10.5. Consultation

11. Table 10.10   Open ▸ presents a summary of the key issues raised during consultation activities undertaken to date specific to marine mammals for the Array and in the Ossian Array Scoping Opinion (Marine Directorate – Licensing Operations Team (MD-LOT, 2023) along with how these have these have been considered in the development of this marine mammal EIA Report chapter. Further detail is presented within volume 1, chapter 5. To date, consultation activity has included the pre-Scoping workshop with MD-LOT, NatureScot and Marine Scotland Science (November 2022), the Scoping Opinion from MD-LOT (June 2023) and post-scoping consultation with NatureScot (via email) for further key areas of agreement (Marine Mammal Consultation Notes 1 and 2; volume 3, appendix 5.1, annexes D and E, respectively).

Table 10.10: Summary of Issues Raised During Consultation and Scoping Opinion Representations Relevant to Marine Mammals

10.6. Methodology to Inform Baseline

12. A range of existing studies and datasets (including historic surveys) have been reviewed and analysed to inform this marine mammal baseline. In addition, consultation with MD-LOT and NatureScot has been carried out to aid the collection of baseline information.

10.6.1. Desktop Study

13. Information on marine mammals within the regional marine mammal study area was collected through a detailed desktop review of existing studies and datasets which are summarised in Table 10.11   Open ▸ .
14. Both the literature review of the reports, and numerical modelling using the datasets available, were used to characterise the baseline. The marine mammals technical report (volume 3, appendix 10.2) includes full details of the analysis undertaken to develop the marine mammals baseline.

Table 10.11: Summary of Key Desktop Reports

10.6.2. Identification of Designated Sites

15. A three-step process was used to identify all designated sites within the regional marine mammal study area and qualifying interest features that could be affected by the construction, operation and maintenance, and decommissioning phases of the Array. This process is described below:

• Step 1: All designated sites of international, national, and local importance within the regional marine mammal study area were identified using a number of sources, including JNCC (2023c), NatureScot (2023b), Natural Resources Wales (NRW) (2023a) and the Department of Agriculture, Environment and Rural Affairs (DAERA) (2023).
• Step 2: Information was compiled on the relevant marine mammal features for each of these sites using data in the public domain (e.g. JNCC (2023b)).
• Step 3: Using the above information and expert judgement, sites were included for further consideration if:

–           a designated site directly overlaps with the Array and therefore has the potential to be directly affected by the Array;

–           a designated site and associated features are located within the potential Zone of Influence (ZoI) for impacts associated with the Array (e.g. potential effect ranges of underwater noise as a result of piling activities during construction; see section 10.11); or

–           a designated site and associated features are located within the regional marine mammal study area and have a potential for connectivity with the Array (features are likely to regularly use the Array marine mammal study area).

16. Detailed consideration of designated sites located within the regional marine mammal study area and those taken forward to the assessment is provided in volume 3, appendix 10.2.

10.6.3. Site-Specific Surveys

17. Site-specific surveys were undertaken to inform the marine mammal Array EIA Report chapter for the Array (see volume 3, appendix 10.2 for further details). A summary of the surveys undertaken used to inform the marine mammal assessment of effects is outlined in Table 10.12   Open ▸ .

Table 10.12: Summary of Site-Specific Survey Data

10.7. Baseline Environment

10.7.1. Overview of Baseline Environment

18. The following sections provide a summary of the marine mammal baseline environment. The marine mammal technical report, volume 3, appendix 10.2, includes full details of the analysis undertaken to develop the marine mammal baseline and information on species ecology, distribution, seasonality as well as density and abundance.
19. There are 11 species of cetaceans and two species of pinnipeds that are regularly encountered within the regional marine mammal study area (Gilles et al., 2023, Hammond et al., 2021, Hammond et al., 2013, Weir et al., 2001). The distribution and abundance of marine mammals is highly correlated with the distribution of prey. Certain areas along the east coast of Scotland, like the northern North Sea, adjacent deep Atlantic waters, continental shelf edge, and trench parallel to the Aberdeenshire coastline, consistently host higher numbers of marine mammals than other locations within the regional marine mammal study area, due to abundant prey (NatureScot, 2019, Weir et al., 2001).
20. Although some species may occur within the regional marine mammal study area occasionally, e.g. killer whale Orcinus orca, these are unlikely to travel through or use the Array marine mammal study area as important foraging grounds (see volume 3, appendix 10.2 for more details). The DAS of marine mammals commenced in March 2021 and continued monthly up to and including February 2023. The 24 months of data collection allowed identification of the most common species likely to be encountered within the Array marine mammal study area. For more details on DAS data analysis please refer to volume 3, appendix 10.2, annex A.
21. There were four cetaceans observed that could not be assigned to species level, and sightings classified as ‘seal species’ (due to the difficulty of identifying pinnipeds to species level from aerial survey data) occurred in 16 of the 24 months surveyed. Following advice from NatureScot and MD-LOT ( Table 10.10   Open ▸ ), unidentified marine mammal sightings were not apportioned to a species and were excluded from further analysis. As the unidentified marine mammals numbered only four individuals, the exclusion of these from quantitative analyses would not result in any material change to the outcomes of the assessment. Moreover, the suite of mitigation measures described in section 10.10 are expected to minimise the potential impacts of the Array to all marine mammal species in the area.
22. The summary of the marine mammal baseline within the Array marine mammal study area, in the context of the regional marine mammal study area, is presented in Table 10.13   Open ▸ . Densities and reference populations taken forward to assessment for each species are presented in Table 10.14   Open ▸ , and all densities and reference populations have been agreed with NatureScot (see Table 10.10   Open ▸ ). Further detail is given in volume 3, appendix 10.2. The relevant Management Units (MUs) are presented in Figure 10.2   Open ▸ .

