5. Species Accounts

  1. The following section provides detailed baseline information for each of the key species identified as common within the Array and regional marine mammal study areas (see section 4.1). These are:
  • harbour porpoise;
  • bottlenose dolphin;
  • white-beaked dolphin;
  • minke whale;
  • harbour seal; and
  • grey seal.
  1. Additionally, given increased frequency of sightings of humpback whale in the Firth of Forth, this species will also be accounted for in this section. However, it should be noted that there are no species-specific studies of these species in Scottish waters and therefore available desktop data is sparse.
  2. Species-specific densities presented in this section were consulted on with stakeholders via the Array Marine Mammal Methodology Note (volume 3, appendix 5.1, annex B) and Array Marine Mammal Consultation Note 1 (volume 3, appendix 5.1, annex D).

5.1. Odontocetes

5.1.1. Harbour Porpoise

                        Ecology

  1. The harbour porpoise is a small odontocete (toothed whales) inhabiting coastal temperate and boreal waters of the northern hemisphere. It reaches a maximum length of 1.9 m (Bjørge and Tolley, 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. Harbour porpoise have a large extensible stomach (up to six times the relaxed size). They are capable of ingesting up to 90% of their daily energetic requirements in one hour and can feed again shortly afterwards (Kastelein et al., 2019a, Booth et al., 2023). Harbour porpoise feed on a wide range of fish species, but mainly small shoaling species from demersal or pelagic habitats (Santos and Pierce, 2003a). There are regional and seasonal differences in diet, interannual variation depending on the availability of prey species as well as variation according to individual age, with juveniles targeting smaller species such as gobies Gobiidae or smaller individuals of the same prey species targeted by adults (Santos and Pierce, 2003a). A harbour porpoise’s metabolic rate remains stable over seasonally changing water temperatures. Heat loss is deemed to be managed via cyclical fluctuations in energy intake to build up a blubber layer that offsets the extra cost of thermoregulation during winter (Rojano-Doñate et al., 2018).
  3. Ransijn et al. (2019) produced energy maps for various harbour porpoise prey species and found that the energy available in the North Sea is highest in the summer and the main energic contributions were from sandeels Ammodytidae and whiting Merlangius merlangus. During the winter season European sprat Sprattus sprattus and Atlantic herring Clupea harengus also contributed to overall energy density (Ransijn et al., 2019). This study corroborated previous findings that predominant prey item of harbour porpoise during the summer off the east coast of Scotland is sandeel (Santos, 1998, Santos and Pierce, 2003b). Although harbour porpoise generally hunt alone or in small groups, this species can be seen in larger aggregations of 50 or more individuals, either during seasonal migrations or associated with increased concentrations of prey. Within these aggregations, segregation may occur, with females travelling with their calves and yearlings, and immature animals of each sex segregating into groups. The largest group of harbour porpoises recorded during DAS of the Array marine mammal study area consisted of 144 individuals (refer to volume 3, appendix 10.2, annex A).
  4. 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., 2018, Kastelein et al., 2019b, 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., 2019a). 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., 2019a). 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).
  5. The age of sexual maturation for the harbour porpoise is approximately three to four years and reproduction is strongly seasonal, with mating occurring between June and August (Lockyer, 1995). Gestation is ten to 11 months and there is a peak in birth rate around the British Isles during the months of June and July (Boyd et al., 1999).
  6. Bycatch in fisheries is the predominant threat to harbour porpoise in the North Sea (Lusseau et al., 2023). Harbour porpoise are particularly vulnerable to being caught in bottom-set gill nets, due to their feeding behaviour. Other threats include prey depletion, pollution affecting the health of individuals, and acoustic and physical disturbance (Evans and Prior, 2012).

