6. Anthropogenic activities causing indirect effects on seabirds

6.1. Climate change

71. Climate change is leading to dramatic changes in ecosystem structure, through effects on ocean temperature, water stratification and nutrient availability, leading to changes in the abundance and diversity of communities at all trophic levels, from primary producers to top predators (Walther, 2010). Effects of climate change have been identified over a variety of timescales. Short-term variability in environmental conditions impacts interactions between trophic levels and species (Howells et al., 2017). Limitations in prey availability can adversely affect top predators, with population-level changes likely to occur over longer timescales, propagating up trophic levels with prolonged exposure (Frederiksen et al., 2006; Howells et al., 2017).
72. Indirect effects on seabirds are primarily mediated through prey availability, diversity and quality, related to changes in primary producers and directly to key prey in the mid-trophic levels (Lynam et al., 2017; Mitchell et al., 2020). Lynam et al (2017) statistically modelled complex patterns of trophic control in the North Sea, driven by fishing mortality and climatic variables. The average success of seabird reproduction was linked to climate change through temperature effects on primary production and primary consumers (e.g. plankton species) and pressure from commercial fisheries, and the subsequent effects on forage fish species ( Figure 4.1   Open ▸ ). Hakkinen et al. (2022) ranked climate change threats to seabirds in western Europe and concluded reduced prey availability was the greatest threat. Access to enough prey, with sufficient nutrient quality, at the right time and location is more critical than the absolute abundance of prey (ICES, 2015; Mitchell et al., 2020). Changes to prey availability and quality has potential consequences over moderate to long timescales following mismatch in life-history events between species (Visser and Gienapp, 2019). Other indirect effects include range shifts, which may be catastrophic for nest-building species where new environments may have reduced nesting materials or suitable habitat, changes in interactions with predators or potentially harmful diseases and parasites (Mainwaring et al., 2016). 
73. In the Forth and Tay region, the SST has increased by 0.05°C per decade on average since 1870, and an increase of 0.21°C per decade between 1988 and 2017, suggesting that warming has accelerated in the last 30 years (Marine Scotland, 2020). An assessment of the vulnerability of seabirds in the Forth and Tay region demonstrated negative correlations between SST and abundance, adult survival and/or productivity of 57% of the investigated bird species in the area (Burthe et al., 2014). This was predominantly linked to the impact of climate change on the lowest trophic levels, such as plankton, and the subsequent effects on seabird prey availability. 

