Summary of potential effects
297 In contrast, behavioural effects are expected over larger ranges, as discussed above. To illustrate this, Figures 9.1 and 9.2 show the modelled underwater noise levels for SPLpk relative to the six SACs designated for Annex II diadromous fish and freshwater pearl mussel taken forward to Appropriate Assessment. Figure 12.1 Open ▸ and Figure 12.2 Open ▸ show noise contours for two hammer energies (i.e. the maximum 4,000 kJ hammer energy and the average maximum hammer energy of 3,000 kJ, respectively) at the south-west modelled location. This location was chosen as it is closest to the coastline and, therefore, most likely to cause barrier effects to diadromous species at that location.
298 Diadromous fish species may experience behavioural effects in response to piling noise, including a startle response, disruption of feeding, or avoidance of an area. These would be expected to occur at ranges of 10 km to 20 km, depending on the species and their relative sensitivities to underwater noise (i.e. in order of lowest to highest sensitivities: lamprey species, Atlantic salmon and sea trout, European eel and shad species). Research from Harding et al. (2016) failed to produce physiological or behavioural responses in Atlantic salmon when subjected to noise similar to piling. However, the noise levels tested were estimated at <160 dB re 1 µPa RMS, below the level at which injury or behavioural disturbance would be expected for Atlantic salmon. Due to the distance between the Proposed Development array area and the coast, these behavioural impacts are unlikely to cause barrier effects between the Proposed Development fish and shellfish ecology study area and the migration routes of diadromous species along the east coast of Scotland, due to the relatively small area around piling events where noise levels are high enough to cause behavioural responses (as demonstrated in Figure 12.1 Open ▸ and Figure 12.2 Open ▸ ). This is the case for both downstream migration of smolts and upstream migration of adults.
299 The low risk of effects on migration of diadromous fish species extends to the freshwater pearl mussel, which is included in the diadromous species assessment, as part of its life stage is reliant on diadromous fish species including Atlantic salmon.
Figure 12.1: Special Areas of Conservation for Annex II Fish with Underwater Noise Contours (Unweighted SPLpk) Associated with the Southwest Piling Location at 4,000 kJ Hammer Energy
Figure 12.2: Special Areas of Conservation for Annex II Fish with Underwater Noise Contours (Unweighted SPLpk) Associated with the Southwest Piling Location at 3,000 kJ Hammer Energy
12.3.2 Increased Suspended Sediment Concentrations and Associated Sediment Deposition
301 Increases in SSC and associated sediment deposition during construction and decommissioning have the potential to cause behavioural responses (avoidance) in migratory fish (see paragraph 315 for further detail). Increases in SSC and associated sediment deposition are predicted to occur during the construction and decommissioning phases as a result of seabed preparation (seabed feature clearance prior to cable installation), the installation/removal of wind turbine and OSP/Offshore convertor station platform foundations and installation/removal of inter-array, interconnector and offshore export cables.
302 Impacts are predicted to be of local spatial extent (i.e. largely within the Proposed Development fish and shellfish ecology study area), short-term duration, and intermittent during construction and decommissioning.
Maximum design scenario relevant to the assessment of adverse effects on integrity
303 The maximum design scenarios considered for the assessment of potential impacts on Annex II diadromous fish from increases in SSC and sediment deposition during construction and decommissioning are set out in Table 12.10 Open ▸ .
Table 12.10: Maximum Design Scenarios Considered for the Assessment of Potential Impacts on Annex II Diadromous Fish from SSC and Sediment Deposition during Construction and Decommissioning
Designed-in Measures Relevant to the Assessment of Adverse Effects on Integrity
304 Designed-in measures (and the associated commitments) of relevance to the assessments of potential impacts on Annex II diadromous fish from increased SSC and associated sediment deposition during construction and decommissioning are set out in Table 12.11 Open ▸ .
