
monitoring stations approximately 15km away.
Behavioural observations showed that during
Tougaard et al.
(2003a; 2003b)
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