6.1.1.    Prey availability, quality and distribution

74. Declines in abundance and quality of mid-trophic level-species have been linked to multiple climate change-related factors, such as increasing SST, changes in stratification and alterations in the North Atlantic Oscillation (Johnston et al., 2021). Generally, scenarios with colder conditions were expected to benefit seabird populations through the increase in primary consumers (such as small copepods and other zooplankton) and therefore sandeel abundance, meaning that SST increases related to climate change may be detrimental to the abundance of sandeels and similar mid-trophic species (Lynam et al., 2017).
75. For example, in the North Sea, kittiwake over-winter survival has been observed to be lower following winters with a higher SST, with lower breeding success in the following summer which is likely related to reduced sandeel availability (Frederiksen et al., 2004, 2005, 2007). However, in the Celtic Seas region, where kittiwake diets are predominantly composed of sprat and herring, no relationship has been observed between SST and kittiwake breeding success, evidencing the vulnerability of North Sea kittiwake populations to sandeel populations declines (Lauria et al., 2013; Cook et al., 2014b).
76. Guillemot population collapse and recovery in Norway has been linked to climate mediated bottom-up impacts on prey species capelin Mallotus villosus, herring and cod (Erikstad et al., 2013), and breeding success has been repeatedly cited as correlating with prey abundance of sprat in the Baltic Sea (Kadin et al., 2012), sandeel, within the North Sea (Rindorf, Wanless and Harris, 2000; Frederiksen et al., 2006; Burthe et al., 2012); cod, in the Norwegian Sea (Barrett and Erikstad, 2013) and herring, in the Celtic and Norwegian Seas (Lauria et al., 2012; Barrett and Erikstad, 2013). Puffin fledgling success has been negatively correlated with SST on the Isle of May (Burthe et al., 2012) and St Kilda (Harris, Murray and Wanless, 1998) relating to bottom-up influences on sandeel abundance (Frederiksen et al., 2013).
77. Sandeels are an important trophic link between plankton and predators in North Sea ecosystems; however, climate driven changes to phytoplankton and zooplankton (further discussed in Section 6.1.2) and commercial fishing (further discussed in Section 6.2) have led to declines in the abundance and nutritional quality of these species and other small planktivorous fish since 2000 (Macdonald et al., 2015; Clausen et al., 2017; Wanless et al., 2018; MacDonald et al., 2019). This is correlated with community-wide declines in sandeel abundance in the diets of chicks of auks, shags and kittiwakes observed over 30 years at the Isle of May (Wanless et al., 2018), and sandeels becoming largely confined to the early part of the chick rearing period of guillemot (Harris et al., 2022).
78. At the Isle of May between 1973 and 2015, it is estimated that the energy content of sandeels decreased by approximately 70% and 40% for 0 and 1+ year groups, respectively, indicated by a decrease in the mean length-at-age of sandeel prey (Wanless et al., 2018) which has been correlated with the productivity of guillemot, kittiwake and razorbill (Burthe et al., 2012; Wanless et al., 2018). The breeding productivity of shag, kittiwake, puffin and guillemot on the Isle of May have also been associated with the mean size of 1-group sandeels (Frederiksen et al., 2006). In 2004, the calorific densities of sprat and sandeel were less than 25% of that expected compared with previous years, which is thought to be the primary cause of guillemot breeding failures in that year (Wanless et al., 2005). Similar observations for a range of marine birds and mammals have given support to the ‘junk food’ hypothesis which states that the energy density of low-lipid prey is inadequate to meet the energetic demands of breeding, even if such prey are abundant (Piatt and Anderson 1996; Merrick, Chumbley and Byrd, 1997; Rosen and Trites 2000; Litzow et al. 2002).
79. Like sandeel, Atlantic mackerel Scomber Scombrus population declines have been linked with SST, which may have an adverse effect on their growth, recruitment and migration (Jansen and Gislason, 2011). Jansen et al. (2012) also observed a decline in mackerel larval abundance in the North Sea since the 1970s. Whilst this cannot necessarily be attributed to climate change, mackerel eggs have shown sensitivity to seawater temperature (Mendiola et al., 2007). Burrows et al. (2019) considered the temperature affinity of bottom-dwelling fish species. They demonstrated that, with the warming climate, there has been a shift towards warm-water species such as lesser-spotted dogfish, hake and horse mackerel and away from cold-water species such as Atlantic cod, Atlantic herring and sprat) across the North Sea. Seabird species which are able to exploit these warm-water species may have higher resilience to changes in prey availability associated with climate change.
80. The resilience of seabirds to changing prey availability may be affected by their feeding strategy (Burthe et al., 2014). Guillemot’s pursuit diving behaviour, allowing them to forage at a range of depths, may provide resilience to fluctuations in prey availability, making them more resilient to climate change effects (Furness and Tasker, 2000; Johnston et al., 2021). Shags have been observed to diversify their diet with increased SST, associated with a decrease in the proportion of sandeels in their diets, possibly leading to consequences in population dynamics (Howells et al., 2017). Additionally, species which are able to be more generalist in their diet, such as gull species and gannets, are likely to be able to better respond to changes in prey availability, however species such as kittiwake which are more dependent on sandeels as their primary food source are likely to be more adversely affected by changes to prey availability (Burthe et al., 2014; Furness and Tasker, 2000; Carroll et al., 2017).

