5.2.2.    Marine Mammal Counts

75. Six species of marine mammals were identified during the DAS ( Table 5.3   Open ▸ ). Of the cetaceans, harbour porpoise was the most frequently recorded species and was sighted in every month of the year. Minke whale and white beaked dolphin were seasonally sighted with most observations between the months of May to September each year. Bottlenose dolphin were sighted in only two months over the 25 months of survey: October 2019 (one individual) and April 2021 (group of six individuals).
76. Seals were typically difficult to identify to species level from the aerial survey data. Grey seals were recorded in each month, with the exception of March 2021. Similarly, ‘seal species’ were recorded in each month, with the exception of February 2020. Only three sightings of harbour seal were made over the 25 months of survey with one individual recorded in each of January, February and April 2021. It is therefore considered likely that the majority of ‘seal species’ will be grey seal.

Table 5.3: Monthly Raw Sightings Data (Number of Animals) (Uncorrected for Effort) Across the Aerial Survey Area

*For the purposes of analyses the February 2020 dataset will serve as the dataset for January 2020

**For the purposes of analyses the 5 May 2020 dataset will serve as the dataset for April 2020

5.2.3.    Density Estimates

77. Relative monthly densities of marine mammal species were estimated from the aerial survey data. The data were analysed using a non-parametric bootstrap approach with replacement to provide variance estimates for mean monthly densities (Buckland et al., 2001).
78. Density estimates with bootstrapping were undertaken for grey seal with the inclusion of data for ‘seal species’ on the assumption that most seals within the site were likely to be grey seal. This is supported by the at-sea maps and telemetry data which showed that grey seals are more likely to use the offshore waters of the Proposed Development array area whilst harbour seal densities are very low in the offshore section of the Proposed Development array area (see section 6.3 for more details). Note that telemetry data suggest that there is some movement of harbour seals within the very north-west of the Proposed Development array area (closest boundary to the Firth of Tay and Eden Estuary) and therefore the presence of this species has not been discounted, however there are insufficient data to allow density estimates in this report.
79. Spatial density estimates were also produced for harbour porpoise and grey seal (including ‘seal species’) on a seasonal basis: winter (December, January February); spring (March, April, May); summer (June, July, August); and autumn: (September, October, November). It was not possible to produce model-based density estimates for other marine mammal species within the Proposed Development marine mammal study area due to low numbers of sightings. Model-based analyses was undertaken in the programme MRSea (Scott-Hayward et al., 2013) with environmental covariates used to predict species distributions. To reduce the potential for edge effects near the boundaries of the survey area, the maps were clipped to a smaller area: Proposed Development array area plus ~12 km buffer.
80. Mean seasonal abundance estimates were also derived from the spatial density maps by summing densities within each km2 grid cell and scaling the data up from the clipped area to cover the Proposed Development plus 16 km survey area. Seasonal abundance estimates are presented in the species accounts for harbour porpoise (section 6.2.1) and grey seal (including ‘seal species’) (section 6.3.2).
81. Densities and abundance, presented as relative estimates, were subsequently corrected for availability bias to provide an approximation of absolute numbers. Correction factors were derived from studies on dive behaviour of marine mammals and their availability at the surface (further detail of correction factors is provided in section 3.5 of Annex A).
82. Annex A provides a full description of the analyses and a summary of the mean monthly density estimates are provided in Table 5.4   Open ▸ .

Table 5.4: Estimated Densities Based on the Aerial Survey Data (March 2019 to April 2021)

6. Species Accounts

83. The following section provides more detailed baseline information for each of the key species identified within the Proposed Development marine mammal study area. These are:

• harbour porpoise;
• bottlenose dolphin;
• white-beaked dolphin;
• minke whale;
• harbour seal; and
• grey seal.

