Publication - Publication

Offshore wind energy - draft sectoral marine plan: habitat regulations appraisal

Published: 18 Dec 2019
Directorate:
Marine Scotland Directorate
Part of:
Energy, Marine and fisheries
ISBN:
9781839603754

The habitats regulations appraisal is completed in accordance with the Habitats Regulations that implement the EC Habitats and Birds Directives in UK waters and has been completed for the sectoral marine plan for offshore wind.

Contents
Offshore wind energy - draft sectoral marine plan: habitat regulations appraisal
8 Potential for Adverse Effects on Fish and Freshwater Pearl Mussel Features

8 Potential for Adverse Effects on Fish and Freshwater Pearl Mussel Features

8.1 Introduction

8.1.1 Following the screening process, a total of 468 European/Ramsar sites were identified for which there is a LSE (or the potential for a LSE cannot be excluded) (Table C1, Appendix C). Of these sites, a number of European/Ramsar sites were identified as it was not possible to conclude that there would be no LSE from the Sectoral Offshore Wind Plan on qualifying fish or freshwater pearl mussel interest features.

8.1.2 Given the broad area covered by the draft Plan and the large number of sites screened into these assessments, the same method as agreed in previous HRAs [237] [238] [239] has been used where it is not necessary to individually review the full list of all sites and the qualifying fish and freshwater pearl mussel interest features that they support within this report.  The individual sites that were screened in for each of the 17 DPOs are shown in the schedules (Tables D1-D17) and maps (Figures E1-E17).  The locations of screened in SAC and Ramsar sites with qualifying fish and/or pearl mussel features beyond the 100 km buffer are provided in Appendix F (Figure F8).

8.1.3 European sites support additional fish species as ‘typical species of habitat’ features; for example, sparling (the European smelt Osmerus operlanus). The impact pathways for these supporting features are considered to be the same as for qualifying interest fish features and have, therefore, not been considered separately and specifically as part of this assessment. It is recognised that differences in their life histories may mean they are more (or less) susceptible to impacts than other species and this may in turn influence the levels of risk that are relevant and, at a project-level, the detailed requirements for mitigation. However, the assessment process has been undertaken and the mitigation measures selected such that they encompass all the levels of risk to relevant qualifying species.

8.1.4 Some of these SACs and Ramsar sites also contain other interest features for which it could not be concluded that there was no LSE (e.g. otter) and these are reviewed separately under the relevant section(s) that encompass these other habitat/species groups in this report. In addition, where there are interest features at these sites which have been ‘screened out’ because there will be no LSE then these are also recorded (Table C1).

8.1.5 In summary, the screening phase concluded that there is a possibility of a LSE (or that it was not possible to conclude no LSE) for the following fish and freshwater pearl mussel features:

  • Atlantic salmon Salmo salar (1106);
  • Sea lamprey Petromyzon marinus (1095);
  • River lamprey Lampetra fluviatilis (1099);
  • Allis shad Alosa alosa (1102);
  • Twaite shad Alosa fallax (1103); and
  • Freshwater pearl mussel Margaritifera margaritifera (1029).

8.1.6 To assess whether there is any adverse effect on the integrity of relevant European/Ramsar sites, the following sections review the sensitivities of the associated qualifying fish and freshwater pearl mussel features, identify the conservation objectives and assess, in tabular format, the effects arising in the context of the proposed plan-level mitigation measures.

8.2 Sensitivities of Fish Interest Features to Sectoral Offshore Wind Plan Activities

8.2.1 This section reviews the sensitivities that are relevant for the fish interest features.  These reviews focus on the fish species because any effect on freshwater pearl mussel will only arise as an indirect consequence of effects on Atlantic salmon. Initially a generic review of the sensitivities is presented under the impact pathways identified during the screening phase:

  • Physical loss/gain of habitat (Loss of Onshore and Offshore Habitat);
  • Physical Loss/Gain of Habitat (Fish Aggregation);
  • Physical Damage to Habitat (Reduction in Foraging Habitat Quality);
  • Physical Damage to Species (Collision Risk);
  • Non-Physical Disturbance (Noise Disturbance causing Barrier or Exclusion Effects);
  • Non-Physical Disturbance (Electromagnetic field);
  • Toxic Contamination (Contamination and Spillages); and
  • Non-toxic Contamination (Increased Turbidity).

8.2.2 Following this review, the general sensitivities for the relevant interest features are identified and tabulated in addition to the impact pathways.

8.3 Physical Loss/Gain of Habitat (Damage to Onshore and Offshore Habitat; Impact Pathway 2)

8.3.1 Although the direct loss of freshwater habitats may occur as a result of cable installation or any landside infrastructure works, the potential effects from terrestrial development are outside the scope of the plan level HRA.  However, there is potential for loss of migratory fish foraging areas or pearl mussel habitat in marine and estuarine environments. This could be a habitat that is designated for qualifying features (in which case there would be the highest risk of an effect) or it could be located along the migratory routes of fish.

8.3.2 It is anticipated that any sensitive habitats would be avoided wherever possible and during the construction period that the worst-case scenario would involve temporary effects.

8.3.3 Damage to offshore habitats during the operation phase may influence foraging areas for migratory fish species. However, the high mobility and ranges of this group of fish will enable them to use other offshore foraging areas if required.

8.4 Physical Loss/Gain of Habitat (Fish Aggregation; Impact Pathway 3)

8.4.1 Many fish are attracted to solid man-made structures and artificial reefs are often deployed to enhance fisheries [240]. Structures constructed for other purposes such as oil platforms and breakwaters [241] can also serve as new habitats for fish. However, unlike for some fish species, the presence of windfarm infrastructure is unlikely to result in the direct aggregation of migratory fish such as Atlantic salmon.