6.1.2.    Copepod availability and distribution

81. Changes in the phenology, community composition, abundance and distribution shifts are anticipated at lower trophic levels as a result of rising SST) and climate change, which could cascade through the food webs and affect the availability of seabird prey species at mid-trophic levels, and thus seabird populations (Burthe et al., 2012; Lynam et al., 2017). Off the east coast of Scotland between 1973 and 2015, slow growth was observed in sandeels which correlated with temperature and zooplankton and phytoplankton biomass, indicated by a reduction in the length and energy value (MacDonald et al., 2019). Similar trends have also been observed in herring and sprat in the west of Scotland (Hunter, Speirs and Heath, 2019), and sprat, sandeel, herring and Norway pout more widely across the North Sea (Clausen et al., 2017).
82. The copepod Calanus finnmarchius constitutes more than 50% of the total copepod biomass in the North Atlantic and is an important prey species for small fish which seabirds feed on (Frederiksen et al., 2013). Frederiksen et al (2013) found a strong correlation between C. finnmarchicus environmental suitability and the distribution of kittiwakes, guillemots and puffins in the North Sea. They also found that C. finnmarchicus is adversely correlated with SST. Therefore, increasing temperatures related to climate change could see a northward distributional shift in C. finnmarchicus and contribute towards a northward shift in small pelagic fish and seabirds (Frederiksen et al., 2013). Similarly, anomalously high SSTs during the breeding season in the Northwest Atlantic have been correlated with reduced prey availability and accessibility due to the formation of a thermocline, which subsequently reduced the condition of gannet, shortened the chick rearing period (Franci et al., 2015) and reduced breeding success (Montevecchi et al., 2013).
83. Similarly, northward-distribution shifts were predicted in copepod communities across the North Atlantic, by McGinty et al (2021). Models also predicted basin-wide shifts in community composition, with an increase in carnivorous species and a reduction in herbivorous species, and a decrease in body sizes of lower trophic groups as they move northward (reference). These changes may reduce energy and carbon transfer to higher trophic levels and have subsequent impacts to trophic links and ecosystem functioning (McGinty et al., 2021). This may be correlated with a northward shift in the distribution of forage fish species, such as sandeel and sprat (Burthe et al., 2012).
84. Climate change is also leading to ocean acidification, by chemical processes related to increased temperatures increasing dissolved levels of carbon dioxide in seawater. Decreasing pH is affecting phytoplankton, which can inhibit shell generation of calcifying marine organisms and may impact skeletal development in larval fish, with potential consequences to forage species of seabirds (Riebesall et al., 2013). However, these impacts are difficult to predict at species and population levels due to the complexity of these food web interactions (Heath et al., 2012).
85. In the Forth and Tay region, there has been limited study of plankton and assessments which have been undertaken are too short in duration to understand the local impacts on climate change on the lowest trophic levels (Marine Scotland, 2020). The Scottish Environment Protection Agency has monitored some phytoplankton (diatoms and dinoflagellates) in the Firth of Forth and the Clyde between 2010 and 2017, which estimated no change in their abundance during this period (Marine Scotland, 2020). Due to insufficient knowledge, it is difficult to predict the future of the lowest trophic levels (e.g., primary producers and primary consumers such as phytoplankton and plankton) in the Forth and Tay region, or in the Proposed Development area.

6.1.3.    Mismatch in life-history events

86. A further key factor in sandeel larval success is synchrony between the larval hatching times and the spring zooplankton bloom (MCCIP, 2018).
87. Warming has been demonstrated to lead to earlier zooplankton blooms in higher latitudes (Greve et al., 2004; Mackas and Beaugrand, 2010; McGinty et al., 2021), resulting in a decrease in zooplankton available for sandeels to feed upon and a reduction in sandeel growth and survivorship (Réginer, Gibb and Wright, 2017). Bloom timing can also have knock-on impacts to other species, for example by introducing competition between species which did not previously overlap spatially, or in the timing of key reproductive events such as foraging.
88. Increased sea temperatures are expected to lead to later larval hatch times in sandeel (Boulcott and Wright, 2008; Wright, Orpwood, and Scott, 2017), which may also have contributed to reduced sandeel size (Wanless et al., 2004). Adult sandeels feed on plankton in the spring and summer months; building up lipids to survive the winter period buried in sand when plankton production is lower. Increased temperatures lead to increased energy usage whilst overwintering, meaning less energy can be allocated to gonad development. (Boulcott and Wright, 2008; Wright, Orpwood, and Scott, 2017). Sprat feed and spawn repeatedly through spring and summer and therefore do not rely on winter energy stores and so are less sensitive to the timing of the onset of plankton production than sandeels (MCCIP, 2018), which may have contributed to prey-shifts in auks and kittiwakes from sandeels towards sprat in the North Sea (Wanless et al., 2018). However, for such prey to provide an adequate alternative to traditional prey like sandeels, they must also be of sufficient abundance, availability, and quality.
89. Warming climates and SST have also been correlated with later laying dates of puffin at the Isle of May and St Kilda (Burthe et al., 2012) which also correlated with a reduction in the success of chicks (Harris et al., 1998). Delayed breeding may be a response to the timing of peak prey abundance (Durant, Anker-Nilssen, and Stenseth, 2003), however the shift towards later breeding may be insufficient, leading to a mismatch in the timing of puffin chick rearing and adequate prey quality, size and quantity and contribute to declines in chick success (Burthe et al., 2012; Harris, Murray and Wanless, 1998; Johnston et al., 2021).

