Site conclusion
232 In conclusion, with reference to the conservation objectives set for the Annex I habitat features of this site and the information presented in section 11.5, it can be concluded beyond all reasonable scientific doubt that there will be no Adverse Effect on Integrity on the Berwickshire and North Northumberland Coast SAC.
233 This finding is in relation to potential impacts associated with the Proposed Development during construction, decommissioning and operation and maintenance, acting alone and or in-combination.
12 Appraisal of Adverse Effects on Integrity: Diadromous Fish
12.1 Introduction
234 The Screening exercise (at Stage One of the HRA process) as updated in response to consultation on the HRA Stage One LSE Screening Report (SSE Renewables, 2021b) (see Section 7.37) identified LSEs on the following European sites designated for Annex II diadromous fish features and freshwater pearl mussel (as summarised in Table 9.1 Open ▸ ):
- Tweed Estuary SAC;
- River Tweed SAC;
- River South Esk SAC;
- River Tay SAC;
- River Dee SAC; and
- River Teith SAC.
235 This section explains the approach taken to assessing the potential impacts of the Proposed Development on European sites designated for Annex II diadromous fish features and Annex II freshwater pearl mussel and presents the Stage Two assessments for the above sites. Freshwater pearl mussel has been considered within this chapter because part of its life stage is reliant on the diadromous fish species Atlantic salmon. The potential for significant effects to freshwater pearl mussel would be indirect and would occur as a result of direct effects on Atlantic salmon, one of freshwater pearl mussel’s host species. Broadly, the potential effects to these sites are as follows and addressed explicitly in the sections below:
236 During construction and decommissioning phase:
- Injury and/or disturbance from underwater noise and vibration: direct injury or mortality and or behavioural changes (barriers to migration) due to exposure to underwater noise generated by construction activities (e.g. piling, UXO clearance).
- Increased suspended sediment concentrations and associated sediment deposition: behavioural changes (barriers to migration) due to sediment resuspension during construction and decommissioning (e.g. foundation installation/removal).
237 During operation and maintenance phase:
- Electromagnetic Fields (EMF) from subsea electrical cabling: emission of localised EMF due to the presence of subsea electrical cabling may result in behavioural changes, including interference with the navigation of migratory fish.
- Colonisation of foundations, scour protection and cable protection: Potential changes to prey-predator interactions, changes to fish migration patterns due to the fish aggregation effect, and potential spread of marine invasive and non-native species.
238 The Stage Two Appropriate Assessments (considering effects of the Proposed Development both alone and in-combination) for sites designated for diadromous fish and freshwater pearl mussel are presented in section 12.5. Integrity matrices summarising the assessments for the sites are provided in Table 15.2 through to Table 15.7 in section 15. A summary of all Appropriate Assessments undertaken within this report is provided in the concluding section of this report (see section 14).
12.2 Assessment Information
12.2.1 Maximum Design Scenarios
239 The maximum design scenario relevant to Annex II diadromous fish features and freshwater pearl mussel are set out in Table 12.2 Open ▸ , Table 12.10 Open ▸ , Table 12.12 Open ▸ and Table 12.15 Open ▸ in this chapter. An overview of the maximum design scenario for all receptor groups is provided in Table 10.1 Open ▸ in chapter 10, for reference.
12.2.2 Designed-in Measures
240 Designed-in measures relevant to Annex II diadromous fish features are set out in Table 12.3 Open ▸ , Table 12.11 Open ▸ and Table 12.13 Open ▸ in this chapter. An overview of the designed-in measures for all receptor groups is provided in Table 10.2 Open ▸ in chapter 10, for reference.
