Information to inform the assessment

                        Overview of potential changes to prey availability

675. As concluded in the Array HRA Stage One LSE2 Screening Report (Array RIAA Part 1, appendix 1A) Annex II grey seal, harbour porpoise, and bottlenose dolphin are likely to be present within the Array marine mammal study area and may forage within the area. Effects on prey fish populations across all phases of the Array are likely to be temporary, of a short duration, localised and not significant. The widest ranging effect will be from increased underwater noise during the construction phase (mainly due to piling) and is unlikely to be significant in other phases (Array RIAA Part 1, appendix 1A). However, as impacts to prey species have been assessed as part of the underwater noise modelling assessment that has been undertaken for the EIA, this potential impact was included for the construction phase as a precaution for the Annex II marine mammal features of their respective SACs.
676. The underwater noise modelling for all fish hearing groups (i.e. Groups 1 to 4, as opposed to just the results of Groups 1 and 2 presented in section 5.3.1 for the Annex II diadromous fish assessment) was summarised and assessed in volume 2, chapter 9 of the Array EIA Report. For the SPLpk metric associated with the MDS presented in Table 6.42   Open ▸ , the maximum recoverable injury range is estimated at 138 m to 228 m from the piling location. The potential for mortality or mortal injury to fish eggs would also occur at distances of up to 228 m. However, this was considered to be highly conservative due to the implementation of soft starts during piling operations which may allow some fish to move away from the areas of highest noise levels, before the received noise reaches a level that would cause an injury ( Table 6.43   Open ▸ ). As such, the maximum injury ranges predicted for soft start initiation (i.e. of the order of tens of metres) are likely to be more realistic. For the SELcum metric, underwater noise modelling showed that TTS, for the various fish hearing groups could occur out to a maximum distance of 4,161 m for single piling scenario at 4,000 kJ. The potential onset of behavioural effects (such as elicitation of a startle response, disruption of feeding, or avoidance of an area) may occur to ranges of low tens of kilometres. However, responses will differ depending on the sensitivity of the species and the presence/absence of a swim bladder (Popper et al., 2014). Underwater noise only has the potential to impact prey species over a relatively small area in terms of the regional marine mammal study area as a whole. As presented in volume 2, chapter 9 of the Array EIA Report, this potential impact was assessed as being of negligible to minor adverse significance for all fish and shellfish species.
677. With respect to indirect effects on marine mammals, no additional indirect effects other than those assessed for injury and disturbance to marine mammals as a result of elevated underwater noise during piling and UXO clearance have been predicted. This is because if prey were to be disturbed from an area as a result of underwater noise from these activities, it is assumed that marine mammals would be disturbed from the same or greater area. Thus, any changes to the distribution of prey resources would not affect marine mammals as they would already be disturbed from the same (or larger) area. Whilst there may be certain prey species that comprise the main part of their diet, all Annex II marine mammals in this assessment are generalist opportunistic feeders and are thus not reliant on a single prey species. Given that marine mammals are wide-ranging in nature and have a generalist feeding strategy, with the ability to exploit numerous food sources, there would be a variety of prey species available for marine mammal foraging.
678. The key prey species for marine mammals include sandeels, gadoids (including cod, haddock, Norway pout Trisopterus esmarkii, and whiting), clupeids (herring, mackerel Scomber scombrus, and sprat), flatfish (plaice, lemon sole Microstomus kitt, and Pleuronectiformes) (see volume 3, appendix 10.2 of the Array EIA Report for further detail on marine mammal feeding ecology). These prey species have been identified as being of regional importance within the fish and shellfish ecology study area, except for sandeel which is deemed to be of national importance (see volume 2, chapter 9 of the Array EIA Report). The site boundary overlaps with spawning grounds for cod, lemon sole, mackerel, Norway pout, plaice, sandeels, and whiting based on Coull et al. (1998) and Ellis et al. (2012). For herring, no high intensity spawning grounds identified by Coull et al. (1998) directly overlap with the Array marine mammal study area (noting low intensity grounds overlap). Outputs of modelling conducted by Langton et al. (2021) show that the whole Array marine mammal study area has extremely low probability of sandeel presence, with areas where predicted density is high closer to the coasts or towards the Firth of Forth.
679. As the impact of underwater noise affecting fish and shellfish species was assessed as neglgilbe to minor adverse significance within volume 2, chapter 9 of the Array EIA Report, changes in prey availability is not predicted to affect the integrity of the SACs or have population-level effects upon Annex II marine mammals.