Figure 10.2: Relevant Marine Mammal Management Units and Study Areas

Table 10.13: Summary of Marine Mammal Baseline

Table 10.14: Densities and Reference Populations for Each Species Taken Forward to the EIA

10.7.2. Designated Sites

23. A screening of designated sites in the vicinity of the Array has been carried out and has identified that there were no designated sites relevant to marine mammals which fulfilled the screening criteria described in section 10.6.2.
24. Sites designated for the conservation of internationally important Annex II marine mammal species within the regional marine mammal study area include the Berwickshire and North Northumberland Coast SAC and Isle of May SAC both designated for grey seal, the Moray Firth SAC designated for bottlenose dolphin and the Southern North Sea SAC designated for harbour porpoise. Following a comprehensive assessment of potential connectivity as well as feedback from NatureScot, Natural England and MD-LOT provided as part of the Scoping Opinion ( Table 10.10   Open ▸ ), only sites presented in Table 10.15   Open ▸ will be considered further in the EIA and HRA processes (see volume 3, appendix 10.2 for more details).
25. The Firth of Tay and Eden Estuary SAC designated for harbour seal also lies within the regional marine mammal study area. However following review of connectivity between the Array marine mammal study area and harbour seal populations of the east coast of Scotland it was concluded that the potential for significant effects was highly unlikely. Following consultation with NatureScot ( Table 10.10   Open ▸ ) (whilst a detailed assessment of harbour seal ecology and distribution within the regional marine mammal study area has been included in volume 3, appendix 10.2) the species was therefore excluded as a key species in the EIA and therefore the Firth of Tay and Eden Estuary SAC is not considered in the EIA. The Dornorch Firth and Morrich More SAC is also designated for harbour seal but was scoped out early on following the Scoping Opinion ( Table 10.10   Open ▸ ).
26. Marine Mammal Consultation Note 1 confirmed the designated sites taken forward to the assessment in the EIA and HRA (refer to volume 3, appendix 5.1, annex D). NatureScot were content with the approach for the inclusion of Moray Firth SAC, and deferred to advice from Natural England on Berwickshire and North Northumberland Coast SAC and Southern North Sea SAC. Natural England advised in the Scoping Opinion that both Berwickshire and North Northumberland Coast SAC and Southern North Sea SAC are to be included.
27. In line with advice received from stakeholders during the Scoping Workshop (see Table 10.10   Open ▸ ), given the overlap of the noise contours with the Southern Trench ncMPA (see section 10.11.2 for more details), the site is also considered further in the EIA ( Table 10.15   Open ▸ ). NatureScot further confirmed agreement in their response to marine mammal Consultation Note 2 (see Table 10.10   Open ▸ ; volume 3, appendix 5.1, annex E) to the inclusion of the noise impacts on the minke whale feature of the Southern Trench ncMPA in the EIA, and a separate supporting MPA assessment document was not required.
28. Designated sites and relevant qualifying interest features identified for the marine mammals Array EIA Report chapter are described in Table 10.15   Open ▸ and presented in Figure 10.3   Open ▸ .

