Surveys
  1. Relative density estimates of white-beaked dolphin from DAS of the Array marine mammal study area were corrected for availability bias using the conversion factor of 18% based on Rasmussen et al. (2013) (refer to volume 3, appendix 10.2, annex A for more detail). White-beaked dolphin were not observed in sufficient numbers for robust modelling, and as such their density within the Array marine mammal study area can only be estimated via design-based methods. Given seasonality of white-beaked dolphin sightings and higher number of records during summer, design-based density estimates were calculated across four seasons, with absolute densities of 0.024 and 0.057 animals per km2 for winter and summer respectively.
  2. After correcting for availability, Mackenzie et al. (2012) estimated absolute abundance for the TCE aerial and Seagreen boat-based survey areas across the survey period as 293 (95% CI = 267 to 1,055). An availability bias correction for white-beaked dolphin was unavailable, therefore, this study applied a value for bottlenose dolphin (0.11). Absolute density estimates presented in Mackenzie et al. (2012) for the TCE aerial and Seagreen boat-based surveys had high uncertainty and ranged from zero to one individual per km2 in a single grid cell over the survey period. Mean monthly density of white-beaked dolphin estimated from Berwick Bank aerial surveys was 0.009 (95% CI = 0.003 to 0.017) animals per km2 (SSE Renewables, 2022a). 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.
                        Summary of the densities
  1. Overall, white-beaked dolphins are abundant in the central and northern North Sea. Comparison of key data sources for white-beaked dolphin is shown in Table 5.3   Open ▸ .
  2. Predicted estimate 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 the highest, however these are based on one estimate for a large block ( Figure 3.3   Open ▸ ) and do not take into account variability in cetacean density associated with environmental covariates (such as depth, slope, distance from the coast). As described in paragraphs 131 and 134, temperature and depth are important predictors for white-beaked dolphin distribution. Therefore, studies that take into account the environmental conditions allowing to discriminate among different habitats (e.g. shallow vs deep) are preferrable when predicting white-beaked dolphin density, such as Lacey et al. (2022) and/or Waggitt et al. (2020).
  3. As presented in paragraph 140, given the relatively high number of white-beaked dolphin sightings over 24 months of the DAS, it was possible to analyse the data and provide site-specific design-based density estimates. To provide the most precautionary figure, the design-based absolute density estimates from the DAS presented in Table 5.3   Open ▸ are based on summer meteorological season (June to August).
  4. The calculated absolute density of 0.057 animals per km2 is approximately an order of magnitude lower when compared to density values from Waggitt et al. (2020) and Lacey et al. (2022). Although the reasons for such discrepancies are unknown, it can be hypothesised that the abundance of white-beaked dolphins on the east coast of Scotland may be lower compared to historic accounts due to rising sea surface temperature (van Weelden et al., 2021). The white-beaked dolphin is endemic to the colder waters of the North Atlantic and prefer water temperatures ranging from 8°C to 13°C (MacLeod et al., 2008). A number of studies have suggested that the abundance of white-beaked dolphins in the UK waters is declining as a result of increases in local water temperature (van Weelden et al., 2021, MacLeod et al., 2005, MacLeod et al., 2008, MacLeod  et al., 2007, Lambert et al., 2014). Findings from SCANS IV surveys conducted in 2022 also suggest a decline in the number of white-beaked dolphins on the east coast of Scotland with an estimated density of 0.0799 animals per km2 for block NS-D (Gilles et al., 2023) compared to the density of 0.243 animals per km2 for block R during SCANS III surveys carried out in 2016 (Hammond et al., 2021). Given that Waggitt et al. (2020) use the data collated between 1980 and 2018, the authors highlighted that the density estimates based on this study may not reflect recent changes in distribution over the study period. Therefore, to ensure that the density estimate is precautionary (with respect to corrected density estimates based on DAS of the Array marine mammal study area) and based on the most recent data and methodology that accounts for the habitat characteristic, it is considered that density estimates based on Lacey et al. (2022) are the most appropriate to use and a density of 0.120 animals per km2 will be taken forward to the assessment