                        Distribution and occurrence

  1. The harbour porpoise is widespread throughout the cold and temperate seas of Europe, including the North Sea, the Skagerrak, Kattegat, Irish Sea, the seas west of Ireland and Scotland, northwards to Orkney and Shetland and off the coasts of Norway (JNCC, 2023f). Heinänen and Skov (2015) found that in the North Sea MU the water depths and hydrodynamic variables are the most important factors predicting the presence of harbour porpoise. During summer, animals were predicted to avoid well-mixed areas showing preference for more stable areas. Studies indicated lower presence of harbour porpoise with lower salinity, reflecting an avoidance of estuarine water masses Heinänen and Skov (2015).
  2. The Heinänen and Skov (2015) analysis concluded that in the summer months, harbour porpoise presence in the North Sea MU was best predicted by season, water depth and salinity of surface waters. In the winter months the presence of harbour porpoise was best predicted by the season, water depth and seabed surface sediments. In winter months a peak in presence was observed at water depths of 30 m to 40 m. Williamson et al. (2016) found that the proportion of hours with acoustic detection of harbour porpoise in muddy habitats within the Moray Firth increased during hours of darkness by 18%. Harbour porpoise detections also differed in response to depth in different sediment types between hours of darkness and daylight. In muddy areas with a water depth of between 50 m to 60 m, detections at night were almost double those during daylight hours. Therefore, it can be concluded that harbour porpoise use different types of habitats during hours of daylight and darkness and their distribution may change accordingly.
  3. Harbour porpoise was the most commonly identified cetacean during TCE aerial surveys (Grellier and Lacey, 2011), Berwick Bank aerial surveys (SSE Renewables, 2022b) and Seagreen boat-based surveys (Sparling, 2012). During the TCE aerial surveys, a greater number of sightings were recorded offshore, with most individuals observed alone, although group size ranged from 0 to six individuals. The Berwick Bank aerial survey and Seagreen boat-based survey results showed that sightings occurred throughout the respective survey areas ( Figure 3.2   Open ▸ ). Harbour porpoise was also the most frequently recorded species of cetacean during Neart na Gaoithe boat-based surveys undertaken each month between November 2009 and October 2012 (Mainstream Renewable Power, 2019).
  4. Harbour porpoise accounted for the highest number of sightings across all species in the DAS of the Array marine mammal study area, with a total of 839 animals recorded across 21 months. No clear spatial patterns were observed in the distribution of harbour porpoise sightings.
  5. Based on the Seagreen boat-based survey data (Seagreen Wind Energy Limited, 2018), it seems that the morphological bank features such as Scalp Bank are particularly important for harbour porpoise. These areas may represent good foraging grounds due to the sandy banks providing good habitat for prey species such as sandeel and whiting, both of which have been recorded as important constituents of the diet of harbour porpoises on the east coast of Scotland, with the relative proportion of each of these in the diet changing seasonally (Santos and Pierce, 2003b).

                        Density/abundance

                        Published literature
  1. Density and abundance estimates of harbour porpoise are available from various studies carried out across a broader area within the regional marine mammal study area. IAMMWG (2022) estimated abundance for the North Sea MU ( Figure 5.1   Open ▸ ) as 346,601 animals (CV = 0.09, 95% confidence interval (CI) = 289,498 to 419,967). The SCANS III data (Hammond et al., 2021) estimated the abundance of harbour porpoise within block R ( Figure 3.3   Open ▸ ) as 38,646 animals (CV = 0.29, 95% CI = 20,584 to 66,524). The abundance of harbour porpoise within SCANS IV block NS-D is comparable to this reported for SCANS III block R with a population of 38,577 individuals indicating no changes in harbour porpoise abundance (Gilles et al., 2023).
  2. Hammond et al. (2021) reported densities for harbour porpoise across block R as 0.599 animals per km2. Recently modelled density surfaces using the SCANS III data (paragraph 29) (Lacey et al., 2022) gave a mean density of 0.763 animals per km2 and a maximum of 0.835 animals per km2 for the Array marine mammal study area ( Figure 5.2   Open ▸ ), with areas of higher density to the south-east of the Array marine mammal study area. The harbour porpoise density estimates for SCANS IV block NS-D are analogous to these reported for SCANS III block R at 0.5985 harbour porpoises per km2 (Gilles et al., 2023).

Figure 5.1:
North Sea Management Unit

Figure 5.1: North Sea Management Unit


Figure 5.2:
Harbour Porpoise Density Surface Derived From SCANS III Data (from Lacey et al. (2022))

Figure 5.2: Harbour Porpoise Density Surface Derived From SCANS III Data (from Lacey et al. (2022))


  1. Monthly predicted distribution maps of harbour porpoise from Waggitt et al. (2020) suggest that harbour porpoise densities are higher throughout autumn and summer months ( Figure 5.3   Open ▸ to Figure 5.5   Open ▸ ). Highest densities within the Array marine mammal study area were predicted in August with a mean of 0.604 animals per km2 ( Figure 5.4   Open ▸ ). The density of harbour porpoises increases towards the southern North Sea, south-east of the site boundary.
  2. To provide additional context, JCP Phase III analyses estimated abundance for harbour porpoise in 2010 by season for the Firth of Forth area of commercial interest region (Paxton et al., 2016) ( Figure 3.5   Open ▸ ). Highest abundance of harbour porpoise was estimated for the winter months (January to March), with 7,000 (97.5% CI = 5,200 to 11,800) animals estimated. Abundance estimates for spring (April to June) and summer (July to September) were 3,500 (97.5% CI = 1,900 to 6,600) and 4,400 (97.5% CI = 2,900 to 6,800) animals respectively. The lowest abundance was estimated in autumn (October to December) with 2,500 (97.5% CI = 1,600 to 3,600) animals (Paxton et al., 2016). These equated to density estimates of 0.492 animals per km2 in the winter, 0.246 animals per km2 in the spring, 0.309 animals per km2 in the summer and 0.176 animals per km2 in the autumn (Paxton et al., 2016). These densities are lower than the ones reported by Waggitt et al. (2020), Hammond et al. (2021) and Lacey et al. (2022).
  3. The Heinänen and Skov (2015) analysis concluded that the density estimates within the outer Firth of Forth and Firth of Tay region were predicted to be relatively low compared to other parts of the North Sea. The areas of persistent high densities are predicted in the outer Moray Firth. Paxton et al. (2016) corroborated this finding by reporting that the Firth of Forth and the east coast of Scotland was not associated with the highest density for this species, compared to other regions such as the west coast of Ireland or the Hebrides, and that higher abundance was correlated with the Moray Firth. The study reported the predicted abundance in the Firth of Forth as 1.4% (95% CI = 0.6 to 2.3) of the overall predicted number for the North Sea MU (based on estimates for summers 2007 to 2010).