12.2.3 Baseline Information
241 Baseline information on the Annex II diadromous fish and freshwater pearl mussel features of the European sites identified for appropriate assessment has been gathered through a comprehensive desktop study of existing studies and data sets, as well as site-specific surveys undertaken (as agreed with MS-LOT, MSS and NatureScot) to inform the fish and shellfish baseline characterisation of volume 2, chapter 9 of the Offshore EIA Report: Fish and Shellfish Ecology. Fish and shellfish are spatially and temporally variable, therefore for the purposes of the fish and shellfish ecology characterisation, two study areas have been defined for the EIA (see volume 2, chapter 9 of the Offshore EIA Report for further detail) which are considered to provide an appropriate baseline for the consideration of adverse effects on the European sites screened-in to the HRA:
- The Proposed Development fish and shellfish ecology study area has been defined with reference to the Proposed Development boundary that existed prior to the boundary refinement in June 2022. As the refinements resulted in a reduction of the Proposed Development array area, the fish and shellfish ecology study area is considered to remain representative, as it encompasses the updated Proposed Development boundary, and therefore presents a conservative baseline against which the fish and shellfish appropriate assessment is undertaken. The Proposed Development fish and shellfish ecology study area has not therefore been realigned to the current Proposed Development boundary;
- The Proposed Development northern North Sea fish and shellfish ecology study area encompasses the Proposed Development fish and shellfish ecology study area and a surrounding area defined by the boundary of the northern North Sea. This is the regional study area and also encompasses waters of the Forth and Tay Scottish Marine Region (SMR).
242 The key data sources are presented in detail within volume 2, chapter 9 of the Offshore EIA Report, and the chapters that supported its findings as summarised below:
- volume 2, chapter 7: Physical Processes;
- volume 2, chapter 8: Benthic Subtidal and Intertidal Ecology;
- volume 3, appendix 9.1: Fish and Shellfish Ecology Technical Report;
- volume 3, appendix 10.1: Subsea Noise Technical Report;
- volume 3, appendix 10.1: Annex G Particle motion review to subsea noise report
243 Detailed European site information is presented in appendix A.
12.2.4 Conservation Objectives
244 The conservation objectives for sites designated for Annex II diadromous fish and freshwater pearl mussel features identified for Stage Two Appropriate Assessment are provided in section 12.5. Where Supplementary Advice to the conservation objectives, or site-specific conservation advice describes minimum targets for qualifying features in more detail, this detail is provided in appendix A and/or referenced within the relevant Stage Two Appropriate Assessments.
12.2.5 Species Accounts
Atlantic salmon Salmo salar
245 Atlantic salmon are anadromous (i.e. spawns in freshwater but completes its life cycle in the sea). They spend two to three years in freshwater, with downstream migration (to open sea) occurring between April and May. Atlantic salmon remain at sea for one to three years. Upstream migration into freshwater occurs year-round, with a peak in late summer/early autumn. A study by Malcolm et al. (2015) suggests that most fish across Scotland leave natal rivers between mid-April and the end of May.
246 Following spawning by adult salmon in Scottish east coast rivers, the ova mature into fry and then parr before migrating to sea as smolts. At sea, the smolts grow rapidly and after one to three years they return as adults to spawn, most commonly to their natal river. Many Atlantic salmon die after spawning, but some return to sea as kelts and may return again to rivers to spawn (Mills, 1989). Atlantic salmon are known to migrate in relation to diurnal cues. Evidence provided by Smith and Smith (1997) suggests that Atlantic salmon upstream migration into rivers is related to tidal phase and time of day. Up-estuary movements leading to river entry were found to be predominantly nocturnal and occur during ebb tides, with entry into nontidal reaches of rivers also being nocturnal, however significantly associated with tidal phase (Smith and Smith, 1997). Smolts migrating downstream/offshore have also been found to increase migratory activity nocturnally, with daytime utilised more for prey detection and predator avoidance (Hedger et al., 2008). Dempson et al. (2011) also found a small but significant increase in migratory movements nocturnally when compared to daytime, which suggests a slight preference for nocturnal migration.
248 Migration of Atlantic salmon smolts through the Cromarty Firth and into the Moray Firth was tracked in a study undertaken for Beatrice Offshore Windfarm (BOWL) Ltd. by Glasgow University (BOWL, 2017). The study results indicated an eastwards migration of the tagged fish along the southern coast of the Moray Firth. Results also showed the majority of fish to remain predominantly within the upper 1 m of the water column during migration. Mortality of smolts was considered to be mainly attributable to predation and there was a strong relationship between group survival, early migration and group size.
