6. Assessment of Potential Adverse Effects on Integrity: Annex II Marine Mammals

6.1. Introduction

  1. This section provides background information and explanation for the approach taken to assess the potential impacts of the Array on European sites designated for Annex II Marine Mammals.
  2. As stated in section 3.1, the potential for LSE2 was identified for the Annex II marine mammal features of three SACs, which are listed in Table 6.1   Open ▸ and Figure 6.1   Open ▸ . These SACs were agreed to be screened in for further assessment with NatureScot, Natural England, and MD-LOT during the Ossian Array Scoping Opinion and LSE2 Screening process (see Table 2.1   Open ▸ for all relevant consultation).

 

Table 6.1:
European Sites Designated for Annex II Marine Mammal Features for which an Appropriate Assessment is Presented

Table 6.1: European Sites Designated for Annex II Marine Mammal Features for which an Appropriate Assessment is Presented

 

  1. LSE2s on the SACs presented in Table 5.1   Open ▸ were identified for the construction and operation and maintenance phases of the Array, which are outlined below in Table 6.2   Open ▸ . These impacts were agreed upon with NatureScot, Natural England, and MD-LOT during the Ossian Array Scoping Opinion and LSE2 Screening process (see Table 2.1   Open ▸ for all relevant consultation).

 

Table 6.2:
Potential Impacts to Annex II Marine Mammals of the European Sites Identified for Appropriate Assessment

Table 6.2: Potential Impacts to Annex II Marine Mammals of the European Sites Identified for Appropriate Assessment

Figure 6.1:
Location of European Sites Designated for Annex II Marine Mammals for which an Appropriate Assessment is Presented

Figure 6.1: Location of European Sites Designated for Annex II Marine Mammals for which an Appropriate Assessment is Presented

6.2. Baseline

  1. Baseline information on the Annex II marine mammal features of the three European sites identified for Appropriate Assessment within the HRA process has been gathered through a comprehensive desktop study of existing datasets and materials and site-specific Digital Aerial Surveys (DAS). Full detail is provided in volume 2, chapter 10 and volume 3, appendix 10.2 of the Array EIA Report.
  2. Within the Array EIA Report, two marine mammal study areas were defined for the purposes of the baseline characterisation (Ossian OWFL, 2024):

6.2.1. Berwickshire and North Northumberland Coast SAC

                        Site description

  1. At its closest point, the Berwickshire and North Northumberland Coast SAC is located 113.95 km south-west from the site boundary. The Berwickshire and North Northumberland Coast SAC is one of the most varied coastlines in the UK, stretching from Alnmouth to north of St Abbs head ( Figure 6.1   Open ▸ ). It contains a complex mix of marine habitats, associated species and communities which is unusually diverse for the North Sea, in both a UK and European context (Natural England, 2020). It covers an area of 65,226.12 ha and is designated for Annex I habitats and Annex II grey seal (JNCC, 2024b).
  2. The SAC is an extensive and diverse stretch of coastline which provides important habitats for grey seal, supporting approximately 3% of the British annual pup production (JNCC, 2024b, Natural England, 2020). Grey seals use areas within the SAC, such as Staple Island within the Farne Islands, for breeding, hauling out and moulting (Natural England, 2020).  A large number of grey seal also haul out around Holy Island sands, Lindisfarne, however, no breeding has been recorded here to date (Natural England, 2020). The SAC represents the most south eastern grey seal breeding colonies in the UK, and it is the most south-easterly SAC designated for this species (JNCC, 2024b).