6.2. Cetaceans

6.2.1.    Harbour Porpoise

Ecology

84. Porpoises comprise a group of relatively small-bodied Odontoceti (toothed) cetaceans within the family Phocoenidae. The harbour porpoise is one of the smallest cetacean species, reaching a maximum length of 1.9 m. On average females grow to a 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, 2003).
85. Often living in cool, high latitude waters, harbour porpoise have a higher metabolic rate than dolphins and therefore need to feed more frequently and consume more prey per unit body weight, in order to maintain their body temperature and other energy needs (Rojano-Doñate et al., 2018). For this reason, porpoise may be highly susceptible to changes in the abundance of prey species or disturbance from foraging areas. Harbour porpoise feed on a wide range of fish species, but mainly small shoaling species from demersal or pelagic habitats (Santos and Pierce, 2003; Aarfjord, 1995). There are regional and seasonal differences in diet; interannual variation depending on the availability of prey species; and ontogenetic variation (adult and juveniles), with juveniles targeting smaller species such as gobies (Gobiidae) or smaller individuals of the same prey species targeted by adults (Santos and Pierce, 2003). A harbour porpoise’s field 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). 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 the overall energy density (Ransijn et al., 2019). This study corroborated findings of previous studies of harbour porpoise off the east coast of Scotland which reported that sandeel is the dominant prey item during summer (Santos et al., 2004).
86. Harbour porpoise regularly forage around tidal races, overfalls, and upwelling zones during the ebb phase of the tide (Pierpoint, 2008). Embling et al. (2010) analysed results of the dedicated surveys conducted in the southern Inner Hebrides and found that maximum tidal current is the best environmental explanation of persistent harbour porpoise abundance, although in contrast to other studies, they found that densities were higher in areas of low current. Although harbour porpoise generally hunt alone or in small groups, this species is often seen in larger aggregations of 50 or more individuals, either associated with food concentrations or seasonal migrations. Within these loose aggregations, segregation may occur, with females travelling with their calves and yearlings, and immature animals of each sex being segregated into groups.
87. The age at 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 eleven months and there is a peak in birth rate around the British Isles during the months of June to July (Boyd et al., 1999).
88. The main threats to the harbour porpoise in the northern North Sea in by-catch in fishing gears. Harbour porpoise are particularly vulnerable to getting caught in bottom-set gill nets as a result of their feeding behaviour. Other threats include prey depletion, pollution that may affect the health of individuals, as well as acoustic and physical disturbance (Evans and Prior, 2012).

Distribution and occurrence

89. Harbour porpoise is widely distributed throughout the North Sea and through the regional marine mammal study area. Heinänen and Skov (2015) found that in the North Sea MU the water depths and hydrodynamic variables are the most important factors for the probability of presence of harbour porpoise. During summer, animals seem to avoid well-mixed areas showing preference to more stable areas. Studies indicated lower presence with decreasing practical salinity unit values, reflecting an avoidance of estuarine water masses.
90. Based on spatio-temporal modelling using species and environmental data, Heinänen and Skov (2015) concluded that during summer harbour porpoises avoid muddy sediments and hard bottom areas. A study using long term passive acoustic data revealed, however, that, within the Moray Firth, harbour porpoise occurred in both sandy and muddy habitats (Williamson et al., 2016). The study also found that the proportion of hours with acoustic detection in muddy habitats increased during the night by 18% (Williamson et al., 2016). Porpoise detections also differed in response to depth in the different sediment types during the night and day. In muddy, deeper areas (50 m to 60 m) detections at night were nearly double those during the day. Therefore, it can be assumed that harbour porpoises use different types of habitats during the day and at night and therefore their distribution may shift accordingly.
91. 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 the seabed surface sediments. For the winter months the modelling showed a peak in presence was observed at water depths of 30 to 40 m and that animals seemed to avoid waters with high current speeds as well as avoiding areas with muddy bottom substrates.
92. Harbour porpoise was the most commonly identified cetacean during historic aerial surveys in the FTOWDG region (Grellier and Lacey, 2011) and Seagreen Firth of Forth Round 3 boat-based surveys (Sparling, 2012). Harbour porpoises were distributed across the survey area ( Figure 6.1   Open ▸ ) but there were a greater number of sightings offshore, most often seen singly although group size ranged from one to six individuals. The harbour porpoise was also recorded on all boat-based surveys and in all parts of the site (particularly near the morphological bank features such as Scalp Bank to the north from the Proposed Development array area running down to the centre of the Proposed Development array area; Figure 6.2   Open ▸ ). These areas may represent good foraging grounds due to the sandy banks providing good habitat for prey species such as sand eel 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 et al., 2004).

Figure 6.1: Harbour Porpoise Distribution and Group Size During Historical Aerial Surveys Across All Seasons from May 2009 to March 2010. Source: Grellier and Lacey (2011)

Figure 6.2: Positions of Harbour Porpoise Sightings Across All Seasons During the Firth of Forth Round 3 Boat-based Surveys from May 2010 to November 2011 (Sparling, 2012)

93. The Proposed Development aerial digital survey data showed that harbour porpoise was distributed throughout the Proposed Development marine mammal study area (see species distribution maps in Annex A). Sightings occurred throughout the survey area, however the presence of harbour porpoise in May 2019 and June 2019 is more evident in the south-east area of the Proposed Development array area (see Figure 3.4 to Figure 3.10 in Annex A). The spatial density maps produced using MRSea showed that during spring, the eastern half of the survey area appeared to be favoured by harbour porpoise (see Figure 3.19 in Annex A). The highest encounter rate of harbour porpoise during these aerial surveys was 0.212 individuals per km in April 2021 ( Figure 6.3   Open ▸ ). Mean monthly encounter rate was calculated as 0.037 (95% CI = 0.011 to 0.062). Harbour porpoise also had the second greatest overall encounter rate (0.013 sightings per km) from all marine species recorded during historic aerial surveys in the FTOWDG region (Grellier and Lacey, 2011).