Table 10.15: Designated Sites and Relevant Qualifying Interest Features for the Marine Mammal Array EIA Report Chapter

Figure 10.3: Marine Mammals Relevant Designated Sites

10.7.3. Important Ecological Features

29. Important Ecological Features (IEFs) for the purposes of the marine mammal EIA have been identified using best practice guidelines (Chartered Institute of Ecology and Environmental Management (CIEEM, 2022). The potential impacts of the Array which have been scoped into the assessment (see section 10.8) have been considered in relation to the IEFs to determine whether or not they are important, therefore, the IEFs assessed are those that are considered to be important and potentially impacted by the Array. Marine mammal IEFs have been identified based on biodiversity importance, recognised through international or national legislation, conservation status/plans and on assessment of value according to the functional role of the species within the context of the regional marine mammal study area. Relevant legislation/conservation plans for marine mammals would include, for example: Annex II species under the Habitats Directive; Annex IV(a) of the Habitats Directive as EPS; species listed as threatened and/or declining by Oslo and Paris Conventions (OSPAR); IUCN Red List species; UK Biodiversity Action Plan (BAP) priority species either alone or under a grouped action plan; and PMFs in Scotland.
30. Table 10.16   Open ▸ lists all of the IEFs within the Array marine mammal study area. All marine mammals with the potential to be affected by the Array are protected under some form of international legislation and/or are important from a conservation perspective in an international/national context and therefore the value of all marine mammal IEFs was determined to be international.
31. Bottlenose dolphin (quantitatively) and humpback whale (qualitatively) have been scoped into the assessment following advice from MD-LOT and NatureScot on the Array EIA Scoping Report and subsequent consultation (see Table 10.10   Open ▸ ). Harbour seal has been included within volume 3, appendix 10.2 but has been excluded from the impact assessment due to low likelihood for significant effects based on DAS, telemetry, and low densities in the Array. This was agreed with NatureScot following Marine Mammal Consultation Note 1 (see Table 10.10   Open ▸ ; volume 3, appendix 5.1, annex D) on the basis that there was sufficient evidence provided that the likelihood of significant effects on harbour seal are low.

Table 10.16: IEFs within the Array Marine Mammal Study Area

10.7.4. Future Baseline Scenario

32. The EIA Regulations require that “a description of the relevant aspects of the current state of the environment (baseline scenario) and an outline of the likely evolution thereof without implementation of the project as far as natural changes from the baseline scenario can be assessed with reasonable effort, on the basis of the availability of environmental information and scientific knowledge” is included within the Array EIA Report.
33. If the Array does not come forward, the ‘without development’ future baseline conditions is described within this section.
34. Marine mammal species face direct adverse impacts from various anthropogenic activities (Avila et al., 2018), encompassing offshore developments and associated underwater noise, fisheries and increased rates of vessel activity. According to Avila et al. (2018), almost all global marine mammal species (98%) were documented to be affected by at least one threat between 1991 and 2016. Bycatch in active fishing gear was the most prevalent threat for odontocetes and mysticetes, followed by pollution (solid waste), commercial hunting, and boat collisions. Pinnipeds were documented as primarily threatened by ghost-net entanglements, solid and liquid wastes, and infections (Avila et al., 2018). As discussed in volume 2, chapter 9, fisheries management measures will affect marine mammal prey species, such as the recent closure of sandeel fisheries in Scottish waters (i.e. The Sandeel (Prohibition of Fishing) (Scotland) Order 2024) which will see a ban on the fishing for sandeel from March 2024 within the Scottish zone. It is anticipated that this closure will provide wider potential benefits to the marine ecosystem including direct benefits to sandeel populations (through reduction of pressures from fishing) and indirect benefits to marine mammal species through potential increased prey availability, as sandeel is an important prey species for many marine mammal species (detailed in volume 3, appendix 10.2).
35. Beyond the direct anthropogenic impacts detailed in paragraph 34 above, marine mammals are susceptible to non-direct effects from human activities (Avila et al., 2018), such as climate change and global warming leading to rising sea temperatures. A common response of marine mammals to temperature changes is shifts in their spatial distribution, potentially modifying the ranges of certain species (e.g. white-beaked dolphin). Changes in water temperatures may also impact the life cycles of marine mammal prey species, creating discrepancies in prey abundance that affect migratory marine mammal species and those exhibiting site fidelity. Additionally, global warming could influence marine mammal survival rates by impacting reproductive success, increasing stress, and promoting pathogen infections (Albouy et al., 2020).
36. Given that climatic changes now compound anthropogenic pressures, predicting future trajectories of marine mammal populations without comprehensive data is challenging. Monitoring is not consistently in place at relevant temporal or spatial scales for some species, especially minke whale. Therefore, information presented in this section provides a summary of current and anticipated pressures. Where data are available, information about population dynamics is presented.
37. Any changes that may occur during the design life span of the Array have been considered in the context of both greater variability and sustained trends occurring on national and international scales in the marine environment. Whilst there is an indication that some populations are increasing (i.e. bottlenose dolphin, grey seal) or remain stable (harbour porpoise, minke whale, white-beaked dolphin), it is challenging to define a future trajectory of marine mammal populations, especially without regular survey data (i.e. white-beaked dolphin, minke whale).