                        Feature accounts

                        Grey seal
  1. Grey seal is the larger of the two pinniped species which occur around the UK and Ireland, with the other being harbour seal. Males weigh up to 300 kg and females weigh up to 200 kg (SCOS, 2023). The average lifespan for grey seal ranges between 20 to 30 years, however, females tend to live longer than males. Females mature at between three and five years old and males around six years, although it is reported they they are unlikely to be socially mature until eight years old (Hall et al., 2009).
  2. Grey seals breed, rest, moult and engage in social activity when they gather in colonies on land (known as haul outs). Haul out events occur also at sea on exposed sandbanks, but their frequency is low, and their duration is on average shorter than those events on land (Russell et al., 2012).
  3. Female grey seal tends to return to the same breeding site at which they were born in order to give birth. Preferred breeding locations in the UK include remote, uninhabited islands or coasts and in small numbers in caves (SCOS, 2022). These sites allow females with young pups to move inland away from busy beaches and storm surges. Seals may also breed on exposed, cliff-backed beaches but these locations limit the opportunity to avoid storm surges and it may result in higher levels of pup mortality (SCOS, 2022). In the UK, grey seals breed in the autumn, but there is a clockwise cline in the mean birth date around the UK (SCOS, 2022). The majority of pups in south-west Britain are born between August and October; in north and west Scotland pupping occurs mainly between September and late November; in east Scotland between August and December and in eastern England pupping occurs mainly between early November to mid-December. Grey seal give birth to a single, white-coated pup which is weaned over a period of 17 to 23 days (SCOS, 2022). Pups shed their white natal coat (lanugo) and develop their first adult coat, with moult occurring at the time of weaning after which pups remain on the breeding colony for up to two to three weeks before going to sea. Following this, the female comes into oestrus and mating occurs, after which adult females return to sea to forage and build up fat reserves.
  4. Along the Scottish coast, grey seals exhibit an offshore foraging behaviour (Damseaux et al., 2021). Wyles et al. (2022) studied the influence of geomorphological features of the seabed on at-sea behaviour of grey seal. The study found that features such as slopes, foot slopes and hollows attract grey seal individuals as these may host prey aggregations, and/or lead to increased prey capture success. Grey seal have a selective diet. A study on the diet of grey seals in Scottish waters found that 50% of prey items were plaice Pleuronectes platessa and sole and 46% of prey items were sandeels (Damseaux et al., 2021). Hammond et al. (2005) also highlighted that grey seal diet comprises primarily sandeels, gadoids and flatfish, in that order of importance, but varying seasonally and from region to region. Gosch (2017) also reported that there are significant regional and temporal differences in the diet of grey seal. Those in shallow waters show a preference for demersal and groundfish species such as cephalopods and flatfish, whilst seals foraging in deeper waters, over sandy substrates, will target pelagic and benthopelagic species such as blue whiting Micromesistius poutassou and sandeels (Gosch, 2017).
  5. Grey seals tend to forage in the open sea, returning to land regularly to haul out. Foraging trips can be wide-ranging, however, tracking studies have shown that most foraging is likely to occur within 100 km of a haul out site (SCOS, 2022). During breeding season grey seal tend to forage within 20 km from the breeding site (pers. comm. with NatureScot).
  6. The east coast of Scotland and northern England where this SAC is located provide important breeding and haul-out habitats for grey seal. The UK total grey seal population size at the start of the 2022 breeding season was estimated to be 162,000 grey seals of which 129,100 (approximately 80%) were in Scotland (Stevens, 2023). The most recent August grey seal counts took place in 2021 in both East Scotland and Northeast England SMU and resulted in a scaled August population estimates of 10,783 and 25,913 grey seals, respectively (SCOS, 2023), using the 25.15% scalar derived from Russell et al. (2021). Based on density heatmaps by Carter et al. (2022), mean grey seal at-sea usage within the site boundary is low, as the hotspots are located closer to the shore and in the vicinity of the Berwickshire and North Northumberland Coast SAC, Firth of Forth, Tay and Eden Estuary and north of Aberdeen. Grey seal was recorded in low numbers during monthly site-specific DAS with 18 animals recorded over nine months. The annual mean design-based density (corrected for availability bias) was estimated as 0.021 animals per km2 with density during non-breeding season (January to August) being higher at 0.034 animals per km2. Tagging data illustrated a high-level of connectivity between the Array marine mammal study area and the Berwickshire and North Northumberland Coast SAC, with approximately 9% of tagged individuals being tracked within both. Given the uncertainty associated with identification of seals to species level based on DAS data, density estimates reported by Carter et al. (2022) are considered the most appropriate to use and a density of 0.180 animals per km2 has been taken forward for Appropriate Assessment (see section 5.3.2 in volume 3, appendix 10.2 of the Array EIA Report for more details regarding the most appropriate density value to be taken forward to the assessment).

                        Conservation objectives

  1. The conservation objectives for Berwickshire and North Northumberland Coast SAC have been developed jointly by NatureScot and Natural England and apply to the site and the individual species (e.g. grey seal) for which the site has been classified. These high-level objectives are to ensure that, subject to natural change, the integrity of the site is maintained or restored as appropriate, and that the site contributes to achieving the FCS of its qualifying features, by maintaining or restoring:
  • the extent and distribution of qualifying natural habitat and habitats of the qualifying species;
  • the structure and function (including typical species) of qualifying natural habitats;
  • the structure and function of the habitats of the qualifying species;
  • the supporting processes on which qualifying natural habitats and the habitats of qualifying species rely;
  • the populations of each of the qualifying species; and
  • the distribution of qualifying species within the site (Natural England, 2020).
  1. The second conservation objective: ‘the structure and function (including typical species) of qualifying natural habitats’ is only relevant to the Annex I habitat features of the Berwickshire and North Northumberland Coast SAC and is therefore not included further in this assessment on Annex II marine mammals.
  2. Supplementary advice on conservation objectives (published on 9 May 2023) (Natural England, 2023a) provides the site-specific attributes and targets specific to the grey seal feature of the SAC. Conservation targets for grey seal are summarised here:
  • maintain the population size within the site;
  • maintain the reproductive and recruitment capability of the species;
  • maintain the presence and spatial distribution of the species and their ability to undertake key life cycle stages and behaviours;
  • maintain connectivity of the habitat within sites and the wider environment to ensure recruitment, and/or to allow movement of migratory species;
  • restrict the introduction and spread of INNS and pathogens, and their impacts;
  • maintain the extent and spatial distribution of the following supporting habitats: haul out sites;
  • maintain the cover and abundance of preferred food items required by the species;
  • maintain the natural physico-chemical properties of the water;
  • maintain all hydrodynamic and physical conditions such that natural water flow and sediment movement is not significantly altered or constrained;
  • reduce aqueous contaminants to levels equating to High Status according to Annex VIII and Good Status according to Annex X of the WFD, avoiding deterioration from existing levels;
  • maintain water quality at mean winter dissolved inorganic nitrogen levels where biological indicators of eutrophication (opportunistic macroalgal and phytoplankton blooms) do not affect the integrity of the site and features; and
  • maintain natural levels of turbidity in areas where this species is, or could be, present (Natural England, 2023a).

