Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
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Potential impacts <strong>and</strong> mitigration measures<br />
not be travelling at over 10 knots during installation operations, thus reducing<br />
the risk <strong>of</strong> fatal injury, should a collision occur.<br />
Visual disturbance<br />
Marine mammals may be disturbed by the presence <strong>of</strong> vessels <strong>and</strong> human<br />
activities, particularly in sensitive locations such as in close proximity to seal<br />
haul out sites <strong>and</strong> marine mammal foraging areas. Such disturbance, during<br />
sensitive periods (such as the breeding <strong>and</strong> pupping season <strong>of</strong> seals), may<br />
lead to significant impacts such as the ab<strong>and</strong>onment <strong>of</strong> young <strong>and</strong> reduced<br />
reproductive success (Brown <strong>and</strong> Prior, 1997).<br />
Underwater noise<br />
There is increasing concern over the impacts <strong>of</strong> underwater noise as a result<br />
<strong>of</strong> anthropogenic activities upon marine life in general. This issue is <strong>of</strong> greater<br />
relevance to marine mammals, given both their physiological capacity for<br />
detecting <strong>and</strong> responding to sound, <strong>and</strong> the high levels <strong>of</strong> protection that they<br />
are afforded.<br />
The sources <strong>and</strong> intensities <strong>of</strong> sound associated with <strong>of</strong>fshore wind farm<br />
construction <strong>and</strong> the related impact on marine life has been investigated by<br />
Nedwell et al. (2003) <strong>and</strong> Nedwell & Howell (2004). Further useful information is<br />
provided in Jansy et al. (2005) <strong>and</strong> Madsen et al. (2006). The impact <strong>of</strong> noise on<br />
marine mammals can be divided into three levels:<br />
●<br />
●<br />
●<br />
Those that cause fatal injury;<br />
Those that cause non-fatal injury such as deafness <strong>and</strong> other auditory damage<br />
such as temporary threshold shift (TTS); <strong>and</strong><br />
Those that cause behavioural change (e.g. avoidance, cessation <strong>of</strong> feeding<br />
etc.).<br />
Similarly to the impacts <strong>of</strong> underwater noise on fish, available information<br />
suggests that species <strong>of</strong> marine mammal will show a strong avoidance reaction<br />
to sound levels <strong>of</strong> 90 dB ht (species) <strong>and</strong> above. It is, however, considered highly<br />
unlikely that cable installation would produce noise at a level that would cause<br />
a behavioural reaction in marine mammals. For a more detailed discussion <strong>of</strong><br />
the dB ht (species) measurement, an example <strong>of</strong> where the measurement has<br />
been applied to cable installation <strong>and</strong> the likely levels <strong>of</strong> effect on both marine<br />
mammals <strong>and</strong> fish, see Section 5.4.2.<br />
Entanglement<br />
The risk <strong>of</strong> marine mammals becoming entangled in a cable under low<br />
tension, or in any other lines used to connect the installation tool to the vessel,<br />
is considered to be extremely limited. Most seals <strong>and</strong> cetaceans would be<br />
expected to avoid areas <strong>of</strong> human activity <strong>and</strong> significant disturbance <strong>and</strong>, as<br />
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