Figure 5.3:
Harbour Porpoise Density from January to April Based on Waggitt et al. (2020)

Figure 5.3: Harbour Porpoise Density from January to April Based on Waggitt et al. (2020)


Figure 5.4:
Harbour Porpoise Density from May to August Based on Waggitt et al. (2020)

Figure 5.4: Harbour Porpoise Density from May to August Based on Waggitt et al. (2020)


Figure 5.5:
Harbour Porpoise Density from September to December Based on Waggitt et al. (2020)

Figure 5.5: Harbour Porpoise Density from September to December Based on Waggitt et al. (2020)


                        Surveys
  1. Relative density estimates of harbour porpoise from DAS were corrected for availability bias using the most conservative conversion factor of 42.5% based on Teilmann et al. (2013) (refer to volume 3, appendix 10.2, annex A for more detail). The most robust method was developed by combining the data by bio-season specific to harbour porpoise (“winter” (October to March) and “summer” (April to September) seasons), as the most biologically relevant approach Heinänen and Skov (2015). Design-based approaches gave absolute densities of 0.062 and 0.651 animals per km2 for winter and summer respectively. The mean absolute density estimate across all transects and all monthly surveys for the 24-month survey period, with bootstrapping, was estimated as 0.357 animals per km2 (95% CLs = 0.200, 0.510; CV = 1.367). Mean absolute density from the model-based approach was 0.064 for winter (95% CL = 0.030 to 0.121, CV = 0.54) and 0.648 for summer (95% CL = 0.102 to 0.916, CV = 0.0.422).
  2. Spatial modelling using linear models showed harbour porpoise density hotspots during winter in north-west and south-west of the Array marine mammal study area and during summer in the south-east of the Array marine mammal study area ( Figure 5.6   Open ▸ ). This is in line with findings presented by Waggitt et al. (2020) and Lacey et al. (2022) which show that the density of harbour porpoises increases towards the southern North Sea. This may be correlated with information provided previously for the Southern North Sea SAC in paragraph 76 as the northern part of this SAC, located south-east from the site boundary supports higher densities of porpoises during the summer season (April to September) (JNCC, 2023c).
  3. Grellier and Lacey (2011) reported the mean density of harbour porpoise during the TCE aerial surveys ( Figure 3.2   Open ▸ ) as 0.080 (CV=0.11) individuals per km2. Summer density estimates were higher compared to winter estimates with 0.099 (CV=0.12) and 0.048 (CV=0.24) individuals per km2, respectively. The analysis indicated that depth was a significant predictor of occurrence, with fewer animals in shallow water. After correcting for availability, Mackenzie et al. (2012) estimated absolute abundance for the survey area (TCE aerial surveys and Seagreen boat-based surveys, Figure 3.2   Open ▸ ) across the survey period as 582 (95% CI = 581 to 1235; using a correction factor of 0.434). Relative mean monthly density using Berwick Bank aerial survey ( Figure 3.2   Open ▸ ) data was estimated as 0.127 (95% CI = 0.066 to 0.277) animals per km2 with a peak mean density during spring months of 0.826 (95% CI = 0.440 to 1.616) animals per km2 (SSE Renewables, 2022c).


Figure 5.6:
Predicted Mean Relative Density of Harbour Porpoise for the ‘Winter’ (Top) and ‘Summer’ (Bottom) Bio-Seasons

Figure 5.6: Predicted Mean Relative Density of Harbour Porpoise for the ‘Winter’ (Top) and ‘Summer’ (Bottom) Bio-Seasons

 

