Page 100 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
of anthropogenic underwater noise on the behaviour of fish are particularly difficult to determine
as they are context dependent, and must be statistically based.
Table 14. Criteria suggested for the effects of underwater noise on marine
mammals and fish
Level in dBht (Species) Effect
Less than 50 Mild reaction by minority of individuals
50 to 75 Mild reaction by majority of individuals
75 to 90 Stronger reaction by majority of individuals
90 to 130 Strong avoidance reaction by all individuals and increasing risk of physiological injury
Above 130 Possibility of traumatic hearing damage from single event
Above 140 Risk of lethal injury
* In their decibel hearing threshold (dBht, species) scale a frequency dependent filter is used to weight the sound. The suffix ‘ht’ relates to
the fact that the sound is weighted by the hearing threshold of the species.
(Source: Nedwell et al., 2007)
In terms of vibration, many fish utilise a lateral line sensory system to detect subtle movements
(prey and predators) in the surrounding area through vibrations. Similar to the effects of noise,
large-scale vibrations could mask other signals used by fish to detect prey and evade
predators, whilst also leading to behavioural responses (e.g. avoiding the area). Furthermore,
high level vibrations in close proximity to fish could lead to physical injury (e.g. internal organ
rupture) or even death.
Based on the precautionary assumption that piling may be required as part of the Draft Plan,
the sensitivity of fish and shellfish to noise and vibration is considered to be moderate during
the construction phase of the tidal turbine devices and offshore substations and low during all
other phases/elements of the Draft Plan.
Noise and vibration disturbance during construction of the tidal turbine devices and offshore
substations will generally only be short-term. Given the unconfined nature of the area, any fish
that do pass through areas of disturbance are considered to be able to easily move away from
any temporary noise disturbance and return once the disturbance has ceased. However, given
the relatively large distances that behavioural changes can occur over, exposure to change
from a single tidal array and associated infrastructure (i.e. substation) is considered to be
negligible to medium (assuming piling is required), resulting in an insignificant to moderate
adverse impact. In all other phases, levels of exposure are expected to be low, resulting in an
insignificant to minor adverse impact. The potential concurrent installation of tidal arrays in
Alderney’s territorial waters (see Section 2.2.2) as a result of the Draft Plan is considered to
result in a high level of exposure to change from cumulative noise sources (assuming piling is
required) and an overall moderate to major adverse impact to fish.
5.3.2.4 Toxic contamination (spillage)
There is potential for the spillage of fluids, fuels and/or construction materials into the marine
environment, originating from the survey, construction, decommissioning and maintenance
vessels associated with the tidal device, cabling and offshore substation, in addition to the tidal
device itself. Toxic contaminants may be consumed by the biotic community and result in the
bioaccumulation, particularly in shellfish and the prey of various fish species. The sensitivity of
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