 

Table 5.3:
Comparison of Main Data Sources Densities for White-beaked Dolphin (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

Table 5.3: Comparison of Main Data Sources Densities for White-beaked Dolphin (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

 

                        Seasonality

  1. Grellier and Lacey (2011) reported that during the TCE aerial surveys sightings of white-beaked dolphins were more common in summer than in winter. These results were corroborated by the Seagreen boat-based survey results, where the highest rates of white-beaked dolphins were seen in the summer months (Sparling, 2012). The Seagreen bird surveys in summer 2017 recorded white-beaked dolphins on two of the five surveys in June and July (Seagreen Wind Energy Limited, 2018). White-beaked dolphin sightings were recorded during the Berwick Bank aerial surveys during summer months only, between June and September each year, with peak sightings in September 2020 (SSE Renewables, 2022a). During DAS, white-beaked dolphin encounters took place between March and September. These seasonal peaks are in line with Weir et al. (2007), who 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.

5.2. Mysticetes

5.2.1. Minke Whale

                        Ecology

  1. Minke whale is the smallest mysticete (baleen whale) found in UK waters, measuring 7 m to 10 m when fully grown, with females usually slightly longer than males. Minke whales typically live up to 60 years and reach sexually maturity at the age of five to eight years (males) and six to eight years (females). In the northern hemisphere, mating occurs between October to March and the gestation period lasts approximately ten months, with the peak birth period between December and January (Sea Watch Foundation, 2012). Calves usually nurse for a period of four to six months.
  2. Minke whales tend to be observed either solitarily or in pairs or threes. However, in higher latitudes, including northern Scotland, larger groups of ten to 15 individuals can be observed, particularly in areas of high prey density (Anderwald and Evans, 2007). The largest group of minke whales recorded during DAS of the Array marine mammal study area consisted of five individuals (recorded in July 2022; refer to volume 3, appendix 10.2, annex A for more detail). This species mostly inhabits continental shelf waters, occurs in depths of less than 200 m and can often be seen close to land. Minke whale follow prey distribution and sandeel are the key food resource throughout the North Sea, with sprat, shad and herring also preferred prey items (Robinson and Tetley, 2005). Samples taken from the stomach contents of specimens within the North Sea determined that in UK waters the dominant prey items were sandeels, followed by clupeids and to a lesser extent mackerel Scomber scombrus (Robinson and Tetley, 2007). Around Scotland (including the Moray Firth) the primary constituent (70% of the diet of minke whales was sandeel (Tetley et al., 2008) as well as herring and sprat (Robinson et al., 2021). A recent study in Moray Firth, Scotland, has shown that juveniles tend to exploit passive (low energy) feeding methods, targeting low-density patches of inshore prey, while adult minke whales use a range of active entrapment specialisations, exhibiting seasonal flexibility in targeted prey with interindividual variation (Robinson et al., 2021). Regional differences exist with respect to diet (Eerkes-Medrano et al., 2021).