                        Summary of the densities
  1. Harbour porpoise are the most abundant marine mammal species within the North Sea with areas of higher density located in the southern North Sea. Comparison of key data sources for harbour porpoise is shown in Table 5.1   Open ▸ .
  2. As presented in paragraph 99, Heinänen and Skov (2015) reported that pooling data according to temporal patterns of harbour porpoise distribution is the most biologically relevant approach to studying harbour porpoise abundance/densities. As such, the most precautionary estimates of harbour porpoise density from DAS presented in Table 5.1   Open ▸ are based on the “summer” bio-season (April to September).
  3. Predicted estimates of mean density for the Array marine mammal study area from Waggitt et al. (2020) are comparable to the SCANS III block R and SCANS IV block NS-D estimates ( Table 5.1   Open ▸ ), but provide densities at a higher resolution (10 km x 10 km) and monthly frequency, rather than a single estimate over a wide area (as is the case with SCANS surveys which use large blocks). It should be noted that SCANS densities do not take into account variability in cetacean density associated with environmental covariates (such as depth, slope, distance from the coast). Additionally, both Gilles et al. (2023) and Hammond et al. (2021) highlight that the very short timeframe over which the SCANS surveys are conducted (summer) means that there is limited understanding of species distribution and abundance in other seasons.
  4. Densities from Lacey et al. (2022) are derived from the same resolution as Waggitt et al. (2020) (10 km x 10 km) and are comparable to the design and model-based densities from DAS ( Table 5.1   Open ▸ ). It should be noted that Lacey et al. (2022) used SCANS III data alongside the environmental covariates such as depth and slope in the density surface modelling. As reported by Heinänen and Skov (2015) (see paragraph 90), the depth, amongst other parameters is an important predictor for harbour porpoise distribution. As such, studies that consider environmental factors are perhaps more robust when predicting harbour porpoise density.
  5. When compared to studies analysing data from large scale surveys, such as SCANS, the results of the analysis of the site-specific DAS data are considered to be the most robust as these are based on the most recent data, collected regularly (monthly) over two years and over a specific area of interest (Array marine mammal study area). As such, it is considered that density estimates based on DAS data are the most appropriate to inform impact assessments and the absolute density of 0.651 animals per km2 will be taken forward to the assessment.

 

Table 5.1:
Comparison of Density Estimates for Harbour Porpoise (DAS Design-Based Density Will Be Taken Forward to the Assessment)

Table 5.1: Comparison of Density Estimates for Harbour Porpoise (DAS Design-Based Density Will Be Taken Forward to the Assessment)

 

                        Seasonality

  1. Across datasets, harbour porpoise counts were consistently higher during the summer months. During the TCE aerial surveys ( Figure 3.2   Open ▸ ) harbour porpoises 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 and Lacey, 2011). The same pattern of higher encounter rates during summer months was also recorded during the Seagreen boat-based surveys (Sparling, 2012). The Seagreen boat-based surveys in summer 2017 recorded the highest counts of harbour porpoise between May and July (Seagreen Wind Energy Limited, 2018).
  2. Similarly, analysis of Berwick Bank aerial survey data suggest 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, 2022a).
  3. The monthly encounter rate for harbour porpoise from Array marine mammal study area 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 ( Table 4.2   Open ▸ ).

5.1.2. Bottlenose Dolphin

                        Ecology

  1. Bottlenose dolphin are members of the family Delphinidae, which are odontocete cetaceans 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 cod Gadus morhua, saithe Pollachius virens, whiting, salmon Salmo salar and haddock Melanogrammus aeglefinus (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. Mean group size across the SCANS III survey areas was 5.25 individuals (Hammond et al., 2021). Robinson et al. (2017) reported that in the outer Moray Firth observed group sizes varied between two and 70 animals.