                        Harbour porpoise

38. Harbour porpoise are severely vulnerable to incidental entanglements in fishing gear, known as bycatch (Moan et al., 2020). Harbour porpoise are likely to die shortly after entanglement, as they cannot drag fishing gear to the surface to breathe, and this mortality can have large population-level effects, causing adverse population trajectories (IMR/NAMMCO, 2019). In the North Sea, harbour porpoise are considered vulnerable to bycatch in gillnets (Calderan and Leaper, 2019). Assuming that fishing vessels of 12 m or over follow the obligation to use pingers, Kindt‐Larsen et al. (2019) estimated harbour porpoise bycatch in the UK in 2018 to be between 845 and 1,633 individuals with a best estimate of 1,150 individuals (CV=0.087), which is an increase compared to the 2017 estimate of 1,098 animals. (IJsseldijk et al., 2022) investigated the pathological findings related to anthropogenic and natural causes of death in harbour porpoises that stranded between 2008 and 2019. The largest anthropogenic category was bycatch (17%), with mainly juveniles affected and peak periods in March and September to October. Other, infrequently diagnosed anthropogenic causes of death were trauma (4%), largely most likely due to ship collisions, and marine debris ingestion and entanglement (0.3%).
39. Prey availability may also influence harbour porpoise abundance. Harbour porpoise have a high metabolic rate (Rojano-Doñate et al., 2018) and therefore have to feed regularly. As a result of this, harbour porpoise are highly dependent on year-round proximity to food sources and their distribution and condition is considered likely to reflect the availability and energy density of prey (Lambert, 2020, Santos and Pierce, 2003). Any changes in the abundance and density of harbour porpoise prey species (e.g. sandeel, whiting, sprat and herring) (e.g. as result of closures of sandeel fisheries in Scotland) therefore have the potential to affect harbour porpoises foraging in an area.
40. Harbour porpoise have high parasitic exposure, with post-mortem examinations regularly revealing heavy parasitic worm burdens (Bull et al., 2006). A causal immunotoxic relationship between polychlorinated biphenyl (PCB) exposure and infectious disease mortality has also been highlighted (Murphy et al., 2015), with total PCB levels significantly higher in the infectious disease group compared to a physical trauma group (Bull et al., 2006), suggesting that anthropogenic contaminants are having adverse effects on harbour porpoise. In a study conducted by (van den Heuvel-Greve et al., 2021), it was found lower halogenated and more toxic contaminants were transferred to calves, exposing them to high levels of contaminants early in life. Of all animals included in the study, 38.5% had PCB concentrations exceeding a threshold level for adverse health effects (>9 mg/kg lipid weight (lw)). The study also stated that results provide further evidence for potential health effects of persistent organic pollutants (POPs) on harbour porpoises of the southern North Sea, which may consequently increase their susceptibility to other pressures (van den Heuvel-Greve et al., 2021).
41. The impact of climate change on harbour porpoise remains poorly understood (Evans and Bjørge, 2013) with existing research limited and uneven in distribution. Potential impacts of climate change on marine mammals in general have included geographical range shifts ((Gilles et al., 2011, Lambert et al., 2011) (Nøttestad et al., 2015, Silber et al., 2017, Víkingsson et al., 2015), food web changes (Nøttestad et al., 2015, Víkingsson et al., 2015), and increased susceptibility to disease and contaminants (Fire and Van Dolah, 2012, Jensen et al., 2015, Mazzariol et al., 2018, Twiner et al., 2011).
42. Data from SCANS I to SCANS IV suggested that the abundance of harbour porpoise in the NS MU (for which there are enough data to assess trends) is stable between surveys (Gilles et al., 2023, IAMMWG, 2021, IAMMWG. et al., 2015). A study of the impact of climate change on the species range and distribution in van Weelden et al. (2021) suggested a northward shift and expansion of harbour porpoise range, similar to MacLeod et al. (2009), but no increase in maximum latitude. This shift may lead to range contraction and present a risk for north-west European populations with their preference for sub-polar to temperate water temperature.
43. Climate change may impact on harbour porpoise prey distribution and abundance (see volume 2, chapter 9 for effects on prey species) (Evans and Bjørge, 2013). Evans and Bjørge (2013) predicted that rising sea temperatures may enhance stratification as discussed in volume 2, chapter 7, forcing earlier occurrence of the spring phytoplankton bloom and potential cascading effects through the food chain. A study by Sadykova et al. (2020) predicted a large future distribution shift in sandeel and harbour porpoise habitat overlap (164 km) but a small shift (16 km) in overlap between herring Clupea harengus and harbour porpoise.
44. The most recent UK assessment of favourable conservation status shows that the current range of harbour porpoise covers all of the UK’s continental shelf and there appears to have been no change in range since 1994 (JNCC, 2019d, Paxton et al., 2016).The future trend in the range of this species has therefore been assessed as ‘overall stable (good)’. Due to insufficient data, the future trend in the population and consequently future prospects of harbour porpoise was assessed as ‘unknown’ (JNCC, 2019d). As a result of the establishment of SACs for this species in UK waters, the future prospects for the supporting habitat was assessed as ‘good’. The report on conservation status assessment for the species concluded that, assuming that conservation measures are maintained and further measures are taken should other pressures emerge (or existing pressures change) then the future prospects for harbour porpoise in UK waters (which includes the Array marine mammal study area) should remain ‘favourable’ (JNCC, 2019d).