                        Construction phase

                        Berwickshire and North Northumberland Coast SAC

                        Grey seal

680. The results of the underwater noise modelling suggest that prey species may be impacted due to underwater noise up to tens of kilometres from the site boundary (paragraph 675 et seq.). Therefore, underwater noise only has the potential to impact prey species over a relatively small area in terms of the regional marine mammal study area as a whole.
681. As detailed in paragraphs 410 and 411, grey seals forage offshore out to and over 100 km and prey on a range of fish, such as flatfish, sandeels, and gadoids (Damseaux et al., 2021, Gosch, 2017, Hammond et al., 2005). Given that the impacts of underwater noise on prey species will be highly localised (in terms of injury) and within tens of kilometres for behavioural disturbance, only a small area will be affected when compared to available foraging habitat for grey seals in the regional marine mammal study area. There may be an energetic cost associated with increased travelling if prey patches are disturbed, however, grey seal is not considered to be particularly vulnerable to this, as foraging trips tend to be wide-ranging (e.g. up to and over 100 km (SCOS, 2023)). There is also evidence that grey seal in Scotland tend to stay within 20 km of their breeding colonies during the breeding season (pers. comm. with NatureScot). The availability of wider suitable habitat across the regional marine mammal study area suggest that individuals may move to alternative foraging grounds without health impairment. It is expected that grey seal population would be able to tolerate the effect without any potential impact on reproduction and survival rates.
682. As outlined in paragraph 675 et seq., no significant adverse effects were predicted to occur to fish and shellfish species during the construction phase of the Array (volume 2, chapter 9 of the Array EIA Report)
683. Therefore, this potential impact is not predicted to result in adverse effects (i.e. disruption to foraging) for the grey seal feature of this SAC.

                        Conclusion

684. Adverse effects on the qualifying Annex II marine mammal features of the Berwickshire and North Northumberland Coast SAC which undermine the conservation objectives of the SAC will not occur as a result of changes in prey availability during the construction phase. Potential effects from this activity on the relevant conservation objectives (as presented in in section 6.2.1) are discussed in turn below in Table 6.44   Open ▸ .

Table 6.44: Conclusions Against the Conservation Objectives of the Berwickshire and North Northumberland Coast SAC from Changes in Prey Availability during the Construction Phase of the Array Alone

685. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Berwickshire and North Northumberland Coast SAC as a result of changes in prey availability in the construction phase of the Array alone.

                        Southern North Sea SAC

                        Harbour porpoise

686. The results of the underwater noise modelling suggest that prey species may be impacted due to underwater noise up to tens of kilometres from the site boundary (paragraph 675 et seq.). Given that the impacts of underwater noise on prey species will be highly localised (in terms of injury) and within tens of kilometres for behavioural disturbance, underwater noise only has the potential to impact prey species over a relatively small area in terms of the regional marine mammal study area as a whole. As detailed in paragraph 420, harbour porpoise has a high metabolic rate. Therefore, there may be an energetic cost associated with disruption to foraging and this species may be particularly vulnerable to this impact. However, harbour porpoises have a widespread distribution throughout the North Sea as a whole, and individuals have been documented either switching to different prey species depending on the prey availability (Santos et al., 2003), or moving relatively large distances on a daily basis (Nielsen et al., 2013). Based on the findings of Benhemma-Le Gall et al. (2021), it can be anticipated that harbour porpoise can compensate for any resulting loss in energy intake by increasing foraging activities beyond potentially affected areas. The availability of wider suitable habitat across the regional marine mammal study area suggest that individuals may move to alternative foraging grounds without health impairment.
687. As outlined in paragraph 675 et seq., no significant adverse effects were predicted to occur to fish and shellfish species during the construction phase of the Array (volume 2, chapter 9 of the Array EIA Report)
688. Therefore, this potential impact is not predicted to result in adverse effects (i.e. disruption to foraging) for the harbour porpoise feature of this SAC.

                        Conclusion

689. Adverse effects on the qualifying Annex II marine mammal features of the Southern North Sea SAC which undermine the conservation objectives of the SAC will not occur as a result of changes in prey availability during the construction phase. Potential effects from this activity on the relevant conservation objectives (as presented in section 6.2.2) are discussed in turn below in Table 6.45   Open ▸ .

Table 6.45: Conclusions Against the Conservation Objectives of the Southern North Sea SAC from Changes in Prey Availability during the Construction Phase of the Array Alone

690. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Southern North Sea SAC as a result of changes in prey availability in the construction phase of the Array alone.