Figure 6.3: Monthly Encounter Rate of Harbour Porpoise within the Proposed Development marine mammal study area (Aerial Survey Data March 2019 to April 2021)

Density/abundance

94. Density and abundance estimates were available across a broader area within the regional marine mammal study area. The abundance estimated for cetaceans, outlined in IAMMWG (2021) are based on the results of the SCANS III (Hammond et al., 2017) and the ObSERVE Programme (Rogan et al., 2018). IAMMWG (2021) estimated abundance for the North Sea MU ( Figure 6.4   Open ▸ ) as 346,601 (CV = 0.09, 95% CI = 289,498 to 419,967) harbour porpoise. These results are much higher than previous estimates reported by IAMMWG (2015) with 227,298 (CI = 0.13, 95% CI = 176,360 to 292,948) animals. However, IAMMWG (2021) results are aligned with those presented by Hague et al. (2020), as this study reported harbour porpoise estimated abundance in the North Sea MU as 345,373 animals (CV =0.18, 95% CI = 246,526 to 495,752).
95. SCANS II estimated the average density in Block V as 0.293 animals per km2 (CV = 0.36), with a mean group size of 2.37 (CV = 0.21) ( Figure 6.5   Open ▸ ; Hammond et al., 2013). The total abundance in Block V was estimated as 47,048 animals (CV = 0.36) corrected for group size. The more recent SCANS III data estimated the density in block R as 0.599 animals per km2 with abundance estimates of 38,646 animals (CV = 0.29, 95% CI = 20,584 to 66,524; Figure 6.6   Open ▸ ; Hammond et al., 2021). Due to the change in survey blocks used in the SCANS II and SCANS III surveys, direct comparison between the surveys for abundance and density estimation is not possible.

Figure 6.4: Management Unit (MU) for Harbour Porpoise

Figure 6.5: SCANS II Survey Blocks

Figure 6.6: SCANS III Survey Blocks

96. The JCP Phase III analyses provided estimated abundances for harbour porpoise in 2010 by season for the Firth of Forth area of commercial interest region which covered 14,241 km2 ( Figure 6.7   Open ▸ ; Paxton et al., 2016). Highest abundance of harbour porpoise was estimated for the winter months, with 7,000 (97.5% CI = 5,200 to 11,800) animals. Similar abundances were estimated in spring and summer with 3,500 (97.5% CI = 1,900 to 6,600) and 4,400 (97.5% CI = 2,900 to 6,800) harbour porpoise respectively. The lowest abundance was estimated in autumn 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 values are lower compared to the estimated density presented in SCANS III report with 0.599 animals per km2 (Hammond et al., 2021).

Figure 6.7: JCP Phase III Areas of Interest

97. Paxton et al. (2016) reported the predicted abundance in the Firth of Forth as a percentage of the overall predicted number for the North Sea MU (based on estimates for summers 2007 to 2010) as 1.4% (97.5% CI = 0.6 to 2.3). Estimated trend (average annual population change) for harbour porpoise in the Firth of Forth between reporting period 1992 to 2000 and 2007 to 2010 was indicating a 14% (95% CI = 1 to 31) increase per year with a statistically significant trend at the 5% level.
98. The Heinänen and Skov (2015) analysis concluded that areas of persistent high densities are estimated in the outer Moray Firth. 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. Paxton et al. (2016) corroborated this finding by reporting that the Firth of Forth and the east coast of Scotland was not identified as associated with the highest density for this species, compared to other regions such as west coast of Ireland or the Hebrides and that higher abundance was correlated with Moray Firth.
99. Harbour porpoise was the most common cetacean species encountered during historic aerial surveys with the mean density of 0.080 (CV=0.11) individuals per km2 (Grellier and Lacey, 2011). Summer density estimates were calculated to be 0.099 (CV=0.12) individuals per km2, and winter 0.048 (CV=0.24) individuals per km2. These density estimates were minimum estimates based on inherent negative bias due to the survey methodology (Mackenzie et al., 2012). Therefore, spatially explicit density surfaces were generated using all FTOWDG aerial and Round 3 boat-based sightings (Mackenzie et al., 2012, section 5.2). When all data across all years were pooled, depth was a significant predictor of occurrence, with fewer animals in shallow water. The data showed a great deal of variation in the spatial distribution of harbour porpoise across the survey years, with the main predictor of density being survey methodology. The likely explanation for variation in densities across the survey area may relate to changes in prey distribution. After correcting for availability, Mackenzie et al. (2012) estimated absolute abundance for the survey area (aerial and boat-based) across the survey period as 582 (95% CI = 581 to 1235). The correction factor (i.e. probability of an animal being available to be seen at the sea surface) for harbour porpoise was 0.434 (McKenzie et al., 2012). 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 (Neart na Gaoithe, 2018).
100. Seasonal density estimates calculated from the Proposed Development aerial digital survey data highlighted that in spring months there were more harbour porpoise within the Proposed Development marine mammal study area. Mean monthly density was estimated as 0.127 (95% CI = 0.066 to 0.277) animals per km2. Correcting this for availability bias based on tagged porpoises in the Baltic/North Sea (Teilman et al., 2013) mean monthly density was estimated as 0.299 (95% CI = 0.155 to 0.652) animals per km2 with a peak mean density during spring months of 0.826 (95% CI = 0.440, 1.616) animals per km2 (Table 6.1:). Corrected abundance of harbour porpoise within the Proposed Development marine mammal study area ranged between 460 animals in winter and 4,108 animals in spring.