                        Condition assessment

  1. There was no condition assessment currently available on the Natural England Designated Sites Portal (Natural England, 2020), however, the condition of grey seal was assessed by NatureScot in 2014 as:
  • grey seal: favourable – maintained (NatureScot, 2024).

6.2.2. Southern North Sea SAC

                        Site description

  1. At its closest point, the Southern North Sea SAC is located 129.86 km south-east from the site boundary. The Southern North Sea SAC covers an area of 36,951 km2, and is designated solely for harbour porpoise (JNCC, 2023d, JNCC and Natural England, 2019). The site lies along the east coast of England, predominantly in the offshore waters of the central and southern North Sea, from north of Dogger Bank to the Straits of Dover in the south ( Figure 6.1   Open ▸ ).
  2. The Southern North Sea SAC is an area of importance for harbour porpoise, supporting an estimated 17.5% of the UK North Sea MU population. Approximately two-thirds of the site, the northern part, is recognised as important for the species during the summer, whilst the southern part supports persistently higher densities during the winter (JNCC, 2023d). The majority of this site lies offshore but does extend from the coastal areas of Norfolk and Suffolk out to the 12 nm limit. Therefore, both Natural England and JNCC are responsible for providing statutory advice (JNCC and Natural England, 2019).

                        Feature accounts

                        Harbour porpoise
  1. The harbour porpoise is a small odontocete (i.e. toothed whale) inhabiting coastal temperate and boreal waters of the northern hemisphere. It reaches a maximum length of 1.9 m (Bjørge et al., 2009), with females growing to an average length of 1.6 m whilst males reach 1.45 m in length (Lockyer, 1995). Although the recorded longevity is 24 years, most individuals do not live past 12 years of age (Lockyer, 2013).
  2. The geographic range of harbour porpoise coincides with cool, high latitude waters. Because harbour porpoise have a greater body surface area to volume ratio than other, larger cetacean species, this causes them to potentially lose energy through radiation and conduction to the surrounding water (Kastelein et al., 2018a, Kastelein et al., 2019a, Lambert, 2020). To maintain their body temperature and other energy needs, they need to feed frequently and consume enough prey per unit body weight (Rojano-Doñate et al., 2018). For this reason, porpoise may be susceptible to changes in the abundance of prey species or disturbance from foraging areas. Given that harbour porpoise are predated on by other odontocetes (killer whale) and pinnipeds (grey seal), they often flee when encountering predators (Kastelein et al., 2019b). As such, it can be anticipated that harbour porpoise have adaptive mechanisms over certain time scales and the time when harbour porpoise are not feeding may extend to up to 9 to 12 hours (Kastelein et al., 2019b). Recent studies in Iceland suggest that despite ecosystem changes in the study region, harbour porpoise show no long term changes in trophic ecology, indicating that this species may be able to adapt to spatial changes in prey distribution or shift to other prey at similar trophic levels (Samarra et al., 2022).
  3. Across various datasets, harbour porpoise counts were consistently higher during the summer months. During aerial surveys of the Firth of Forth, harbour porpoise were recorded nearly three times as often in summer (2.01 sightings per 100 km) compared to winter (0.70 sightings per 100 km) (Grellier et al., 2011). The same pattern of higher encounter rates during summer months was also recorded during boat-based surveys for Seagreen 1 Offshore Wind Farm, which lies in the inner Firth of Forth (Sparling, 2012). Boat-based surveys in summer 2017 recorded the highest counts of harbour porpoise between May and July within the Seagreen 1 Offshore Wind Farm (Seagreen Wind Energy Limited, 2018). Similarly, analysis of aerial survey data for the Berwick Bank Offshore Wind Farm (also within the Firth of Forth) presented highest encounter rates during spring each year (April and May) and lowest during winter and autumn (from November 2019 to March 2020 and from October 2020 to February 2021) (SSE Renewables, 2022d). The monthly encounter rate for harbour porpoise from the site-specific DAS data varied across months with the encounter rate for summer (specifically July 2021, April 2022, June 2022, and July 2022) estimated to be considerably higher compared to other seasons of the year.
  4. Harbour porpoise accounted for the highest number of sightings identified to species level (based on raw count data) during site-specific DAS and was recorded in all but three survey months. It was the most commonly identified cetacean during historic aerial surveys in the wider Firth of Forth and Tay region (Grellier et al., 2011, Sparling, 2012, SSE Renewables, 2022d). IAMMWG (2022) presented estimated abundance for the North Sea MU as 346,601 individuals. The most recent Small Cetaceans in European Atlantic Waters and the North Sea (SCANS) survey data (SCANS-IV) estimated the density in block NS-D, where the site boundary is located, as 0.5985 harbour porpoise per km2 and presented an abundance of 38,577 individuals (Gilles et al., 2023). Site-specific modelled estimates from the DAS provided a mean encounter rate of 0.041 animals per km with a monthly peak of 0.154 animals per km in July 2021. The annual mean model-based density (corrected for availability bias) was estimated as 0.355 animals per km2 with summer density being higher at 0.648 animals per km. Design-based absolute density estimates using DAS sightings data are considered the most appropriate to use to reflect densities of harbour porpoise within the Array marine mammal study area, as these are based on the most recent data, collected regularly (monthly) over two years and over the specific area of interest. Therefore, a peak seasonal density of 0.648 animals per km2 has been used for Appropriate Assessment (see section 5.1.1 in volume 3, appendix 10.2 of the Array EIA Report for more details regarding the most appropriate density value to be taken forward to the assessment).