                        Moray Firth SAC

                        Bottlenose dolphin

691. The results of the underwater noise modelling suggest that prey species may be impacted due to underwater noise up to tens of kilometres from the site boundary (paragraph 675 et seq.). Given that the impacts of underwater noise on prey species will be highly localised (in terms of injury) and within tens of kilometres for behavioural disturbance, underwater noise only has the potential to impact prey species over a relatively small area in terms of the regional marine mammal study area as a whole. In addition, the bottlenose dolphin feature of the Moray Firth SAC are typically coastal, and the site boundary (approximately 80 km offshore) is not likely to represent a key foraging ground for this population.
692. The habitat use of bottlenose dolphin varies greatly, even within a population, and generally the distribution of this species is influenced by factors such as tidal state, weather conditions, resource availability, life cycle stage, or season (Hastie et al., 2004). Typical prey items for bottlenose dolphin in Scottish waters include Atlantic salmon, cod, haddock, saithe, and whiting (Santos et al., 2001), therefore, they have been considered to be generalist feeders.
693. There is a seasonal pattern of bottlenose dolphin movement from the Tay estuary and adjacent waters to the Moray Firth SAC in the early summer months, and from the Moray Firth SAC to the Tay estuary and adjacent waters in late summer (Arso Civil et al., 2021). This movement is anticipated to be driven by environmental and biological factors (Arso Civil et al., 2021). Studies by Wilson et al. (1997) and Hastie et al. (2004) reported that these two areas share topographically distinct characteristics with increased observations of dolphins foraging. Seasonal changes in prey presence over variable temporal scales throughout the year may therefore enable bottlenose dolphins to exploit these areas within their range at different times.
694. As outlined in paragraph 675 et seq., no significant adverse effects were predicted to occur to fish and shellfish species during the construction phase of the Array (volume 2, chapter 9 of the Array EIA Report)
695. Therefore, this potential impact is not predicted to result in adverse effects (i.e. disruption to foraging) for the bottlenose dolphin feature of this SAC.

                        Conclusion

696. Adverse effects on the qualifying Annex II marine mammal features of the Moray Firth SAC which undermine the conservation objectives of the SAC will not occur as a result of changes in prey availability during the construction phase. Potential effects from this activity on the relevant conservation objectives (as presented in section 6.2.3) are discussed in turn below in Table 6.46   Open ▸ .

Table 6.46: Conclusions Against the Conservation Objectives of the Moray Firth SAC from Changes in Prey Availability during the Construction Phase of the Array Alone

697. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Moray Firth SAC as a result of changes in prey availability in the construction phase of the Array alone.

6.3.5. Entanglement

698. The LSE2 assessment during the HRA Stage One process identified that during the operation and maintenance phase, LSE2 could not be ruled out for entanglement. This relates to the following sites and relevant Annex II marine mammal features:

• Berwickshire and North Northumberland Coast SAC;

–           grey seal.

• Southern North Sea SAC; and

–           harbour porpoise.

• Moray Firth SAC;

–           bottlenose dolphin.

699. The MDS and secondary mitigation measures considered for the assessment of entanglement are shown in Table 6.47   Open ▸ and Table 6.48   Open ▸ , respectively.

Table 6.47: MDS Considered for the Assessment of Potential Impacts to Annex II Marine Mammals due to Entanglement during the Operation and Maintenance Phase

Table 6.48: Designed In Measures Considered for the Assessment of Potential Impacts to Annex II Marine Mammals to Entanglement during the Operation and Maintenance Phase