                        Bottlenose dolphin

45. The observed distribution of bottlenose dolphins in SCANS-IV was similar to SCANS-III in the southern areas but different in the north west, with more sightings in the northern Celtic Sea, Irish Sea and the Hebrides in 2022 (Gilles et al., 2023). Gilles et al. (2023) states there is no information on abundance of bottlenose dolphin in the central North Atlantic, but the differences in distribution and abundance estimates between SCANS surveys (2005, 2016 and 2022) may reflect animals responding to interannual spatial variation in prey availability across the wider range. According to the recent OSPAR Quality Status Report (QSR) 2023, the population in the East Coast Scotland MU is showing signs of increase and range expansion in recent years (Geelhoed et al., 2022a).
46. Over the last 20 years, the size of the population of bottlenose dolphins off the east coast of Scotland has increased (Arso Civil et al., 2021, Cheney et al., 2018, Cheney et al., 2013) and their distribution has observed a southern range expansion, with the same identifiable individuals regularly occurring off eastern England (Arso Civil et al., 2021, Arso Civil et al., 2019). The boundaries of the Moray Firth SAC initially intended to include the main Scottish population's core range, following research conducted in the 1980s and early 1990s. However, Wilson et al. (2004) documented a range shift of the east coast of Scotland population outside of the designated Moray Firth SAC. This was evidenced by photo identification studies and bottlenose dolphin carcasses which were found in areas considered to be outside the original range of the species, raising questions about the efficacy of this area-based protection. Surveys over the past ten years have shown that around 50% of the population use the Tay Estuary and adjacent waters during summer months (Arso Civil et al., 2019).
47. The movement of bottlenose dolphin individuals may be driven by environmental and biological factors, including seasonal changes in prey presence as well as social bonds within the population (Arso Civil et al., 2021). These findings are in line with a study by Lusseau et al.(2004) which reported that bottlenose dolphin group sizes in the Moray Firth were significantly related to prey abundance and that changes in the abundance of fish prey would result in interannual variation in grouping patterns of bottlenose dolphin. Therefore, this study suggested that extrinsic factors could influence the structure of social community and parameters such as dispersal rate. Changes in prey abundance as a result of climate change are therefore likely to be a major factor driving changes in bottlenose dolphin distribution. A study on a Mediterranean population of bottlenose dolphin found that regardless of the sex and social unit to which the animals belong, from 2017 to 2020 individual home range size increased threefold (on average from 5 km2 to 15 km2) compared to 2013 to 2016, when sea surface temperature was on average 1.34 °C lower and marine heat waves shorter than 29 days/year (La Manna et al., 2023). Demonstrating the influence of sea surface temperature and marine heatwaves on bottlenose dolphins spatial traits, these results are thought to be potentially useful in mitigating the effects of climate change on coastal dolphins in other regions (La Manna et al., 2023).
48. Evans and Waggitt (2020) highlighted that the frequency and severity of toxic phytoplankton blooms are predicted to increase as a result of nutrient enrichment (via increased rainfall and freshwater runoff) and increased temperature (via climate change) and salinity. Mass die-offs have been reported in bottlenose dolphin due to fatal poisonings relating to phytoplankton blooms (Fire et al., 2007, Fire et al., 2008).
49. The results of the most recent UK assessment of favourable conservation status showed that the future trend in the range of bottlenose dolphin is ‘overall stable (good)’ (JNCC, 2019a). However, although the pressures impacting bottlenose dolphin populations and available habitat are not thought to be increasing and there are no threats identified which are likely to impact in the next 12 years, due to insufficient data to establish a current trend for this species the future trend and consequently the future prospects for the population and habitat parameters are ‘unknown’ (JNCC, 2019a). Therefore, the overall assessment of future prospects and conservation status for bottlenose dolphin is ‘unknown’ (JNCC, 2019a).