6.1.4.    Competition

90. The change in prey availability and distribution, and in available nesting habitat in the North Sea could also increase the inter-specific (between species) and intra-specific (within species) competition in seabirds. Northward shifts of birds could see populations which previously did not overlap spatially become closer, leading to competition for prey and nesting habitat in the same area (Mainwaring et al., 2016; Sadykova et al., 2020). This may also lead to an increase in the transmission of disease and parasites between populations whose ranges may not have overlapped, historically (Mainwaring et al., 2016). 
91. Climate change is also affecting the distributional range of other marine predators, such as European hake Merluccius merluccius which has expanded its spatial distribution in the North Sea in correlation with temperature (Cormon et al., 2016). This may have a direct impact on its prey species Norway pout and herring, which could have knock-on food web impacts on prey availability for seabirds (ICES, 2014). Climate change and overfishing has also been linked to a global increase in jellyfish populations (Purcell, Uye and Lo, 2007). Jellyfish directly compete with planktivorous fish in the lower-mid trophic levels for food such as copepods, whilst also predating on fish larvae in some species, and provide refuge for juvenile gadoids (e.g. cod and hake), which may increase competition for seabirds and their prey (Lynam and Brierly, 2007; Lynam et al., 2017).

6.2. Commerical fisheries

92. Forage fish landings account for approximately one third of global landings of marine fish, not considering additional loss from bycatch discards (Alder et al., 2008). Fisheries can disrupt the food web by removing target species from the mid-trophic levels, such as sandeel and herring, which are important prey species for top predators such as seabirds. This can have significant indirect impacts on seabird growth, survival, foraging behaviour, chick provisioning and breeding success, by affecting the amount of prey available, the energy available per prey item and the timing of seasonal dietary shifts (e.g. Frederiksen, 2008a; Sherley et al, 2018).
93. In the North Sea, annual landings of sandeels have halved since the late 1990s, when landings peaked at over one million tonnes (ICES, 2019). The fishery at the Wee Bankie sandbank, 40 km off the east coast of Scotland outside of the Firth of Forth, was closed to the sandeel industrial fishery in 2000 as part of the northeast UK sandeel closure after concerns were raised about the effect of sandeel population decreases on predators, particularly seabirds (Scottish Marine Assessment, 2021). The northeast UK sandeel fishery (ICES sandeel area 4) span across a large portion of the foraging seabirds from the Proposed Development area. Following closure, sandeel abundance significantly increased, most likely due to stronger recruitment of 0 group individuals (Furness and Camphuysen 1997; Greenstreet et al., 2010). Despite this, there are still concerns over the management of the fishery as the fishery currently operates within the foraging range of internationally important seabird species and the management plan does not include protective measures to ensure species dependent on sandeels such as seabirds or lower trophic level species can still function effectively, in addition to the effect of concentrating fishing effort into smaller areas, which can ultimately lead to the reduction of localalised sandeel stocks (Dunn, 2021). 
94. Kittiwakes have been found to be particularly susceptible to changes in sandeel populations caused by commercial fisheries. While the Wee Bankie fishery was in operation, a strong decline was observed in breeding success for kittiwake colonies which overlapped with the closed fishery area, including the Isle of May (Searle et al., 2022). Kittiwake populations increased by approximately 8% in this area between the closure of the fishery and 2018 (Searle et al., 2022), and the shift from 1+ to 0-group sandeels were found to occur earlier in the years following the closure (Daunt et al., 2017). There was no evidence for adverse effects from the fishery on guillemot, puffin or razorbill (Searle et al., 2022).
95. Whilst other seabirds do feed on sandeel, kittiwakes may be particularly susceptible to changes in sandeel abundance as they are surface feeders. Other seabirds are able to access more of the water column and therefore a greater proportion of sandeel so continue to survive and breed despite decreases in absolute abundance (Daunt et al., 2017).  
96. Fishing can also affect seabirds by changing the prey-predator balance of different species. For example, fishing mortality of sprat has an adverse impact on whiting, which reduces predation pressure on whiting prey species, such as sandeel. Fishing of herring has an adverse effect on haddock, but positive effects on Norway pout, sprat and the copepod Calanus finnmarchicus, leading to increased saith and whiting but decreases in the copepod C. helgolangicus which could benefit sandeel ( Figure 4.1   Open ▸ ; Lynam et al., 2017). The complexity of these interactions demonstrates the complexity of marine food webs.