                        Information to inform the assessment

                        Overview of entanglement

700. To provide stability and the fixed positioning of floating wind turbines within the Array, effective mooring systems will be implemented. Additionally, a connection to dynamic inter-array cables will facilitate interlinking between individual wind turbines.
701. There are concerns regarding the hazards that mooring lines and dynamic cables may pose to marine mammals, which could inadvertently become entangled or entrapped (MD-LOT, 2023). The entanglement risk can be categorised into two types: primary and secondary (SEER, 2022). Primary entanglement refers to the direct entanglement of marine life with mooring lines or dynamic cables. Secondary entanglement occurs when marine life becomes entangled with marine debris, such as derelict fishing gear, that has become snagged on a mooring line or dynamic cable (SEER, 2022). According to Benjamins et al. (2014), the entanglement risk is contingent upon various physical and biological parameters. Physical parameters, integral to the wind farm design, encompass mooring tension characteristics, cable/mooring line diameter, swept volume and curvature. In parallel, biological parameters include body size, the ability of animals to detect moorings, body flexibility and general feeding modes.
702. As outlined in the MDS ( Table 6.47   Open ▸ ), the Array will have up to 116 km of dynamic inter-array cables within the water column. Each wind turbine will be equipped with a mooring system, which introduces the additional potential for entanglement, with up to 1,590 mooring lines. The Project Description for the Array considers various mooring line design options for semi-submersible floating wind turbines, including full chain catenary, semi-taut and taut, both incorporating a top fibre rope section (nylon or polyester) and a bottom chain section.
703. According to Benjamins et al. (2014), tension characteristics in moorings significantly affect entanglement risk, with taut moorings under high tension being less likely to cause entanglement than flexible ones under low tension. The potential impact of dynamic moorings can be assessed by the concept of swept volumes, as it considers the volume of the water column occupied by mooring lines under energetic conditions (Benjamins et al., 2014). A useful physical parameter in the assessment of entanglement is also curvature, as it assesses the bending of mooring lines, with taut configurations exhibiting smaller curvatures compared to catenary configurations (Benjamins et al., 2014). Harnois et al. (2015) found that the catenary moorings with chains configuration shows the highest curvature values.
704. Benjamins et al. (2014) findings indicate a greater risk of entanglement to marine mammals with catenary moorings, particularly those containing nylon. Across all potential mooring line types considered for the Array, catenary moorings represent the MDS for entanglement risk. It can be anticipated that, especially for catenary mooring type, there will be some horizontal movement of the floating wind turbine and therefore the mooring line may experience stretching (representing the maximum length in the water column) or slackness (representing the maximum length resting on the seabed). To address this, clump weights may be strategically placed around the touchdown point to mitigate the length of the mooring line between the anchor and the wind turbine.
705. While Harnois et al. (2015) suggest that certain features of mooring systems may influence entanglement risk, the study also concluded that the absolute risk of primary entanglement is low regardless of mooring configuration. Garavelli (2020) suggested that all mooring configurations (catenary/taut) have too much tension to create a loop that could entangle a whale. This has been corroborated by SEER (2022), as the study also concluded that the risk of primary entanglement at floating offshore wind farms is very low due to the weight of the cable systems. The potential for heavy mooring gear combined with relatively taut mooring lines to entangle whales has been shown to be negligible (Wursig et al., 2002) and Marine Renewable Energy (MRE) device moorings are unlikely to pose a major threat (Benjamins et al., 2014). Statoil (2015) stated for mooring lines at the Hywind Scotland Pilot Park Project, it was a design requirement that no line should ever go into slack, even in extreme weather conditions, and it was considered effectively impossible for entanglement on a marine mammal to occur. For inter-array cables in the water column cables have a very high bending stiffness and therefore the cable cannot bend around a marine mammal (Statoil, 2015). Therefore, there is a very low risk that primary entanglement can actually occur.
706. Research on the risk to marine mammals has focussed on injury or mortality by entanglement of fishing gear (e.g. nets of slack lines) or submarine telecommunication cables, however these have loose ends or loops that could ensnare animals (Benjamins et al., 2014, Moore et al., 2006) and therefore mooring lines/cables from floating wind turbines are not comparable and has not been considered a significant concern (Copping et al., 2020). Evidence of entanglement of marine animals with MRE mooring lines and cables has not been observed to date (Isaacman et al., 2011, ORJIP Ocean Energy, 2022, Sparling et al., 2013) and even entanglement with offshore aquaculture is rare (Fujita et al., 2023), but it is important to consider absence of evidence is not evidence of absence of risk. However, there is a risk of entanglement in anthropogenic debris caught in mooring lines/cables (Clavelle et al., 2019) (secondary entanglement).
707. The Array will use fibre rope diameters ranging from 110 mm to 300 mm and chain diameters between 76 mm to 175 mm. Fishing gear, which pose the greatest entanglement risk to marine species, were reported to fall between 1 mm to 9.5 mm in diameter (Knowlton et al., 2016, Wilcox et al., 2015). Thus, marine mammals are more likely to be at risk from secondary entanglement through interactions with fishing gears than through direct entanglement with the large, thick mooring and cable components.
708. Lost fishing gear is made of synthetic materials, including nylon, polyethylene, and polypropylene, that resist natural biodegradation and can endure in the marine environment for extended periods, promoting the phenomenon known as 'ghost fishing' (Stelfox et al., 2016). Ghost fishing occurs when lost or discarded gear continues to catch wildlife from various taxa, including marine mammals. Indirect entanglement in anthropogenic debris caught on mooring lines and inter-array cables, e.g. secondary entanglement, poses the risk of direct injury and is anticipated to result in significant fitness reduction for the affected marine mammals though tissue damage, infection, and mobility restrictions that prevent foraging or migration (Garavelli, 2020, Van Der Hoop et al., 2016). However, the quantification of the actual amount of abandoned, lost, or discarded fishing gear and other anthropogenic debris poses significant challenges due to its elusive nature.
709. As a part of the designed in measures ( Table 6.48   Open ▸ ), mooring lines and dynamic inter-array cables will undergo regular inspections during the operation and maintenance phase. The inspection frequency for mooring lines and dynamic inter-array cables is anticipated to be more frequent initially (e.g. years 1 and 2), and likely to decline in frequency after this, following a risk based approach. Any inspected or detected debris on the floating lines and cables will be recovered based on a risk assessment which considers impact on environment including risk to marine mammal, risk to asset integrity, and health & safety. In addition, Ossian OWFL will consider new technologies for monitoring of mooring lines/snagged gear and will agree the approach to monitoring of mooring lines and associated removal of gear with NatureScot and MD-LOT prior to the operation and maintenance phase. As such, the removal of debris from mooring lines and cables further reduces the likelihood of secondary entanglement.
710. Finally, the risk of entanglement will be highly localised around the cables and mooring lines themselves and is not a wide-ranging impact such as those associated with elevated underwater noise.