                        Distribution and occurrence

  1. Based on the data collected in 1980s and early 1990s, the Moray Firth SAC boundary is thought to encompass the core area of occurrence of the resident, coastal population of bottlenose dolphins in the North Sea.
  2. Acoustic occupancy rates and habitat modelling in the East Coast Marine Mammal Acoustic Study (ECOMMAS) highlighted that the waters between Stonehaven and Aberdeen are also a potential area of high occupancy (Palmer et al., 2019). It is worth noting that the ECOMMAS study did not deploy any hydrophone stations on the north-east English coast. Quick et al. (2014) established that a high proportion of bottlenose dolphins from the Coastal East Scotland population use both the Tayside and Fife area as well as the Moray Firth SAC, over a range of temporal scales. These findings were corroborated by Arso Civil et al. (2019) who reported that that more than half of the estimated CES population was consistently using the St Andrews Bay and the Tay estuary. The data collected during boat-based trips between Moray Firth and Fife Ness (during summers 2017 to 2019) show that the Tay estuary area and adjacent waters continue to be used by more than half of the total estimated population every summer (Arso Civil et al., 2021). The same study suggested that it is likely that changes in the distribution range are continuing with a further southern range expansion. Ongoing citizen science projects suggest that some members of this population are relocating from Scottish waters into waters off the coast of eastern England (as far as south of Scarborough, Figure 5.7   Open ▸ ) (Hackett, 2022).
  3. North East Cetacean Project (NECP) is a community engaging people involved in marine mammal watching. Citizens can share their whale, dolphin, porpoise and other interesting marine wildlife sightings anywhere from the Humber to the Scottish Border (NECP, 2021). Another project which combines research and citizen science photo-identification data, specifically of bottlenose dolphins, is called Citizen Fins (Citizen Fins, 2023). This collaboration allows for photo identification work to match photos taken by citizens in England with the East Coast Scotland Bottlenose Dolphin Photo-ID Catalogue. Many individuals from the East Coast Scotland population were positively identified from the Northumberland coast at numerous locations, including Cresswell, Beacon Point, King Edward's Bay (Tynemouth), Whitburn Beach and Roker Beach (Citizen Fins, 2023). As such, the results of photo-identification analysis suggest that animals found off the north-east coast of England are not a separate, isolated population from those in the Moray Firth SAC. Although historic accounts suggest that bottlenose dolphins are not new to the area between Firth of Forth and Withernsea (Bloom, 1991), the data detailed in the Sea Watch Foundation's National Whale and Dolphin Watch reports have revealed an influx of animals in the last decade (Hackett, 2022, Sea Watch Foundation, 2023). Photo-identification study and analysis of sightings data conducted by Hackett (2022) corroborated these findings and showed that annual sightings of bottlenose dolphins along north-east England have steadily increased since 2019. Sixteen post-construction surveys were undertaken between March and October 2018 for the Blyth Offshore Demonstrator project, located 5 km off the coast of Blyth, Northumberland (EDF Renewables, 2019). Bottlenose dolphins were recorded on two separate surveys, noting that no bottlenose dolphins were recorded during preconstruction surveys carried out between March and October 2016 (EDF Renewables, 2019).
  4. The ECOMMAS C-POD study (Palmer et al., 2019) found that broadband acoustic occupancy rates throughout the survey were generally higher for C‐PODs closer to the shoreline which corroborates findings of Thompson et al. (2015) suggesting the bottlenose dolphins are more likely to be observed in coastal waters, within 5 km of shore and therefore are unlikely to be present in the offshore areas that may be exposed to significant construction noise from offshore wind farms. These results were corroborated by Quick et al. (2014) which reported that dolphins were mostly encountered in waters less than 30 m deep, generally in waters between 2 m and 20 m and within 2 km from the coast. Paxton et al. (2016) also describes bottlenose dolphin distribution as coastal.
  5. Bottlenose dolphins were recorded in low numbers during the Berwick Bank aerial surveys, with one and six individuals encountered in October 2019 and April 2021, respectively (SSE Renewables, 2022a). However, there were no records of bottlenose dolphins in the offshore waters during three years (2009 to 2012) of boat-based surveys within the Neart na Gaoithe Offshore Wind Farm area (Mainstream Renewable Power, 2019). There were also no records of bottlenose dolphins during the Seagreen boat-based surveys, which took place approx. 25 km offshore (Sparling, 2012). No bottlenose dolphins were recorded during DAS of the Array marine mammal study area.

                        Density/abundance

                        Published literature
  1. Cheney et al. (2013) reported that the population estimate of bottlenose dolphin for the Coastal East Scotland MU ( Figure 5.7   Open ▸ ) is 195 individuals (95% CI = 162 to 253) based on photo ID counts between 2006 and 2007. Following this publication, Cheney et al. (2018) estimated that the bottlenose dolphin population on the east coast of Scotland is increasing and varied from 129 (95% CI = 104 to 155) in 2001 to 189 (95% CI = 155 to 216) in 2015. IAMMWG (2022) published the most up-to-date bottlenose dolphin population estimate for Coastal East Scotland MU of 224 individuals (based on Arso Civil et al. (2021). Cheney et al. (2018) reported that the proportion of the population that uses the Moray Firth SAC has declined due to an overall increase in population size and expansion of range.
  2. The SCANS III estimated abundance for block R ( Figure 3.3   Open ▸ ) was 1,924 bottlenose dolphins (95% CI = 0 to 5,408) (Hammond et al., 2021). This is a much higher estimate than the abundance estimate for the Coastal East Scotland population derived from the dedicated photo-identification surveys described in paragraph 118 (Cheney et al., 2018). However, studies for the Coastal East Scotland population are focussed on inshore waters, and SCANS III results were obtained through large-scale surveys, including offshore waters. Studies suggest that inshore and offshore populations are often ecologically and genetically discrete (Cheney et al., 2013).
  3. Hammond et al. (2021) reported densities for bottlenose dolphin across block R as 0.0298 animals per km2. Recently modelled density surfaces using the SCANS III data (refer to paragraph 29) (Lacey et al., 2022) gave a mean density of 0.00303 animals per km2 and a maximum of 0.00432 animals per km2 for the Array marine mammal study area ( Figure 5.8   Open ▸ ), with density maps showing higher areas of density in the inshore waters close to the Firths of Forth and Tay estuaries. There were no bottlenose dolphin sightings in block NS-D during the SCANS IV survey and therefore SCANS IV density values for bottlenose dolphins within this block are not available (Gilles et al., 2023).