Table 6.1: Harbour Porpoise Modelled Absolute Density Estimates by Season for Proposed Development Array Area Including Lower Confidence Intervals (LCI) and Upper Confidence Intervals (UCI). Mean Seasonal Abundance is Scaled up to the Proposed Development Array Area Plus ~16 km Buffer

Seasonality

101. Comparison of harbour porpoise encounter rate during different seasons based on the historic aerial surveys in the FTOWDG region showed that 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 boat-based surveys (Sparling, 2012). The Seagreen boat-based surveys in summer 2017 recorded the highest counts of harbour porpoise between in May and July (Seagreen Technical Report, 2018). These findings are different to JCP Phase III results, as the study reported highest densities of harbour porpoise during winter months (Paxton et al., 2016).
102. Similarly, there is a temporal trend emerging from the DAS, with highest encounter rates during spring months each year (April and May, Figure 6.3   Open ▸ ). Harbour porpoise encounter rate was lowest during winter and autumn (from November 2019 to March 2020 and from October 2020 to February 2021). MRSea modelling corroborated the above as the results showed highest densities during spring months and lowest densities during winter (see Annex A for more details).

6.2.2.    Bottlenose Dolphin

Ecology

103. Bottlenose dolphin are members of the family Delphinidae, which are oceanic dolphins found in temperate and tropical waters worldwide. The largest of the beaked dolphins, this species ranges in size from 1.9 to 3.8 m and 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).
104. There is variation in the patterns of habitat use of bottlenose dolphin, even within a population, and generally the distribution of this species is influenced by factors such as tidal state, weather conditions, resource availability, life cycle stage, or season (Hastie et al., 2004). Typical prey items in Scottish waters include cod Gadus morhua, saithe Pollachius virens, whiting, salmon Salmo salar and haddock Melanogrammus aeglefinus (Santos et al., 2001).
105. Bottlenose dolphin is frequently seen in groups rather than individually, although group size in coastal populations may be smaller than offshore populations; however, very little is known about offshore populations (Rogan et al., 2018). Mean group size across the SCANS III survey areas was 5.25 individuals (Hammond et al, 2021). Robinson et al. (2017) reported that in north-east Scotland observed group sizes varied between two and 70 animals, with a mean of 14.2. It is important to highlight that the surveys were conducted along the southern coastline of the outer Moray Firth, in close vicinity of the SAC (between the coastal ports of Lossiemouth and Fraserburgh).

