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
7 Potential for Adverse Effects on Marine Mammal Features

7 Potential for Adverse Effects on Marine Mammal Features

7.1 Introduction

7.1.1 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).  These 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 marine mammal interest features.

7.1.2 In total there were 99 SACs with qualifying marine mammal interest features that were screened in.  This large number of sites resulted from the broad scope of the Draft Plan and the extensive ranges of some marine mammals.

7.1.3 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 [123] [124] [125] has been used where it is not necessary to individually review the full list of all sites and the qualifying marine mammal 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 screening tables (Tables D1-D17) and maps (Figures E1-E17).  The locations of screened in SAC and Ramsar sites with qualifying marine mammal features beyond the 100 km buffer are provided in Appendix F (Figures F6 and F7).

7.1.4 Some of these SACs also contained other interest features for which it could not be concluded that there was no LSE (e.g. subtidal sandbanks) and these are reviewed separately under the relevant section(s) of this report. In addition, where there are interest features at these sites which have been ‘screened out’ as there will be no LSE these are also recorded (Table C1).

7.1.5 In summary, the screening phase concluded that there was a possibility of a LSE (or that it was not possible to conclude no LSE) for the following qualifying marine mammal interest features:

  • Common (Harbour) seal (1365);
  • Grey seal (1364);
  • Bottlenose dolphin (1349); and
  • Harbour porpoise (1351).

7.1.6 To assess whether there is any adverse effect on the integrity of relevant European/Ramsar sites, the following sections review the sensitivities of marine mammal features, identify the conservation objectives and assess the effects arising in the context of the proposed plan-level mitigation measures.

7.2 Sensitivities of Marine Mammal Interest Features to the Sectoral Offshore Wind Plan Activities

7.2.1 This section reviews the sensitivities that are relevant for the marine mammal interest features.  A generic review of the sensitivities of relevant bird features is presented under the impact pathways identified during the screening phase (see Table 2):

  • Physical Loss/Gain of Habitat (Loss of Foraging area);
  • Physical Loss/Gain of Habitat (Fish Aggregating Effects);
  • Physical Damage to Habitat (Reduction in Foraging Habitat Quality);
  • Physical Damage to Species (Damage to Seal Haul-Outs);
  • Physical Damage to Species (Collision Risk);
  • Non-Physical Disturbance (Noise/Visual Disturbance causing Barrier and Exclusion effects);
  • Non-Physical Disturbance (Electromagnetic Fields);
  • Toxic contamination (Contamination and Spillages); and
  • Non-toxic contamination (Increased Turbidity).

7.2.2 Following this review, the individual characteristics and sensitivities for each of the relevant qualifying marine mammal interest features are presented and the activities that could cause an impact are identified and tabulated.  These interest feature reviews are set out in the following sections:

  • Pinnipeds (grey and common seals) (Section 7.12); and
  • Cetaceans (bottlenose dolphin and harbour porpoise) (Section 1.1).

7.3 Physical Loss/Gain of Habitat (Loss of Foraging Area; Impact Pathway 2)

7.3.1 Marine mammals have extensive ranges and cover very large distances to forage in the pelagic environment. Critical (key) habitats for marine mammals are those that are essential for day-to-day well-being and survival, as well as for maintaining population growth. Areas that are regularly used for feeding, breeding, raising calves and socialising, as well as, sometimes, migrating, are the key components of critical habitat [126].  In addition to places used regularly for feeding, breeding, raising calves and socialising, locations where associated and supporting activities such as hunting, courtship, singing, calving, nursing, resting, playing and communication take place are important to consider.  For a complete consideration of critical habitat, it should also extend to the critical habitat of marine mammal prey and areas where important ecosystem processes occur such as productive upwellings and fish spawning grounds.  These critical habitat areas will be the most sensitive parts of a marine mammal’s range to any developments that cause loss (or gain) of habitat.

7.4 Physical Loss/Gain of Habitat (Fish Aggregating Effects; Impact Pathway 3)

7.4.1 Marine mammals feed on a variety of pelagic and demersal prey.  The diet of seals, bottlenose dolphin and harbour porpoise species around Scotland and the North Sea is summarised below (Table 11).

Table 11: Prey species commonly consumed by the marine mammals around Scotland and the North Sea

Species Diet
Common Seal Sandeels with octopus, gadoids and clupeids also consumed.  
Grey Seal Sandeels, gadoids (particularly cod), flatfish (particularly plaice) and sculpins.
Harbour Porpoise Sandeels, gadoids such as whiting and clupeids (herring and sprats).  
Bottlenose Dolphin Primarily feed on gadoids such as cod, saithe and whiting as well as Atlantic salmon and cephalopods. 

(Based on information from DECC[127], Reid et al.[128], Santos et al.[129], MacLeod et al.[130]

7.4.2 Fish are attracted to solid man-made structures placed on the seabed and artificial reefs are often deployed to enhance fisheries [131]. These structures 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 [132]. A study by Raoux et al. [133] recorded an increase in biomass on piles and turbine scour protections post construction of a wind farm, suggesting that fish, marine mammals and seabirds responded positively to the increase in biomass.

7.4.3 Structures can change local abiotic conditions allowing species assemblages to form that are different from natural communities present [134].  Therefore, the potential for prey items of marine mammals to be attracted to underwater structures which could act as a Fish Aggregating Device (FAD) will largely be dependent on the habitat preference of specific species. For example, pelagic species such as salmon, which undertake large migrations and seasonal movements, are less likely to aggregate around structures than demersal species such as gadoids which show a greater association with the seabed.