                        Sensitivity of Annex II marine mammals to entanglement

711. In line with the approach applied in Benjamins et al. (2014), for the purpose of assessing marine mammal sensitivity to primary entanglement, the Annex II marine mammals considered in this Part of the RIAA were classified into broad groups based on taxonomic relationship as well as body size:

• odontocetes – harbour porpoise and bottlenose dolphin; and
• pinnipeds – grey seal.

712. Due to the infancy of the floating offshore wind farm industry there is a paucity of empirical evidence for secondary entanglement associated with floating offshore wind farms components (as discussed in paragraph 704), sensitivity to secondary entanglement has been assessed based on potential entanglement with lost or abandoned fishing gear (mostly nets, lines) that are most likely to be caught on the Array infrastructure. Since the impacts to marine mammals from entanglement in free floating fishing gear in the water column will be similar to entanglement in fishing gear caught on Array infrastructure, sensitivity to free floating fishing gear entanglement is considered to be a suitable proxy for the purposes of the assessment.
713. When considering the size of marine animals, mooring lines and cables may pose a reduced risk to smaller animals compared to larger ones simply because smaller animals ‘cannot physically become entangled’ (Benjamins et al., 2014). Consequently, odontocetes as well as pinnipeds, face a lower risk of primary entanglement with mooring lines and inter-array cables compared to larger mysticetes.
714. In terms of flexibility, marine mammals exhibit variations in the degree to which they flex their bodies while swimming. Benjamins et al. (2014) made an assumption that animals with greater flexibility would be able to avoid entanglement more easily compared to those with more rigid bodies. The study assigned a consistent entanglement risk based on body flexibility for odontocetes. Pinnipeds, presumed to be relatively flexible, were consequently assigned a lower score for the risk of entanglement when compared to odontocetes and mysticetes (Benjamins et al., 2014). As discussed in paragraph 705, it is highly unlikely that the mooring cables will be flexible enough to loop around passing marine mammals.
715. Due to the size of mooring lines and inter-array cables considered for the Array (see paragraph 707), they are detectable at considerable distances for echolocating odontocetes (such as harbour porpoise or bottlenose dolphin). Various mooring components are likely to influence audibility, with chain, for instance, being inherently noisier than fibre rope due to metal-on-metal movement and a larger surface area that can generate turbulence (Benjamins et al., 2014). The smoothness of mooring elements surface will also impact the amount of turbulence produced, which is likely to be detectable by pinnipeds (Benjamins et al., 2014). Nevertheless, detectability at a distance may be altered under adverse conditions such as storms or turbid waters, regardless of the sensory modality used or the extent of device motion. Benjamins et al. (2014) assessment of the entanglement risk across marine mammal groups, based on their ability to detect moorings, revealed that odontocetes who possess echolocation are more likely to detect mooring components at larger distances than pinnipeds which rely on passive acoustic detection or pressure wave detection. Pinnipeds however possess acute mechanosensitivity through their vibrissae or whiskers (Dehnhardt et al., 2001, Hanke et al., 2013) which may allow them to detect wakes formed downstream of a mooring or cable.
716. Foraging behaviour appears to be an important risk factor contributing to entanglement in fishing gears. Entanglements in ropes often occur as the rope wraps around animals' extremities or passes through their mouths, particularly during foraging activities (Benjamins et al., 2014). Mysticetes are at a higher risk of entanglement when lunge feeding as opposed to filter feeding (Benjamins et al., 2014), noting that studies have been based upon entanglement in fishing gear (Knowlton et al., 2020), rather than mooring lines. The substantial thickness of mooring lines and inter-array cables associated with the Array, in comparison to the ropes used in fishing gears, may largely prevent such entanglements except in very specific cases (Benjamins et al., 2014). Considering the mode of foraging alone, odontocetes and pinnipeds are assessed to be at a low risk of primary entanglement.
717. It must be noted that it is considered that marine mammals are highly unlikely to get entangled in the first place, given their advanced hearing and echolocation which would allow them to detect any noise from cables (such as ‘bangs’, ‘creaks’, ‘rattle’, ‘snapping’ or ‘pinging’) as described in Burns et al. (2022) and Liu (1973). Statoil (2015) assessed the sensitivity of marine mammal entanglement as low, given the risk of entanglement is considered highly unlikely. Furthermore, the evidence base for sensitivity is largely based off fishing gear or submarine telecommunications cables and therefore it is unlikely that the design of cables (see paragraphs 705 to 706) will physically allow primary entanglement of marine mammals to an extent that would entrap them and cause drowning. Thus, on the basis that primary entanglement is considered highly unlikely and the lack of any evidence for entanglement from MRE, there is considered to be some resilience and survivability largely due to avoidance behaviour of MRE structures.