Figure 5.7:
Coastal East Scotland Management Unit and Southern Limit of Bottlenose Dolphin Sightings

Figure 5.7: Coastal East Scotland Management Unit and Southern Limit of Bottlenose Dolphin Sightings


Figure 5.8:
Density Surface Maps From SCANS III Data for Bottlenose Dolphin Based on Lacey et al. (2022)

Figure 5.8: Density Surface Maps From SCANS III Data for Bottlenose Dolphin Based on Lacey et al. (2022)


  1. To capture the patchiness in coastal distribution of bottlenose dolphins and estimate density, an analysis of ECOMMAS data has been provided as a part of the Berwick Bank marine mammal technical report (SSE Renewables, 2022a). The analysis considered the most up-to-date coastal population size based on Arso Civil et al. (2021), distributional range between the Moray Firth and Firth of Forth as presented in Cheney et al. (2013), coastal distribution within 5 km from the shore (Palmer et al., 2019, Arso Civil, 2014, Oudejans et al., 2015) and depth preference of 2 m to 20 m (Quick et al., 2014). Assuming even distribution of 50% population of bottlenose dolphin between Peterhead and the Farne Islands, excluding the outer Firth of Tay, a density of 0.197 animals per km2 was calculated. In order to reflect the relative importance of the outer Firth of Tay in terms of bottlenose dolphin distribution, the habitat preference map for bottlenose dolphins in the Firth of Tay and adjacent areas as modelled by Arso Civil et al. (2019) was used. Four distinct segments were identified on the habitat preference maps: Fife Ness to St Andrews, Outer Firth of Tay, Arbroath, and Montrose; a number of bottlenose dolphins was estimated for each of the segments. The density within the Firth of Tay and 2 m to 20 m depth contour was estimated as 0.294 animals per km2. It should be noted that this analysis did not consider individuals from the Coastal East Scotland bottlenose dolphin population that range further south and along the Northumberland coast (refer to paragraph 115 for more detail).
  2. Predicted distribution maps of bottlenose dolphin at monthly scales by Waggitt et al. (2020) demonstrated bottlenose dolphin densities to be consistently low throughout the year ( Figure 5.9   Open ▸ to Figure 5.10   Open ▸ ). Highest densities within the Array marine mammal study area were predicted in August with a maximum of 0.00271 animals per km2 ( Figure 5.10   Open ▸ ). However, as a limitation authors of this study highlight that small and isolated sub-populations would have little influence on these broad scale models and that there may have been substantial changes in populations across the study period. As such, density estimates provided by Waggitt et al. (2020) may not be a true reflection of densities for the Coastal East Scotland bottlenose dolphin population due to its small size and recent southward expansion.

Figure 5.9:
Bottlenose Dolphin Density from January to April Based on Waggitt et al. (2020)

Figure 5.9: Bottlenose Dolphin Density from January to April Based on Waggitt et al. (2020)


Figure 5.10:
Bottlenose Dolphin Density from May to August Based on Waggitt et al. (2020)

Figure 5.10: Bottlenose Dolphin Density from May to August Based on Waggitt et al. (2020)


Figure 5.11:
Bottlenose Dolphin Density from September to December Based on Waggitt et al. (2020)

Figure 5.11: Bottlenose Dolphin Density from September to December Based on Waggitt et al. (2020)


                        Surveys
  1. Given that no bottlenose dolphins were recorded during DAS of the Array marine mammal study area, design or model-based density and abundance estimates for this species are not available. Similarly, low numbers of bottlenose dolphins were recorded during the historic surveys in the wider Firth of Forth and Tay areas and therefore there are no density estimates, that were informed by these surveys.
                        Summary of the densities
  1. Overall, bottlenose dolphins are present across the northern North Sea, however, only the coastal population, distributed within the 2 m to 20 m depth contour and approximately 2 km from the shore, is well documented in literature. Comparison of key data sources for bottlenose dolphin is shown in Table 5.2   Open ▸ .
  2. As presented in paragraph 123, design or model-based density and abundance estimates for bottlenose dolphin based on DAS are not available.
  3. Predicted estimates of mean density for the Array marine mammal study area from Waggitt et al. (2020) are comparable to the Lacey et al. (2022) estimate and are provided at the same resolution (10 km x 10 km). Densities published by Hammond et al. (2021) are an order of magnitude higher, however these are based on one estimate for a large block ( Figure 3.3   Open ▸ ) that covers both inshore and offshore waters. As presented in paragraph 116, the distribution of bottlenose dolphins within the Coastal East Scotland MU is restricted to coastal areas within 2 km to 5 km of the shore and therefore the density within these areas is expected to be higher than offshore.
  4. As such, it is considered that densities presented in Hammond et al. (2021) may not be representative of the offshore waters, where the Array marine mammal study area is located. Lacey et al. (2022) maps reflect coastal distribution of CES bottlenose dolphin population. Moreover, it should be noted that Lacey et al. (2022) used SCANS III data alongside the environmental covariates such as depth and slope (refer to section 3.4.1 for more details) in the density surface modelling. As described in paragraph 116, depth is an important predictor for bottlenose dolphin distribution. Therefore, studies that consider the environmental conditions allowing to discriminate among different habitats (e.g. shallow vs deep) are preferrable to be used when predicting bottlenose dolphin density. As such, density estimates reported by Lacey et al. (2022) are considered more appropriate to use to reflect densities of bottlenose dolphins in offshore waters where the site boundary is located and a density of 0.00303 animals per km2 will be taken forward to the assessment.