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

7.5.1 Foraging areas are a critical habitat for marine mammals. ACCOBAMS (Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and contiguous Atlantic area) described critical habitat as ‘a place or area regularly used by a cetacean group, population or species to perform tasks essential for survival and equilibrium maintenance’ [135].  Marine mammals have very large ranges, typically to undertake foraging, but mammals can often be aggregated in ‘hotspot’ areas where key prey resources are found in high densities.  For example, important foraging habitat for harbour porpoises includes areas of strong tidal currents, usually near islands or headlands, where the currents combine with the seafloor topography and seem to create conditions where a higher abundance of prey are recorded [136] [137] [138].  Spawning and nursery sites for prey species will be particularly sensitive to any environmental change.

7.6 Physical Damage to Species (Damage to Seal Haul-Outs; Impact Pathway 7)

7.6.1 Impacts to intertidal areas from cable laying or other infrastructure could affect established seal haul out location.  Seals use haul-outs for resting between foraging trips, giving birth (pupping) in the moulting season and also as a nursery for pups [139].  In the UK, grey seals typically breed on remote uninhabited islands or coasts and in small numbers in caves. Harbour seals come ashore in sheltered waters, typically on sandbanks and in estuaries, but also in rocky areas.  Harbour seals haul out on land in a pattern that is often related to the tidal cycle.  In general, both grey and harbour seals are highly sensitive to disturbance by humans hence their preference for remote breeding sites [140].

7.6.2 Grey seals in the UK spend longer hauled out during their annual moult (between December and April) and during their breeding season (between August and December).  Harbour seals give birth to their pups in June and July and moult in August.  At these times of the year seals will be the most susceptible to human disturbance at haul out sites.

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

7.7.1 Marine mammals have quick reflexes, good sensory capabilities and fast swimming speeds (over 6 m/s for harbour porpoise). These qualifying species are also considered to be very agile [141] [142]. These are all attributes which increase the chance of close-range evasion with an object.  However, marine mammal collisions with anthropogenic structures, such as fishing gear and ships, are well documented [143] [144]. Reduced perception levels of a collision threat through distraction, whilst undertaking other activities such as foraging and social interactions, are possible reasons why collisions are recorded in marine mammals [145].  Young grey seal pups, which are inexperienced at sea, could be particularly vulnerable to collision risk. Dive patterns of juvenile grey seal pups have shown that the majority of their time is spent either at the surface or close to the maximum dive depth, which is usually the seabed. Results show that they swim directly to the bottom and so, spend little time in mid water.

7.7.2 Marine mammals can also be very curious of new foreign objects placed in their environment and so curiosity around an object could also increase the risk of collision. Marine mammals are relatively robust to potential strikes as they have a thick sub-dermal layer of blubber which would defend their vital organs from the worst of any blows [146]. Nevertheless, a direct collision still has the potential to cause injury to marine mammals.

7.7.3 For offshore wind farm projects, the underwater structures are essentially static (either fixed or floating) therefore, collision risk during operational phases to these structures is considered low. There is an additional risk of collision with vessels associated with the various phases of the development; however, these vessels will be carrying out activities at low speeds and the risk is therefore minimal.

7.7.4 Marine mammals have the potential to become entangled with rope and/or lines.  There are a number of risk factors associated with entanglement including biological characteristics of marine mammals and the physical features of the mooring themselves [147]. Biological factors include body size, flexibility, ability to detect mooring lines, and mode of feeding. However, pinnipeds, harbour porpoise and bottlenose dolphins are considered to have comparatively small risk of entanglement as they are small and agile and are able to detect objects in the water from tens of metres away [148].

7.7.5 The echo locating ability of cetaceans, such as the bottlenose dolphin and harbour porpoise, allows them to detect small objects at these distances. The narrow bisonar beam of harbour porpoise uses a very high peak frequency (~130 kHz) and is able to detect small objects such as fishing nets mesh and floats [149].

7.7.6 Pinnipeds have the ability to detect objects through acute mechanosensitivity through their vibrissae or whiskers [150] [151].

7.7.7 Marine mammals may become entangled with a rope or line if the animal’s ability to detect the object is compromised under particular environmental conditions such as low light conditions, or during storms.  Marine mammals may also be distracted while feeding on mobile prey species and so not detect the hazard [152].

7.7.8 In addition, large whales have been anecdotally seen seeking out cables in search of a surface to scratch themselves [153] [154].  If pinnipeds or cetaceans were to show this behaviour, it could increase the risk of entanglement. Entanglement in mooring lines is unlikely to be an issue given the latest available evidence [155].  If necessary, however, potential entanglement in mooring lines can be mitigated by using high visibility mooring lines.

7.8 Non-Physical Disturbance (Noise/Visual Disturbance Causing Barrier and Exclusion Effects; Impact Pathways 9 to 11)

Visual

7.8.1 Disturbance caused by an external visual influence can cause marine mammals to stop feeding, resting, travelling and/or socialising, with possible long-term effects of repeated disturbance including loss of weight, condition and a reduction in reproductive success [156] [157].  The group which are most at risk from visual disturbance are seals (when they are resting or breeding on land).  In general, ships more than 1,500 m away from grey seal haul out areas are unlikely to evoke any reactions from grey seals. Between 900 m and 1,500 m, grey seals could be expected to detect the presence of vessels and at closer than 900 m a flight reaction could be expected [158].

7.8.2 In the UK, there are currently no good-practice guidelines for minimisation of disturbance by shipping or commercial vessels [159].  However, the Scottish Marine Wildlife Watching Code that was designed for recreational water users advises that the minimum approach distance for vessels to avoid visual and noise disturbance to dolphins and porpoises is 50 m (200-400 m for mothers and calves, or for animals that are clearly actively feeding or in transit).  The code however isn’t necessarily appropriate for repeated commercial activities.