718. The primary source of small cetacean bycatch is thought to be gillnets (Read et al., 2006). One hypothesis explaining cetacean entanglement in gillnets suggests that these animals may either be incapable of detecting the nets due to low target strength or may detect the nets too late to avoid entanglement (Mackay, 2011). Limited information is available regarding how odontocete cetaceans utilise echolocation in the wild and the ecological as well as behavioural contexts in which the echolocation is used (Mackay, 2011). Bottlenose dolphin, for example, has been observed to use echolocation sparingly in the wild, predominantly relying on passive listening to detect prey (Gannon et al., 2005). In contrast, free-ranging harbour porpoise has been documented to echolocate frequently (Akamatsu et al., 2007).
719. Cox et al. (2004) reported that harbour porpoise are often found in the vicinity of commercial gillnets more frequently than actual entanglement events occur. Kastelein et al. (1995) examined the circumstances in which three captive harbour porpoises reacted to gillnets in a pool. The initial encounters of the animals with standing gillnets resulted in entanglement, and the harbour porpoises would have faced the risk of drowning if not rescued. Subsequent to these experiences, the harbour porpoises in the study learned from one or more encounters and developed behaviours that reduced their chances of colliding with or becoming entangled in the gillnet (Kastelein et al., 1995). It is important to note that this learning process may not occur in the wild, where animals do not have the opportunity to be rescued. The authors also suggested that harbour porpoises learned to detect the gillnet by using echolocation in complete darkness, highlighting the adaptability of their sensory capabilities in response to the new environmental challenge posed by the gillnet (Kastelein et al., 1995).
720. Read et al. (2003) investigated the fine-scale movements of bottlenose dolphins around commercial Spanish mackerel gillnets and found that the most commonly recorded interaction was avoidance, wherein dolphins altered their course to navigate around the net and then resumed their original path once past it. Avoidance behaviours were observed at distances of up to 100 metres from the net (Read et al., 2003). The authors concluded that bottlenose dolphins frequently interact with gillnets but rarely become entangled (Read et al., 2003). When entanglement does occur, it is attributed to dolphins being either unaware of the net or distracted by other stimuli in the net's vicinity, such as fish (Read et al., 2003).
721. Between August 1990 and September 1995, a comprehensive examination of 422 cetacean carcasses representing 12 species that had died around the coasts of England and Wales was conducted (Kirkwood et al., 1997). Among the examined specimens, there were 234 harbour porpoises and 188 individuals from ten other species of dolphins and whales. For the harbour porpoises, the most frequent cause of death was entanglement in fishing gear (Kirkwood et al., 1997). A more recent study by Reeves et al. (2013) showed that bycatch continues to affect many odontocete species, as 61 of 74 studied species (82%) have reportedly been bycaught in some kind of fishing gear within their range between 1990 and 2011. Harbour porpoise faces significant challenges due to high bycatch rates in coastal gillnet fisheries across its range, leading to conservation concerns for several populations (Kindt-Larsen et al., 2023).
722. Based on sighting records and a photo-identification catalogue from a grey seal haul-out site in southwest England, Allen et al. (2012) reported that over the period from 2004 to 2008, the annual mean entanglement rates fluctuated between 3.6% and 5%. Among the 58 entangled cases in the catalogue, 64% exhibited injuries classified as serious and in 15 cases where the entangling debris was visible, 14 were found to be entangled in fisheries materials (Allen et al., 2012).
723. Statoil (2015) considered the risk of marine mammal entanglement in mooring lines and inter-array cables to be unlikely, but concluded that it is possible for smaller marine mammals (i.e. bottlenose dolphin, harbour porpoise and grey seal) using the offshore area to become entangled in lost or derelict fishing gear which may become entangled in mooring lines and cables. Based on the species most likely at risk, the sensitivity of marine mammals to entanglement was concluded to be low in Statoil (2015). It must be noted that these smaller species (such as bottlenose dolphin and grey seal) are found in lower densities in the Array marine mammal study area, though small cetaceans such as harbour porpoise may be present in greater numbers. Quantifying sensitivity on the basis of little scientific evidence is complex, with only a few examples given to date (Statoil, 2015).
724. It is important to consider that mooring lines and dynamic inter-array cables will undergo regular inspections during the operation and maintenance phase. The inspection frequency for mooring lines and dynamic inter-array cables is anticipated to be more frequent initially (e.g. years 1 and 2), and likely to decline in frequency after this following a risk based approach. Any inspected or detected debris on the floating lines and cables will be recovered based on a risk assessment which considers impact on environment including risk to marine mammal, risk to asset integrity, and health & safety. In addition, Ossian OWFL will consider new technologies for monitoring of mooring lines/snagged gear and will agree approach to monitoring of mooring lines and associated removal of gear with NatureScot and MD-LOT prior to the operation and maintenance phase. This is considered to further reduces the potential risk to marine mammals from secondary entanglement.