8.4.2 Subsea structures can change local abiotic conditions allowing species assemblages to form that are different from the natural communities present. The monopiles of turbines, for example, become encrusted with epibiota such as mussels and barnacles [242]. These modify the habitat and provide food and shelter for fish and invertebrate species leading to increased fish abundance and enhancement of the local seabed habitat [243].

8.4.3 While it is unlikely that the windfarm devices would result in aggregation of migratory fish species, their presence may attract prey species and therefore indirectly attract migratory fish. Wilhelmsson et al. [244] investigated this potential for devices to function as artificial reefs and Fish Aggregation Devices (FADs). Fish abundance was found to be greater in the vicinity of the turbines than in surrounding areas, while species richness and Shannon-Wiener diversity (H′) were similar.

8.5 Physical Damage to Habitat (Reduction in Foraging Habitat Quality; Impact Pathway 6)

8.5.1 There is potential for damage to migratory fish foraging areas in marine and estuarine environments from cable routeing and at landfall. This could be a habitat that is designated for migratory fish or freshwater pearl mussel qualifying features (in which case there would be the highest risk of an effect) or it could be located along the migratory routes of fish.

8.5.2 In offshore locations, baseline survey work (e.g. boreholes and trawls), installation, maintenance and removal of cables and turbines could all potentially result in a reduction of foraging habitat quality and prey species availability, as a result of physical disturbance.

8.6 Physical Damage to Species (Collision Risk; Impact Pathway 8)

8.6.1 The ability for fish to avoid a potential collision with an object is dependent on sensory capabilities (such as vision and hearing), perception levels and swimming speeds of the species.  As lamprey could be attached to a range of different pelagic and demersal species while undertaking the marine phase of the lifecycle, general information on fish sensitivity to collisions is considered.

8.6.2 Marine animals in high latitude coastal areas have to contend with variable and often poor visual conditions, resulting from fluctuations in ambient light levels and in the light transmission properties of the water.  Fish have well developed eyes and the variety of colour patterns and specific movements that they display invites comparisons between the most visually orientated species among birds and mammals [245] [246].

8.6.3 Fish have been recorded colliding or becoming entrapped within a range of anthropogenic structures such as fishing nets and power station intakes [247] [248].  The level of light and clarity of water are important factors in fish collision risk.  In poor visibility conditions, fish have been observed only just avoiding collision with an obstacle, whereas in good visibility conditions, fish react further away from otter trawl boards and swim over/under/around trawls [249].  More recent experiments quantified the light level thresholds for the visual reactions of mackerel to monofilament netting were -1 log lux and - 4 log lux (1 - 0.001 lux) for multifilament [250].  At light levels below these thresholds, fish were unaware of the netting barriers and swam straight through them.

8.6.4 Fish may avoid collisions with an object through "startle" (or "C-start") responses.  The C-start response can be initiated by transient sound, visual or touch stimuli.  For example, herring escape behaviour is a reflex response stimulated by transient sound stimuli, detected in the labyrinth (inner ear) [251].  ‘Visually looming’ objects will also trigger evasion behaviour in most if not all species, with a greater response rate to edges moving horizontally rather than vertically [252].  The behavioural response to an approaching net is to turn and swim in the direction of the moving net, using the minimum swimming speed to avoid the object (resulting in them ‘holding position’ at the mouth of the net) whilst reserving energy for an escape response.  However, on exhaustion, the fish turn and allow the net mouth to overtake them [253].

8.7 Non-Physical Disturbance (Barrier or Exclusion Effects; Impact Pathway 9)

8.7.1 Salmon and lamprey are highly mobile species that undergo large seasonal movements and migrations to forage and breed [254] [255] [256].  They can, therefore, be particularly vulnerable to any structures which could act as a barrier, preventing movement to key foraging or nursery grounds.

8.7.2 However, the presence of offshore wind turbines is unlikely to prevent movement for these highly mobile and wide-ranging species who could circumvent the arrays if required.

8.8 Non-Physical Disturbance (Noise/vibration Disturbance; Impact Pathway 11)

8.8.1 Sound has two components: sound pressure and particle motion. All fish can sense the particle motion component of an acoustic field via the inner ear as a result of whole-body accelerations [257], and noise detection (‘hearing’) becomes more specialised with the addition of further hearing structures.  Although many fish are also likely to detect sound pressure, particle motion is considered equally or potentially more important [258]. Particle motion is especially important for locating sound sources through directional hearing [259] [260] [261].

8.8.2 From the few studies of hearing capabilities in fishes that have been conducted, it is evident that there are potentially substantial differences in auditory capabilities from one fish species to another [262].  Since it is impossible to determine hearing sensitivity for all fish species, one approach to understand hearing has been to distinguish fish groups on the basis of differences in their anatomy and what is known about hearing in other species with comparable anatomy.  Popper et al. [263] proposed categories based on anatomical differences:

  • Fishes with no swim bladder or other gas chamber – e.g. lamprey.  These species are sensitive only to sound particle motion and show sensitivity only to a narrow band of frequencies.
  • Fishes with swim bladders in which hearing does not involve the swim bladder or other gas volume – e.g. salmonids, such as Atlantic salmon; European eel.  Salmonids are more sensitive to particle motion than sound pressure [264] [265] and European eel is sensitive to both particle motion and sound pressure [266] [267].
  • Fishes in which hearing involves a swim bladder or other gas volume – e.g. clupeids such as shad species.  These species are primarily sensitive to sound pressure, although they also detect particle motion [268].