 

Table 5.2:
Comparison of Main Data Sources Densities for Bottlenose Dolphin (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

Table 5.2: Comparison of Main Data Sources Densities for Bottlenose Dolphin (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

 

                        Seasonality

  1. Thompson et al. (2011) reported that in the Moray Firth, three times as many individuals occurred within inshore waters in the summer compared to the winter months. Paxton et al. (2016) suggested that within the Firth of Forth bottlenose dolphins are more abundant during spring and summer. Similarly, photo-identification study and analysis of sightings data conducted by Hackett (2022) showed that although sightings of bottlenose dolphins between Firth of Forth and Withernsea are recorded year-round, the rates at which bottlenose dolphins are being seen are three to seven times higher during summer than other seasons. It has been suggested that this seasonal inshore occurrence of bottlenose dolphin may be linked to periods when animals move into warmer shallow waters to calve and nurse their young during the summer months. Breeding in bottlenose dolphins is usually seasonal and varies with location but in the Moray Firth the peak calving period is in the late summer (Culloch and Robinson, 2008). Other driving factors may also include seasonal distribution of prey species. Seasonal trends in offshore populations are unknown.

5.1.3. White-Beaked Dolphin

                        Ecology

  1. The white-beaked dolphin belongs to the family Delphinidae (oceanic dolphins) in the suborder Odontoceti. It is a robust species that can grow up to 3.5 m for males and 3.05 m for females. Adults become sexually mature at a length of approximately 2.6 m and at approximately 12 to 13 years of age (Reeves et al., 1999). The mating season for white-beaked dolphin is in July and August with the gestation period lasting about 11 months (Culik, 2010).
  2. Little is known about the reproductive behaviour of this species and whilst it was thought that births often occur offshore in the northern North Sea (Evans, 1991), there is also evidence to suggest that females move into inshore waters to give birth (Canning et al., 2008, Weir et al., 2007).
  3. The white-beaked dolphin is considered to be of Least Concern on the International Union for Conservation of Nature (IUCN) Red List of species. However, there are concerns about the potential impact of climate change causing a reduction in its range (MacLeod et al., 2005). In general, white-beaked dolphin is only found in waters cooler than around 18˚C and is most common in waters below about 13˚C (Tetley and Dolman, 2013). It has been suggested that due to the increase in sea surface temperature (SST) between 1948 and 2003, the suitable habitat of white-beaked dolphins in Scottish waters decreased, which resulted in reduced species presence (van Weelden et al., 2021, MacLeod et al., 2005).
  4. The white-beaked dolphin is known to have a broad diet (Samarra et al., 2022), however, the main prey species for this species in Scottish waters is whiting and in lesser extent other clupeids Clupeidae (e.g. herring), gadoids (e.g. haddock and cod) and shad (Alosa spp.) (Canning et al., 2008). Although the distribution and abundance of prey species affects the distribution and abundance of white-beaked dolphin, this species tends to be influenced by temperature with larger numbers and group sizes associated with cooler temperatures (Evans, 1991, Canning et al., 2008, Weir et al., 2007). Recent studies in Iceland demonstrate that despite ecosystem changes in the study region, white-beaked dolphin showed no long-term changes in trophic ecology, suggesting that it adapts to spatial changes in prey distribution or shifts to other prey at similar trophic levels (Samarra et al., 2022).