249 Furthermore, recent evidence from the Moray Firth (Newton et al., 2017; Newton et al., 2019; Gardiner et al., 2018a) suggest that smolts migrating from their rivers in the Moray Firth head directly across the North Sea relatively rapidly. It is thought that this route, rather than moving in a coastal direction upon leaving their natal rivers, allows them to take advantage of east flowing currents which cross the North Sea. This fast progress away from the coast limits exposure to predators close to the coast. It also reduces the potential for interaction with marine renewables developments (including offshore wind). Similar evidence of a rapid easterly migration out into the North Sea has also been shown for the River Dee in Aberdeenshire (Gardiner et al., 2018b). Therefore, it could be assumed that smolts from other east coast rivers (e.g. Tay, Forth and South Esk) would move in a similar fashion.
250 Atlantic salmon in Scotland have been experiencing a decline in recent decades, with rod catch data declining across much of the species’ range (Scottish Government, 2020b). Pressures on Atlantic salmon stocks in marine and freshwater environments are numerous and include commercial and recreational exploitation of stocks, disease, impacts related to farmed salmon and climate change (ICES, 2017b). A Marine Scotland report (Marine Scotland, 2017) showed salmon stocks to be at a historically low level.
Sea lamprey Petromyzon marinus
251 The sea lamprey is a primitive, jawless fish resembling an eel. It is the largest of the lampreys found in the UK. It occurs in estuaries and easily accessible rivers and is an anadromous species (i.e. spawning in freshwater but completing its life cycle in the sea) (JNCC, 2021a).
252 In Europe, sea lamprey are distributed from Norway down to the Iberian Peninsula, with the largest populations often observed in the estuaries and large rivers flowing into the Atlantic Ocean in Western Europe, in particular in the Iberian Peninsula, France and the UK (Guo et al., 2016).
253 Like the other species of lamprey, sea lampreys need clean gravel for spawning, and marginal silt or sand for the burrowing juveniles (ammocoetes). Sea lampreys spend most of their adult life at sea, and are parasitic in their marine phase, feeding off a variety of marine and anadromous fishes, including shad, herring, pollack, salmon, mullets, cod, haddock, Greenland sharks and basking sharks (Marine Scotland Directorate, 2019). They are rarely captured in coastal and estuarine waters, suggesting that they are solitary hunters and widely dispersed at sea, and can be found at considerable depths (up to 4,099 m) (Marine Scotland Directorate, 2019). Given that they are parasites in their adult phase, however, their distribution is largely dictated by their host species (Marine Scotland Directorate, 2019). As such it is not expected that they will be particularly attracted to structures associated with offshore wind developments. However, this is not certain, as there is limited information available on the utilisation of the marine environment by sea lamprey. It is a possibility that sea lamprey will be present in the vicinity of the Proposed Development.
River lamprey Lampetra fluviatilis
Freshwater pearl mussel Margaritifera margaritifera
257 The freshwater pearl mussel is an endangered species of freshwater mussel. It is widely distributed in Europe but has suffered widespread decline and is highly vulnerable in every part of its former range. A Scottish national survey undertaken in 2015 found that freshwater pearl mussel had been lost from a number of rivers. More widely, since 1999 a total of 11 rivers in Scotland have seen their freshwater pearl mussel populations become extinct (JNCC, 2019).
258 Freshwater pearl mussel are similar in shape to common marine mussels but grow much larger and live far longer. They can grow as large as 20 cm and live for more than 100 years, making them one of the longest-lived invertebrates (Skinner et al., 2003). These mussels live on the beds of clean, fast flowing rivers, where they can be buried partly of wholly in coarse sand or fine gravel. Mussels have a complex life cycle, living on the gills of young Atlantic salmon or sea trout, for their first year, without causing harm to the fish (Skinner et al., 2003). While there is no potential for direct impacts on this species from the Proposed Development (as this is an entirely freshwater species), freshwater pearl mussel have been included in the assessment, as a dependant qualifying species, as there is the potential for indirect impacts to occur due to effects on their host species (i.e. Atlantic salmon and sea trout) during their marine phase. Due to effects on Atlantic salmon populations being the only route to impact, where it is concluded that no adverse effects on integrity are to be found on Atlantic salmon, the same can be concluded for freshwater pearl mussel.