                        Operation and Maintenance Phase

                        Berwickshire and North Northumberland Coast SAC

Grey seal

725. Given the background information presented in paragraphs 700 to 710, primary entanglement is considered to be rare, with secondary entanglement considered a greater risk where there is potential for accumulation of marine debris on mooring lines. Pinnipeds (such as grey seal) are perceived to be at a lower risk of inadvertently becoming entangled primarily in moorings (as discussed in paragraph 714 to 716) and inter-array cables associated with Array infrastructure (Benjamins et al., 2014). In addition, as discussed in paragraph 717, marine mammals are highly unlikely to experience primary entanglement, given their advanced hearing (such as that of grey seals) and echolocation which would allow them to detect any noise from cables (such as ‘bangs’, ‘creaks’, ‘rattle’, ‘snapping’ or ‘pinging’) as described in Burns et al. (2022) and Liu (1973). As presented in paragraph 715, pinnipeds, such as grey seals, possess acute mechanosensitivity through their vibrissae or whiskers which may allow them to detect wakes formed downstream of a mooring or cable (Dehnhardt et al., 2001, Hanke et al., 2013). As such, grey seal is deemed to have some resilience to primary entanglement, largely due to avoidance and design of mooring lines/cables.
726. Although the potential risk of secondary entanglement for grey seal is more probable than primary entanglement, the risk is considered to be sufficiently reduced with the application of the designed in mitigation measures (e.g. routine surveys of the moorings and dynamic cabling). As per paragraph 723, grey seal density is relatively low within the Array marine mammal study area, which further reduces risk of secondary entanglement. This, combined with the consideration with the background information summarised in paragraphs 700 et seq., supports the conclusion that population-level effects on grey seal are highly unlikely.

                        Conclusion

727. Adverse effects on the qualifying Annex II marine mammal features of the Berwickshire and North Northumberland Coast SAC which undermine the conservation objectives of the SAC will not occur as a result of entanglement during the operation and maintenance phase. Potential effects from this activity on the relevant conservation objectives (as presented in in section 6.2.1) are discussed in turn below in Table 6.49   Open ▸ .

Table 6.49: Conclusions Against the Conservation Objectives of the Berwickshire and North Northumberland Coast SAC from Entanglement during the Operation and Maintenance Phase of the Array Alone

728. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Berwickshire and North Northumberland Coast SAC as a result of entanglement during the operation and maintenance phase of the Array alone.