6.3. Offshore wind energy

97. Expansion of renewable wind energy generation in marine environments may have population, community and ecosystem-level indirect impacts by introducing new habitat, locally restricting fishing and altering physical processes (van der Molen et al., 2014; Cazenave et al., 2016; Zijl et al., 2021).
98. The submerged parts of offshore wind farms, such as the foundations and any scour or cable protection on the seabed, introduces new hard substrate. Typically, offshore wind farms are placed in soft substrate environments, so addition of hard substrate results in a change of habitat type which acts like an artificial reef. In the North Sea, natural reefs are rare, so whilst sandy habitat is lost, there is an increase in available habitat for reef formation (Coolen, 2017). Artificial habitats have been reported to have a positive effect on the production of benthic carnivores, due to the increased food availability and the low fishing mortality (Cresson et al., 2019).
99. Artificial reefs are populated in a variety of ways. Mobile organisms can walk or swim to the new reef, animals may travel on floating objects, or pelagic larvae may be transported to the reef through currents. Artificial reefs can also act as stepping-stones, which allow organisms to colonise areas not typical of their species or they may increase the connectivity between natural sub-populations (Coolen et al., 2017). The impacts of this can extend beyond the scale of a single operation (e.g. at the scale of individual wind turbines or Project scale) with multiple adjacent offshore wind farms creating stepping stones over wider areas and creating a large-scale effect (Degraer et al., 2020). For example, the Project is adjacent to several offshore wind farms in the Forth and Tay area: Seagreen 1 and Seagreen 1A Project to the north, Inch Cape to the northwest and Neart na Gaoithe to the west.
100. Like in communities found on natural hard substrates, vertical zonation is observed on wind turbine foundations, with different species colonising different zones ( Figure 6.1   Open ▸ ; Degraer et al., 2020). However, due to structural differences between natural reefs and wind turbine foundations, the species composition of artificial reefs can be significantly different to natural ones. For example, a monopile at the water surface may harbour species which are typical of the intertidal coastal zone, which is not natural in the offshore North Sea. Only 19 of 123 species observed at the seabed (at the base of wind turbine installations, and on scour protection) were also found in natural reefs in the North Sea (Coolen, 2017). The amphipod Jassa herdmani and crab Pisidia longicornis are rare on natural habitats (Zintzen, 2007), so whilst artificial reefs may increase local biomass and biodiversity, these communities cannot necessarily be compared to natural ones. In the North Sea, blue mussels Mytilus edulis have been observed to populate anthropogenic structures, such as oil and gas platforms (Schutter et al., 2019) and wind turbines monopiles (De Mesel et al., 2015; Maar et al., 2009). It has been predicted that should all offshore wind farms which are currently under construction, planned or consented be completed, the overall abundance of blue mussels could increase in the southern North Sea by more than 40%. This could lead to a decrease in available primary production, increased prey for species which feed on mussels, and decreased prey availability for other species due to competition between mussels and other prey species. This could lead to changes in food webs and ecosystem functioning (Slavik et al., 2019).