Noise

7.8.3 Marine mammals (particularly cetaceans) are sensitive to acoustic disturbance in the marine environment, due to their use of echolocation and vocal communication[160].  In comparison to fish, marine mammal species are sensitive to a very broad bandwidth of sound (being responsive at frequencies from 100 Hz to 170 kHz and possessing sensitive hearing over the frequency range from 20 kHz to 150 kHz). The hearing sensitivity and frequency range of marine mammals varies between different species and is dependent on their physiology.  For example, odontocete cetaceans (toothed whales, porpoises and dolphins) are particularly sensitive to high frequencies.

7.8.4 The impacts of noise on marine mammals can broadly be split into lethal and physical injury, auditory injury and behavioural response.  Chronic stress related disorders can also occur with long-term, repeated exposure to a noise source.  These responses are discussed in more detail below.

7.8.5 At very high exposure levels, such as those typical close to underwater explosive operations or offshore impact piling (pile driving) operations, the possibility exists for lethality and physical damage to occur. As the time period of the exposure increases (represented by the impulse), there is also an increase in likelihood of fatality.  A permanent threshold shift (PTS) is permanent hearing damage caused by very intensive noise or by prolonged exposure to noise.  A temporary threshold shift (TTS) involves a temporary reduction of hearing capability caused by exposure to underwater noise.  The level of PTS or TTS will depend on the hearing sensitivity of marine mammals at different frequencies and the overall tolerance of their auditory systems to intense noise.  Lucke et al. [161], for example, undertook an auditory study to derive data on TTS induced by single impulses for harbour porpoise after exposure to seismic airgun stimuli.  At 4 kHz the predefined TTS criterion was exceeded at a received sound pressure level of 199.7 dBpk-pk re 1 µPa and a sound exposure level (SEL) of 164.3 dB re 1 µPa2 s.

7.8.6 At lower Sound Pressure Levels (SPLs), it is more likely that behavioural responses to underwater sound will be observed in marine mammals.  These reactions may include the animals leaving the area for a period of time, or a startle reaction may be observed.  Interference with the detection of biologically relevant communication signals such as echolocation clicks or social signals (masking) may also occur at lower levels of noise.  Masking has been shown in acoustic signals used for communication among marine mammals (see Clark et al. [162]).  Masking may in some cases hinder echolocation of prey or detection of predators.  If the signal-to-noise ratio prevents detection of subtle or even prominent pieces of information, inappropriate or ineffective responses may be shown.

7.8.7 NOAA [163] provides technical guidance for assessing the effects of underwater anthropogenic (human-made) sound on the hearing of marine mammal species.  Specifically, the received levels, or acoustic thresholds, at which individual marine mammals are predicted to experience changes in their hearing sensitivity (either temporary or permanent) for acute, incidental exposure to underwater anthropogenic sound sources are provided.  These thresholds update and replace the previously proposed criteria in Southall et al. [164] for preventing auditory/physiological injuries in marine mammals.

7.8.8 The NOAA [165] thresholds are categorised according to marine mammal hearing groups.  According to NOAA [166], harbour porpoise is categorised as a high-frequency (HF) cetacean, bottlenose dolphin as a mid-frequency (MF) cetacean, and grey seal and common seal are categorised as a phocid pinniped (PW).  The acoustic thresholds for the onset of TTS and PTS due to impulsive sound sources (e.g. percussive piling) for these marine mammal groups are presented in Table 12.

7.8.9 Behavioural reactions to acoustic exposure are less predictable and difficult to quantify than effects of noise exposure on hearing or physiology as reactions are highly variable and context specific [167].  Whilst recognising these limitations, Southall et al. [168] reviewed a number of disturbance studies to determine possible behavioural response criteria for individual marine mammals exposed to single pulses.  There are no equivalent behavioural response criteria for multiple pulses that would represent percussive piling.  The single pulse criteria could be compared to the weighted model outputs for different hearing group categories to provide a high-level indication of the potential scale of disturbance. Another potential approach to assessing the behavioural reaction to noise is through consideration of dose-response curves[169],[170].

7.8.10 New recommendations have recently been published regarding marine mammal noise exposure [171] which complement the NOAA [172] thresholds.  Southall et al. [173] looks at a wider range of marine mammal species and also consider the hearing sensitivity of amphibious mammals (namely seals and otters) to airborne noise.

Table 12: Marine mammal noise exposure criteria

Hearing group PTS TTS
High-frequency cetacean (HF) 202 dB peak SPL 155 dB SELcum 196 dB peak SPL 140 dB SELcum
Mid-frequency cetacean (MF) 230 dB peak SPL 185 dB SELcum 224 dB peak SPL 170 dB SELcum
Phocid pinniped (PW) 218 dB peak SPL 185 dB SELcum 212 dB peak SPL 170 dB SELcum
Peak SPL has a reference value of 1 μPa. SELcum denotes cumulative SEL with a reference value of 1 μPa2 s over a 24-hour period.

7.8.11 Dähne et al, [174] monitored the response of harbour porpoise during percussive piling for the foundations of 12 wind turbines at the first offshore wind farm in Germany, ‘Alpha Ventus’. Visual monitoring was carried out prior to and during construction by 15 aerial transects from 2008-2010. In addition, Static Acoustic Monitoring (SAM) with echolocation click loggers was deployed at 12 locations between 1 and 50 km from the centre of the wind farm between 2008-2011. The results suggest a pile driving related behavioural reaction at much larger distances than just an avoidance radius would suggest [175].

7.8.12 A more recent study by Graham et al. [176] studied responses of bottlenose dolphins and harbour porpoises to two types of pile driving: impact and vibration during harbour construction in northeast Scotland. Both species were not excluded from the area during both piling activities, however, Bottlenose dolphins spent less time in the area (under both piling activities), which may be attributable to the strongly pulsed sound signature from the vibration piling. Whilst vibration piling is considered as a mitigation measure because it is a quieter alternative to impact piling, the study advised that caution should be granted to its efficacy as a mitigation measure as vibration piling exhibited greater impacts on behavioural responses on the two species, than originally anticipated.