Table 12.11: Designed-in Measures Relevant to the Assessment of Adverse Effects on Integrity on European Sites Designated for Annex II Diadromous Fish from Increased SSC and associated Sediment Deposition during Construction and Decommissioning
Information to inform the appropriate assessments
305 The Appropriate Assessments for sites for Annex II diadromous fish are presented in section 9.5. Information common to inform the Appropriate Assessments in presented in this section.
306 The installation of infrastructure within the Proposed Development fish and shellfish ecology study area may lead to increases SSC and associated sediment deposition. Full details of the modelling undertaken to inform this assessment are presented in volume 3, appendix 7.1 of the Offshore EIA Report, including the individual scenarios considered and assumptions within these and full modelling outputs for suspended sediments and associated sediment deposition. For the purposes of this assessment, the following activities have been considered:
- seabed feature clearance prior to cable installation;
- drilling for foundation installation; and
- inter-array, OSP/Offshore convertor station platform interconnector, and offshore export cable installation.
307 Seabed feature (sand wave) clearance for cable installation would involve disturbance of seabed material within a corridor of up to 25 m width for the 20% the Proposed Development offshore export cables, where it is necessary. Modelling of suspended sediments associated with the site preparation showed a large variation. SSC reaches its peak in the disposal phase with concentrations reaching 2,500 mg/l at the release site, but the plume is at its most extensive when the deposited material is redistributed on the successive tides, under these circumstance concentrations of 100 mg/l – 250 mg/l have been modelled (see volume 3 appendix 7.1 of the Offshore EIA Report for further details on modelling assumptions for SSC). The average SSC during the course of the clearance activities showed values less than 100 mg/l with a plume width of 10 km. Sedimentation of deposited material is focussed within 100 m of the site of release with a maximum depth 0.5 m – 0.75 m whilst the finer sediment fractions are distributed in the vicinity at much lesser depths circa 5 mm – 10 mm within a range of hundreds of meters to a small number of kilometres. Sedimentation one day following cessation of operation is similar to during operation with a small extension to the area over which sedimentation has occurred but with no increase in maximum sedimentation depth.
308 The maximum design scenario for the inter-array cable sand wave clearance also accounts for up to a 25 m wide corridor. The resulting SSC showed similar characteristics to the Proposed Development offshore export cable clearance. At the Proposed Development array area, the greatest area of increased SSC was also shown to be associated with re-mobilisation of the deposited material on subsequent tides. In this scenario, the plume was found to extend 10 km from the site, with peak concentrations of 100 mg/l – 250 mg/l and average levels are less than 100 mg/l. Again, SSCs were predicted to reach their peak in the deposition phase with concentrations reaching 2,500 mg/l at the release site. The average sedimentation depth is typically half that of the Proposed Development offshore export cable works, with maximum sedimentation of 100 mm – 300 mm, which is only reached in very small areas along the Proposed Development export cable corridor, and almost all within the Proposed Development Fish and Shellfish Ecology study area. The sedimentation one day following the cessation of the clearance operation shows deposited material at the site of release with depth 0.2 m – 0.4 m, whilst in the locality, lower depths, typically less than 5 mm, are present at 50 m distance from the release.
309 The maximum design scenario for foundation installation assumes all wind turbine and OSP/Offshore convertor station platform foundations will be installed by drilling 5.5 m diameter piles for jacket foundations ( Table 12.10 Open ▸ ). Drilling was modelled for three wind turbines at different locations in the Proposed Development array area. The locations represent the dominant physical environmental conditions experienced in the Proposed Development array area. Modelling of SSCs associated with the foundation installation showed the plume related directly to the sediment releases was less than 5 mg/l and this drops to lower levels within a very short distance, typically less than 500 m. Furthermore, these sediment plumes are predicted to be temporary, returning to background levels within a few tides. The maximum sedimentation depth is typically 0.05 mm to 0.1 mm during pile installation, with that maximum dropping to 0.0005 mm – 0.001 mm one day following cessation of operations. These demonstrate the dispersive nature of the site, dispersing material the full extent of the tidal excursion (12 km), and even using a very small contour interval this settlement would be imperceptible from the background sediment transport activity with plotted sediment depths less than typical grain diameters.
