Page 102 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
elements of the Draft Plan. As previously discussed, the sensitivity to toxic contamination
varies between species and the mobility of shellfish species is reduced compared to fish and,
therefore, overall the sensitivity is considered to range between low to moderate.
It is considered that for the installation and decommissioning of the tidal stream turbines and
offshore substation the exposure to change is negligible to low (Section 4.3.2.3). For cable
routeing the exposure to change is considered to be low. Overall, this will result in an
insignificant to minor adverse impact.
5.3.2.8 Barrier to movement
The presence of sub-surface tidal structures may present a barrier to movement and migratory
pathways depending on array design. Fish are considered particularly vulnerable to any
structures which could act as a barrier that may prevent movement to key foraging or nursery
grounds and therefore their sensitivity to this impact pathway is considered to be moderate.
The significance of any obstruction is also dependent on the spatial confines and size of the
array (e.g. whether it spans across the entire mouth of an estuary). Given the unconfined
nature of the study area, the turbines are not considered likely to act as a barrier to movement.
Therefore, the exposure to change is considered to be low, resulting in an insignificant to
minor adverse impact.
5.3.2.9 Introduction of new structures
The construction and decommissioning activities of the tidal turbine devices and offshore
substations may provide new habitat and suitable conditions for wildlife to flourish. In time, the
structures may be colonised and used as artificial reefs by the marine community and much
research has been conducted on fish aggregating devices (FADs); floating or moored
structures which attract fish and provide new habitat. A number of reasons why fish are
attracted to FADs have been hypothesised by Freon and Dagorn (2000); these include shelter
from predators, concentration of food supply, spatial reference in otherwise featureless
environments, resting opportunities, indicators of other characteristics, such as productive
areas and meeting points.
The introduction of new structures can lead to the modification of the benthic environment by
providing hard substrate upon which sessile organisms can attach (e.g. mussels). In turn, this
could provide an additional food source to other species and lead to increased biodiversity
compared to previous levels due to the artificial reef effects (Wilhelmsson et al., 2006; Linley et
al., 2007). It is therefore possible that the introduction of tidal devices and/or offshore
substations around Alderney will actually increase benthic fish and shellfish stocks, perhaps
even on a commercial scale. In such cases, it would be potentially feasible to leave such
structures on the seabed after the operational period has ceased. This would provide a further
benefit in that no decommissioning activities would be required and, consequently, the
development would have a lesser impact on the surrounding environment. Overall, sensitivity
of fish and shellfish species to change is considered to range from low to moderate, and the
exposure to change is considered to be low given the relatively small footprint of the change in
the context of the study area, resulting in an overall insignificant to minor beneficial impact.
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