                        Conservation objectives

  1. The conservation objectives for the Southern North Sea SAC have been jointly developed by the JNCC and Natural England (2019) to ensure that the integrity of the site in maintained and that it makes the best possible contribution to maintaining FCS for harbour porpoise in UK waters. In the context of natural change, this will be achieved by ensuring the following conservation objectives:
  1. harbour porpoise is a viable component of the site;
  2. there is no significant disturbance of the species; and
  3. the condition of supporting habitats and processes, and the availability of prey is maintained (JNCC and Natural England, 2019).
  1. In the advice on operations for this site, noise disturbance from a project individually or in-combination with others is regarded as significant if it excludes harbour porpoise from more than 20% of the part of the SAC that was designated on the basis of higher persistent densities for a specific season (summer or winter; see paragraph 418) (thereafter referred to as relevant area) in any given day, and an average of 10% of the relevant area of the site over the specific season (JNCC and Natural England, 2019).
  2. To assess impacts to Conservation Objective 1 (‘harbour porpoise is a viable component of the site’), the Advice on Operations states that the reference population for assessments against this objective is the MU population in which the SAC is situated (JNCC and Natural England, 2019). At the time of writing the Advice on Operations, the most recent MU population for harbour porpoise was from IAMMWG (2015). Given that more recent data are now available, and to align with the approach undertaken in the Array EIA Report, IAMMWG (2022) abundance data have been used for the reference population for harbour porpoise. The estimated abundance for the North Sea MU is 346,601 individuals (IAMMWG, 2022). As described in paragraph 422, it was considered that design-based absolute density estimates from the DAS data were the most appropriate to inform impact assessments, and the absolute density of 0.651 animals per km2 has been taken forward to the assessment in the Array EIA Report and in this Part of the RIAA.
  3. Further information on the conservation objectives for the Southern North Sea SAC is provided in JNCC and Natural England (2019). This document lists the following pressures as relevant to the harbour porpoise feature of the SAC:
  • removal of non-target species by fisheries, in this case referring to bycatch (and probable mortality) of harbour porpoise;
  • contaminants, which may affect harbour porpoise directly, or indirectly via prey and/or habitat contamination;
  • anthropogenic underwater noise;
  • death or injury from collision with vessels and/or installations; and
  • removal of target species, in this case referring to harbour porpoise prey species (JNCC and Natural England, 2019).

                        Condition assessment

  1. A condition assessment for harbour porpoise was not provided (JNCC and Natural England (2019), however the status of both the harbour porpoise feature and the SAC itself were presented as ‘Favourable’ on the JNCC site (JNCC, 2023d).

6.2.3. Moray Firth SAC

                        Site description

  1. At its closest point, the Moray Firth SAC is located 175.86 km north-west of the site boundary. This SAC covers an area of 1,512 km2 and extends from the inner firths to Helmsdale on the north coast and Lossiemouth on the south coast (JNCC, 2023b). It is designated primarily for bottlenose dolphin, as this SAC supports the only known resident population of bottlenose dolphin in the North Sea (JNCC, 2023b, NatureScot, 2021). Based on data collected in 1980s and early 1990s, the Moray Firth SAC is thought to encompass the core area of occurrence of the resident, coastal population of bottlenose dolphins in the North Sea. The CMA document for this site (NatureScot, 2021) states that the site reference population is between 101 to 250 bottlenose dolphin, which is based on data from 2005. However, more recently Arso Civil et al. (2021), published an estimated abundance of 224 individuals based on a five year average between 2015 to 2019.
  2. Data from the site condition monitoring suggests that the proportion of population that use the SAC has declined, although the overall population along the coast is increasing (Cheney et al., 2018), and it is thought that their range is extending (Arso Civil et al., 2021, Arso Civil et al., 2019, Cheney et al., 2018, IAMMWG, 2023, Quick et al., 2014).