Figure 6.1 Example of the population structure and zonation on wind turbine foundations (Illustrated by Hendrik Gheerardyn; from Degraer et al., 2020).

101. Artificial reef habitats can accommodate high densities of fish, compared to both sand-bottom habitats and natural reefs (Reubens, Degraer and Vincx, 2014; De Mesel et al., 2015; Mavari, Degraer and Vanaverbeke, 2021). This is likely due to a combination of attraction to the offshore wind farm from surrounding areas, as well as increasing the carrying capacity due to increased productivity. The increased structural complexity of the artificial reefs offers protection against predators and strong currents, and increased food availability. Species which have been demonstrated to have increased abundance around offshore wind farms in the North Sea include pouting, juvenile cod species, which feed on J. herdmani and sculpin feeding on decapods (Reubens, Degraer and Vincx, 2014; Mavari, Degraer and Vanaverbeke, 2021). Both prey species are strongly associated with subtidal artificial hard substrates such as offshore wind farms and shipwrecks (De Mesel et al., 2015). This, in turn, may attract predators and scavengers, which might include marine mammals (e.g. harbour seal harbour) seal Phoca vitulina, grey seal Halichoerus grypus, harbour porpoise Phocoena phocoena), predatory fish (e.g. saithe Pollachius virens, cod Gadus morhua, Allis shad, Alosa alosa, twaite shad Alosa fallax ) and elasmobranchs (e.g. spotted ray Raja montagui, spurdog Squalus acanthias, tope Galeorhinus galeus common skate Dipturus batis, and thornback ray Raja ecommi) in the vicinity of the Proposed Development (see volume 2, chapter 9).
102. The Forth and Tay region has a variety of benthic habitats, ranging from moderately exposed rocky habitats to large areas of sand and mud, and glacial sand and soft sediments in the sheltered Montrose Basin, the Firths of Tay and Forth and the Eden Estuary (Marine Scotland, 2020). Organisms from rocky habitats close to the Proposed Development could populate the wind farm structures, creating an artificial hard-substrate environment. It is expected that the foundations and scour and cable protection will be colonised by species already occurring in the benthic subtidal and intertidal ecology study area (e.g. tunicates, bryozoa sp., mussels and barnacles which are typical of temperate seas; see volume 2, chapter 9). There are also potential beneficial effects for crab and lobster which are commercially exploited in the vicinity of the Proposed Development due to expansion of their natural habitats (Linley et al., 2007) and the creation of additional refuge areas. Post-construction monitoring surveys at the Horns Rev offshore wind farm, in Danish Waters in the North Sea, noted that the hard substrates were used as a hatchery or nursery grounds for several species, and was particularly successful for brown crab (BioConsult, 2006). As both fish and shellfish ecology study area, there is potential for benefits to the fisheries, depending on the materials used in construction of the offshore wind farm.
103. Based on the outcomes of similar structures in the North Sea, whilst there is a reduction in soft-substrate habitats within the footprint of the wind farm, this could lead to an increase in productivity and fish at the wind farm resulting from the artificial reef effect (Reubens, Degraer and Vincx, 2014; De Mesel et al., 2015; Mavari, Degraer and Vanaverbeke, 2021). Overall, colonisation of foundations, scour protection and cable protection at the Proposed Development is expected to have a negligible to minor effect on marine species and diadromous species (see volume 2, chapter 9).
104. Zijl et al (2021) modelled the impact of offshore wind farms on a variety of physical processes across the central and southern North Sea for two scenarios: the present wind farms (as of 2020) and future hypothetical wind farms (based on targets for offshore wind for 2050). In the Forth and Tay region, there were no existing wind farms at the time of study, and several wind farms were included in the future hypothetical scenario which are in planning, have been consented or are now under construction: Inch Cape, Neart na Gaoithe, Seagreen 1 and Berwick Bank (the Project). Although the model uncertainty was high, tentative results suggested there was no significant impact on the annual mean temperature and salinity. However, enhanced mixing could lead to a reduction in stratification in and around offshore wind farms by up to 60% in worst affected areas (equivalent to a decrease in mean vertical temperature difference of 0.5°C and 0.5 psu in 2050). This was consistent with modelling by Carpenter et al (2016), which found that offshore wind farms could have large-scale impacts by reducing wave action and stratification. This has the potential to increase food and oxygen transportation to the seabed, which may benefit benthic communities and their predators but be detrimental to water column and surface species.
105. In shallow, shelf seas such as the North Sea, density stratification is one of the key physical features affecting the structure of the marine environment (van Leeuwen et al., 2015). Typically, in these areas changes to water density due to salinity and temperature become more important than other factors such as turbulence or mixing due to winds and tides (van Leeuwen et al., 2015).
106. The presence of major estuaries within the wider Forth and Tay have a considerable impact on salinity and turbidity (Marine Assessment, 2020). Stratification models for this region of the North Sea characterised the area as a ‘region of freshwater influence’ where a fluctuating environment of stratification and break up is expected, as a result of riverine inflow (van Leeuwen et al., 2015). Although the area tends to already experience large fluctuations in stratification compared to the wider North Sea, the addition of offshore wind farms has the potential to affect stratification, the timing and strength of which affects primary production and therefore the distribution and abundance of higher trophic level species, such as seabirds and their prey (Scott et al., 2006; Cox et al., 2018). In relatively shallow regions, such as the Forth and Tay, the presence of wind turbines can increase water column mixing as well as the potential to reduce surface mixing by wind as less energy will be available after energy extraction (van Berkel et al., 2020). However, the Proposed Development is anticipated to have only a negligible to minor effect on physical processes such as tidal currents, wave climate and sediment transport both at project scale, and cumulatively with other nearby projects (see volume 2, chapter 7).