                        White-beaked dolphin

50. SCANS IV large scale population survey results revealed no significant change in abundance of white-beaked dolphins in the North Sea since the mid-1990s (Gilles et al., 2023).
51. White-beaked dolphin is a species endemic to cold temperate waters of the North Sea and has an estimated population of around 36,000 individuals.(IJsseldijk et al., 2018). Increasing water temperature may lead to reduced areas suitable for foraging and also habitat loss, both of which may result in decline in the population numbers in certain areas of the species range (IJsseldijk et al., 2018). The study reported the first indication of a change in habitat-use and population distribution whereby changes in densities from southern to northern regions of the North Sea were evidenced from strandings data, and IJsseldijk et al. (2018) suggested this may result from changes in prey distribution and availability. The status of white-beaked dolphin is evaluated as ‘least concern’ due to its widespread abundance, however their range is expected to shrink in response to increasing sea temperature (IJsseldijk et al., 2018). In study of white-beaked dolphin strandings between 1948 and 2003, MacLeod et al. (2005) reported a decline in the relative frequency of white-beaked dolphin strandings and sightings in north-west Scotland, and attributed climate change as a major cause of this decline.
52. The results of the most recent UK assessment of favourable conservation status shown that the future trend in the range of white-beaked dolphin is ‘overall stable (good)’ (JNCC, 2019b). Population estimates suggest that the population is relatively stable (JNCC, 2019b). While pressures on white-beaked dolphin populations and their habitat are not believed to be increasing, no threats have been identified that are likely to be impactful. However, due to insufficient data to establish a current trend for this species, the future trajectory of their population and habitat parameters remains ‘unknown’ (JNCC, 2019b).Therefore, the overall assessment of future prospects and conservation status for white-beaked dolphin is ‘unknown’ (JNCC, 2019b).

                        Minke whale

53. In coastal waters off east Scotland, Ammodytes marinus are the main constituent of minke whale diet, however fish species such as pelagic herring and Sprattus sprattus are equally important for foraging whales in offshore waters (NatureScot, 2023a, Robinson et al., 2009, Santos and Pierce, 2003). (Robinson et al., 2023) examined the distribution and feeding behaviours of adult and juvenile minke whales from long term studies in the Moray Firth; Geographical Information System (GIS) data revealed spatial separation/habitat partitioning by age-class, with juveniles preferring shallower, inshore waters with sandy-gravel sediments, and adults preferring deeper, offshore waters with greater bathymetric slope. Generalised Additive Models (GAMs) suggested that the partitioning between age-classes was predominantly based on the differing proximity of animals to the shore, with juveniles showing a preference for the gentlest seabed slopes, and both adults and juveniles showing a similar preference for sandy-gravel sediment types. The results of analysis of minke whales stomach contents in Icelandic waters suggested that a decrease in the proportion of sandeel and cold water species in the diet and an increase in Gadidae and herring may reflect responses of minke whales to a changed environment, possibly driven by increased sea surface and bottom temperatures (Víkingsson et al., 2013). Studies also suggest that minke whales are likely to shift their distribution as a response to the decrease in the abundance of the preferred prey species (Víkingsson et al., 2015). There may be potential increases in prey availability in the area in the future due to sandeel closures in Scotland (see paragraph 34), though the effects of closure would be unlikely to present at higher trophic levels immediately.
54. Major threats affecting minke whale in UK waters include direct and indirect interactions with fisheries (Leaper et al., 2022). In Scotland, for example, evidence of entanglement in static fishing gear (pots or creels) was present in as many as 50% of stranded minke whales examined from 1990 to 2010 (Leaper et al., 2022), Northridge et al. (2010) also estimated 30 minke whales becoming entangled each year within Scottish creel fishing gear. Minke whale are also affected by shipping due to direct mortality caused by ship strikes. 7% of minke whales necropsied by the Cetacean Strandings Investigation Programme (CSIP) between 2000 and 2017 had a cause of death of physical trauma due to ship strike (CSIP, 2024). Other impacts include ingestion of contaminants and exposure to persistent noise disturbance which may interrupt key life-cycle activities such as feeding and breeding, causing them to avoid or even abandon critical habitat areas (Anderwald et al., 2013, Gill et al., 2000, Robinson et al., 2009). Data from SCANS II, SCANS III and SCANS IV suggested that the abundance of minke whales in the CGNS MU is stable (IAMMWG, 2022).
55. The results of the most recent UK assessment of favourable conservation status showed that there is no evidence to suggest that minke whale range has changed since last report on conservation status in 2013 and therefore it has been assessed as overall stable (good) (JNCC, 2019c). The OSPAR Intermediate Assessment (OSPAR IA, 2017) concluded that there was no evidence of change in abundance in the North Sea over the period 1994 to 2016 (JNCC, 2019c). However, although the pressures impacting minke whale population and available habitat are not considered to be increasing (JNCC, 2019c), due to insufficient data to establish a current trend for this species, the future trend and consequently the future prospects for the population and habitat parameters are ‘unknown’ (JNCC, 2019c). Therefore, the overall assessment of future prospects and conservation status for minke whale is ‘unknown’ (JNCC, 2019c).