                        Distribution and occurrence

  1. The white-beaked dolphin inhabits the temperate and subarctic waters of the North Atlantic (Schick et al., 2020). It is the second most numerous cetacean in the North Sea, recorded more frequently in the western sector of the central and northern North Sea across to western Scotland and is generally sighted in small groups of three to four animals (Reid et al., 2003).
  2. In the north-east Atlantic white-beaked dolphins are generally restricted to shelf waters and prefer waters less than 120 m deep (Tetley and Dolman, 2013) . However, Weir et al. (2009) suggested that individuals were encountered in significantly deeper waters around Scotland, with a range from 106.5 m to 134.5 m and with no sightings in waters of less than 70 m. This indicates the preference of white-beaked dolphins to inhabit open waters located outside of the immediate coastal zone. Moreover, other habitat variables, such as slope and seabed aspect, were thought to be important factors in driving occurrence (Tetley and Dolman, 2013). White-beaked dolphins are capable of long-range regional movements, although individuals can also show repeated inter-annual site fidelity.
  3. During the TCE aerial surveys, white-beaked dolphins were encountered in both, inshore and offshore waters, although most encounters were recorded offshore ( Figure 3.2   Open ▸ ) with group sizes ranging from one to six individuals (Grellier and Lacey, 2011). During Seagreen boat-based surveys, white-beaked dolphins occurred most often in groups: with a mean group size of three and a maximum group size of 15 individuals (Sparling, 2012) with most sightings further offshore. A peak in sightings and therefore density, was apparent to the north-east of the survey area. During the Berwick Bank aerial surveys, white-beaked dolphins were most often in the south-east of the Berwick Bank survey area ( Figure 3.2   Open ▸ ). No clear patterns in distribution of white-beaked dolphin across the Array marine mammals study area can be concluded based on DAS sightings (refer to volume 3, appendix 10.2, annex A for more detail).

                        Density/abundance

                        Published literature
  1. The relevant MU for white-beaked dolphins is the CGNS MU ( Figure 5.12   Open ▸ ) which has an estimated population size of 43,951 animals (CV = 0.22, 95% CI = 28,439 to 67,924) . The SCANS III estimated abundance for block R ( Figure 3.3   Open ▸ ) was 15,694 white-beaked dolphins (CV=0.48, 95% CI = 3,022 to 33,340) (Hammond et al., 2021). The SCANS IV reported white-beaked dolphin abundance within block NS-D of 5,149 individuals representing approximately one-third of the SCANS III estimates for block R indicating a reduction in white-beaked dolphin abundance (Gilles et al., 2023).
  2. Hammond et al. (2021) reported densities for white-beaked dolphin across block R as 0.243 animals per km2. Recently modelled density surfaces using the SCANS III data (refer to paragraph 29) (Lacey et al., 2022) gave a mean density of 0.120 animals per km2 and a maximum of 0.181 animals per km2 for the Array marine mammal study area ( Figure 5.13   Open ▸ ), with density maps showing higher areas of density in the offshore waters north of the site boundary. The SCANS IV surveys reported lower white-beaked dolphin density of 0.0799 animals per km2 for block NS-D when compared to SCANS III block R (Gilles et al., 2023).
  3. The JCP Phase III analysis provided estimated abundances for white-beaked dolphin in 2010 by season for the Firth of Forth area of commercial interest ( Figure 3.5   Open ▸ ). Highest abundance was estimated in the spring months with 1,760 animals (97.5% CI = 620 to 4,530) with lower estimates in all other seasons; summer with 720 animals (97.5% CI = 360 to 1,840), autumn with 540 animals (97.5% CI = 220 to 1,130) and winter with 410 animals (97.5% CI = 170 to 1,110) (Paxton et al., 2016). This equated to density estimates between 0.029 individuals per km2 in winter and 0.124 individuals per km2 in summer and therefore were lower compared to the mean density estimate for SCANS-III block R (0.243 animals per km2) as described previously. Additionally, the study reported predicted abundance of white-beaked dolphins in the Firth of Forth as a percentage of the predicted number from CGNS MU, based on estimates for summers 2007 to 2010 as 4.6% (97.5% CI = 0.1 to 5.9).
  4. Predicted distribution maps of white-beaked dolphin at monthly scales by Waggitt et al. (2020) demonstrated white-beaked dolphin densities to be relatively low throughout the year ( Figure 5.14   Open ▸ to Figure 5.16   Open ▸ ). Highest densities within the Array marine mammal study area were predicted in August with a maximum of 0.131 animals per km2 ( Figure 5.15   Open ▸ ).

Figure 5.12:
Celtic and Greater North Seas Management Unit

Figure 5.12: Celtic and Greater North Seas Management Unit


Figure 5.13:
Density Surface Maps From SCANS III Data for White-beaked Dolphin Based on Lacey et al. (2022)

Figure 5.13: Density Surface Maps From SCANS III Data for White-beaked Dolphin Based on Lacey et al. (2022)


Figure 5.14:
White-beaked Dolphin Density from January to April Based on Waggitt et al. (2020)

Figure 5.14: White-beaked Dolphin Density from January to April Based on Waggitt et al. (2020)


Figure 5.15:
White-beaked Dolphin Density from May to August Based on Waggitt et al. (2020)

Figure 5.15: White-beaked Dolphin Density from May to August Based on Waggitt et al. (2020)


Figure 5.16:
White-beaked Dolphin Density from September to December Based on Waggitt et al. (2020)

Figure 5.16: White-beaked Dolphin Density from September to December Based on Waggitt et al. (2020)