8.8.3 Particle motion rather than sound pressure is considered to be potentially more important to fish without swim bladders, salmonids and European eel.  However, there is no published literature on the levels of particle motion generated during construction activities (e.g. pile-driving and dredging) and the distance at which they can be detected).  This may be due to the fact that there are far fewer devices (and less expertise in their use) for detection and analysis of particle motion compared to hydrophone devices for detection of sound pressure [269].  Direct measurements of particle motion have also been hampered by the lack of guidance on data analysis methods.

8.8.4 Steps that are required to improve knowledge of the effects of particle motion on marine fauna have recently been set out [270]. However, at present there continues to be a lack of particle motion measurement standards, lack of easy to use and reasonably priced instrumentation to measure particle motion, and lack of sound exposure criteria for particle motion.  As such, the scope for considering particle motion in underwater noise assessments is currently limited [271].  Hence, this review considers the effects of sound pressure rather than particle motion.

8.8.5 The extent to which intense underwater sound might cause an adverse environmental impact in a particular fish species is dependent upon the level of sound pressure or particle motion, its frequency, duration and/or repetition [272].  The range of potential effects from intense sound sources, such as pile driving, includes immediate death, permanent or temporary tissue damage and hearing loss, behavioural changes and masking effects.  Tissue damage can result in eventual death or may make the fish less fit until healing occurs, resulting in lower survival rates.  Hearing loss can also lower fitness until hearing recovers.

8.8.6 Behavioural changes can potentially result in animals avoiding migratory routes or leaving feeding or reproduction grounds with potential population level consequences.  Biologically important sounds can also be masked where the received levels are marginally above existing background levels [273].  The ability to detect and localise the source of a sound is of considerable biological importance to many fish species and is often used to assess the suitability of a potential mate or during territorial displays and during predator prey interactions.

8.8.7 Published noise exposure criteria for fish are included in Table 17. The Popper et al. [274] peak Sound Pressure Level (SPL) and cumulative Sound Exposure Level (SEL) criteria for piling driving can be used to determine the mortality/potential mortal injury and recoverable injury for each of the fish hearing categories described above.  These criteria are based on an understanding that fish will respond to sounds and their hearing sensitivity.  However, there is a lack of specific data on exposure or received levels that enable guideline thresholds to be provided for all fish hearing categories.

8.8.8 While these noise exposure criteria provide thresholds for auditory impairment, there are many data gaps that preclude the setting of specific noise exposure criteria for behavioural responses in fish [275] [276] [277].  The onset of behavioural responses is much more difficult to quantify as reactions are likely to be strongly influenced by behavioural or ecological context and the effect of a particular response is often unclear and may not necessarily scale with received sound level [278] [279] [280].  In other words, behaviour may be more strongly related to the particular circumstances of the animal, the activities in which it is engaged, and the context in which it is exposed to sounds [281] [282].  For example, a startle or reflex response to the onset of a noise source does not necessarily lead to displacement from the ensonified area.

8.8.9 This uncertainty is further compounded by the limitations of observing fish behavioural responses in a natural context.  Few studies have conducted behavioural field experiments with wild fish and laboratory experiments may not give a realistic measure of how fish will respond in their natural environment [283] [284] [285].  As a consequence, only hearing data based on behavioural experiments is acceptable for assessing the ability of fish to detect sound [286].

8.8.10 Recent studies have considered approaches to quantify the risk of behavioural responses, for example through dual criteria based on dose-response curves for proximity to the sound source and received sound level [287].  An empirical behavioural threshold could also be adopted using in situ observed responses of fish to similar sound sources [288].  A study observing the responses of caged fish to nearby air gun operations found that initial increases in swimming behaviour may occur at a level of 156 dB re 1µPa rms [289].  At levels of around 161-168 dB re 1µPa rms active avoidance of the air gun source would be expected to occur [290] [291].  These responses may however differ from those of unconfined fish.

8.8.11 More recent work has been undertaken by Hawkins et al. [292] reporting behavioural responses of schools of wild sprat and mackerel to playbacks of pile driving.  At a single-pulse peak-to-peak SPL of 163 dB re 1 μPa (equivalent to peak SPL of 157 dB re 1 μPa and SEL of 135 dB re 1 μPa2 s), schools of sprat and mackerel were observed to disperse or change depth on 50 % of presentations.  Sprat and mackerel have specialised hearing structures.  This threshold is likely to be an indicator of more subtle behavioural responses in fish without specialised hearing structures (i.e. salmonids, European eel and lampreys).

Table 17: Fish noise exposure criteria

Fish Hearing Group Mortality/ Potential Mortal Injury Recoverable Injury Behaviour/ Displacement
Swim bladder involved in hearing > 207 dB re 1 μPa > 207 dB SELcum > 207 dB re 1 μPa > 203 dB SELcum > 157 dB re 1 μPa > 135 dB SELsingle
Swim bladder is not involved in hearing
(particle motion detection)
> 207 dB re 1 μPa > 210 dB SELcum > 207 dB re 1 μPa > 203 dB SELcum  
No swim bladder
(particle motion detection)
> 213 dB re 1 μPa > 219 dB SELcum > 213 dB re 1 μPa > 216 dB SELcum  
SELcum denotes cumulative SEL with a reference value of 1 μPa2 s over a 24-hour period. SELsingle denotes single pulse SEL with a reference value of 1 μPa2 s over a 1 second period. All criteria are presented as sound pressure even for fish without swim bladders since no data for particle motion exists [293].  