Distribution and occurrence

106. The Moray Firth SAC boundary encompassed the core area of occurrence of the resident population of bottlenose dolphins in the North Sea based on the data collected in 1980s and early 1990s. However, studies have shown that the population of bottlenose dolphins off the east coast of Scotland is highly mobile with individuals ranging from Moray Firth to Firth of Forth (Quick et al., 2014; Cheney et al., 2018; Arso Civil et al., 2019; Arso Civil et al., 2021). Therefore, this range was established as the main distributional range of the population (Quick et al., 2014; Cheney et al., 2013).
107. Acoustic occupancy rates and habitat modelling in the ECOMMAS study highlighted that the waters between Stonehaven and Aberdeen are a potential area of high occupancy (Palmer et al., 2019). Instruments deployed in the Stonehaven group showed the second highest acoustic occupancy rates behind the Cromarty group (area close to Moray Firth). Quick et al. (2014) established that a high proportion of bottlenose dolphins from the east coast of Scotland population use both the Tayside and Fife area and the Moray Firth SAC, over a range of temporal scales. The same study reported that most encounters occurred at the entrance of the Tay (35 to 46% of the east coast of Scotland population) and that bottlenose dolphins were only seen on the north side of the Forth, mostly between Anstruther and Fife Ness. These findings were corroborated by Arso Civil et al. (2019) who reported that that the east coast population expanded its distribution range since more than a half of the estimated population was consistently using the St Andrews Bay and the Tay estuary. The ECOMMAS study reported that between 2013 and 2015 there was relatively low number of detections at the St. Andrews survey location nearest the bay and it has been suggested that this area may represent habitat associated with rest or socializing rather than foraging, therefore there are fewer clicks to detect (Palmer et al., 2019). The most recent data collected during boat-based trips between Moray Firth and Fife Ness (during summers 2017 to 2019) shows that the Tay estuary area and adjacent waters continues to be used by more than a half of the total estimated population every summer (in 2019 approx. 53.5%; Arso Civil et al., 2021). This study also reported that the number of animals estimated to be using this area has increased by around 4.3% per year between 2009 and 2019, although it decreased between 2017 and 2019. The author suggested that it is likely that changes in the distribution range are continuing with a further southern range expansion (Arso-Civil et al., 2021). In 2007 there was one confirmed sighting of a group near Whitley Bay and the Tyne River mouth (Cheney et al., 2013) and there are ongoing citizen science projects, which results in bottlenose dolphin sightings being reported as far as the Farne Islands (Chronic Live, 2020). However, C‐PODs deployed at St. Abbs had very low (<5%) broadband occupancy rates for all survey years (2013 to 2015). There is currently no reported survey effort to the south of the Firth of Forth that would indicate an increase in numbers of bottlenose dolphins present in the area.
108. The ECOMMAS C-POD study (Palmer et al., 2016) 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) as the study 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 ( Figure 6.10   Open ▸ ). Paxton et al. (2016) also described bottlenose dolphin distribution as coastal and no bottlenose dolphins were recorded offshore for three years (2009 to 2012) of boat-based surveys within the Neart na Gaoithe Offshore Wind Farm area (Neart na Gaoithe, 2018).
109. Bottlenose dolphins were also positively identified in historic inshore (inside 12 nm) and offshore (outside 12 nm) aerial surveys between May 2009 and March 2010 (Grellier and Lacey, 2011). During summer there was just one encounter of one individual outside 12 nm and during winter two sightings of three individuals were recorded inside 12 nm. The average encounter rate of bottlenose dolphin during aerial surveys was 0.0002 individuals per km (Grellier and Lacey, 2011). Some unidentified cetacean and dolphin species were also recorded, in each case with an encounter rate of 0.0012 individuals per km, although no distinction was made between species for these sightings. No bottlenose dolphins were encountered during Seagreen Firth of Forth Round 3 boat-based surveys between 2010 and 2011 (Sparling, 2012).
110. Bottlenose dolphins were recorded in low numbers during the DAS, with one and six individuals encountered in October 2019 and April 2021, respectively. The encounter rate varied between 0.0005 individuals per km in October 2019 and 0.0024 individuals per km in April 2021 (see Annex A for more details).

Density/abundance

111. Cheney et al. (2013) reported that the population estimate of bottlenose dolphin abundance for the Coastal East Scotland MU ( Figure 6.8   Open ▸ ) population is 195 individuals (95% CI = 162 to 253) based on photo ID counts between 2006 and 2007. More recently, a study 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 ( Figure 6.9   Open ▸ ). Based on this later study, the IAMMWG recommended that the population in the Coastal East Scotland MU for bottlenose dolphin is taken as 189 individuals (IAMMWG, 2021). However, advice from NatureScot and MSS provided during the Road Map Meetings (see Table 3.1   Open ▸ ) was to adopt the 5-year weighted average population estimate from data gathered between 2015 and 2019 (Arso Civil et al., 2021). Thus, the most up-to-date bottlenose dolphin population estimate for Coastal East Scotland MU was taken as 224 individuals (Arso Civil et al., 2021). Despite inter annual variability, the number of dolphins using the Moray Firth SAC between 2001 and 2016 appeared to be stable (Cheney et al., 2018). Interestingly, 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; whilst the Moray Firth is clearly an important area for this population, they are not restricted to either the Moray Firth SAC or the wider Moray Firth (Cheney et al., 2018).