                        Distribution and occurrence

  1. Minke whale is the most frequently sighted mysticete species in UK waters and is particularly common around the Northern Isles and in regions of the North Sea (Weir, 2001, Robinson et al., 2007). By far the most sightings within continental shelf waters occur between May and September, with peak numbers from July to September, depending on the region (Evans et al., 2003). Although there are no obvious latitudinal trends in migration and distribution based on the Sea Watch database (Sea Watch Foundation, 2023), sightings in the north and east of Scotland have increased since the 1990s (Evans et al., 2003), most likely due to an increase in prey availability. The Moray Firth in particular attracts above average densities of minke whale relative to the adjacent and wider North Sea waters (Paxton et al., 2014), likely due to rich feeding grounds during summer and autumn months, with the Southern Trench ncMPA designated for the species along the southern coast of the outer Moray Firth. The boundaries of the Southern Trench ncMPA enclose deep shelf waters (~200 m in depth) and core frontal systems, which concentrates nutrients and plankton attracting fish species, and geodiversity features (such as burrowed mud) provides optimal nursery areas.
  2. Robinson et al. (2009) analysed data from boat-based studies in the Moray Firth (2001 to 2006) and reported that spatial and temporal distribution of minke whales was highly variable and non-uniform. Monthly encounter rates were highly inconsistent from one year to the next, with annual encounter frequencies ranging from 0 to 0.042 individuals per km2 across the six year study period. Robinson et al. (2009) highlighted that such variability is common in studies of baleen whales on their feeding grounds. Robinson et al. (2021) reported that in 2006, disproportionate numbers of both adult and juvenile minkes were sighted inshore within the Moray Firth study area. This coincided with the introduction of the European Union (EU)-wide ban on the North Sea sandeel fishery and therefore it has been hypothesised that minke whales were profiting from high densities of sandeel prey.
  3. Following the Geographic Information System (GIS) analyses of sightings data, Robinson et al. (2009) estimated that over 70% of the whales recorded in the Moray Firth study area occurred in steeply sloped areas at depths of between 20 m and 50 m. The arrival of whales each year appeared to be synchronised with the emergence of sandeels into the water column to feed, and in the GIS results over 66% of the whale encounters showed a clear spatial preference for sandy-gravel sediments (i.e. optimal sandeel habitat). The study proved strong correlation of the sediment type with the distribution of whales. Robinson et al. (2021) corroborated the fact that occurrence of minke whales on their feeding grounds is linked to the environmental variables which influence the distribution of their prey. The study reported that the benthic slope, water depth and proximity to shore were found to be significant predictors for the occurrence of adult minke whales, whilst proximity to shore, water depth and sediment-type were the most important predictors for juveniles (Robinson et al., 2021). More recently, Robinson et al. (2023) suggested that the partitioning between the age-classes in the Southern Trench ncMPA was largely based on the differing proximity of animals to the shore, with juveniles showing a preference for the shallower, gentler seabed slopes, and adults preferring deeper offshore waters with greater slope. Both adults and juveniles show a similar preference for sandy gravel sediment types (optimal sandeel habitat).
  4. During the historic TCE aerial surveys (Grellier and Lacey, 2011) minke whales were encountered throughout the survey area, with slightly more sightings in the northern part of the survey area ( Figure 3.2   Open ▸ ). Minke whales were mostly recorded as single animals, although three animals were sighted together in May 2010 and two in June 2011. During the Berwick Bank aerial surveys, minke whales were recorded throughout the surveyed area ( Figure 3.2   Open ▸ ) (SSE Renewables, 2022a). Given that minke whales were recorded in four months only during DAS of the Array marine mammal study area, no clear pattern in their distribution across the Array marine mammal study area can be concluded (refer to volume 3, appendix 10.2, annex A for more detail).

                        Density/abundance

                        Published literature
  1. All minke whales in UK waters are considered to be part of the CGNS MU ( Figure 5.12   Open ▸ ). Based on the most up to date estimates, the abundance of minke whales in this MU is 20,118 animals (CV = 0.18, 95% CI = 14,061 to 28,786) (IAMMWG, 2022). The SCANS III estimated abundance for block R ( Figure 3.3   Open ▸ ) was 2,498 minke whales (CV = 0.61, 95% CI = 604 to 6,791) (Hammond et al., 2021). SCANS IV reported minke whale abundance within block NS-D of 2,702 individuals indicating an increase in minke whale abundance when compared to SCANS III results for block R (Gilles et al., 2023).
  2. Hammond et al. (2021) reported densities for minke whale across block R as 0.0387 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 0.0284 animals per km2 and a maximum of 0.0358 animals per km2 for the Array marine mammal study area ( Figure 5.17   Open ▸ ), with density maps showing higher areas of density in the offshore waters east of the site boundary. The SCANS IV surveys reported relatively higher minke whale density of 0.0419 animals per km2 for block NS-D when compared to SCANS III block R (Gilles et al., 2023).
  3. The JCP Phase III analyses presented abundances for minke whales in 2010 by season for the Firth of Forth area of commercial interest region ( Figure 3.5   Open ▸ ) estimated highest abundance in the summer months at 360 (97.5% CI = 140 to 990) animals, with low estimates in all other seasons (20 animals during autumn and winter). This equates to density estimates between 0.025 individuals per km2 and 0.001 individuals per km2. Additionally, the study reported predicted abundance of minke whales in the Firth of Forth as a percentage of the predicted number from CGNS MU ( Figure 5.13   Open ▸ ), based on estimates for summers 2007 to 2010 as 1.4% (97.5% CI = 0.6 to 2.3).