8.8.12 Potential behavioural effects in the past have also been inferred by comparing the received sound level with the auditory threshold of marine fauna.  Richardson et al. [294] and Thomsen et al. [295], for example, have used received levels of noise in comparison with the corresponding hearing thresholds of marine fauna in order to estimate the range of audibility and zones of influence from underwater sound sources.  This form of analysis has been taken a stage further by Nedwell et al. [296], where the underwater noise is compared with receptor hearing threshold across the entire receptor auditory bandwidth in the same manner that the dB(A) is used to assess noise sources in air for humans.  These include behavioural thresholds, where received sound levels around 90 dB above hearing threshold (dBht) are considered to cause a strong behavioural avoidance, levels around 75 dBht a moderate behavioural response and levels around 50 dBht a minor response.

8.8.13 The dBht criteria have been applied in a number of offshore renewables EIAs and the Environment Agency has previously recommended it to be used in impact assessments in coastal/estuarine environments [297] [298].  However, it is worth noting that the dBht criteria have not been validated by experimental study and have not been published in an independent peer-reviewed paper.  The dBht approach does not take into account potential for sound sensitivity to changes with that of the life stage of the organism, time of year, animal motivation, or other factors that might affect hearing and behavioural responses to sound [299].  Furthermore, the dBht criteria are based on measures of inner ear responses and should rather be based on behavioural threshold determinations [300] [301].  The use of dBht criteria is therefore not recommended for underwater noise assessments [302].

8.8.14 Disturbance effects on migratory fish from noise are most likely to occur during the construction phase of a wind farm. The potential for activities such as impact piling, means migratory fish are all assessed as highly sensitive to noise during construction.

8.9 Non-Physical Disturbance (Electromagnetic Field; Impact Pathway 12)

8.9.1 Power export cables generate an electromagnetic field (EMF) with two components: an electric (E) field contained within the cable by armouring and a magnetic (B) field that can be detected outside of the cable.  The magnetic field also produces an induced electric field (iE) outside the cable.

8.9.2 Potential impacts could result from repulsion effects, leading to exclusion of animals from an area of seabed, attraction effects and disruption to migrations for magnetically sensitive species such as eels and salmonids that may use the earth’s geomagnetic field for navigational cues[303].  Although Atlantic salmon may be sensitive to the magnetic fields associated with operational cables, their navigation and migration is unlikely to be affected based on existing evidence [304] [305]. For example, Armstrong et al.[306] found no significant differences in approach, traverse or departure times of large Atlantic salmon to activated Helmholtz coils and no significant difference in the numbers of small post-smolts passing through the coils, in relation to magnetic field intensity.

8.9.3 River lamprey and sea lamprey are considered to be magnetically and electrically sensitive [307].  However, like most UK species that are EM-sensitive, knowledge of their interaction with anthropogenic EMFs is limited.  A recent review by Gill and Bartlett [308] confirmed the limitations of understanding about the effects on fish species.  It concluded that, based on current knowledge, Atlantic salmon S. salar, Sea trout S. trutta or European eel A. anguilla may respond to B or iE fields generated from subsea power cables, either by short-term attraction or avoidance.  If such behaviour occurs, then they noted that it may waste time and energy for the fish, and perhaps be a causal effect in delayed migration or alterations to movement and distribution.  It was also noted that there was an incomplete understanding about how these species move around their environment and interact with natural, anthropogenic and subsea EMF (and noise).  However, Gill and Bartlett [309] noted that there was no clear evidence that either attraction or repulsion due to anthropogenic EMFs would have an effect on the fish species which they reviewed.

8.9.4 A review by NIRAS on the potential effects of subsea cables, notes how the implications of the potential effects of EMF (if any) originating from subsea cables remain unclear, with no significant impacts found to date[310]. However, much of the literature focuses on elasmobranchs and lampreys with comparatively little understanding on how EMFs can affect other migratory fish or fish species.

8.10 Toxic Contamination (Contamination and Spillages; Pathways 14 and 15

8.10.1 For all phases of the development, there is the potential for accidental discharges/spillages from machinery and vessels. However, adoption of standard safety measures would be employed throughout these phases to reduce the likelihood of accidental spillages occurring.

8.10.2 Leaching of toxic compounds from sacrificial anodes, antifouling paints or leakage of hydraulic fluids (if present) from the device is a potential effect during offshore wind farm operation. Any chemical or microbiological contaminants associated with sediments being resuspended into the water column may be dispersed, redistributed and deposited elsewhere.

8.10.3 There is a risk that some of these contaminants may be temporarily bioaccumulated in the tissues of certain fish prey, such as polychaete worms and marine bivalves, and made available for uptake by feeding fish. The accumulation of moderate or high levels of contaminants in fish can cause or contribute to a range of lethal and sub-lethal effects, including genetic, reproductive and growth changes. There is less information available on the effects of low levels of contaminants. Pelagic fish, including Atlantic salmon, would experience a lower exposure to contaminated sediments than demersal fish species which remain close to the seabed and feed mainly on benthic organisms. Lampreys attach onto a variety of pelagic and demersal fish species in the marine phase of their lifecycle and so their movements and distribution are largely dictated by their host.