Figure 6.8: Management Unit for Bottlenose Dolphin

Figure 6.9: Annual Estimates of the East Coast of Scotland Bottlenose Dolphin Population from 1990 to 2015 with 9% Highest Posterior Density Intervals (HPDI). Source: Cheney et al., 2018

112. Based on historical photo ID data collected from 1997 to 2010 and 2012 to 2013 in the Tayside and Fife area (including Firth of Forth), Quick et al. (2014) reported that the majority of dolphin encounters were recorded within the Tay estuary ( Figure 6.10   Open ▸ ). Between 71 and 91 bottlenose dolphins (35 to 46% of the total Scottish east coast population) were estimated to be using the Tay area during 2009 – 2013 (Quick et al., 2014). Arso Civil et al. (2019) analysed and compared photoidentification data collected during consistent dedicated surveys from 2009 and 2015 in similar study areas to Quick et al. (2014), St Andrews Bay and the Tay estuary as well as the Moray Firth SAC. Over the study period, 35.2% of the marked animals were seen only in St Andrews Bay and the Tay estuary, 35.9% were seen only in the Moray Firth SAC, and 28.9% were seen in both areas. The study reported that the number of dolphins using the Tay estuary and adjacent waters increased and ranged from a minimum of 85 (95% CI = 77 to 93) animals in 2011 to a maximum of 121 (95% CI = 84 to 173) in 2014 which represented 52.5% of the estimated total east coast population (i.e. using the population’s main range). The most recent study in the Tay estuary and adjacent waters integrated data collected during boat-based surveys in summers 2017 to 2019 (May to September) and data collected under the Moray Firth Marine Mammal Monitoring Programme (Arso Civil et al., 2021; Graham et al., 2017). This study corroborated previous findings and reported that this area continues to be used by more than half of the total estimated east coast population every summer; 53.8% between 2009 and 2019 (Arso-Civil et al. 2021).

Figure 6.10: Encounter Locations from All Years (1997 to 2013) in the Tayside and Fife Data Collection Area as Defined in the Quick et al. (2014) Dolphin Project Database

113. The JCP Phase III analysis provided abundances for bottlenose dolphins in 2010 by season and estimated highest abundance in the Firth of Forth area of commercial interest ( Figure 6.7   Open ▸ ) in spring and summer, with 460 (95% CI = 130 to 1340) and 430 (95% CI = 190 to 780) animals, respectively (Paxton et al., 2016). This equates to density estimates between 0.032 individuals per km2 in the spring and 0.030 individuals per km2 in the summer. The lowest abundance was reported in the autumn as 190 (95% CI = 80 to 290) resulting in a density of 0.013 individuals per km2. This density estimate for summer abundance is more than double the estimate for the east coast Scotland bottlenose dolphin population derived from Cheney et al. (2018). However, the JCP report authors highlight that given the patchy distribution of the JCP data resource and assumptions that had to be made to render its datasets comparable, the estimates of abundance from the JCP Phase III are less reliable than those from well-designed dedicated abundance surveys (Paxton et al., 2016). Therefore, the abundance estimates obtained from the photo-ID surveys in the main population range (Cheney et al., 2013; Cheney et al., 2018; Arso Civil et al., 2019; Arso Civil et al., 2021) are likely to be better reflections of the true bottlenose dolphin population abundance along the east coast of Scotland.
114. The SCANS III estimated abundance for block R was 1,924 bottlenose dolphins (CI = 0.86,
     95% CI = 0 to 5,408), with an estimated density of 0.0298 individuals per km2 and mean group size of 5.25 individuals ( Figure 6.6   Open ▸ ; 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-ID surveys (Cheney et al., 2018). However, studies for the Coastal East Scotland population are focused 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).
115. To estimate the density of bottlenose dolphin in coastal areas, it was important to understand both the abundance and distribution of the east coast population. A five-year weighted average of the east coast bottlenose dolphin population provided an estimated population of 224 individuals (95% CI = 214 to 234) (Arso Civil et al., 2021). The main distributional range of this population is Moray Firth to the Firth of Forth (Cheney et al., 2013), however, as mentioned previously, approximately 53.8% of the east coast population (=120 individuals) use the Tay area and adjacent waters (Arso Civil et al., 2021). Therefore, it was assumed that the same proportion is likely to be present anywhere between Peterhead and further south as far as the Farne Islands (as recent studies reported that the east coast population is extending their range south). Previous studies reported that bottlenose dolphins are likely to be recorded within 5 km from the shore (Arso Civil et al., 2014; Palmer et al., 2019; Oudejans et al., 2015). Quick et al. (2014) provided that in the Tayside and Fife area as well as between Montrose and Aberdeen, dolphins were encountered usually in waters 2 m to 20 m deep. Therefore, the 2 m to 20 m depth contour polygon was identified as the key habitat preference of bottlenose dolphin along the east coast, between Peterhead and Farne Islands ( Figure 6.11   Open ▸ ).
116. ECOMMAS data suggested that there was a patchiness in distribution along the east coast with occupancy of bottlenose dolphin (dolphin positive minutes) different across the five monitored locations (Palmer et al., 2019). Recent literature (Arso Civil et al. 2019, Arso Civil et al. 2021) and feedback from consultees during the Proposed Development Road Map Meetings indicated that, in particular, the Firth of Tay is an important area for the east coast bottlenose dolphin population. There were, however, no C-POD arrays located in the Firth of Tay ( Figure 6.11   Open ▸ ) and therefore the occupancy of this area could not be compared with the other five areas monitored using ECOMMAS datasets. To capture the patchiness in coastal distribution of bottlenose dolphins and estimate density, a dual approach was applied. First, for all areas except the outer Firth of Tay, the east coast proportion of the population (120 animals), was assumed to be evenly distributed across the area between the 2 m to 20 m bathymetric contours, between Peterhead and the Farne Islands, giving a density of 0.197 animals per km2 ( Figure 6.11   Open ▸ ). Second, 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. The map of habitat preference was analysed using the most precautionary scenario when current direction was between 300 to 010 degrees and associated bottlenose dolphin presence was recorded during the corresponding tidal condition. Four distinct segments were identified on the habitat preference maps: Fife Ness to St Andrews, Outer Firth of Tay, Arbroath and Montrose. A probability of occurrence value was assigned to each segment based on the value with widest spread across the segment and subsequently these values were used to weight each segment (as a percentage) in relation to other segments. The outer Firth of Tay had the highest weighting with a probability of occurrence of 0.8 ( Figure 6.1   Open ▸ ; Table 6.2   Open ▸ ). As per the advice received from MSS on 9 December 2021, it was conservatively assumed that the 53.8% of the east coast population (120 individuals) may be present within the Firth of Tay and adjacent waters and, using the weightings, the number of bottlenose dolphins was estimated for each of the segments ( Table 6.2   Open ▸ ). Subsequently, to estimate density of bottlenose dolphins specifically within the outer Firth of Tay segment the number of dolphins (53.3 individuals) was divided by the area within that segment to give 0.294 animals per km2 ( Table 6.3   Open ▸ ).