                        Feature accounts

                        Bottlenose dolphin
  1. Bottlenose dolphin is an odontocete and a member of the family Delphinidae. They are found in temperate and tropical waters worldwide. This species is the largest of the beaked dolphins and ranges in size from 1.9 m to 3.8 m. Bottlenose dolphin can live, on average, between 20 to 30 years. On average, males reach sexual maturity at ten to 12 years and females at five to ten years. Mating occurs during the summer months, with gestation taking 12 months and calves suckling for 18 to 24 months. Females generally reproduce every three to six years (Mitcheson, 2008)
  2. 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) and there is variation in the patterns of habitat use, even within a population. Typical prey items in Scottish waters include Atlantic salmon, cod, haddock, saithe Pollachius virens, and whiting Merlangius merlangus (Santos et al., 2001).
  3. Bottlenose dolphin are more frequently seen in groups rather than individually, although group size in coastal populations may be smaller than offshore populations. It should be noted that very little is known about offshore populations (Rogan et al., 2018) and this assessment will focus on coastal bottlenose dolphin population. For example, in the northern North Sea, only the coastal population, distributed within the 2 m to 20 m depth contour and approximately 2 km from the shore, is well studied (Geelhoed et al., 2022). Mean group size across the SCANS III survey areas was 5.25 individuals (Hammond et al., 2021). Robinson et al. (2017) reported observed group sizes varied between two and 70 animals that in the outer Moray Firth.
  4. The Moray Firth SAC is located within the Coastal East Scotland MU for bottlenose dolphin, with the most recent abundance estimate of 224 individuals presented in by the IAMMWG (2022) (based on Arso Civil et al. (2019); paragraph 428). However, there were no bottlenose dolphin recorded during site-specific DAS for the Array. SCANS III estimated their offshore abundance for block R (which overlaps with the site boundary) as 1,924 individuals (Hammond et al., 2021). Given that there were no bottlenose dolphin sightings within the block corresponding with the location of the site boundary during the more recent SCANS IV survey, no density values were published (Gilles et al., 2023). Density estimates reported by Lacey et al. (2022) are considered the most appropriate to use to reflect densities of bottlenose dolphin in the offshore waters where the site boundary is located and a density of 0.00303 animals per km2 has been used for Appropriate Assessment (see section 5.1.2 in volume 3, appendix 10.2 of the Array EIA Report for more details regarding the most appropriate density value to be taken forward to the assessment).

                        Conservation objectives

  1. Conservation objectives for the Moray Firth SAC have been developed by NatureScot and are published as part of a CMA document (NatureScot, 2021). The conservation objectives for all features of the SAC are as follows:
  • to ensure that the qualifying features of Moray Firth SAC are in favourable condition and make an appropriate contribution to achieving FCS; and
  • to ensure that the integrity of Moray Firth SAC is maintained or restored in the context of environmental changes by meeting objectives 2a, 2b and 2c for each qualifying feature (NatureScot, 2021).
  1. Conservation objectives for bottlenose dolphin are as follows:
  • 2a: The population of bottlenose dolphin is a viable component of the site;
  • 2b: The distribution of bottlenose dolphin throughout the site is maintained by avoiding significant disturbance; and
  • 2c: The supporting habitats and processes relevant to bottlenose dolphin and the availability of prey for bottlenose dolphin are maintained (NatureScot, 2021).
  1. As presented in the CMA for the Moray Firth SAC, bottlenose dolphin are considered sensitive to:
  • removal of non-target and target species (i.e. entanglement of bottlenose dolphins in fishing gears as bycatch and removal of their prey species);
  • contaminants (e.g. through effects on water quality and bioaccumulation of contaminants that in turn affect survival and productivity rates);
  • underwater noise, which may cause marine mammals to relocate, interfere with communication, navigation, foraging, and may disrupt social bonds; and
  • death or injury by collision (predominantly in relation to collision with various types of fast moving vessels from commercial shipping to personal leisure craft and potentially from tidal turbines) (NatureScot, 2021).

                        Condition assessment

  1. The condition of bottlenose dolphin was assessed in 2016 as:
  • bottlenose dolphin: favourable – maintained (NatureScot, 2021).
  1. As the bottlenose dolphin feature is in favourable condition at Moray Firth SAC, NatureScot (2021) states that the conservation objectives seek to maintain this condition.

6.2.4. Reference Populations and Densities

  1. A summary of the different MUs and SMUs, associated reference populations, and densities (animals per km2) used within the this Part of the RIAA are presented in Table 6.3   Open ▸ . These were agreed upon with SNCBs. For reference, the MUs and SMUs are illustrated in Figure 6.2   Open ▸ .