7.8.13 Long-term, repeated exposure to a noise source can cause chronic stress in marine mammals.  A range of issues may arise from the extended stress response including accelerated ageing, slow disintegration of body condition, sickness symptoms and suppression of reproduction (physiologically and behaviourally) [177] [178].  Wright et al. [179] found that young animals may be particularly sensitive to stressors for a number of reasons including the sensitivity of their still-developing brains.

7.8.14 One of the greatest potential impacts on marine mammals from offshore wind farm development is from the noise during construction activities such as impact piling [180] [181].  A number of studies have investigated the distances at which marine mammals may be disturbed as a result of piling and blast noise associated with offshore wind farms (Table 13).  Based on the findings from these studies it is apparent that, although hearing injuries from construction are only likely to occur within several hundred metres of pile driving activity, strong avoidance responses could occur several kilometres from the piling with masking of vocalization and mild behavioural changes (e.g. change in swimming direction) occurring as far away as 50km or more from a wind farm development.

7.8.15 Presence of sub-surface structures may present a barrier to movement and migratory pathways depending on array location.  Cetaceans are highly mobile, pelagic species which can undergo large seasonal movements and migrations [182] [183].  They can therefore be vulnerable to any structures which could act as a barrier, preventing movement to foraging or nursery grounds. However, the presence of offshore wind turbines is unlikely to prevent movement for these highly mobile species which could circumvent the arrays if required.

7.8.16 Seals are also highly mobile and as with bottlenose dolphin and harbour porpoise, the sensitivity to this impact pathway (barrier to movement) is considered to be low.

7.8.17 Prolonged disturbance in an area has the potential to displace marine mammals from critical habitat (key sites used for important life processes such as feeding, breeding and raising young) [184].  For some species, areas of critical habitat can be difficult to define, particularly for pelagic species which are often highly dispersed and have large ranges. However, studies have also shown that relatively localised areas may be particularly important for some species in certain areas [185].

Table 13: Summary of research on the spatial extent of piling noise impacts on marine mammals

Activity Study Background Information Reference
Pile driving Empirical study on underwater noise levels during pile-driving at turbines in NE Scotland and potential effects on marine mammals. Pile-driving noise was measured at distances of 0.1 to 80km (when background noise was no longer distinguishable above ambient). The study concluded that for bottlenose dolphins auditory injury would only have occurred within 100m of the pile-driving and behavioural disturbance (defined as modifications in behaviour) could have occurred up to 50km away.   Bailey et al. (2010)[186].
Empirical studies of porpoise behaviour during construction of offshore wind farms at Horns Rev (North Sea) and Nysted (Baltic). At the wind farms, acoustic activity of porpoises decreased shortly after each pile-driving event and returned to baseline conditions after 3-4h.  This effect was not only observed in the direct vicinity of the construction site but also at monitoring stations approximately 15km away.  Behavioural observations showed that during pile-driving, porpoises exhibited relatively more directional swimming patterns. This effect was found at distances of more than 11km, and possibly also up to 15km from the construction site. Tougaard et al., (2003a[187], 2003b)[188].
Assessment of the likely sensitivity of bottlenose dolphins to pile-driving noise.   Research concluded that at 9kHz, masking of strong vocalisations could potentially occur within 10 to 15km.  The potential masking radius was predicted to reduce with increasing frequency to 6km at 50kHz and 1.2km at 115kHz. David (2006)[189].
Attenuation of modelled pile-driving noise at different distances from the source levels. Study concluded that pile-driving noise, under realistic North Sea conditions, would be audible to harbour porpoises and seals over distances of at least 80km. The dBht metric was applied which indicated that mild behavioural reactions (e.g. subtle change in swimming direction) in harbour porpoises might occur between 7 and 20km distance from the pile-driving source. Thomsen et al. (2006)[190].
A two-zone model of effect from pile-driving noise based on measurements from North Hoyle, Scroby Sands, Kentish Flats, Barrow and Burbo Bank. A Noise Injury Zone, bounded by the 130dBht contour, defines the area in which hearing injury can occur, and, in addition, the areas in which lethal and physical injury could occur, since the ranges at which these will occur are much less than those for hearing injury.  This area typically extends to a few hundred metres from pile driving. The Behavioural Effect Zone is bounded by the 90dBht level contour. Within this area, the modelling suggested that harbour porpoise show strong avoidance within ranges of a few kilometres. Milder behavioural effects could occur at ranges of the order of 10 km or more. Noise from pile driving operations can remain above the background underwater noise to ranges of 25 km or more. Nedwell et al., (2003a)[191]; Nedwell et al., (2007a)[192].
Assessment of lethal and physical injury of marine mammals and requirements for Passive Acoustic Monitoring. The estimated likely impact ranges from a 4.7m diameter pile (252 dB re: 1 µPa source level) were predicted to be 4m for lethal range and 81m for injury range. A 6m diameter pile (260 dB re: 1 µPa source level) had a lethal range of 65m and an injury range of 530m. Parvin et al. (2007)[193].
Responses of harbour porpoises to pile driving at the Horns Rev II offshore wind farm in the Danish North Sea. Porpoise acoustic activity was reduced by 100% during 1 hr after pile driving and stayed below normal levels for 24 to 72 hrs at a distance of 2.6 km from the construction site. This period gradually decreased with increasing distance. A negative effect was detectable out to a mean distance of 17.8 km. At 22 km it was no longer apparent. Out to a distance of 4.7 km, the recovery time was longer than most pauses between pile driving events. Porpoise activity and possibly abundance were reduced over the entire 5-month construction period. The behavioural response of harbour porpoises to pile driving lasted much longer than previously reported. Brandt et al. (2011)[194]
Disturbance of harbour porpoises during construction of the first seven offshore wind farms in Germany.  Found a clear gradient in the decline of porpoise detections after piling, depending on noise level and distance to piling. Declines were found at sound levels exceeding 143 dB re 1 µPa2s and up to 17 km from piling. When only considering piling events with noise mitigation system (NMS), the maximum effect distance was 14 km. Compared to 24-48 h before piling, porpoise detections declined more strongly during unmitigated piling events at all distances: at 10-15 km declines were around 50% during piling without NMS, but only 17% when NMS were applied. Within the vicinity (up to about 2 km) of the construction site, porpoise detections declined several hours before the start of piling and were reduced for about 1-2 d after piling, while at the maximum effect distance, avoidance was only found during the hours of piling. Brandt et al. (2018)[195]
Behavioural responses of a harbour porpoise Phocoena phocoena to playbacks of broadband pile driving sounds.  In this study, a harbour porpoise was exposed to pile driving sounds. At and above a received broadband SPL of 136 dB re 1 μPa the porpoise's respiration rate increased in response to the pile driving sounds. At higher levels, he also jumped out of the water more often. Wild porpoises are expected to move tens of kilometres away from offshore pile driving locations; response distances will vary with context, the sounds' source level, parameters influencing sound propagation, and background noise levels. Kastelein et al. (2013)[196]
Blasting Sensitivity of marine mammals to blasting. In this study, an impulse of 69 Pas is given as leading to a low incidence of trivial blast injuries with no eardrum ruptures. The report found that for a 45 kg charge the blast impulse will fall to this level at a range of about 2.2 km. In addition to these figures, dBht levels were calculated from the standoff distances measurements at 600 metres, these are given as 135 dBht Phocoena phocoena harbour seal, 152 dBht (Phocoena vitulina) harbour porpoise and 158 dBht (Orcinus orca) killer whale. The linear SPL at this range was 217 dB re 1 µPa.  These figures are in excess of the 90 dBht reaction threshold. Nedwell et al., (2007a)[197].
Assessment of lethal and physical injury of marine mammals and requirements for Passive Acoustic Monitoring. Blast source levels were found to have lethal ranges of 6-110m and injury ranges of 48-900m. Parvin et al., (2007)[198].

