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 />
Offshore Wind, 2002). The presence <strong>of</strong> this local crab fishery, which is considered<br />
to be <strong>of</strong> local <strong>and</strong> national importance, led to a FEPA consent condition requiring<br />
a crab surveillance programme to be formulated (Cefas, pers. comm.).<br />
Molluscan shellfish species, such as king scallop (Pecten maximus), mussel<br />
(Mytilus edulis), native oyster (Ostrea edulis) <strong>and</strong> cockle (Cerastoderma edule), do<br />
exhibit avoidance behaviour over very short distances, but are less mobile than<br />
crustacean species <strong>and</strong> likely to be directly impacted by trenching operations.<br />
For most shellfish beds any resulting mortality along the width <strong>of</strong> the cable route<br />
is generally not a significant loss in relation to the remaining population. For<br />
small, isolated beds, however, the physical damage <strong>and</strong> disturbance from cablelaying<br />
operations can be significant.<br />
Mussels settling on the seabed attach to surrounding hard surfaces, including<br />
other adjacent mussels. This behaviour can alter the seabed substrate with the<br />
formation <strong>of</strong> biogenic reefs. These reefs can extend over significant areas <strong>of</strong><br />
seabed creating a rich habitat for other species as well as suitable habitat for<br />
further mussel settlement. Such reefs are widespread, but generally found in<br />
large shallow inlets <strong>and</strong> bays in estuarine areas (Holt et al., 1998; BMT Cordah,<br />
2003). Ploughing through these reefs can in some instances destabilise the reef<br />
by leaving exposed edges prone to damage by wave <strong>and</strong> current action. While<br />
biogenic reefs formed by Mytilus are found to be more tolerant <strong>of</strong> disturbance<br />
than other types <strong>of</strong> biogenic reef such as Sabellaria reefs (Holt et al., 1998) (see<br />
Section 5.3), these species-rich habitats should be avoided where possible.<br />
Noise & vibration<br />
The potential impact <strong>of</strong> noise <strong>and</strong> vibration on the natural fish resource within<br />
the affected area will be largely dependant upon the ‘hearing’ sensitivity <strong>of</strong> the<br />
fish species concerned. In this context three main types <strong>of</strong> fish are recognised:<br />
●<br />
●<br />
●<br />
Hearing specialists: These species, including herring <strong>and</strong> sprat, ‘hear’ sound<br />
through the acoustico-lateralis system; a collective term for the inner ear <strong>and</strong><br />
lateral line. Sound vibrations are also detected by a gas-filled swim bladder<br />
which is connected to the inner ear via a gas duct;<br />
Hearing specialists with mid range sensitivity: These species, including cod,<br />
mackerel <strong>and</strong> salmon, are hearing specialists but are deemed less sensitive<br />
to noise, due largely to the lack <strong>of</strong> a gas duct between the inner ear <strong>and</strong> the<br />
swim bladder; <strong>and</strong><br />
Non-hearing specialists: Typical species include flatfish such as dabs, plaice<br />
<strong>and</strong> sole <strong>and</strong> elasmobranchs such as dogfish. These species are non hearing<br />
specialists <strong>and</strong> do not possess a swim bladder.<br />
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