8.11 Non-Toxic Contamination (Increased Turbidity; Pathway 16)

8.11.1 Increased turbidity has been reported to affect salmonids; however, their tolerance to naturally high turbidity levels in estuaries is acknowledged. As all migratory fish species have to spend part of their lifecycle either in or navigating through turbid waters it is considered that they have a high tolerance to this impact pathway. For example, salmon and lamprey successfully pass through estuaries with extremely high suspended sediments such as the Severn and its sub estuaries the Wye, Usk and Parrett, which naturally contain up to several thousand milligrams per litre [311], concentrations as high as 9,000 mg/l have been recorded in the path of runs in the Usk Estuary [312].

8.11.2 Where conditions are particularly adverse, the mobile nature of fish species will generally allow them to avoid such areas. Hence, such impacts will be unlikely to significantly affect a population provided such conditions are temporary.  In the case of migratory fish species; however, the potential significance of an effect can be greater if the increases to suspended sediment were to constitute a barrier to a fish migratory route.

8.11.3 Such conditions would; however, only be significant if they extended across the entire width of a water body, thus comprising the migration route at any given point. Otherwise fish would be able to circumvent the area, avoiding impacts, and thus not inhibiting migration up (or down) stream.  Should significant delay in migration occur, either due to the barrier or as a result of avoidance, these delays may reduce survival rates.  Considering the scope of the Plan for offshore wind farm development, this impact pathway is considered a low risk to migratory fish.

8.11.4 Suspended sediment levels also affect the level of dissolved oxygen (DO), with increased suspended sediments concentrations potentially depleting DO concentrations.

8.11.5 The effects of suspended sediment levels on fish have been considered in a number of studies, including that undertaken by the European Inland Fisheries Advisory Commission [313].  Lethal effects were seldom observed, with Pacific salmon and trout juveniles surviving for 3-4 weeks in suspended sediment concentrations of 300-750 mg/l, which were increased to 2300-6500 mg/l for short periods.  Sub lethal pathological effects included increased mucus production over the body and gills, and at very high suspended sediments, evidence of abrasion and damage to the gill filaments was noted [314].

8.12 Migratory Fish and Freshwater Pearl Mussel Sensitivity Review

8.12.1 Table 18 shows the sensitivities of Atlantic salmon (and freshwater pearl mussel by association) as well as river lamprey, sea lamprey and shad species to the activities associated with the Sectoral Offshore Wind Plan.

Table 18: Potential sensitivities of Atlantic salmon, lamprey and shad features from the Sectoral Offshore Wind Plan

Sensitivity Category Sensitivities Pathway Ref. No. Leasing Activity as identified in Sectoral Offshore Wind Plan HRA (Summary Impact Pathway Description) Survey Construction Operation Decommission
PLG Physical Loss/Gain of habitat 2 Loss of foraging areas from reduction in coastal and offshore habitat due to installation of devices and cable armouring both at the development footprint and outside these areas from associated scour and indirectly from changes to the hydrodynamic regime, as well as from chains anchoring devices disturbing seabed habitat during operation. No impact  No impact  LS No impact 
PLG Physical Loss/Gain of habitat 3 Presence of structures on seabed for the duration of the project resulting in changes to prey and species behaviour (e.g. acting as FAD (Fish Aggregating Device), artificial reef or bird roost). No impact  No impact  LS No impact 
PD Physical Damage to habitat 6 Reduction in quality of foraging areas as result of damage to coastal and offshore habitat from baseline surveys (e.g. boreholes and trawls); from equipment use causing abrasion, damage or smothering during installation; from maintenance and removal of cables/devices or from scour, sediment transport and hydrodynamic change, and damage from chains anchoring devices during operation. No impact LS LS LS
PD Physical Damage to species 8 Collision risk and possible mortality of species due to the presence of devices or from vessels travelling to and from the site (including above and below water collision risk and the influence of lighting); risk of entanglement following a collision with power cables or mooring elements. LS LS LS LS
NPD Non-Physical Disturbance 9 Presence of structures or disturbance (noise or visual) resulting in a barrier to movement, migratory pathways and/or access to feeding grounds depending on array design. No impact  No impact  LS No impact 
NPD Non-Physical Disturbance 11 Noise/vibration disturbance from vessels and other activities during survey work (e.g. seismic exploration and geophysical surveys), construction (e.g. piling, drilling, cable laying), operation (e.g. device noise), maintenance or decommissioning. LS HS LS MS
NPD Non-Physical Disturbance 12 Impacts from Electromagnetic Fields (EMF) and thermal emissions on benthic invertebrates and electromagnetically sensitive fish and cetaceans interfering with prey location and mate detection in some species and creating barriers to migration No impact  No impact  LS No impact 
TC Toxic Contamination 14 Spillage of fluids, fuels and/or construction materials during installation or removal of structures (devices and cables) or during survey/maintenance. LS LS LS LS
TC Toxic Contamination 15 Release of contaminants associated with the dispersion of suspended sediments during installation or removal of structures (devices and cables). No impact  LS No impact  LS
NTC Non-Toxic Contamination 16 Increase in turbidity associated with the release of suspended sediments during installation or removal of structures (devices and cables). No impact  LS No impact  LS
In this table, only the estimated sensitivity levels are shown. The level of risk will be dependent upon exposure.  For instance, there would be a high degree of exposure for migratory fish and freshwater pearl mussel were a development to occur within or near to a European/Ramsar site.  However, at the present time, there is uncertainty regarding the degree of exposure and a worst-case assumption has been made.
LS: Low Sensitivity
LMS: Low to Medium Sensitivity
MS: Medium Sensitivity
HS: High Sensitivity