310 The maximum design scenario for the installation of inter-array and OSP/Offshore convertor station platform interconnector cables assumes installation of all cables through jet trenching, with assumptions (e.g. trench width and depth) summarised in Table 12.10 Open ▸ . Modelling was undertaken for installation of inter-array and OSP/Offshore convertor station platform interconnector cables along a number of paths which connect groups of wind turbines to OSP/Offshore convertor station platforms or connect two OSP/Offshore convertor station platforms to each other. Each route would be undertaken as a separate operation and thus a single example has been selected to quantify the potential suspended sediment levels during the installation. The inter-array cabling was modelled along a route with a trench 2 m wide and 3 m in depth. The modelling outputs for SSCs associated with the installation of cabling showed a very wavy plume extending from trenching route, the majority of which sits within the Proposed Development array area. It is clear that the sediment is re-suspended and dispersed on subsequent tides as the plume envelope is most extensive towards the start of the route to the south-east of the site with peak values of 100 mg/l extending hundreds of meters to a small number of kilometres. The volume of material mobilised is relatively large, and elevated tidal currents disperse the material giving rise to concentrations of up to 500 mg/l. The sedimentation is greatest at the location of the trenching and may be up to 30 mm in depth however within close proximity, circa 100 m, the depths reduce significantly.
311 The modelling for offshore export cables also took a precautionary approach, assuming that cable installation would involve disturbance of seabed material up to 2 m wide and up to 3 m deep. Modelling outputs indicated average SSC along the route ranged between 50 mg/l and 500 mg/l. Average sedimentation peaks at 0.5 mm – 1.0 mm during offshore export cable installation and one day after cessation of operations this maximum increased to 10 mm – 30 mm, however this only accounts for a very small area with most of the impacted area displaying deposition depths considerably reduced at distance from the cable trench.
312 The impact is predicted to be of local spatial extent (i.e. largely within the Proposed Development Fish and Shellfish Ecology study area boundaries), short term duration, intermittent during the construction phase with high reversibility.
313 Decommissioning of the infrastructure will lead to increases in SSCs and associated sediment deposition. The maximum design scenario is represented by the cutting and removal of all infrastructure including piled jacket foundations at seabed level, removal of inter-array, OSP/Offshore convertor station platform interconnector and offshore export cables by jet dredging mobilising material from a 3 m deep and 2 m wide trench.
314 Decommissioning of foundations is predicted to result in increases in suspended sediments and associated deposition that are no greater than those produced during construction, and likely to be less as seabed clearance is less likely to be required. For the purposes of this assessment, the impacts of decommissioning activities are predicted to be no greater than those for construction.
Impacts of increased SSC and sediment deposition on diadromous fish species
316 Diadromous fish species are deemed to be of low vulnerability, high recoverability and therefore low sensitivity.
12.4 Operation and Maintenance
12.4.1 Electromagnetic Fields (EMF) from Subsea Electrical Cabling
317 The installation of inter-array, interconnector and offshore export cables will result in either high voltage alternating current (HVAC) or high voltage direct current (HVDC) under the maximum design scenario ( Table 12.12 Open ▸ ). The conduction of electricity through subsea power cables will result in emission of localised electromagnetic fields (EMFs) which could potentially affect the sensory mechanisms of some species of fish and shellfish, particularly electrosensitive species (including elasmobranchs) and diadromous fish species (Centre for Marine and Coastal Studies (CMACS, 2003).
318 The impact is predicted to be of local spatial extent (within a few metres of the buried cables), of long-term duration, continuous and not reversible during the operation and maintenance phase (impact is reversible upon decommissioning, see paragraph 321 et seq. for further detail).
Maximum design scenario relevant to the assessment of adverse effects on integrity
319 The maximum design scenarios considered for the assessment of potential impacts on Annex II diadromous fish from EMF are set out in Table 12.12 Open ▸ .