12.2.6 Approach to the In-Combination Assessments
259 The nature of effects that have been assessed for each Annex II diadromous fish species, and the scale over which these effects may occur, are based on assessment criteria applied during the HRA Stage One exercise as presented in section 9.3. These effects are detailed within the alone assessment and have not been re-iterated here.
260 The overarching approach to the assessment of effects in-combination is set out in section 10.6 and is not reiterated here.
Relevant plans and projects
261 The plans and projects set out in Table 6.1 have been considered within the in-combination assessment for European sites designated for Annex II diadromous fish features.
262 The plans and projects included in this in-combination assessment for European sites designated for Annex II diadromous fish features have been derived in part, from the Cumulative Effects Assessment (CEA) longlist presented in and volume 3, chapter appendix 6.4 of the Offshore EIA Report.
Table 12.1: List of Other Developments with Potential for In-Combination Effects on Annex II Diadromous Fish.
12.3 Construction and Decommissioning
12.3.1 Injury and/or Disturbance From Underwater Noise and Vibration
263 Increases in underwater noise during construction and decommissioning of the Proposed Development, associated with UXO clearance and piling, have the potential to cause injury and disturbance to Annex II diadromous fish and freshwater pearl mussel.
264 The Screening process concluded there was potential for underwater noise during the construction and decommissioning phase to result in an Adverse Effect on Integrity relating to the following European sites and relevant features:
- Tweed Estuary SAC – sea lamprey and river lamprey;
- River Tweed SAC – Atlantic salmon, sea lamprey and river lamprey;
- River South Esk SAC – Atlantic salmon and freshwater pearl mussel;
- River Tay SAC – Atlantic salmon, sea lamprey and river lamprey;
- River Dee SAC – Atlantic salmon and freshwater pearl mussel; and
- River Teith SAC – Atlantic salmon, sea lamprey and river lamprey.
265 The following sections explain how the potential effects of the Proposed Development on Annex II diadromous fish features during construction and decommissioning have been quantified and assessed.
Maximum design scenario relevant to the assessment of adverse effects on integrity
266 The maximum design scenarios considered for the assessment of potential impacts on Annex II diadromous fish from underwater noise during construction and decommissioning are set out in Table 12.2 Open ▸ .
267 Pile driving during the installation of foundations is predicted to lead to a medium-term, intermittent increase in underwater noise levels that may result in injury and/or disturbance to Annex II diadromous fish. The maximum design scenario considers the greatest effect from underwater noise on Annex II diadromous fish, considering the maximum hammer energy and piling duration (see Table 12.2 Open ▸ ).
269 There will be no pile driving or UXO clearance during decommissioning, therefore any underwater noise associated with the removal of foundations will be at most similar, but more likely, much less than during construction.
Table 12.2: Maximum Design Scenarios Considered for the Assessment of Potential Impacts on Annex II Diadromous Fish from Underwater Noise during Construction and Decommissioning
Designed-in measures relevant to the assessment of adverse effects on integrity
270 Designed-in measures (and the associated commitments) of relevance to the assessments of potential effects on Annex II diadromous fish from underwater noise during construction and decommissioning are set out in Table 12.3 Open ▸ .
Table 12.3: Designed-in Measures Relevant to the Assessment of Adverse Effects on Integrity on European Sites Designated for Annex II Diadromous Fish from Underwater Noise and Vibration during Construction and Decommissioning
Information to inform Appropriate Assessments
271 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.