7.9 Non-Physical Disturbance (Electromagnetic Fields; Impact Pathway 12)

7.9.1 The risk to cetacean species of being affected by electromagnetic fields is considered to be low.  These fields arise from electricity transmission power cables, resulting from the current passing along the conductor and the voltage differential between the conductor and earth ground, which is nominally at zero volts.  The nature and strength of the fields produced, depends on the system voltage and the current (AC or DC) passing through.  The effects on the surrounding environment depend on the cable construction, configuration and orientation in space.

7.9.2 In order to standardise terminology, Gill et al. [199] proposed the term EMF should be used to describe the direct electromagnetic field.  The two constituent fields of the EMF should be clearly defined as the E (Electric) field and the B (Magnetic Field) field, whilst the induced electric field should be labelled the iE field.

7.9.3 Magnetic Fields are produced from AC or DC current passing through the conductor and these emanate outwards from the cable in a circular plane, perpendicular to its longitudinal axis.  The field strength produced as a result of the operation of electricity transmission (AC or DC) decreases rapidly with distance away from the source (the decay curve follows the inverse square law).  The magnetic field around an AC cable is constantly changing at the same frequency as the alternating current that is producing it, which means that the modulation it produces in the Earth’s field will also be constantly variable.

7.9.4 Marine mammals are not considered to be electrosensitive species [200].  For magnetosensitive species, sensitivity to the geomagnetic field is associated with a direction-finding ability e.g. migration.  Gill et al. [201] lists cetaceans including the harbour porpoise as magnetosensitive. It is therefore considered that anthropogenic sources of EMF have the potential to affect spatial orientation[202] . No evidence has been found to suggest that pinnipeds are magnetoreceptive [203].

7.9.5 The underlying assumption that cetaceans have ferromagnetic organelles capable of determining small differences in relative magnetic field strength remains, however unproven and is based on circumstantial information.  There is also no apparent evidence that existing cables have influenced migration of cetaceans.  Migration of the harbour porpoise in and out of the Baltic Sea necessitates several crossings over operating subsea HVDC cables in the Skagerrak and western Baltic Sea without any apparent effect on their migration pattern [204]. The current evidence on the potential effects of EMF (if any) originating from subsea cables remains unclear, with no significant impacts found to date[205].

7.10 Toxic Contamination (Contamination and Spillages; Pathways 14 and 15)

7.10.1 Spillage of oils and fluids from construction vessels and machinery into the marine environment could adversely affect sediment or water quality during all phases of a wind farm development.

7.10.2 Leaching of toxic compounds from sacrificial anodes, antifouling paints or leakage of hydraulic fluids (if present) from the device is a potential effect during device operation.  Seals and cetaceans in the study area generally have a low sensitivity to contamination, although the level of sensitivity increases to medium around seal breeding sites [206].

7.10.3 Marine mammals are also exposed to a variety of anthropogenic contaminants, through the consumption of prey. As top predators, they are at particular risk from contaminants which biomagnify through the food chain (i.e. are found at increasing concentrations at higher trophic levels).  Most research has focused on two main groups of contaminants: the persistent organic pollutants (POP) and the heavy metals. However, there is some information on other contaminants including polyaromatic hydrocarbons (PAHs), butyl tins and perfluorinated chemicals[207].