8.13 Potential Effects on European/Ramsar Sites of the Sectoral Offshore Wind Plan

8.13.1 On the basis of the sensitivities of the relevant interest features the following sections review the typical conservation objectives for these features and the potential effects arising for the screened in European/Ramsar sites

8.13.2 The conservation objectives for the qualifying fish interest features seek to avoid deterioration of the habitats of the qualifying species or significant disturbance to the qualifying species, thus ensuring that the integrity of the site is maintained and the site makes an appropriate contribution to achieving favourable conservation status for each of the qualifying features.  The conservation objectives are to ensure for the qualifying species that the following are maintained in the long term:

  • Population of the species, including range of genetic types for salmon, as a viable component of the site;
  • Distribution of the species within site;
  • Distribution and extent of habitats supporting the species;
  • Structure, function and supporting processes of habitats supporting the species;
  • No significant disturbance of the species;
  • Distribution and viability of the species’ host species (e.g. freshwater pearl mussel); and
  • Structure, function and supporting processes of habitats supporting the species’ host species.

8.13.3 Taking account of the conservation objectives and the plan-level activities to which the key interest features are sensitive, this section reviews the potential effects of the Sectoral Offshore Wind Plan on the integrity of the European/Ramsar sites.  The results are presented in Table 18.

Table 19: Assessment of the potential effects of the Sectoral Offshore Wind Plan on the fish features of relevant European sites

Screened-in sites with these qualifying features are provided in Table C1 (Appendix C) Is There an Adverse Effect on Integrity of any European/Ramsar sites? Is There an Adverse Effect on Integrity
Following Application of Mitigation Measures?
Qualifying and Supporting Feature Summary Impact Pathway  Pathway Ref. No.  Sensitivity Level(s) Commentary, and Relevant Conservation Objective
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Physical Loss/Gain of Habitat (Direct Change to habitat within the development footprint)

Loss of foraging areas from reduction in coastal and offshore habitat due to installation of devices and cable armouring both at the development footprint and outside these areas from associated scour and indirectly from changes to the hydrodynamic regime, as well as from chains anchoring devices disturbing seabed habitat during operation.

2 Sensitivity Level(s) considered to be low (see Table 18 for detail and colour code)

Possibility of an adverse effect on integrity

Further work would be required at project-level to ascertain LSE. However, in advance of considering mitigation measures, it cannot be concluded that there will be no AEOI on any European/Ramsar sites. This is because of the inherent uncertainties such as:

  • the detail of the Plan implementation process;
  • future generation capacities;
  • the location, scale and densities of development;
  • the proposed technologies to be used and future advances in these technologies;
  • the scale of the effects arising via some of the defined impact pathways; and
  • the efficacy of some project-level mitigation options.

No adverse effect on integrity

With the application of appropriate and meaningful mitigation measures to accompany the Plan (see Section 11), there will be no AEOI.

Commentary/Risk Review
Atlantic salmon and shad are highly mobile, migratory species undergoing large shifts in distribution during the marine phase of their lifecycle.  Atlantic salmon and shad are also pelagic in lifestyle at sea, having very little association with the seabed.  Unlike certain demersal fish species which could be considered ‘resident’ within the Sectoral Offshore Wind Plan areas, any Atlantic salmon or shad passing through the area can be considered transient. Therefore, any potential damage to the seabed in deployment locations will be of negligible impact to these fish species.

Sea lamprey which attach and then feed on a variety of pelagic and demersal fish species in the marine phase of their lifecycle are unusual in that they could be considered to have similar sensitivities to their host.  However, as sea lamprey are a highly mobile, migratory species which are widely distributed at sea any potential damage to the seabed in deployment locations will be of negligible impact to the sea lamprey.  River lamprey adults live primarily within estuaries before migrating upstream to spawn in freshwater. There would be no direct overlap of the development footprint with river lamprey habitat and/or foraging areas. 

Relevant Conservation Objectives (see Section 8.13)
Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Distribution and extent of habitats supporting the species; and
  • Structure, function and supporting processes of habitats supporting the species.
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Physical Loss/Gain of Habitat (Direct change to habitat around the development footprint)

Presence of structures on seabed for the duration of the project resulting in changes to prey and species behaviour (e.g. acting as FAD (Fish Aggregating Device), artificial reef or bird roost).

3 Sensitivity Level(s) considered to be low (see Table 17 for detail and colour code) As above As above

Commentary/Risk Review
Wilhelmsson et al. [315] investigated the potential for wind turbines to function as artificial reefs and FADs. Fish abundance was found to be greater in the vicinity of the turbines than in surrounding areas, while species richness and Shannon–Wiener diversity (H′) were similar. On the monopiles of the turbines, fish community structure was different, and total fish abundance was greater, while species richness and diversity (H′) were lower than on the surrounding seabed. Blue mussels and barnacles covered most of the submerged parts of the turbines. On the seabed, more blue mussels and less red algae were recorded compared to adjacent areas.

A gill netting survey at the Svante Wind Farm, Sweden, found higher numbers of cod within two hundred metres of an operating turbine compared to the surrounding open waters, and higher still when the turbines were not operating [316]. Diver held video surveys of the North Hoyle offshore wind farm piles found extremely high densities of juvenile whiting, apparently feeding on dense populations of amphipods amongst the fouling biota on the piles [317]. However, it is generally agreed that fish aggregation probably represents a very minor effect[318].  