 

Table 6.3:
Densities and Reference Populations Used for the Assessment on Designated Sites with Relevant Annex II Marine Mammal Features

Table 6.3: Densities and Reference Populations Used for the Assessment on Designated Sites with Relevant Annex II Marine Mammal Features

Figure 6.2:
MUs and SMUs Relevant to the Report to Inform Appropriate Assessment

Figure 6.2: MUs and SMUs Relevant to the Report to Inform Appropriate Assessment


6.2.5. Marine Mammals and Underwater Noise

                        Marine mammals and underwater noise

  1. Marine mammals, in particular cetaceans, are capable of generating and detecting noise and are dependent on noise for many aspects of their life, including prey identification, predator avoidance, communication and navigation (Au et al., 1974, Bailey et al., 2010). Increases in anthropogenic noise may consequently lead to a potential effect within the marine environment (Bailey et al., 2010, Parsons et al., 2008). Underwater noise influence may then subsequently affect marine mammals in a number of ways and vary with the distance from the noise source (Marine Mammal Commission, 2007). It can compete with important signals (masking) and alter behaviour (by inducing changes in foraging or habitat-use patterns, separation of mother-calf pairs). Underwater noise can also cause temporary hearing loss or, if the exposure is prolonged or intense, permanent hearing loss. It can also cause damage to tissues other than the ear if noise is sufficiently intense (Marine Mammal Commission, 2007).
  2. Given that there is sparse scientific evidence to properly evaluate masking (e.g. no relevant threshold criteria to enable a quantitative assessment), the assessment of impacts associated with underwater noise on marine mammals will consider auditory injury (temporary and permanent hearing loss) and behavioural responses (disturbance).
                        Injury
  1. Auditory injury in marine mammals can be either temporary, also referred to as TTS, where an animal’s auditory system recovers over time, or as a Permanent Threshold Shift (PTS), where there is no hearing recovery in the animal. The ‘onset’ of TTS is deemed to be where there is a 6 dB shift in a hearing threshold, defined by the National Marine Fisheries Service (NMFS, 2016) as a “the minimum threshold shift clearly larger than any day to day or session to session variation in a subject’s normal hearing ability”, and which “is typically the minimum amount of threshold shift that can be differentiated in most experimental conditions”. The acoustic threshold that would result in the PTS onset in marine mammals have not been directly measured and therefore are extrapolated from available TTS onset measurements. The PTS onset is conservatively considered to occur where there is 40 dB of TTS (Southall et al., 2007).
  2. Marine mammals exposed to noise levels that could induce TTS are likely to respond by moving away from (fleeing) the ensonified area and therefore avoiding potential injury. It is considered there is a behavioural response (disturbance) that overlaps with potential TTS ranges. Since derived thresholds for the onset of TTS are based on the smallest measurable shift in hearing, TTS thresholds are likely to be very precautionary and could result in overestimates of TTS ranges. In addition, the conservative assumptions applied in the underwater noise modelling (e.g. use of impulsive noise thresholds at large ranges; see paragraph 462 et seq) may also result in the overestimation of ranges.
  3. Hastie et al. (2019) found that during pile driving there were range dependent changes in signal characteristics with received noise losing its impulsive characteristics at ranges of several kilometres, especially beyond 10 km. Therefore, where TTS ranges exceed 10 km it is not considered a useful predictor of the effects of underwater noise on marine mammals. As such, although TTS ranges were modelled for completeness for all noise-related impacts and are presented in volume 3, appendix 10.1 of the Array EIA Report, these are not included in the assessment of auditory injury presented in this section. Alternatively, the assessment of potential auditory injury is assessed in terms of PTS and accounts for the irreversible nature of the effect.
  4. For marine mammals, auditory injury thresholds are based on both SPLpk (i.e. unweighted) and marine mammal hearing-weighted SELcum as per the latest guidance (Southall et al., 2019). Marine mammal hearing-weighted categories are based on the frequency characteristics (bandwidth and noise level) for each group within which acoustic signals can be perceived and therefore assumed to have auditory effects ( Table 6.4   Open ▸ ). To calculate distances using the SELcum metric the noise modelling assessment assumed that an animal would be exposed over the duration of the piling activity and that there would be no breaks in activity during this time. It was assumed that an animal would swim away from the noise source at the onset of activity at a constant rate. The conservative species-specific swim speeds were incorporated into the model ( Table 6.5   Open ▸ ). As a result of the advice received from NatureScot following Marine Mammal Consultation Note 2 (volume 3, appendix 5.1, annex E of the Array EIA Report) ( Table 2.1   Open ▸ ), the assessment of PTS from piling and UXO clearance was based upon the dual metric approach, whereby the maximum injury ranges from SPLpk and SELcum metrics were used in the assessment. This dual metric approach aligns with the approach presented in the Array EIA Scoping Report (for further information see volume 2, chapter 10 of the Array EIA Report).