Figure 5.17:
Density Surface Maps from SCANS III Data for Minke Whale Based on Lacey et al. (2022)

Figure 5.17: Density Surface Maps from SCANS III Data for Minke Whale Based on Lacey et al. (2022)


                        Surveys
  1. Minke whales were recorded in four months during DAS and due to low numbers of sightings (refer to volume 3, appendix 10.2, annex A for more detail), design or model-based density and abundance estimates for this species are not available.
  2. Based on the sightings data from the TCE aerial surveys and Seagreen boat-based surveys, Mackenzie et al. (2012) reported the absolute abundance as 594 individuals for the survey area but also showed a high level of uncertainty due to the low number of sightings (95% CI = 483 to 2,695). An availability bias correction factor was applied to this analysis for minke whale at 0.04 (Mackenzie et al., 2012).
  3. The greatest number of minke whales counted from the Seagreen bird surveys was 13 animals in July 2017. No minke whales were sighted during the June survey and only one animal per survey was recorded in May and August (Seagreen Wind Energy Limited, 2018). Mean monthly density of minke whale based on the Berwick Bank aerial survey data was estimated as 0.007 (95% CI = 0.004 to 0.010) animals per km2 (SSE Renewables, 2022a). Correcting this for availability bias using dive profile data from a visual tracking study in Iceland (McGarry et al., 2017), provided an absolute density of 0.016 (95% CI = 0.009 to 0.023) animals per km2 (SSE Renewables, 2022a).
                        Summary of the densities
  1. Overall, minke whales are widely distributed in the northern North Sea. Comparison of key data sources for minke whale is shown in Table 5.4   Open ▸ .
  2. As presented in paragraph 156, due to low numbers of minke whale sightings during DAS, design or model-based density and abundance estimates for this species are not available.
  3. The predicted estimate of mean density for the Array marine mammal study area from Waggitt et al. (2020) are lowest when compared to the Lacey et al. (2022) and Hammond et al. (2021) estimates. Densities published by Gilles et al. (2023) are the highest, followed by densities published by Hammond et al. (2021) ( Table 5.4   Open ▸ ). However, SCANS III and SCANS IV densities are based on one estimate for large blocks and do not take into account variability in cetacean density associated with environmental covariates (such as depth, slope, distance from the coast). Furthermore, 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. 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 detail) in the density surface modelling. As described in paragraph 151, depth and slope are important predictors for minke whale distribution. As such, studies that consider the environmental conditions allowing to discriminate among different habitats (e.g. shallow vs deep) are preferrable to be used when predicting minke whale density. As such, it is considered that densities presented in Lacey et al. (2022) are the most appropriate to use for the specific area of interest (Array marine mammal study area) and a density of 0.0284 animals per km2 will be taken forward to the assessment.

 

Table 5.4:
Comparison of Main Data Sources Densities for Minke Whale (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

Table 5.4: Comparison of Main Data Sources Densities for Minke Whale (Lacey et al. (2022) Density Will Be Taken Forward to the Assessment)

 