                        Humpback whale

56. Following a severe decline due to commercial whaling, humpback whale populations in the North Atlantic region have been undergoing steady recovery during the latter part of the twentieth century (Johnson and Wolman, 1984, O'Neil et al., 2019). In the western North Atlantic, entanglement in static fishing gear, namely crab and lobster creels (pots), is currently considered to be the largest source of anthropogenic mortality and injury for this species (Leaper et al., 2022, Ryan et al., 2016). There are reported stranding records of humpback whales in the southern North Sea (Haelters et al., 2010), however sightings of large mysticetes are infrequent. Specifically, no abundance estimate exists for humpback whales in Scottish waters and SCANS and Cetacean Offshore Distribution and Abundance visual surveys did not detect any between 1994 and 2017 (Hammond et al., 2017). However, influxes of humpback whales into the Firth of Forth were reported in 2017 and 2018, during migration (O'Neil et al., 2019).
57. The main impacts on humpback whale populations in the southern North Sea includes disturbance, ship collisions, entanglement and crucially, changes in food supply (Leopold et al., 2018). Humpback whales occur close to shore and therefore coastal areas with high human activity. Fournet et al. (2018) showed that humpback whales in foraging grounds in the North Pacific and North Atlantic have increased the source levels of their calls as ambient noise levels increased, suggesting increasing ocean noise may lead to masking impacts on the species. Increased disturbance to humpback whale due to increasing marine tourism is also thought to be potentially significant, if not managed carefully (Schaffar et al., 2010).
58. Another threat to humpback whales is entanglement in fishing gear, which is increasing in Northeast Atlantic and European waters (Basran et al., 2019, Ryan et al., 2016). At least 25% of 379 individual humpback whales photographed off Iceland showed evidence of non-lethal entanglements with fishing gear (Basran et al., 2019). 
59. Concentrations of POPs tend to be lower in mysticetes in comparison with odontocete species due to their foraging preferences for lower trophic levels and generally shorter life spans. In a study by (Ryan et al., 2013), PCB and dichlorodiphenyltrichloroethane (DDT) concentrations in humpback whales sampled in the eastern North Atlantic were found to be lower than threshold toxicity levels for blubber in marine mammals. The relatively low POP concentrations of the Cape Verde humpback whales (as described in Table 10.12) suggested that POPs are unlikely to be a factor in the poor recovery rate of this small putative population (Ryan et al., 2013). The non-selective foraging technique mysticete species such as humpback which involves ingesting material surrounding the intended prey in the water could result in exposure to microplastic (Besseling et al., 2015), with Besseling et al. (2015) reporting the first case of microplastic in intestines of a mysticete from the North Sea. Kahane-Rapport et al. (2022) found that mysticetes (humpback whale, fin whale, blue whale) predominantly feed at depths of between 50 m and 250 m which coincides with the highest measured microplastic concentration in the studied pelagic California Current Ecosystem, predicting whales that feed on fish may be less exposed to microplastic ingestion than those that feed on krill.