272 The installation of foundations within the Proposed Development fish and shellfish ecology study area may lead to injury and/or disturbance to fish and shellfish species due to underwater noise during pile driving. The maximum design scenario considers the greatest effect from underwater noise on diadromous fish, considering both the greatest hammer energy. This scenario is represented by the installation of up to 179 piled jacket foundations (1,432 piles) for wind turbines, and up to ten jacket foundations (256 piles) for OSP/Offshore convertor station platforms, with each pile installed via impact/percussive piling. Two scenarios were modelled with respect to hammer energy: an average maximum hammer energy of 3,000 kJ and absolute maximum hammer energy of up to 4,000 kJ.
273 For wind turbines, piling was assumed to take place over a period of on average nine hours per pile (maximum duration of up to ten hours per pile) with up to five piles installed in each 24-hour period. Installation of OSP/Offshore convertor station platform foundations will take place over a period of on average seven hours per pile (maximum duration of up to eight hours per pile) with up to three piles installed in each 24-hour period. A maximum duration of 16,368 hours of piling activity, over a maximum 372-day period, may take place during the construction phase, based on the maximum duration of the piling phase.
274 UXO clearance (including detonation) will be completed prior to the construction phase (pre-construction). Until detailed pre-construction surveys are completed within the Proposed Development, the precise number of potential UXO which will need to be cleared is unknown. Drawing on the experience of UXO at other North Sea sites, the maximum number of UXO that may require clearance is up to 14 for the Proposed Development. The maximum design scenario assumes that each of these will be detonated using low order processes, with the assumption that one high order detonation may occur (see Table 12.2 Open ▸ ). Many of these may be left in situ and microsited around. Detonation of UXO would represent a short term (i.e. seconds) increase in underwater noise (i.e. sound pressure levels and particle motion) which will be elevated to levels which may result in injury or behavioural effects on diadromous fish.
275 To understand the magnitude of noise emissions from piling and UXO clearance during construction activity, underwater noise modelling was undertaken considering the key parameters summarised above. Full details of the modelling undertaken are presented in volume 3, appendix 10.1 off the Offshore EIA Report. Piling activities were modelled for jacket foundations at six locations within the Proposed Development array area taking into account the varying bathymetry and sediment type across the model areas (see volume 3, appendix 10.1 of the Offshore EIA Report). Underwater noise modelling included the use of ‘soft start’ mitigation to reduce the potential for injury effects (as set out in Table 12.3 Open ▸ ). The implications of the modelling for diadromous fish and freshwater pearl mussel, injury and behaviour are outlined in the subsequent sections.
276 All other noise sources including cable installation and foundation drilling will result in much lower noise levels and therefore much smaller injury ranges (in most cases no injury is predicted) than those predicted for piling operations.
277 The impact is predicted to be of regional spatial extent, medium term duration, intermittent with high reversibility.
Acoustic assessment criteria
- Group 1: fishes with no swim bladder or other gas chamber (e.g. elasmobranchs, flatfishes and lampreys). These species are less susceptible to barotrauma and are only sensitive to particle motion, not sound pressure. Basking shark, which does not have a swim bladder, falls into this hearing group;
- Group 2: fishes with swim bladders but the swim bladder does not play a role in hearing (e.g. salmonids). These species are susceptible to barotrauma, although hearing only involves particle motion, not sound pressure;
- Group 3: Fishes with swim bladders that are close, but not connected, to the ear (e.g. gadoids and eels). These fishes are sensitive to both particle motion and sound pressure and show a more extended frequency range than groups 1 and 2, extending to about 500 Hz; and
- Group 4: Fishes that have special structures mechanically linking the swim bladder to the ear (e.g. clupeids such as herring, sprat and shads). These fishes are sensitive primarily to sound pressure, although they also detect particle motion. These species have a wider frequency range, extending to several kHz and generally show higher sensitivity to sound pressure than fishes in Groups 1, 2 and 3.
280 An assessment of the potential for injury/mortality and behavioural effects to be experienced directly by diadromous fish and indirectly by freshwater pearl mussel with reference to the sensitivity criteria above is presented in turn below.