                        Seasonality

  1. Robinson et al. (2009) reported that in the Moray Firth, minke whales were encountered each month with a peak in annual occurrence from July to August (using sightings data from boat-based surveys carried out between May and October, 2001 to 2006). The distribution of whales showed a progressive inshore movement of animals across the summer and autumn months and then a progressive return to offshore waters again towards the end of the study period at which time whales were evidently less abundant, although the timing of this inshore-offshore movement was clearly variable from one year to the next. The results of this study suggest that while sandeels in the Moray Firth are highly targeted by minke whales in summer months, offshore populations of pelagic herring and sprat may also be equally or sometimes even more accessible to foraging whales at certain periods across the summer or from one year to the next, explaining the seasonal inshore-offshore movements and inter-annual variability of animals. Robinson et al. (2021) reported that there were seasonal differences in prey items with sandeels being targeted by juveniles and adults across all study months (May to October), herring preferentially targeted by adults from early July and sprat between late August to October.
  2. The presence of minke whale pulse trains was recorded across ten sites localised between the southern edge of St. Abbs and northern Moray Firth from 2016 to 2018 (Risch et al., 2019). Across all sites and all years, minke whale pulse trains were first detected in late May and detections generally declined at the end of October. During autumn and spring, minke whale pulse train detections showed strong diel periodicity, with calling rates being lowest during daylight and highest during the night. Diel variation in baleen whale vocalisations has also been attributed to prey distribution, with reduced vocalisation rates during active feeding and an increase in vocalisations in a social context at hours of lowest prey availability (Risch et al., 2019).
  3. The results of the analysis of sightings data from Seagreen boat-based surveys are in line with previous studies of Aberdeenshire coastal waters that reported minke whales to be highly seasonal (Sparling, 2012). Encounter rates were highest in the spring and summer and relatively low in autumn and winter. A similar pattern was reflected in the Neart na Gaoithe boat-based surveys and Berwick Bank aerial surveys, with sightings recorded only between May and November (Mainstream Renewable Power, 2019) and between April and September (SSE Renewables, 2022a), respectively. During DAS of the Array marine mammal study area, minke whale were only recorded in April 2022, June 2022, and July 2021/2022.

5.2.2. Humpback whale

                        Ecology

  1. The humpback whale is a medium-sized mysticete of the Balaenopteridae family, which includes all the rorquals and is found in all oceans of the world (Johnson and Wolman, 1984). At maturity, the humpback whale reaches lengths of up to 17 m and weighs approximately 40 tonnes (HWDT, 2023). Humpback whales are easy to distinguish from other baleen whales due to their distinctive appearance with exceptionally long flippers, which are one-fourth to one-third of their total body length (Johnson and Wolman, 1984, HWDT, 2023).
  2. The behaviour of humpback whale varies according to the season (HWDT, 2023). During breeding periods in the tropics, humpbacks fast, relying on their large fat reserves built up during feeding season (Rizzo and Schulte, 2009). Male whales sing long, complex songs during the breeding season, presumably to attract females and warn off rival males. These songs are known to vary between populations and change over time (HWDT, 2023). Humpback whales are normally seen as solitary individuals or in small groups of up to seven animals, and long-term associations are rare. They can dive for up to 40 minutes and raise their tail fluke when making a deep dive (HWDT, 2023). There are no studies on the prey presence within the Scottish waters, however, humpback whales were reported to prefer sprat and herring in the Celtic Sea (Ryan et al., 2014).
  3. Following a severe decline due to commercial whaling, humpback whale populations in the North Atlantic region have been undergoing steady recovery during the latter part of the twentieth century (Johnson and Wolman, 1984, O’Neil et al., 2019). In the western North Atlantic, entanglement in static fishing gear, namely crab and lobster creels (pots), is currently considered to be the largest source of anthropogenic mortality and injury for this species (Ryan et al., 2016, Leaper et al., 2022).