Relevant Conservation Objectives (see Section 8.13)
All conservation objectives are particularly relevant to this impact pathway:
  • Population of the species as a viable component of the site, including range of genetic types for salmon;
  • Distribution of the species within site;
  • Distribution and extent of habitats supporting the species;
  • Structure, function and supporting processes of habitats supporting the species;
  • No significant disturbance of the species;
  • Distribution and viability of freshwater pearl mussel host species; and
  • Structure, function and supporting processes of habitats supporting freshwater pearl mussel host species.
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Physical damage to habitat (indirect and temporary damage to habitat)

Reduction in quality of foraging areas as result of damage to coastal and offshore habitat from baseline surveys (e.g. boreholes and trawls); from equipment use causing abrasion, damage or smothering during installation; from maintenance and removal of cables/devices or from scour, sediment transport and hydrodynamic change, and damage from chains anchoring devices during operation.

6 Sensitivity Level(s) considered to be low (see Table 17 for detail and colour code) As above As above

Commentary/Risk Review
When considering the impacts on foraging habitat quality, the issues are the same as for foraging habitat quality loss (see Impact pathway 2).  Atlantic salmon and shad are highly mobile, migratory species undergoing large shifts in distribution during the marine phase of their lifecycle.  Atlantic salmon and shad are also pelagic in lifestyle at sea, having very little association with the seabed.  Unlike certain demersal fish species which could be considered ‘resident’ in DPO locations, any Atlantic salmon or shad passing through the area will be considered transient.  Therefore, any potential damage to foraging areas at DPO locations will have a negligible impact on these fish species.

Sea lamprey which attach and then feed on a variety of pelagic and demersal fish species in the marine phase of their lifecycle are unusual in that they could be considered to have similar sensitivities to their host.  However, as sea lamprey are a highly mobile, migratory species which are widely distributed at sea any potential damage to the seabed in deployment locations will have a negligible impact on this species.  River lamprey adults live primarily within estuaries before migrating upstream to spawn in freshwater. There would be minimal overlap of the development activities with river lamprey foraging areas.

Relevant Conservation Objectives (see Section 8.13)
Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Distribution and extent of habitats supporting the species; and
  • Structure, function and supporting processes of habitats supporting the species.
  • tlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Physical Damage (direct damage to species from collision risk)

Collision risk and possible mortality of species due to the presence of devices or from vessels travelling to and from the site (including above and below water collision risk and the influence of lighting); risk of entanglement following a collision with power cables or mooring elements.

8 Sensitivity Level(s) considered to be low (see Table 17 for detail and colour code) As above As above

Commentary/Risk Review
Behavioural responses of fish to perceived threats can be broadly categorized in two ways: avoidance and evasion.  Hence with respect to wind turbine structures, fish may demonstrate two types of response: long range avoidance (i.e. avoiding the area within the vicinity of the device) or close-range evasion depending upon the distance at which the device is perceived and the subsequent behavioural response. Long range avoidance in the context of this report is considered to be avoidance at distances further away than where a visual response can be undertaken i.e. through noise and vibration cues.  Close range evasion is considered to be at distances where the primary stimulus for the response is triggered by a visual reaction to physical characteristics of the device.

The essentially static base of a wind turbine (irrespective of technology) means that collision risk is unlikely. Fish have been recorded colliding with anthropogenic structures, but generally only in areas of poor visibility [319].  

Relevant Conservation Objectives (see Section 8.13)
Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Population of the species as a viable component of the site, including range of genetic types for salmon;
  • Distribution of the species within site;
  • No significant disturbance of the species;
  • Distribution and viability of freshwater pearl mussel host species; and
  • Structure, function and supporting processes of habitats supporting freshwater pearl mussel host species.
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Non-Physical Disturbance

Barrier to movement from the presence of sub-surface structures and disturbance (noise or visual) which may block migratory pathways or access to feeding grounds depending on array design

9 Sensitivity Level(s) considered to be low (see Table 17 for detail and colour code) As above As above

Commentary/Risk Review
Wind turbine arrays will pose minimal barrier effects to the highly mobile migratory fish species.

The significance of any obstruction is partly dependent on the spatial confines and size of the devices and array, e.g. whether it spans across the entire mouth of an estuary, and the functional use of the area by fish.  Considering the scope of the Plan the significance of an effect from this impact pathway would be negligible for migratory fish species.

Relevant Conservation Objectives (see Section 8.13)
Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Population of the species as a viable component of the site, including range of genetic types for salmon;
  • Distribution of the species within site;
  • No significant disturbance of the species;
  • Distribution and viability of freshwater pearl mussel host species; and
  • Structure, function and supporting processes of habitats supporting freshwater pearl mussel host species.
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Non-Physical Disturbance

Noise/vibration disturbance from vessels and other activities during survey work (e.g. seismic exploration and geophysical surveys), construction (e.g. piling, drilling, cable laying), operation (e.g. device noise), maintenance or decommissioning.

11 Sensitivity Level(s) maximum considered to be high (see Table 17 for detail and colour code) As above As above

Commentary/Risk Review
Noise associated with installation activities might arise from vessel traffic, possible requirements for bed levelling, driving and drilling of piles, and installation of the power export cable (i.e. ploughing through sediment areas, rock cutting in hard sea beds, bolting to the sea bed and/or directional drilling).  There is an ever-increasing understanding of the source noise levels and frequencies associated with the marine construction activities of offshore wind farms [320] [321].  The impacts from pile driving and the use of explosives are of most concern (IECS, 2007).  Studies indicate that some exposures can result in changes or damage to sensory structures and hearing capabilities, with mortality even occurring in extreme cases [322] [323]).