 

Table 6.4:
Summary of PTS Onset Acoustic Thresholds for Relevant Annex II Marine Mammal Hearing Groups

Table 6.4: Summary of PTS Onset Acoustic Thresholds for Relevant Annex II Marine Mammal Hearing Groups

 

Table 6.5:
Swim Speeds used in the Underwater Noise Modelling

Table 6.5: Swim Speeds used in the Underwater Noise Modelling

 

                        Disturbance
  1. As noise intensity decreases beyond the injury threshold zone, noise levels have the potential to disrupt the behavioural patterns of marine mammals. The reaction of a marine mammal to disturbance is dependent upon individual factors and contextual considerations (Southall et al., 2019). Prior experiences and acclimatisation play crucial roles in determining whether an individual will manifest an aversive response to noise, especially in regions characterised by elevated underwater noise levels associated with human activities.
  2. For the purposes of HRA, an area-based or fixed threshold approach is more appropriate for assessment, rather than the dose-response approach used in the EIA (which assumes that not all animals within an impact zone are disturbed) (volume 2, chapter 10 of the Array EIA Report). For example, disturbance for harbour porpoise in SACs is defined through spatial and temporal thresholds set out in the SAC conservation objectives (JNCC and Natural England, 2019), and in this regard an area-based assessment is required to obtain the area of ensonified habitat to a level that may lead to significant disturbance.
  3. An unweighted noise threshold value of 143 dB re 1µPa2s SELss was recently recommended in the position statement on assessing behavioural disturbance of harbour porpoise from underwater noise published by Natural Resource Wales (NRW, 2023). Acoustic recordings of the pile driving noise were utilised alongside harbour porpoise monitoring to derive a threshold for behavioural reactions to piling noise. Declines were found at noise levels exceeding an unweighted SELss of 143 dB re 1 µPa2s and up to 17 km from piling. This means that harbour porpoise may react with avoidance only when exposure exceeds a threshold value of 143 dB re 1 µPa2s. It is worth noting that the noise threshold of 143 dB re 1 µPa2s was derived from a modelled average of six different studies of full-scale pile driving operations and thereby represents a large amount of empirical data (Tougaard, 2021). This threshold is relevant to the HRA process as it is an area-based approach and is therefore similar to the guidance on the use of Effective Deterrence Ranges (EDR) to assess the significance of noise disturbance at harbour porpoise SACs (JNCC, 2020). Although the JNCC (2020) guidance applies to England, Wales, and Northern Ireland, it is still relevant to this assessment as the Southern North Sea SAC lies within English waters. Furthermore, as Natural England provided consultation on the inclusion of the Southern North Sea for Appropriate Assessment ( Table 2.1   Open ▸ ), the EDR approach has been included in the assessment for harbour porpoise as the JNCC (2020) guidance was also produced in collaboration with Natural England. For the assessment of piling and UXO clearance, EDRs of 26 km have been used. This is in line with the guidance for UXO clearance, as only one EDR was presented (JNCC, 2020). For piling, the use of a 26 km EDR follows a precautionary approach, as it represents the largest EDR proposed for different piling techniques (e.g. monopiles or pin piles, and conductor piling for oil and gas wells) (JNCC, 2020). The 26 km EDR for piling is also considered precautionary given the lack of guidance surrounding floating offshore wind developments.
  4. Therefore, for harbour porpoise, the derived threshold presented by Tougaard (2021) and the EDRs presented in JNCC (2020) have been used to assess behavioural disturbance from piling to the harbour porpoise feature of the Southern North Sea SAC. There are, however, limited studies to support the derivation of similar thresholds for the other marine mammal species.
  5. Therefore, for grey seal and bottlenose dolphin, the NMFS level B harassment threshold (analogous to strong disturbance) of 160 dB re 1 μPa (rms) has been applied for an area-based assessment of impulsive noise sources (such as some site-investigation surveys) (NMFS, 2005).
  6. Therefore, for impulsive noise sources other than piling ((e.g. some site-investigation survey techniques), this assessment adopts the NMFS (2005) Level B harassment threshold of 160 dB re 1 μPa (rms) for impulsive noise, which is defined as: “having the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioural patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering but which does not have the potential to injure a marine mammal or marine mammal stock in the wild”. This definition is similar to the JNCC (2010b) description of non-trivial (significant) disturbance. The United States (US) NMFS (2005) guidelines also suggest a precautionary threshold of 140 dB re 1 μPa (rms) to indicate the onset of low level marine mammal disturbance effects for all mammal groups for impulsive noise, although this is not considered likely to lead to a ‘significant’ disturbance response and is therefore hereinafter referred to as ‘mild disturbance’.
  7. The NMFS (2005) guidance sets the marine mammal level B harassment threshold for continuous noise at 120 dB re 1 μPa (rms). This threshold has therefore been adopted in the assessment of impacts as a result of continuous noise, such as non-impulsive site-investigation surveys.
  8. A summary of the criteria used throughout to assess disturbance is given in Table 6.6   Open ▸ .