Injury
281 Table 12.4 Open ▸ summarises the fish injury criteria recommended for pile driving based on the Popper et al. (2014) guidelines, noting that dual criteria are adopted in these guidelines to account for the uncertainties associated with effects of underwater noise on fish.
282 The Popper et al. (2014) guidelines set out criteria for injury due to different sources of noise. Those relevant to the Proposed Development are those for injury due to impulsive (piling and UXO detonation) sources only, as non-impulsive sources would result in a much lower impact.
Table 12.4: Criteria for Onset of Injury to Fish due to Impulsive Piling (Popper et al., 2014)
a Relative risk (high, moderate, low) is given for animals at three distances from the source defined in relative terms as near field (N; i.e. 10s of metres), intermediate (I; i.e. 100s of metres), and far field (F; i.e. 1000s of metres); Popper et al. (2014).
283 The full results of the underwater noise modelling are presented in volume 3, appendix 10.1 of the Offshore EIA Report. For the purpose of this assessment, a conversion factor range of 0.5 reducing to 4% was applied as this represents an adequately conservate range for which energy from piling is transferred into sound energy (as explained in volume 3, appendix 10.1, annex A). It should be noted that sensitivity analysis was undertaken on other, more conservative conversion factors, which is presented in volume 3, appendix 10.1 of the Offshore EIA Report. In order to inform this assessment, Table 12.5 Open ▸ and Table 12.6 Open ▸ present the predicted injury ranges associated with the installation of one 5.5 m diameter pile, for peak sound pressure levels (SPLpk) and cumulative sound exposure level (SELcum) respectively. This modelled scenario resulted in the greatest predicted injury ranges and therefore forms the focus of the assessment for injury.
284 For peak pressure noise levels when piling energy is at its maximum (i.e. 4,000 kJ), mortality and recoverable injury to diadromous fish may occur within approximately 138 m (Group 1 fish species including sea and river lampreys) – 228 m (Group 2 fish species including Atlantic salmon) of the piling activity. The potential for mortality or mortal injury to fish eggs would also occur at distances of up to 228 m ( Table 12.5 Open ▸ ), with a low to moderate risk of recoverable injury to eggs and larvae within the range of hundreds of metres (see Table 12.4 Open ▸ for qualitative criteria). It should be noted that these ranges are the maximum ranges for the maximum hammer energy, and it is unlikely that injury will occur in this range due to the implementation of soft starts during piling operations, which will allow fish to move away from the areas of highest noise levels, before they reach a level that would cause an injury. The initial injury ranges for soft start initiation will be considerably smaller than those maximum ranges presented in Table 12.5 Open ▸ (i.e. of the order of tens of metres, depending on the fish species considered).
285 For cumulative SEL, injury ranges were calculated for piling activities undertaken for the maximum energy scenario and for a realistic hammer energy scenario (i.e. average maximum; Table 12.6 Open ▸ ). These ranges indicate that with the implementation of soft start initiation, the mortality and recoverable injury ranges are considerably smaller than those predicted for peak sound pressure levels (i.e. mortality thresholds were not exceeded and recoverable injury to maximum ranges of 67 m; see Table 12.6 Open ▸ ). This table also presents ranges of effect for Temporary Threshold Shift (TTS) for all fish groups. As outlined above, TTS is a temporary reduction in hearing sensitivity caused by exposure to intense sound. Normal hearing ability returns following cessation of the noise causing TTS, though the recovery period is variable, during which fish may have decreased fitness due to a reduced ability to communicate, detect predators or prey, and/or assess their environment. Table 12.7 Open ▸ presents the ranges at which TTS in fish may occur as a result of piling for one 5.5 m pile, with TTS predicted to occur to maximum ranges of 4.161 km from piling operations.