Table 6.2: Approach to Estimating Abundance in Different Sectors for the Firth of Tay and Adjacent Areas Based on Arso Civil et al. (2019) Habitat Preference Map

117. Within the Proposed Development array area (offshore), the density of bottlenose dolphin was taken as 0.0298 from SCANS-III (Hammond et al., 2021) as described in paragraph 114 ( Table 6.3   Open ▸ ).

Table 6.3: Summary of Bottlenose Dolphin Densities for Different Sections Within the Regional Marine Mammal Study Area

Figure 6.11: Bottlenose Dolphin Distribution within the 2 m to 20 m Depth Contour

Seasonality

118. Estimates presented by Paxton et al. (2016) for the Firth of Forth area shown that bottlenose dolphins are more abundant during spring and summer.
119. Breeding in bottlenose dolphins is usually seasonal and varies with location; in the Moray Firth the peak calving period is in the late summer (Culloch and Robinson, 2008). Between 2001 and 2016 a total of 169 calves were identified on the east coast of Scotland, with an average of 11 calves born each year (range three to 20) (Cheney et al., 2018). The survival rate for bottlenose dolphins in the Moray Firth SAC has been estimated as 0.93 (95% CI = 0.91 to 0.94) based on data from 161 well marked animals sighted between 1990 and 2014 (Graham et al., 2016).
120. DAS recorded sightings of bottlenose dolphin in October and April only. 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. 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. Other driving factors may also include seasonal distribution of prey species.

6.2.3.    White-Beaked Dolphin

Ecology

121. The white-beaked dolphin occurs over a large part of the northern European continental shelf. 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 (Weir et al., 2001; Reid et al., 2003).
122. White-beaked dolphin 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., 1999b). White-beaked dolphin mating occur in the spring or summer, with calving occurring mainly around 11 months later between May and August (although some may be born in September or October) (Reid et al., 2003). Little is known about the reproductive behaviour of this species and whilst it is 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).
123. The main prey species for white-beaked dolphin in Scottish waters is whiting, but this species also consume other clupeids Clupeidae (e.g. herring), gadoids (e.g. haddock and cod) and shad (Alosa spp.) (Canning et al., 2008; Santos et al., 1994). 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, 1990; Weir et al., 2007; Canning et al., 2008).
124. Due to gaps in knowledge about the ecology of this species, the conservation status of the white-beaked dolphin within North Sea waters is currently unknown (Weir et al., 2007). White-beaked dolphin are endemic to the cold temperate water of the northern North Atlantic and whilst there are no reported decreases in the global abundance of this species, there are concerns about the potential impact of climate change causing a reduction in its range (Kinze et al., 1998; MacLeod et al., 2005). In general, this species is only found in waters cooler than around 18˚C and is most common in waters below about 13˚C (Tetley et al., 2013).