107. Suspended sediment was predicted to increase by up to 5% inside offshore wind farms and decrease by up to 5% outside offshore wind farms at the sea surface (Zijl et al., 2021). At the seabed, a decrease of up to 5 - 10% both inside and outside offshore wind farms was predicted in some areas. The effects of the 2050 scenario on suspended sediment is in the same order of magnitude as some large-scale interventions, such as large infrastructure developments, sand mining and the release of dredged material. Increases in suspended sediment could impact the foraging success of visual hunters, such as cormorant and shags. Changes in wind and water flows also increase available nutrients at the surface and could lead to an increase in average primary production in offshore wind farm areas, particularly during the spring phytoplankton blooms. However, increased suspended sediment in offshore wind farm areas could obstruct sunlight and reduce primary production, particularly in the pelagic zone. These complex, conflicting impacts could result in highly localised net increase or decrease of suspended sediment, depending on the local conditions, making it difficult to predict the outcome at small scales.
108. Approximately 48% of the Forth and Tay region is estimated to be highly disturbed from demersal fishing (Marine Scotland, 2020). This can increase the local suspended sediment, especially in environments with small particulates such as silt (O’Neill and Ivanoić, 2016). The area is also subject to extraction dredging, which can also increase suspended sediment, and has a large volume of river inputs which can influence turbidity (Marine Scotland, 2020). Whilst offshore wind farms may increase suspended sediments locally, this system naturally varies in turbidity due to its freshwater inputs, and other pressures such as fishing, and dredging also impact local suspended sediment levels (Marine Scotland, 2020). Additionally, the proposed array area is predominantly composed of slightly gravelly sand to gravelly sand, which has a low proportion of silt, with project-specific modelling showing only a localised, short-term increase in turbidity which, following the completion of the works, will return to baseline within a couple of tidal cycles. The Proposed Development is anticipated to have only a negligible to minor effect on the suspended sediment content at project scale, and cumulatively with other nearby projects at all phases of the development (see volume 2, chapter 7).
109. Zijl et al (2021) also predicted that currents could be reduced by up to 0.2m/s within offshore wind farms and increase or decrease in magnitude outside of offshore wind farms by up to 0.005m/s in the 2020 scenario, and 0.2 m/s in the 2050 scenario. Drag introduced by piles could decrease the tidal amplitude (the elevation of tidal high water above mean sea level). However, it is not clear how this could impact the marine food web.
110. Changes to physical processes resulting from offshore wind farm development and the addition of new hard substrates to the environment is predicted to impact benthic and pelagic communities differently. Telsnig Duffill et al (2018) used carbon and sulphur isotope analysis to determine the relative contribution of pelagic and benthic pathways to fish consumer production, including seabird prey species such as herring and mackerel, in the North Sea. Approximately 70% of fish biomass was linked to pelagic pathways, with only 30% linked to benthic systems. Mackerel and herring had the highest proportion of biomass from pelagic pathways of the 13 species studied. Increased transport of oxygen and nutrients to the seabed is likely to benefit benthic communities proportionally more than pelagic grazers such as zooplankton (Zijl et al., 2021). This could alter the competitive outcome of pelagic and benthic species, which could be detrimental to fish species that derive the majority of their biomass from pelagic sources like mackerel and herring. This could change the relative importance of various carbon and nutrient pathways through the marine food web and result in a fundamental altering of the functioning of the system.
111. Ongoing research into the impact of offshore wind farms on the environment includes the “Predators + Prey Around Renewable Energy Developments” (PrePARED) project. This Crown Estate Scotland and Offshore Wind Evidence and Change Programme (OWEC) funded project aims to facilitate rapid large-scale offshore wind deployment in the UK by improving understanding of cumulative environmental impacts and benefits from offshore wind farms on protected marine mammal and seabird populations. New evidence is being gathered to look at the relationship between predators and prey distribution and behaviour, in the context of offshore wind farms. The Firth of Forth is one of two case study areas, and studies here are focussing on the fish (predator and prey) landscape, including trophic interactions and reef effects, with an aim of using these data to inform existing assessment tools (e.g. SeabORD). Fish surveys (acoustic, trawl, cameras, baited traps and tagging) and seabird surveys (GPS tracking) are planned for Quarter 3 in 2022 - 2024 in the Firth of Forth. The project will run until early 2026. Also through OWEC, the “Ecological Consequences of Offshore Wind” (ECOWind) Programme awarded two further research projects in the Firth of Forth which will commence in in autumn 2022. The ECOWind programme aims to address two challenges: (1) how will offshore wind expansion, combined with other anthropogenic pressures, affect species interactions and marine ecosystems?; and (2) how can understanding these consequences enable robust approaches to marine environmental restoration and net environmental gain?  