286 The injury ranges presented indicate that injury may occur out to ranges of tens to a few hundred metres, based on the maximum design scenario. However, in reality, the risk of fish injury will be considerably lower due to the hammer energies being lower than the absolute maximum modelled, as demonstrated by the lower injury ranges associated with initiation and soft starts in Table 12.5 Open ▸ . The expected fleeing behaviour of fish from the area affected when exposed to high levels of noise and the soft start procedure, which will be employed for all piling (see Table 12.3 Open ▸ ), mean that it is likely that fish will have sufficient time to vacate the areas where injury may occur prior to noise levels reaching that level.
Table 12.5: Summary of Peak Pressure Injury Ranges for Diadromous Fish due to Phase of Impact Piling Resulting in Maximum Peak Sound Pressure Level, for both Wind turbine Foundations and OSP/Offshore Convertor Station Platform Foundations Based on the Peak Pressure Metric
Table 12.6: Injury Ranges for Fish due to Impact Pile Driving for the “Realistic” and “Maximum” Pile Driving for Wind turbine Jacket Foundations, and for the Piling of the OSP/Offshore Convertor Station Platform Jackets Based on the Cumulative SEL Metric (N/E denotes where thresholds not exceeded)
287 Noise modelling was also undertaken for concurrent piling for wind turbine foundations. Mortality and recoverable injury ranges were unchanged for the concurrent piling scenario and therefore TTS ranges only are presented in Table 12.7 Open ▸ . This indicates that for concurrent piling, TTS ranges may be increased to up to 7.1 km from the piling location for the maximum hammer energy and 5.6 km for realistic hammer energy.
Table 12.7: TTS Injury Ranges for Fish due to Impact Pile Driving at Two Locations Concurrently, for the “Realistic” and “Maximum” Pile Driving for Wind turbine Jacket Foundations Based on the Cumulative SEL Metric
288 Underwater noise modelling has also been completed for underwater noise associated with UXO clearance/detonation. Modelling was undertaken for a range of orders of detonation, from a realistic worse case high order detonation to low order detonations (e.g. deflagration and clearance shots) to be used as mitigation to minimise noise levels. Table 12.8 Open ▸ details the injury ranges for fish of all groups in relation to various orders of detonation. The method of low order has been committed to (see Table 12.3 Open ▸ ) and as such will be the dominant method of UXO clearance, although higher order detonations may also occur if low order is not successful or unintentionally as part of the low order process.
289 The modelling results ( Table 12.8 Open ▸ ) indicate that mortality/mortal injury for all fish (including Group 1, sea lamprey), would occur within a range of 30-45 m from the source following low order detonation. The method of low order has been committed to (see Table 12.3 Open ▸ ) and as such will be the dominant method of UXO clearance. Higher order detonations may also occur if low order is not successful or unintentionally as part of the low order process. In the event of a high order detonation event (absolute worst-case scenario of a detonation of 300 kg UXO) in this case mortality would occur within 410-680 m of the noise source.
Table 12.8: Injury Ranges for all Fish Groups Relating to Varying Orders of UXO Detonation
Behaviour effects
290 Behavioural effects in response to construction related underwater noise include a wide variety of responses including startle responses (also known as C-turn responses), strong avoidance behaviour, changes in swimming or schooling behaviour or changes of position in the water column. The Popper et al. (2014) guidelines provide qualitative behavioural criteria for fish from a range of noise sources. These categorise the risks of effects in relative terms as “high”, “moderate” or “low” at three distances from the source: “near” (i.e. tens of metres), “intermediate” (i.e. hundreds of metres) or “far” (i.e. thousands of metres). The behavioural criteria for piling operations are summarised in Table 12.9 Open ▸ for the four fish groupings.
Table 12.9: Potential Risk for the Onset of Behavioural Effects in Fish from Piling (Popper et al., 2014)a
a Note: Relative risk (high, moderate, low) is given for animals at three distances from the source defined in relative terms as near field (N; i.e. 10s of metres), intermediate (I; i.e. 100s of metres), and far field (F; i.e. 1000s of metres); Popper et al. (2014).