Distribution and occurrence

125. In the north-east Atlantic white beaked dolphins are generally restricted to shelf waters and prefer waters less than 120 m deep (Tetley et al., 2013). However, Weir (2009) suggested that individuals were encountered in waters around Scotland significantly deeper, with a range from 106.5 m to 134.5 m and with no sightings in waters of less than 70 m. That indicated 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 et al., 2013). White-beaked dolphins are capable of long-range regional movements, although individuals can also show repeated inter annual site fidelity.
126. During the historic TCE aerial surveys, white-beaked dolphins were encountered in inshore and offshore waters although almost all encounters were recorded offshore ( Figure 6.12   Open ▸ ) (Grellier and Lacey, 2011). Group size ranged from one to six individuals. During historic 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). White-beaked dolphins were most often seen in the further offshore, easterly region of the site ( Figure 6.13   Open ▸ ), which corroborates findings of Grellier and Lacey (2011). A peak in sightings and therefore density was apparent to the north-east of the survey area.
127. Weir et al. (2007) reported that the presence of white-beaked dolphins within the coastal North Sea area in Aberdeenshire is strictly seasonal, as animals were recorded only between June and August, with a peak in occurrence during August.
128. During the DAS, white-beaked dolphins were most often in the south-east of the Proposed Development marine mammal study area (see Figure 3.4 to Figure 3.10 in Annex A). The mean encounter rate for white-beaked dolphin was comparatively low with 0.0007 (95% CI = 0 to 0.0003) animals per km due to their seasonality.

Density/abundance

129. White-beaked dolphins in the UK are considered to have a favourable conservation status (JNCC, 2013). The relevant MU for white-beaked dolphins is the CGNS MU ( Figure 6.14   Open ▸ ) which has an estimated population size of 43,951 animals (CV = 0.22, 95% CI = 28,439 to 67,924; IAMMWG, 2021). It is almost three times higher than the previous estimate of 15,895 animals (CV = 0.48, 95% CI = 9,107 to 27,743; IAMMWG, 2015). The SCANS III estimated abundance for block R ( Figure 6.6   Open ▸ ) was 15,694 white-beaked dolphins (CV=0.48, 95% CI = 3,022 to 33,340), with an estimated density of 0.243 individuals per km2 (Hammond et al., 2021).
130. 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 6.7   Open ▸ ). Highest abundance was estimated in the spring months with 1,760 animals (97.5% CI = 620 to 4530) with lower estimates in all other seasons; summer with 720 animals (97.5% CI = 360 to 1840), autumn with 540 animals (97.5% CI = 220 to 1130) and winter with 410 animals (97.5% CI = 170 to 1110) (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 Firth of Forth as a percentage of the predicted number from CGNS MU, based on estimated for summers 2007 to 2010 as 4.6% (97.5% CI = 0.1 to 5.9). However, as stated by Paxton et al. (2016), the abundance estimates produced by the JCP Phase III modelling will be less reliable than those obtained from a well-designed dedicated abundance survey given the assumptions made when standardizing the data and the spatial and temporal patchiness of the data available.
131. Mean density calculated from the historic aerial surveys for white-beaked dolphin was 0.042 (CV=0.311) individuals per km2 (Grellier and Lacey, 2011). Summer density estimates were calculated to be 0.052 (CV=0.35) individuals per km2, and winter 0.024 (CV=0.66) individuals per km2. The density estimates given in this report were not corrected for the availability bias and therefore should be considered as the minimum estimated densities. After correcting for availability, Mackenzie et al. (2012) estimated absolute abundance for the survey area (aerial and boat-based) across the survey period as 293 (95% CI = 267 to 1055). An availability bias correction for white-beaked dolphin was unavailable, therefore, this study applied a value for bottlenose dolphin (0.11; Mackenzie et al., 2012). Absolute density estimates also had high uncertainty associated with them and ranged from zero to one individual per km2 in a single grid cell over the survey period.
132. Mean monthly density of white-beaked dolphin estimated from the Proposed Development aerial digital data was 0.009 (95% CI = 0.003 to 0.017) animals per km2. Correcting this for availability bias based on a bio-logging study in Iceland (Rasmussen et al., 2013) gave an absolute density of 0.05 (CV = 1.40, 95% CI = 0.017 to 0.094) animals per km2 and was therefore similar to the minimum summer density estimates provided by Grellier and Lacey (2011).

Figure 6.12: White-Beaked Dolphins Distribution and Group Size During Historical Aerial Surveys Across All Seasons from May 2009 to March 2010, Source: Grellier and Lacey (2011)

Figure 6.13: Positions of White-Beaked Dolphin Sightings Across All Seasons During Firth of Forth Round 3 Boat Based Surveys from May 2010 to November 2011 (Sparling, 2012)

Figure 6.14: Management Unit (MU) for White-Beaked Dolphin and Minke Whale