Table 12.12: Maximum Design Scenarios Considered for the Assessment of Potential Impacts on Annex II Diadromous Fish from EMF during Operation and Maintenance
Designed-in measures relevant to the assessment of adverse effects on integrity
320 Designed-in measures (and the associated commitments) of relevance to the assessments of potential impacts on Annex II diadromous fish from EMF are set out in Table 12.13 Open ▸ .
Table 12.13: Designed-in Measures Relevant to the Assessment of Adverse Effects on Integrity on European Sites Designated for Annex II Diadromous Fish from EMF during Operation and Maintenance
Information to inform Appropriate Assessment
321 The Appropriate Assessments for sites for Annex II diadromous fish are presented in section 12.5. Information common to inform the Appropriate Assessments in presented in this section.
322 The presence and operation of inter-array, interconnector and offshore export cables within the Proposed Development fish and shellfish ecology study area will result in emission of localised EMFs which has the potential to affect diadromous fish. EMF comprise both the electrical (E) fields, measured in volts per metre (V/m), and the magnetic (B) fields, measured in microtesla (µT) or milligauss (mG). Background measurements of the magnetic field are approximately 50 µT in the North Sea, and the naturally occurring electric field in the North Sea is approximately 25 µV/m (Tasker et al., 2010).
323 It is common practice to block the direct electrical field (E) using conductive sheathing, meaning that the EMFs that are emitted into the marine environment are the magnetic field (B) and the resultant induced electrical field (iE). It is generally considered impractical to assume that cables can be buried at depths that will reduce the magnitude of the B field, and hence the sediment-sea water interface iE field, to below that at which these fields could be detected by certain marine organisms on or close to the seabed (Gill et al., 2005; Gill et al., 2009). By burying a cable, the magnetic field at the seabed is reduced due to the distance between the cable and the seabed surface as a result of field decay with distance from the cable (CSA, 2019).
324 A variety of design and installation factors affect EMF levels in the vicinity of the cables. These include current flow, distance between cables, cable orientation relative to the earth's magnetic field (DC only), cable insulation, number of conductors, configuration of cable and burial depth. Clear differences between AC and DC systems are apparent: the flow of electricity associated with an AC cable changes direction (as per the frequency of the AC transmission) and creates a constantly varying electric field in the surrounding marine environment (Huang, 2005). Conversely, DC cables transmit energy in one direction creating a static electric and magnetic field. Average magnetic fields of DC cables are also higher than those of equivalent AC cables (Table 9.27).
325 The strength of the magnetic field (and consequently, induced electrical fields) decreases rapidly horizontally and vertically with distance from source. A recent study conducted by CSA (2019) found that inter-array and offshore export cables buried between depths of 1 m to 2 m reduces the magnetic field at the seabed surface four-fold. For cables that are unburied and instead protected by thick concrete mattresses or rock berms, the field levels were found to be similar to buried cables.
326 CSA (2019) found magnetic field levels directly over live AC undersea power cables associated with offshore wind energy projects range between 65 mG (at seafloor) and 5 mG (1 m above sea floor) for inter‑array cables and 165 mG (at seafloor) and 10 mG (1 m above seafloor) for offshore export cables. At lateral distances from the cable, magnetic fields greatly reduced at the sea floor to between 10 mG and <0.1 mG (from 3 to 7.5 m respectively) for inter-array cables, and at 1 m above the sea floor, magnetic fields reduced to between 15 mG and <0.1 mG (from 3 to 7.5 m respectively) for offshore export cables.
327 The induced electric fields directly over live AC undersea power cables ranged between 1.7 mV/m (at seafloor) and 0.1 mV/m (1 m above seafloor) for inter-array cables and 3.7 mV/m (at seafloor) and 0.2 mV/m (1 m above seafloor) for offshore export cables (CSA, 2019). At lateral distances electric fields at the sea floor reduced to between 0.01 mV/m and 1.1 mV/m (from 3 to 7.5 m respectively) for inter-array cables and 1 m above the sea floor, the magnetic fields reduced to between 0.02 mV/m and 1.3 mV/m (from 3 to 7.5 m respectively) for offshore export cables. There is, therefore, a pattern of reduction in the level of magnetic fields with increasing lateral and vertical distance from export cables.