                        Grey seal

60. Approximately 35% of the world’s grey seals breed in the UK and 80% of these breed Scotland (with highest concentrations in the Outer Hebrides and Orkney) (SCOS, 2023), with the fastest growing colonies located in the central and southern North Sea (SCOS, 2023). UK grey seal numbers are currently stable or increasing throughout their monitored range (SCOS, 2023), suggesting that their population status is not under threat. Population dynamics depend on a colony, however, pup production at colonies in the North Sea is increasing at a rate of approximately 7% per annum (p.a.) (SCOS, 2023), therefore continuing to increase rapidly and does not show any indications of density dependent restraint on growth (SCOS, 2022). SCOS (2023) stated the East Coast of Scotland SMU is continuing to increase rapidly (5.38% p.a.), but the two SACs in the SMU show different trends in abundance. Production at the Isle of May increased exponentially to 9.9% p.a. since surveys began in 1979 (SCOS, 2022), however is now stable or potentially declining (SCOS, 2023). Pup production at Fast Castle, in the Berwickshire and North Northumberland Coast SAC, shows a rapidly increasing pup production (SCOS, 2023) does not show any indication of reaching an asymptote (SCOS, 2022).
61. As top marine predators, grey seal are particularly vulnerable to biotoxins because they possess large fat stores that accumulate POPs. The analysis of POPs in blubber from weaned grey seal pups on the Isle of May detected POP concentrations below the values that could cause severe toxic effect, however highlighted that even low concentrations are likely to cause endocrine disruption with unknown consequence for individual health and survival (Robinson et al., 2019). Most previous research focused on the transfer of contaminants through the trophic levels. However, Wilman et al. (2023) noted that mercury and polycyclic aromatic hydrocarbons (PAHs) in the lungs of the seals, with results suggesting the airborne influx of mercury and PAHs into the lungs from marine mammals to be plausible. This is of particular importance in juveniles (pups) who at the initial stage of life spend time on land and do not obtain food independently. Other threats to grey seals include entanglement in marine and plastic debris, particularly discarded fishing gear, disturbance and climate change affecting availability of prey.
62. In the SCOS Interim 2023 advice (SCOS, 2024), SCOS advised it unlikely that observed high sea surface temperatures in 2023 (with particularly warm sea surface temperatures off the east of the UK from Durham to Aberdeen) will have significant direct impacts on either grey or harbour seals in terms of their physiology or energetics, but any potential medium or longer term impacts are likely to be due to marine heatwave effects on grey seal prey species. SCOS (2024) highlighted that warmer temperatures are more likely to impact animals in terms of thermoregulation on land during breeding or haul out, rather than when swimming at sea (where a large thermal gradient between internal body temperature (37°C) and the cold sea water means seals remain in the thermoneutral zone).
63. The results of the most recent UK assessment of favourable conservation status showed that the future trend in the range of grey seal is ‘overall stable (good)’ (JNCC, 2019e). Modelling of population size at the beginning of each breeding season between 1984 and 2017 demonstrated an increasing trend and although the rate of increase has declined, the abundance estimate is above historic estimates (JNCC, 2019e). As the current conservation status for range and population is favourable for this species, the future prospects for both parameters are considered ‘good’ (JNCC, 2019e). The future trend of grey seal habitat has been assessed as ‘overall stable’ (good) (JNCC, 2019e).

10.7.5. Data Limitations and Assumptions

64. The data assumptions and limitations summarised in this section (and presented in more detail in volume 3, appendix 10.2, annex A) are typical challenges that are encountered in conducting DAS for marine mammals in field settings. A number of measures agreed in consultation with stakeholders (such as a choice of appropriate correction factors, see Table 10.10   Open ▸ ) were applied in data analysis to ensure the most precise results.
65. Although DAS were designed to be carried out monthly, due to logistical issues and/or unsuitable weather conditions, surveys were not conducted in two months: May 2021 and February 2022. Additional surveys were executed in early June 2021 and early March 2022 to fill the potential data gaps and represent the surveys that were not flown. It is essential to acknowledge that the single survey day per month provides only a snapshot of marine mammal distribution, making it challenging to assess the impact of environmental conditions on sighting rates, with consideration given only to seasonal changes. Detection probability may also be constrained by weather conditions, impacting the ability to record marine mammals, particularly distinguishing between grey sea and harbour seal at-sea. In order to ensure that bias is not introduced to the site-specific survey modelling results ( Table 10.10   Open ▸ ), data from broader non-species-specific classifications were not assigned to species categories. As such, sightings classed as ‘cetacean species’, ‘dolphin species’, ‘seal/small cetacean species’ and ‘seal species’ are not considered in species-specific analyses.
66. Availability bias, representing the time when an animal is detectable either at the sea surface or just below, can also be considered as a potential limiting factor. It can lead to under-estimation of the number of animals present, as not all animals in the area may detectable, rather than not being present (e.g. deeper beneath the water surface) (see volume 3, appendix 10.2, annex A for full detail on availability bias). Therefore, relative density calculations for harbour porpoise, white-beaked dolphin, minke whale and grey seal were corrected for availability bias using published correction factors based on the likelihood of individuals being near the surface and detectable as agreed in consultation with stakeholders (volume 3, appendix 5.1, annexes D and E) .
67. Despite the aforementioned limitations for DAS, the baseline assessment is supplemented with information reported in published literature and therefore offers a comprehensive account of marine mammals within the Array marine mammal study area and the regional marine mammal study area. The presented baseline provides a robust and suitable characterisation of the two study areas against which this assessment is conducted. Consequently, it is concluded that the identified data limitations are not anticipated to impact the assessment's conclusions.