Behavioural changes can potentially result in animals avoiding migratory routes or leaving feeding or reproduction grounds with potential population level consequences.  Biologically important sounds can also be masked where the received levels are marginally above existing background levels [324].  The ability to detect and localise the source of a sound is of considerable biological importance to many fish species and is often used to assess the suitability of a potential mate or during territorial displays and during predator prey interactions.

Disturbance effects on migratory fish from noise are most likely to occur during the construction phase of a wind farm. The potential for activities such as impact piling, means migratory fish are all assessed as highly sensitive to noise during construction.

Relevant Conservation Objectives (see Section 8.13) Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Population of the species as a viable component of the site, including range of genetic types for salmon;
  • Distribution of the species within site;
  • No significant disturbance of the species;
  • Distribution and viability of freshwater pearl mussel host species; and
  • Structure, function and supporting processes of habitats supporting freshwater pearl mussel host species.
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Non-Physical Disturbance

Impacts from Electromagnetic Fields (EMF) and thermal emissions on benthic invertebrates and electromagnetically sensitive fish and cetaceans interfering with prey location and mate detection in some species and creating barriers to migration

12 Sensitivity Level(s) considered to be low (see Table 17 for detail and colour code) As above As above
Commentary/Risk Review
The generated magnetic fields from wind farm developments are likely to be perceived by Atlantic salmon, and other migratory species, as a new localised addition to the heterogeneous pattern of geomagnetic anomalies already occurring naturally and anthropogenically in the sea.  However, the expected magnetic field from a cable (up to a few micro Tesla (μT) is very small, particularly relative to the Earth’s own magnetic field (approximately 50 μT) (PMSS Ltd, 2007). The conclusion of most project-specific environmental impact assessments is that whilst there could be an interaction between these species and the subsea cables, the result is unlikely to be of any significance at a population level[325]
Relevant Conservation Objectives (see Section 8.13)
Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Population of the species as a viable component of the site, including range of genetic types for salmon;
  • Distribution of the species within site;
  • No significant disturbance of the species;
  • Distribution and viability of freshwater pearl mussel host species; and
  • Structure, function and supporting processes of habitats supporting freshwater pearl mussel host species.
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Toxic Contamination

Spillage of fluids, fuels and/or construction materials during installation or removal of structures (devices and cables) or during survey/maintenance.

14 Sensitivity Level(s) considered to be low (see Table 17 for detail and colour code) As above As above

Commentary/Risk Review
For all phases of the development, there is the potential for accidental discharges/spillages from machinery and vessels. However, adoption of standard safety measures would be employed throughout all phases of the project to reduce likelihood of accidental spillages occurring. The quantities and toxicities associated with sacrificial anodes and antifouling coatings are generally expected to be extremely small, and therefore this potential effect will be of negligible significance.

Should this impact occur it is not possible to make any realistic estimate of the geographical extent of any contamination impact due to the large numbers of variables involved (quantities leaked, metocean conditions, etc) [326].  Accidental leakage of hydraulic fluids may be more significant, should they occur through storm damage, device malfunction of, or collision with, navigating vessels.  However, the probability of large amounts of oil or hydraulic fluids entering the environment as a result of a major structural failure or spill is very low.  

Relevant Conservation Objectives (see Section 8.13)
Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Population of the species as a viable component of the site, including range of genetic types for salmon;
  • Distribution of the species within site;
  • No significant disturbance of the species;
  • Distribution and viability of freshwater pearl mussel host species; and
  • Structure, function and supporting processes of habitats supporting freshwater pearl mussel host species.
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Toxic Contamination

Release of contaminants associated with the dispersion of suspended sediments during installation or removal of structures (devices and cables

15 Sensitivity Level(s) considered to be low (see Table 17 for detail and colour code) As above As above
Commentary/Risk Review
Sediments are generally expected to be low in contaminant concentrations within the DPO locations, given the characteristically high-energy environments in which the devices will be located and their offshore localities. The large volumes of water and highly dispersive and diluting nature of the surrounding waters will minimise any effects on water quality should contaminants be resuspended.  
Relevant Conservation Objectives (see Section 8.13)
Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Population of the species as a viable component of the site, including range of genetic types for salmon;
  • Distribution of the species within site;
  • No significant disturbance of the species;
  • Distribution and viability of freshwater pearl mussel host species; and
  • Structure, function and supporting processes of habitats supporting freshwater pearl mussel host species.
  • Atlantic salmon
  • Sea lamprey
  • River lamprey
  • Allis shad
  • Twaite shad
  • Freshwater pearl mussel (indirectly)

Non-Toxic Contamination

Increase in turbidity associated with the release of suspended sediments during installation or removal of structures (devices and cables).

16 Sensitivity Level(s) considered to be low (see Table 17 for detail and colour code) As above As above
Commentary/Risk Review
Migratory fish regularly transit through estuaries with extremely high suspended sediments and therefore can be considered largely tolerant of turbid conditions.  The characteristically high-energy offshore environments in which the devices will be located will assist in the dispersion of any localised increases in turbidity, thus minimising any impacts on water quality.
Relevant Conservation Objectives (see Section 8.13)
Of the conservation objectives, the following are particularly relevant to this impact pathway:
  • Population of the species as a viable component of the site, including range of genetic types for salmon;
  • Distribution of the species within site;
  • No significant disturbance of the species;
  • Distribution and viability of freshwater pearl mussel host species; and
  • Structure, function and supporting processes of habitats supporting freshwater pearl mussel host species.

Contact

Email: drew.milne@gov.scot