291 Group 1 Fish (including sea and river lampreys) and Group 2 Fish (including Atlantic salmon) are less sensitive to sound pressure, with these species detecting sound in the environment through particle motion. However, sensitivity to particle motion in fish is also more likely to be important for behavioural responses rather than injury (Hawkins, 2009; Mueller-Blenkle et al., 2010; Hawkins et al., 2014a).
292 A number of studies have examined the behavioural effects of the sound pressure component of impulsive noise (including piling operations and seismic airgun surveys) on fish species. Mueller-Blenkle et al. (2010) measured behavioural responses of cod and sole to sounds representative of those produced during marine piling, with considerable variation across subjects (i.e. depending on the age, sex, condition etc. of the fish, as well as the possible effects of confinement in cages on the overall stress levels in the fish). This study concluded that it was not possible to find an obvious relationship between the level of exposure and the extent of the behavioural response, although an observable behavioural response was reported at 140 dB to 161 dB re 1 µPa SPLpk for cod and 144 dB to 156 dB re 1 µPa SPLpk for sole. However, these thresholds should not be interpreted as the level at which an avoidance reaction will be elicited, as the study was not able to show this.
293 A study by Pearson et al. (1992) on the effects of geophysical survey noise on caged rockfish Sebastes spp. Observed a startle or “C-turn response” at peak pressure levels beginning around 200 dB re 1 µPa, although this was less common with the larger fish. Studies by Curtin University in Australia for the oil and gas industry by McCauley et al. (2000) exposed various fish species in large cages to seismic airgun noise and assessed behaviour, physiological and pathological changes. The study made the following observations:
- A general fish behavioural response to move to the bottom of the cage during periods of high level exposure (greater than root mean square (RMS) levels of around 156 dB to 161 dB re 1 ?Pa; approximately equivalent to SPLpk levels of around 168 dB to 173 dB re 1 ?Pa);
- A greater startle response by small fish to the above levels;
- A return to normal behavioural patterns some 14 to 30 minutes after airgun operations ceased;
- No significant physiological stress increases attributed to air gun exposure; and
- Some preliminary evidence of damage to the hair cells when exposed to the highest levels, although it was determined that such damage would only likely occur at short range from the source.
294 The authors did point out that any potential seismic effects on fish may not necessarily translate to population scale effect or disruption to fisheries and McCauley et al. (2000) show that caged fish experiments can lead to variable results. While these studies are informative to some degree, these, and other similar studies, do not provide an evidence base that is sufficiently robust to propose quantitative criteria for behavioural effects (Hawkins and Popper, 2016; Popper et al., 2014) and as such the qualitative criteria outlined in Table 12.9 Open ▸ are proposed.
295 For the purposes of the underwater noise modelling, an un-weighted sound pressure level of 150 dB re 1 μPa (RMS) was used as the criterion for indicating the extent of behavioural effects due to impulsive piling based on the Washington State Department of Transport Biological Assessment Preparation for Transport Projects Advanced Training Manual (WSDOT, 2011). At sound pressure levels in excess of 150 dB re 1 μPa (RMS) temporary behavioural changes, such as elicitation of a startle response, disruption of feeding, or avoidance of an area may be expected to occur. It is important to note that this threshold is for onset of potential effects, and not necessarily an ‘adverse effect’ threshold and should be considered alongside other information (including those studies outlined above) in addition to the qualitative criteria set out by Popper et al. (2014) in Table 12.9 Open ▸ . Using this criterion, site specific modelling indicated that behavioural responses may occur to ranges of approximately 17 km for single pile driving and 23 km for concurrent piling. Initial outputs of post construction monitoring at the BOWL (BOWL, 2021a) concluded that for sandeel there was no evidence of adverse effects on sandeel populations between pre and post construction levels over a six-year period. Cod spawning was also monitored at the same wind farm site (BOWL, 2021b) and similarly, it was concluded that there was no change in the presence of cod spawning between pre and post construction (although spawning intensity was found to be low across both surveys). From these studies, it can be inferred that noise impacts associated with installation of an offshore wind development are temporary and that fish communities (specifically cod and sandeel in this case) show a high degree of recoverability following construction.