                        Southern North Sea SAC

                        Harbour porpoise

729. Given the background information presented in paragraphs 700 to 710, primary entanglement is considered to be rare, with secondary entanglement more likely. Harbour porpoise are perceived to be at a lower risk of inadvertently becoming entangled primarily in moorings (as discussed in paragraph 715 to 716) and inter-array cables associated with Array infrastructure (Benjamins et al., 2014). In addition, as discussed in paragraph 717, marine mammals are highly unlikely to experience primary entanglement, given their advanced hearing and echolocation (such as that of VHF cetaceans: harbour porpoise) which would allow them to detect any noise from cables (such as ‘bangs’, ‘creaks’, ‘rattle’, ‘snapping’ or ‘pinging’ as described in Burns et al. (2022) and Liu (1973). As such, harbour porpoise is deemed to have some resilience to primary entanglement, largely due to avoidance and design of mooring lines/cables.
730. Although the potential risk of secondary entanglement is more probable than primary entanglement, the risk is considered to be sufficiently reduced with the application of the designed in mitigation measures (e.g. routine surveys of the moorings and dynamic cabling). This, combined with the consideration with the background information summarised in paragraphs 700 et seq., supports the conclusion that the risk of entanglement to harbour porpoise is low and therefore population-level effects on harbour porpoise are highly unlikely.

                        Conclusion

731. Adverse effects on the qualifying Annex II marine mammal features of the Southern North Sea SAC which undermine the conservation objectives of the SAC will not occur as a result of entanglement during the operation and maintenance phase. Potential effects from this activity on the relevant conservation objectives (as presented in section 6.2.2) are discussed in turn below in Table 6.50   Open ▸ .

Table 6.50: Conclusions Against the Conservation Objectives of the Southern North Sea SAC from Entanglement during the Operation and Maintenance Phase of the Array Alone

732. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Southern North Sea SAC as a result of entanglement during the operation and maintenance phase of the Array alone.

                        Moray Firth SAC

                        Bottlenose dolphin

733. Given the background information presented in paragraphs 700 to 710, primary entanglement is considered to be rare, with secondary entanglement likely considered a greater risk where there is potential for accumulation of marine debris on mooring lines. Bottlenose dolphin are perceived to be at a lower risk of inadvertently becoming entangled primarily in moorings and inter-array cables associated with Array infrastructure, due to their ability to echolocate and detect mooring components and their foraging behaviour (as discussed in paragraph 715 to 716) (Benjamins et al., 2014). In addition, as discussed in paragraph 717, marine mammals are highly unlikely to experience primary entanglement, given their advanced hearing and echolocation (such as that of bottlenose dolphin) which would allow them to detect any noise from cables (such as ‘bangs’, ‘creaks’, ‘rattle’, ‘snapping’ or ‘pinging’) as described in Burns et al. (2022) and Liu (1973). As such, bottlenose dolphin is deemed to have some resilience to primary entanglement, largely due to avoidance and design of mooring lines/cables.
734. Although the potential risk of secondary entanglement is more probable than primary entanglement, the risk is considered to be sufficiently reduced with the application of the designed in mitigation measures (e.g. routine surveys of the moorings and dynamic cabling). This, combined with the consideration with the background information summarised in paragraphs 700 et seq., supports the conclusion that population-level effects on bottlenose dolphin are highly unlikely.

                        Conclusion

735. Adverse effects on the qualifying Annex II marine mammal features of the Moray Firth SAC which undermine the conservation objectives of the SAC will not occur as a result of entanglement during the operation and maintenance phase. Potential effects from this activity on the relevant conservation objectives (as presented in section 6.2.3) are discussed in turn below in Table 6.51   Open ▸ .

Table 6.51: Conclusions Against the Conservation Objectives of the Moray Firth SAC from Entanglement during the Operation and Maintenance Phase of the Array Alone

736. It can be concluded, beyond reasonable scientific doubt, that there is no risk of an adverse effect on the integrity of the Moray Firth SAC as a result of entanglement during the operation and maintenance phase of the Array alone.

6.3.6. Injury and Disturbance from Underwater Noise Generated during the Operation of Floating Wind Turbines and Anchor Mooring Lines

737. The LSE2 assessment during the HRA Stage One process identified that during the operation and maintenance phase, LSE2 could not be ruled out for injury and disturbance from underwater noise generated during the operation of floating wind turbines and anchor mooring lines (hereafter: ‘operational noise’). This relates to the following sites and relevant Annex II marine mammal features:

• Berwickshire and North Northumberland Coast SAC;

–           grey seal.

• Southern North Sea SAC; and

–           harbour porpoise.

• Moray Firth SAC;

–           bottlenose dolphin.

738. The MDS considered for the assessment of operational noise is shown in Table 6.52   Open ▸ . There are no designed in measures applicable to this impact.

Table 6.52: MDS Considered for the Assessment of Potential Impacts to Annex II Marine Mammals due to Operational Noise during the Operation and Maintenance Phase