328 Normandeau et al. (2011) provided additional data ( Table 12.14 Open ▸ ) demonstrating the rapid drop off of magnetic fields with increasing vertical and horizontal distance from both AC and DC cables. This supports the findings from the CSA (2019) study, with AC cables ranging from 7.85 µT on the seafloor with no horizontal distance to 0.08µT at 10 m above the seafloor and 10 m horizontal distance. DC cables showed a similar decrease albeit starting from a higher level with cables ranging from 78.27µT on the seafloor with no horizontal distance to 0.46µT at 10 m above the seafloor and 10 m horizontal distance.
Table 12.14: Average Magnetic Fields (μT) Generated for AC and DC Offshore Export Cables at Horizontal Distances from the Cable (Assuming Cable Burial to a Depth of 1 m; Source: Modified from Normandeau et al., 2011)
329 Fish species, particularly elasmobranchs (sharks, skates and rays), are able to detect applied or modified magnetic fields. Species for which there is evidence of a response to E and/or B fields include, elasmobranchs and diadromous fish species (including river lamprey, sea lamprey, and Atlantic salmon) (Gill et al., 2005; CSA, 2019). It can be inferred that the life functions supported by an electric sense may include detection of prey, predators or conspecifics to assist with feeding, predator avoidance, and social or reproductive behaviours. Life functions supported by a magnetic sense may include orientation, homing, and navigation to assist with long or short-range migrations or movements (Gill et al., 2005; Normandeau et al., 2011).
330 EMF may interfere with the navigation of sensitive diadromous species. Lampreys possess specialised ampullary electroreceptors that are sensitive to weak, low frequency electric fields (Bodznick and Northcutt, 1981; Bodznick and Preston, 1983), but information regarding what use they make of the electric sense is limited. Chung-Davidson et al. (2008) found that weak electric fields may play a role in the reproduction of sea lamprey and it was suggested that electrical stimuli mediate different behaviours in feeding-stage and spawning-stage individuals. This study (Chung-Davidson et al., 2008) showed that migration behaviour of sea lamprey was affected (i.e. adults did not move) when stimulated with electrical fields of intensities of between 2.5 and 100 mV/m, with normal behaviour observed at electrical field intensities higher and lower than this range. It should be noted, however, that these levels are considerably higher than modelled induced electrical fields expected from AC subsea cables (see Table 12.14 Open ▸ ).
331 Atlantic salmon has been found to possess magnetic material of a size suitable for magnetoreception, and this species can use the earth’s magnetic field for orientation and direction-finding during migration (Gill and Bartlett, 2010; CSA, 2019).
333 Diadromous fish are therefore considered to be of low vulnerability and high recoverability. The sensitivity to EMF is considered to be low.
12.4.2 Colonisation of Foundations, Scour Protection and Cable Protection
334 Foundation, cable protection and scour protection components of offshore wind farms can be viewed as artificial reefs, as these add hard substrate to areas typically characterised by soft, sedimentary environments. Man-made structures placed on the seabed attract many marine organisms including benthic species normally associated with hard substrates and therefore, may have indirect effects on fish and shellfish populations through their potential to act as artificial reefs and to bring about changes to food resources (Inger et al., 2009). Additionally, man-made structures may also have direct effects on fish through their potential to act as fish aggregation devices (Petersen and Malm, 2006).