7.10.4 POPs accumulate in fatty tissues, are persistent and commonly resistant to metabolic degradation; they are often found in high concentrations in marine mammal blubber. They may affect the reproductive, immune and hormonal systems which can eventually lead to mortality.  For example, Jepson et al. [208] suggested a possible link between high levels of PCB (polychlorinated biphenyls) recorded in the blubber of stranded dead bottlenose dolphins in the UK with the decline in bottlenose dolphins observed in this region between 1960s and 1990s.  A strong association has also been found between poor health status (mortality due to infectious disease) and PCB chemical contamination for a large sample of UK-stranded harbour porpoises collected since 1990 [209].

7.10.5 Cadmium, lead, zinc and mercury are the heavy metals of greatest importance in marine mammals. They are frequently present in the highest concentrations in the liver, kidney and bone, with levels varying considerably with the geographic location of the species.  Marine mammals are able to produce certain proteins (metallothioneins) which can sequester certain metal ions into less toxic complexes; this enables many species to cope with relatively high dietary exposures to certain metals.  Whilst there are few studies that show major impacts of heavy metals, it is possible that they may have combined effects as they often co-occur with the persistent organic contaminants[210].

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

7.11.1 Increased turbidity could affect foraging, social and predator/prey interactions of marine mammals, although marine mammals around the UK are regularly recorded foraging in highly turbid environments such as estuaries and tidal streams.

7.11.2 All UK marine mammals use vision to navigate in their environment, avoid obstacles and forage. Marine mammals can forage throughout the diurnal cycle, in very turbid waters and therefore are able to function as predators in very low light levels.  Marine mammals are also known to have acute hearing capabilities. Seals just use passive listening while Odontocetes are known to use both passive and active listening when navigating and foraging (echolocation). This also helps marine mammals operate in low visibility, turbid conditions [211].

7.12 Grey and Common Seals (Pinnipeds) Sensitivity Review

7.12.1 Table 14 shows the sensitivities of qualifying seal interest features to the activities associated with the draft Plan. The level of sensitivity is low for all impact pathways with the exception of noise/vibration disturbance which is considered high.

Table 14: Potential sensitivities of seal 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. LS LS LS LS
PD Physical Damage to habitat 7 Damage to seal haul out locations during the installation, decommissioning and operation of the cables and cable armouring.   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 10 Visual disturbance and exclusion from areas as a result of surveying, cable and device installation/operation and decommissioning activities and movements of vessels. LS LS LS LS
NPD Non-physical disturbance 11 Noise/vibration disturbance and exclusion from areas as a result of vessels and other activities during survey work (e.g. seismic exploration and geophysical surveys, UXO clearance), construction (e.g. piling, drilling, cable laying), operation (e.g. device noise), maintenance or decommissioning. LS HS LS MS
TC Toxic Contamination (Reduction in water quality) 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 (Reduction in water quality) 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 (Elevated turbidity) 16 Increase in turbidity (and possibly reduced dissolved oxygen) 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 marine mammals 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

7.13 Bottlenose Dolphin and Harbour Porpoise (Cetaceans) Sensitivity Review

7.13.1 Table 15 shows the sensitivities of qualifying cetacean interest features (namely bottlenose dolphin and harbour porpoise) to the activities associated with the Sectoral Offshore Wind Plan.

Table 15: Potential sensitivities of cetacean 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. LS 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 10 Visual disturbance and exclusion from areas as a result of surveying, cable and device installation/operation and decommissioning activities and movements of vessels. LS LS LS LS
NPD Non-physical disturbance 11 Noise/vibration disturbance and exclusion from areas as a result of 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 (Reduction in water quality) 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 (Reduction in water quality) 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 (Elevated turbidity) 16 Increase in turbidity (and possibly reduced dissolved oxygen) 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 marine mammals 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

7.14 Potential Effects on European/Ramsar Sites from the Sectoral Offshore Wind Plan

7.14.1 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 European/Ramsar sites.

7.14.2 In the UK the conservation objectives for the four qualifying features (grey seal, common seal, bottlenose dolphin and harbour porpoise) are typically the same across different European/Ramsar sites.  The UK objectives 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 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; and
  • No significant disturbance of the species.

7.14.3 Taking account of the conservation objectives and the plan-level activities to which the key interest features (all marine mammal qualifying features within the SAC/Ramsar sites) 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 16.

Table 16: Assessment of the potential effects of the Sectoral Offshore Wind Plan on the marine mammal features of relevant European/Ramsar sites

Screened-in sites with these qualifying features are provided in Table C1 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
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

Physical Loss/Gain of habitat

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 14 and Table 15 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
Marine mammals are highly mobile and have large foraging ranges. Any loss of habitat because of a wind farm development is likely to only constitute a very small fraction of the total area used by a species for foraging. In addition, a study by Diederichs et al. [212] found no significant influence of wind farms on the occurrence of harbour porpoises which were found to be recorded moving through and foraging in two wind farm areas (Horns Rev-North Sea and Nysted-Baltic Sea) almost daily.
Relevant Conservation Objectives (see Section 7.14)
Of the 5 objectives, two are considered to be particularly relevant to impacts from physical loss/gain of habitat during the operational phase of the Sectoral Offshore Wind Plan:
  • Distribution and extent of habitats supporting the species; and
  • Structure, function and supporting processes of habitats supporting the species.
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

Physical Loss/Gain of habitat

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 14 and Table 15 for detail and colour code) As above As above

Commentary/ Review (see Section 7.14))
The base of wind turbines could potentially act both as artificial reefs and as FADs for prey species of marine mammals. Wilhelmsson et al. [213] investigated this 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. 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 [214]. 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 [215]. Both cod and whiting are prey items for marine mammals such as harbour porpoise and grey seal. Harbour porpoise have also been regularly recorded foraging around wind farm areas which could be because of an increase in prey species [216]. A study by Raoux et al. [217] concluded that increased biomass around offshore wind turbines resulted in positive feeding opportunities for marine mammals. The size of an array will be a key consideration and devices with the highest FAD potential are therefore those with large elements e.g. large mooring points or floating structures.  Devices with large moorings may provide additional shelter and food (habitat) for small demersal fish such as territorial blennies and gobies (Love et al., 2000).  Increases in demersal fish have been observed around the piles of off-shore wind farms [218] [219]. However, it is generally agreed that fish aggregation probably represents a very minor effect DECC (2009). Empirical data on the relationship between marine mammals and prey that might be aggregating around wind turbines is currently limited. 