                        Distribution and occurrence

  1. Humpback whales are known for travelling long annual migration distances (Rizzo and Schulte, 2009). During summer, they spend their time in high latitudes, feeding as much as they can to create a great blubber layer, but do not mate. In winter, they travel to low latitude areas, in tropical waters, where they mate and calve, fasting for long periods such as weeks or even months (Rizzo and Schulte, 2009). Studies focussing on humpback whales in feeding areas found preferences for areas of upwelling, high chlorophyll-a concentration and frontal areas with changes in temperature, depth and currents, where prey can be found in high concentration (Meynecke et al., 2021). Preferred calving grounds were identified as shallow, warm and with slow water movement to aid the survival of calves (Meynecke et al., 2021). Although they favour inshore waters and continental shelf areas, humpback whales travel through open waters during their migration (HWDT, 2023).
  2. Ramp et al. (2015) investigated the temporal variation in the occurrence of humpback whales in a North Atlantic summer feeding ground, the Gulf of St. Lawrence (Canada), from 1984 to 2010 using a long-term study of individually identifiable animals. The study found that humpback whales shifted their date of arrival at a previously undocumented rate of more than one day per year earlier over the study period and that the departure date also shifted earlier (Ramp et al., 2015). The analysis revealed that the trend in arrival was strongly related to earlier ice break-up and rising SST, likely triggering earlier primary production. The findings presented by Ramp et al. (2015) suggest that further changes to humpback whale distribution or annual life cycle may occur with ongoing climatic changes.
  3. The first match from the British Isles to any breeding ground was made when a humpback whale photographed off the Shetland Islands, Scotland in 2016 was identified as having been seen off Guadeloupe in 2015 (Jones et al., 2017). The calculated great-circle distance between these sighting locations is approximately 6,900 km. As reported by Ryan et al. (2022), humpback whales in Scottish waters have been matched with both recovering (western North Atlantic) and non-recovering (Cape Verde) breeding populations. In 2022, the 100th humpback whale was added to the Scottish Humpback ID Catalogue (HWDT, 2022a).

                        Density/abundance

                        Published literature
  1. There is little information that exists on the historical distribution and abundance of humpback whales in Scottish waters prior to commercial whaling. A few sources indicate that they were present in low densities (O’Neil et al., 2019, Weir et al., 2001). Based on archived logbooks detailing landings at Scottish shore-based whaling stations, most humpback whale catches were to the north of Shetland, although several were taken to the west of the Outer Hebrides at the continental shelf edge (Ryan et al., 2022). Of the baleen whale landings, humpback whales comprised a very small proportion of the total, e.g. approximately 0.7% of the entire catch (Ryan et al., 2022).
  2. Although all records of humpback whale presence, including visual, acoustic and strandings, remain relatively low, there have been increasing records for this species in Scotland and the wider eastern North Atlantic region since the mid-1980s (O’Neil et al., 2019, Evans and Waggitt, 2023). The first confirmed record of a humpback whale in the Firth of Forth, occurred in February 2003, with further records from August 2006, October 2012, and August 2017. Opportunistic sightings by citizen science projects in recent years suggest an increase in occurrence in inshore waters (Hague, 2023). Some individuals from the Firth of Forth were matched with records off the Scottish west coast (Isle of Coll, Hebrides) (HWDT, 2022b). Based on photographs made by citizen scientists between January 2017 and March 2018 in the Firth of Forth, O’Neil et al. (2019) reported that individuals present in the Firth of Forth had been previously photographed in Svalbard, Norway. The same study provided the first confirmed record of an individual humpback whale returning to the Firth of Forth in consecutive years (O’Neil et al., 2019). It has been suggested that the Firth of Forth may represent a migratory stopover, or a feeding or recovery opportunity en-route of a longer migration (O’Neil et al., 2019).
  3. No contemporary density or abundance estimate exists for humpback whales in Scottish waters and SCANS surveys did not detect any between 1994 and 2022 (Hammond et al., 2021, Gilles et al., 2023, Hammond et al., 2013, Hammond et al., 2002).
                        Surveys
  1. Humpback whales were not recorded in any of the historical surveys that took place within the wider Firth of Forth and Tay (refer to Table 3.3   Open ▸ and Figure 3.2   Open ▸ ) nor the DAS surveys of the Array marine mammal study area (refer to volume 3, appendix 10.2, annex A for more detail).

                        Seasonality

  1. Over recent years, most of the sightings in the Firth of Forth were reported in winter, between December and March (O’Neil et al., 2019, Hague, 2023).