335 The presence of infrastructure associated with the Proposed Development may result in the colonisation of foundations, scour protection and cable protection. The maximum design scenario is for up to 10,198,971 m2 of habitat created due to the installation of jacket foundations, associated scour protection and cable protection associated with inter-array cables, OSP/Offshore convertor station platform interconnector cables and offshore export cables ( Table 12.15 Open ▸ ). This value is, however, likely to be an over estimation of habitat creation as it is based on solid panels being used for the 317 jacket foundations. The four sides of these jackets will be made of a lattice structure; however, the precise dimensions of these lattices are unknown at the time of writing. A solid structure has therefore been assumed from the values available, noting that this will result in an overestimate of the habitat created. It is expected that the foundations and scour and cable protection will be colonised by species already occurring in the area (e.g. tunicates, Bryozoa sp., mussels and barnacles which are typical of temperate seas). The increased availability of prey species may lead to increased numbers of fish and shellfish species utilising the additional prey resource and hard substrate habitats.
336 These effects are only considered for the operation and maintenance phase as it takes time for organisms to colonise a structure post-installation. The impact is predicted to be of long term duration (35-year operation phase), continuous with medium reversibility and local spatial extent.
Maximum design scenario relevant to the assessment of adverse effects on integrity
337 The maximum design scenarios considered for the assessment of potential impacts on Annex II diadromous fish from colonised structures during the operation and maintenance phase are set out in Table 12.15 Open ▸ .
Table 12.15: Maximum Design Scenario Considered for the Assessment of Potential Impacts on Annex II Diadromous Fish from Colonised Structures during Operation and Maintenance
Designed-in measures relevant to the assessment of adverse effects on integrity
338 There are no designed-in measures which are of relevance to the assessment of potential impacts on Annex II diadromous fish features from colonisation of structures during the operation and maintenance phase.
Information to inform Appropriate Assessments
339 Appropriate Assessments for sites for Annex II diadromous fish are presented in section 9.5. Information common to inform the Appropriate Assessments in presented in this section.
340 Hard substrate habitat created by the introduction of wind turbine foundations and scour/cable protection are likely to be primarily colonised within hours or days after construction by demersal and semi-pelagic fish species (Andersson, 2011). Continued colonisation has been seen for a number of years after the initial construction, until a stratified recolonised population is formed (Krone et al., 2013). Feeding opportunities or the prospect of encountering other individuals may attract fish aggregate from the surrounding areas, which may increase the carrying capacity of the area (Andersson and Öhman, 2010; Bohnsack, 1989).
341 The dominant natural substrate character of the Proposed Development fish and shellfish ecology study area (e.g. soft sediment or hard rocky seabed) will determine the number of new species found on the introduced vertical hard surface and associated scour protection. When placed on an area of seabed which is already characterised by rocky substrates, few species will be added to the area, but the increase in total hard substrate could sustain higher abundance (Andersson and Öhman, 2010). Conversely, when placed on a soft seabed, most of the colonising fish will be normally associated with rocky (or other hard bottom) habitats, thus the overall diversity of the area may increase (Andersson et al., 2009). A new baseline species assemblage will be formed via recolonisation and the original soft-bottom population will be displaced (Desprez, 2000). This was observed in studies by Leonhard et al. (Danish Energy Agency, 2013) at the Horns Rev offshore wind farm, and Bergström et al. (2013) at the Lillgrund offshore wind farm. An increase in fish species associated with reefs such as goldsinny wrasse Ctenolabrus rupestris, lumpsucker Cycloplerus lumpus and eelpout Zoarces viviparous, and a decrease in the original sandy-bottom fish population were reported (Danish Energy Agency, 2012; Bergström et al., 2013). A decrease in soft sediment species is contradictory to findings of Degraer et al. (2020) where an increase in density of soft sediment species was seen, although this increase may be related to reduced fishing pressure within the array. However, it is noted by Degraer et al. (2020) that these effects were site specific and therefore may not necessarily be extrapolated to other offshore wind farms.
342 The longest monitoring programme conducted to date at the Lillgrund offshore wind farm in the Öresund Strait in southern Sweden, showed no overall increase in fish numbers, although redistribution towards the foundations within the offshore wind farm area was noticed for some species (i.e. cod, eel and eelpout; Andersson, 2011). More species were recorded after construction than before, which is consistent with the hypothesis that localised increases in biodiversity may occur following the introduction of hard substrates in a soft sediment environment. Overall, results from earlier studies reported in the scientific literature did not provide robust data (e.g. some were visual observations with no quantitative data) that could be generalised to the effects of artificial structures on fish abundance in offshore wind farm areas (Wilhelmsson et al., 2010). More recent papers are, however, beginning to assess population changes and observations of recolonisation in a more quantitative manner (Krone et al., 2013).