Table 6.6:
Summary of Criteria used in the Appropriate Assessment of Disturbance for the Relevant Annex II Marine Mammal Species

Table 6.6: Summary of Criteria used in the Appropriate Assessment of Disturbance for the Relevant Annex II Marine Mammal Species

 

                        Assumptions and limitations

  1. By applying the fixed-threshold based criteria, the magnitude of impact can be quantified with respect to the spatial extent of disturbance. However, Southall et al. (2021) noted that it is challenging to develop a comprehensive set of empirically derived criteria for such a diverse group of animals. Since there are broad differences in hearing across the frequency spectrum for different marine mammal hearing groups, noises that disturb one species may be irrelevant or inaudible to other species. Variance in responses even across individuals of the same species are well documented to be context and noise-type specific (Ellison et al., 2012). In addition, the potential interacting and additive effects of multiple stressors (e.g. reduction in prey, noise and disturbance, contamination, etc.) is likely to influence the severity of responses (Lacy et al., 2017).
  2. As such, the recent recommendations by Southall et al. (2021) steer away from a single overarching approach. Instead, the study proposes a framework for developing probabilistic response functions for future studies. The paper suggests different contexts for characterising marine mammal responses for both free-ranging and captive animals with distinctions made by noise sources (i.e. active sonar, seismic surveys, continuous/industrial noise and pile driving). Three parallel categories have been proposed within which a severity score from an acute (discrete) exposure can be allocated:
  • survival – defence, resting, social interactions and navigation;
  • reproduction – mating and parenting behaviours; and
  • foraging – search, pursuit, capture and consumption.
  1. Although some studies have been able to assign responses to these categories based on acute exposure, there is still limited understanding of how longer-term (chronic) exposure could translate into population level effects. The potential for behavioural disturbance to lead to population consequences has been considered using the iPCoD approach and is summarised in paragraphs 517 et seq.
  2. Southall et al. (2021) reported observations from long term whale-watching studies and suggested that there were differences in the ability of marine mammals to compensate for long term disturbance which related to their breeding strategy. For example, baleen whales and grey seal, as ‘capital breeders’, accumulate energy in their feeding grounds and transfer it to calves in their breeding ground, whilst other species such as harbour porpoise and bottlenose dolphin are ‘income breeders’ as they balance the costs of pregnancy and lactation by increased food intake, rather than depending on fat stores. Reproductive strategy can impact the energetic consequences of disturbance and cause variation in an individual’s vulnerability to disturbance based on both its reproductive strategy and stage (Harwood et al., 2020).
  3. Marine mammal ability to compensate for chronic exposure to noise will also depend on a range of ecological factors, including the relative importance of the disturbed area and prey availability within their wider home range, the distance to and quality of other suitable sites, the relative risk of predation or competition in other areas, individual exposure history, and the presence of concurrent disturbances in other areas of their range (Gill et al., 2001). Animals may be able to compensate for short term disturbances by feeding in other areas, for example, which would reduce the likelihood of longer-term population consequences. Booth (2019) reported that although minimising the anthropogenic disturbance is an important factor to animal’s health, if animals can find suitable high-energy-density prey they may be capable of recovering from some lost foraging opportunities. Christiansen et al. (2015) studied the effect of whale-watching on minke whale Balaenoptera acutorostrata in Faxafloi Bay, Iceland and found no significant long-term effects on vital rates, although years with low sandeel density led to increased exposure to whale-watching as whales were forced to move into disturbed areas to forage. Odontocetes may be more vulnerable to whale-watching compared to mysticetes (i.e. baleen whales) due to their more localised, and often, coastal home ranges. Bejder et al. (2006) documented a decrease in local abundance of bottlenose dolphin which was associated with an increase in whale-watching in a tourist area compared to a control area. Studies of changes in abundance as a result of disturbance should be considered in light of findings presented in Gill et al. (2001) who reported that if there is no suitable habitat nearby animals may be forced to remain in an area despite the disturbance, regardless of whether or not it could affect survival or reproductive success.
  4. The Annex II marine mammals considered in this assessment vary biologically and therefore have different ecological requirements that may affect their sensitivity to disturbance. This point is illustrated by the differences between marine mammals identified as key biological receptors in the baseline. Grey seals are capital breeders and store energy for reproduction and survival, while harbour porpoise (and other cetaceans whose ecology is well studied, e.g. bottlenose dolphin) are income breeders and they use energy that is acquired on a continual basis, including during the reproductive period (Stephens et al., 2009).
  5. Recognising the inherent uncertainty in the quantification of effects using threshold approaches, this assessment has adopted a precautionary approach, consisting of:
  • conservative assumptions in the marine mammal baseline (e.g. use of seasonal density peaks for harbour porpoise densities);
  • conservative assumptions in the MDS for the project parameters; and
  • conservative assumptions in the underwater noise modelling (see volume 3, appendix 10.1 for more details).
  1. These assumptions have been referred to throughout this assessment, illustrating that the systematic incorporation of layers of conservatism is likely to result in a very precautionary assessment.