Relevant Conservation Objectives (see Section 7.14))
Of the 5 objectives, three are considered to be most relevant to impacts from non-physical disturbance as a result of an increase in prey species:

  • Distribution of the species within site;
  • Distribution and extent of habitats supporting the species; and
  • Structure, function and supporting processes of habitats supporting the species.
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

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 during operation.

6 Sensitivity Level(s) considered to be low (see Table 14 and Table 15 for detail and colour code) As above As above
Commentary/ Review
Marine mammals are highly mobile and have large foraging ranges. The extent of habitat that might be reduced in quality is only going to constitute a very small fraction of the total area used by a species for foraging making any impact negligible.

Relevant Conservation Objectives (see Section 7.14))
Of the 5 objectives, two are considered to be particularly relevant to impacts from reduction in the quality of foraging habitat:

  • Distribution and extent of habitats supporting the species; and
  • Structure, function and supporting processes of habitats supporting the species.
  • Common seal
  • Grey seal

Physical Damage to Habitat

Damage to seal haul out locations during the installation, decommissioning and operation of the cables and cable armouring.  

7 Sensitivity Level(s) considered to be low (see Table 14 and Table 15 for detail and colour code) As above As above
Commentary/ Review
Seals use haul-out sites for a range of purposes including breeding, resting and moulting [220]. Seals generally choose remote areas to haul-out and are generally highly sensitive to damage and disturbance (particularly in the breeding season). Cable routes are most likely to come ashore where infrastructure already exists on the mainland. Most seals haul-out on uninhabited islands, offshore sandbanks and rocky areas.  Therefore, any damage to seal haul-outs is considered to be unlikely. 

Relevant Conservation Objectives (see Section 7.14)
Of the 5 objectives, two are considered to be particularly relevant to impacts from physical damage of haul-out habitat:

  • Distribution and extent of habitats supporting the species; and
  • Structure, function and supporting processes of habitats supporting the species.
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

Damage to Species

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 14 and Table 15 for detail and colour code) As above As above

Commentary/ Review
Pinnipeds and cetaceans can potentially collide with construction vessel propellers and machinery possibly leading to physical injury and, in the worst case, fatalities.  Juvenile grey seal pups, which are inexperienced in the water, are likely to be particularly vulnerable to collision risk.  Ships travelling at 14 knots (~7 m/s) or faster are most likely to cause lethal or serious injuries if there is a collision [221].  Vessels involved in the construction phase are either likely to be stationary or travelling at much slower speeds than this, and, therefore, risk of injury by collision would be considerably lower. Marine mammals have the potential to become entangled with ropes and/or lines.  Echo locating cetaceans, such as the bottlenose dolphin and harbour porpoise, will be able to detect the object at a distance of tens of metres [222]. Pinnipeds have the ability to detect objects underwater through acute mechano-sensitivity using their vibrissae or whiskers [223] [224].  There are a number of risk factors associated with entanglement including biological characteristics of marine mammals and the physical features of the mooring themselves [225].  Biological factors include body size, flexibility, ability to detect moorings, and mode of feeding.  Pinnipeds, harbour porpoise and bottlenose dolphins are considered to have a low risk of becoming entangled as they are small and agile and are able to detect objects in the water from tens of metres away [226].  Marine mammals may become entangled with a rope or line if the animal’s ability to detect the object is compromised under particular environmental conditions such as low light conditions, or during storms.  Marine mammals may also be distracted while feeding on mobile prey species and so not see the hazard [227].

Entanglement in mooring lines is unlikely to be an issue given the latest available evidence [228].  If necessary, however, potential entanglement in mooring lines can be mitigated by using high visibility mooring lines.

Behavioural responses of marine mammals to perceived threats can be broadly categorized in two ways: avoidance and evasion.  Hence with respect to wind farm developments, marine mammals may demonstrate two types of response: long range avoidance (i.e. avoiding the area within the vicinity of the device(s)) or close-range evasion, depending upon the distance at which the device is perceived and the subsequent behavioural response.  However, collision risk with wind turbine structures is considered low.

Relevant Conservation Objectives (see Section 7.14)
Of the 5 objectives, three are considered to be particularly relevant to impacts from physical damage as a result of collision risk during all phases of the Sectoral Offshore Wind Plan:

  • Population of the species as a viable component of the site;
  • Distribution of the species within site; and
  • No significant disturbance of the species.
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

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 14 and Table 15 for detail and colour code) As above As above
Commentary/ Review
The potential for wind turbines to act as a barrier to movement will be partly dependent on the extent that noise and visual cues from the device(s) cause an avoidance response.  It is also dependent on the ability of marine mammals to navigate around the devices.  The significance of any obstruction will ultimately depend on the spatial confines and size of the array.  Considering the highly manoeuvrable nature of the marine mammal interest features and the offshore locations of the DPOs a low sensitivity has been assessed for marine mammals to this impact pathway. 

Relevant Conservation Objectives (see Section 7.14)
The conservation objectives are designed 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.  All of the 5 objectives are pertinent to the potential effects; however, the following are considered to be most relevant:

  • Distribution of the species within site;
  • Distribution and extent of habitats supporting the species; and
  • Structure, function and supporting processes of habitats supporting the species.
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

Non-Physical Disturbance

Visual disturbance and exclusion from areas as a result of surveying, cable and device installation/
operation and decommissioning activities and movements of vessels.