343 There is uncertainty as to whether artificial reefs facilitate recruitment in the local population, or whether the effects are simply a result of concentrating biomass from surrounding areas (Inger et al., 2009). Linley et al. (2007) concluded that finfish species were likely to have a neutral to beneficial likelihood of benefitting, which is supported by evidence demonstrating that abundance of fish can be greater within the vicinity of wind turbine foundations than in the surrounding areas, although species richness and diversity show little difference (Wilhelmsson et al., 2006a; Inger et al., 2009). A number of studies on the effects of vertical structures and offshore wind farm structures on fish and benthic assemblages have been undertaken in the Baltic Sea (Wilhelmsson et al., 2006a; 2006b). These studies have shown evidence of increased abundances of small demersal fish species (including gobies Gobidae, and goldsinny wrasse) in the vicinity of structures, most likely due to the increase in abundance of epifaunal communities which increase the structural complexity of the habitat (e.g. mussels and barnacles Cirripedia spp.). It was speculated that in true marine environments (e.g. the North Sea), offshore wind farms may enhance local species richness and diversity, with small demersal species such as gobies providing prey items for larger, commercially important species including cod (which have been recorded aggregating around vertical steel constructions in the North Sea; Wilhelmsson et al., 2006a). Monitoring of fish populations in the vicinity of an offshore wind farm off the coast of the Netherlands indicated that the offshore wind farm acted as a refuge for at least part of the cod population (Lindeboom et al., 2011; Winter et al., 2010).
344 In contrast, post construction fisheries surveys conducted in line with the Food and Environmental Protection Act (FEPA) licence requirements for the Barrow and North Hoyle offshore wind farms, found no evidence of fish abundance across these sites being affected, either beneficially or adversely, by the presence of the offshore wind farms (Cefas, 2009; BOWind, 2008) therefore suggesting that any effects, if seen, are likely to be highly localised and while of uncertain duration, the evidence suggests effects are not adverse.
Impacts to diadromous fish from colonisation of structures
345 Diadromous species that are likely to interact with the Proposed Development are only likely to do so by passing through the area during migrations to and from rivers located on the east coast of Scotland. In most cases, it is expected that diadromous fish are unlikely to utilise the increase in hard substrate within the Proposed Development fish and shellfish ecology study area for feeding or shelter opportunities as they are only likely to be in the vicinity when passing through during migration.
346 However, there is potential for impacts upon diadromous fish species resulting from increased predation by marine mammal species within offshore wind farms. Tagging of harbour seal Phoca vitulina and grey seal Halichoerus grypus around Dutch and UK wind farms provided significant evidence that the seal species were utilising wind farm sites as foraging habitats (Russel et al., 2014), specifically targeting introduced structures such as wind turbine foundations. However, a further study using similar methods concluded that there was no change in behaviour within the wind farm (McConnell et al., 2012), so it is not certain exactly to what extent seals utilise offshore wind developments and therefore effects may be site specific. Assuming that seals do utilise offshore wind developments as foraging areas, diadromous fish species may be impacted by the increased predation in an area where predation was lower prior to development. It is, however, unlikely that this would result in significant predation on diadromous species.
348 The low risk of effects on diadromous fish species extends to the freshwater pearl mussel, which is included in the diadromous species section, as part of its life stage is reliant on diadromous fish species including Atlantic salmon.
350 Overall, Annex II diadromous fish species are deemed to be of low vulnerability, high recoverability and therefore low sensitivity. This is based on the expected limited attraction/overlap to offshore structure by diadromous fish species, specifically lamprey species and Atlantic salmon, as discussed above, and therefore there is not expected to be a significant risk of increase predation around colonised foundation structures.