10 Sensitivity Level(s) considered to be low (see Table 14 and Table 15 for detail and colour code) As above As above
Commentary/ Review
Visual disturbance from vessels in the different phases of development will generally only be short term.  However, the level of impact will be dependent on the distance vessels are away from seal haul out sites and key foraging areas for marine mammals.  Overall sensitivities are considered to be low. 
Relevant Conservation Objectives (see Section 7.14)
The conservation objectives are designed 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.  All of the 5 objectives are pertinent to the potential effects; however, the following are considered to be most relevant:
  • Distribution of the species within site;
  • No significant disturbance of the species.
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

Non-Physical Disturbance

Noise/vibration disturbance and exclusion from areas as a result of 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 14 and Table 15 for detail and colour code) As above As above

Commentary/ Review
The sensitivity of marine mammals is considered to be high during the construction phase (especially where there is a need for piling) but low or medium during other phases of development.  Geophysical surveys carried out for installations of marine renewable devices often involve side scan sonar that may cause acoustic disturbance of marine mammals.  Available information on the magnitude impact from side scan sonar indicates that disturbance (for single or multiple devices) of marine mammals is low (MacGillvray et al., 2014[229]) in contrast to seismic surveys employed for oil and gas exploration which generate greater source noise levels [230].

The effect on marine mammals from vessel noise is not clear, with both attraction and avoidance reactions having been observed [231].  Noise levels from the ship’s echo-sounder or acoustic emissions from a dynamic positioning system would not be expected to cause widespread disturbance to marine mammals [232].  For harbour porpoises the zone of audibility of shipping noise ranges from 1-3 km depending on the frequency of noise emitted by the ship [233].  The Scottish Marine Wildlife Watching Code advises that the minimum approach distance for vessels to avoid visual and noise disturbance to dolphins and porpoises is 50m (200-400m for mothers and calves, or for animals that are clearly actively feeding or in transit). The key sources of noise related to construction and device installation are:

  • Shipping and machinery;
  • Dredging; and
  • Pile driving or drilling.
Additionally, cable burial requires the use of trenching or jetting machinery in soft sediments, rock cutting machinery in hard sea-beds, or rock or concrete mattress laying may be used to protect cables in areas where they cannot be buried. 

Relevant Conservation Objectives (see Section 7.14)
Of the 5 objectives, two are considered to be particularly relevant to impacts from non-physical noise and vibration disturbance:

  • Distribution of the species within the site; and
  • No significant disturbance of the species.
  • Bottlenose dolphin
  • Harbour porpoise

Non-Physical Disturbance

Impacts from Electromagnetic Fields (EMF) on 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 14 and Table 15 for detail and colour code) As above As above
Commentary/ Review
It is assumed that cetaceans may be sensitive to electromagnetic fields[234]. 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)[235]. Furthermore, no studies have suggested that the electromagnetic fields around cables have a behavioural effect on cetaceans. Hence, the sensitivity of bottlenose dolphins and harbour porpoise to electromagnetic fields is considered to be low and only relevant during the operational phases.

Relevant Conservation Objectives (see Section 7.14)
Of the 5 objectives, two are considered to be particularly relevant to impacts from non-physical EMF disturbance:

  • Distribution of the species within site; and
  • No significant disturbance of the species.
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

Toxic Contamination

(Reduction in water quality) 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 14 and Table 15 for detail and colour code) As above As above
Commentary/ 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 marine renewables SEA [236] identifies a range of optional contamination sources including from anti-fouling paints and sacrificial anodes and the accidental leakage of fluids and/or spillage fuels or cargo from vessels.  The quantities and toxicities associated with sacrificial anodes and antifouling coatings are generally expected to be extremely small, and it is therefore considered that this potential effect will be of negligible significance.

Relevant Conservation Objectives (see Section 7.14)
Of the 5 objectives, two are considered to be most relevant to impacts from toxic contamination due to spillage incidents:

  • Distribution of the species within site; and
  • No significant disturbance of the species.
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

Toxic Contamination

(Reduction in water quality) 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 14 and Table 15 for detail and colour code) As above As above
Commentary/ Review
Sediments are generally likely to be low in contaminant levels within DPOs, given the distance away from major coastal development and the inherently dispersive and often dynamic nature of the environment.  The characteristically energetic environments in which the devices will be located will also assist in the dispersion of any localised contamination, thus minimising any impacts on water quality.

Relevant Conservation Objectives (see Section 7.14)
The conservation objectives are designed 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.  In total there are 5 objectives (see Section 7.14.2) and of these the ones that are most relevant to this impact pathway are to maintain the following in the long-term

  • Population of the species as a viable component of the site;
  • No significant disturbance of the species; and
  • Distribution of the species within site
  • Common seal
  • Grey seal
  • Bottlenose dolphin
  • Harbour porpoise

Non-Toxic Contamination

(Elevated turbidity) 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 14 and Table 15 for detail and colour code) As above As above
Commentary/ Review
Local suspended sediment concentrations may increase as a result of drilling of the seabed for the installation of the pile, burial of the power export cables and disposal of drill cuttings.  Increased turbidity could affect foraging, social and predator/prey interactions of marine mammals, although marine mammals around the UK are regularly recorded foraging in highly turbid environments such as estuaries and tidal streams.  All features of interest have a low sensitivity to this impact pathway.

Relevant Conservation Objectives (see Section 7.14))
Of the 5 objectives, two are considered to be particularly relevant to impacts from non-toxic contamination as a result of increased turbidity:

  • Distribution of the species within the site; and
  • No significant disturbance of the species

Contact

Email: drew.milne@gov.scot