6.4. Invasive non-native species

112. In the marine environment in Scotland, INNS include wireweed Sargassum muticum, green sea-fingers Codium fragile subsp. Tomentosoides, common cordgrass Spartina anglica, red alga Heterosiphonia japonica, acorn barnacle Austrominius modestus, Japanese skeleton shrimp Caprella mutica and leathery sea squirt Styela clava (NatureScot, 2022b). These can be introduced through a range of pathways, including through ballast water and attachment to ships and underwater equipment (NatureScot, 2022b), which has the potential to occur during offshore wind farm construction, operation and decommission. These species can outcompete native wildlife for space and food resources (NNSS, 2022). There is potential for INNS to compete with forage fish species and their prey species, which can consequently have wider implications on the food web, including on seabirds.
113. The introduction of offshore wind turbines into the marine environment also provides new opportunities for species previously unable to colonise due to habitat or prey constraints. The addition of hard substrate into areas previously lacking this habitat type can cause reef effects, which can lead to localised changes to marine environments (Petersen and Malm, 2006). Some species, such as green sea-fingers, can rapidly colonise disturbed habitats, increasing the importance of INNS control during coastal and offshore development, such as in offshore wind farm construction (NNSS, 2022). Climate change induced movement of species into new areas (such as those associated with movement of prey species and warmer SSTs) is likely to further increase the potential for invasive non-native species to inhabit offshore areas, such as in the North Sea.
114. Wind turbines may pose a relatively high risk of supporting INNS compared to other artificial structures, since they must be cleaned in situ and will be present in the environment for a relatively long time. Vessel traffic within offshore wind farms may also contribute significantly to the risk of INNS being introduced to an area, particularly if these vessels have come from elsewhere but with similar environmental conditions. Despite the potential, no INNS have been identified during post-construction monitoring at Beatrice Offshore Wind Farm in the Moray Firth (see Appendix 22, Annex 22.8). Shown to be effective at the Beatrice Offshore Wind Farm, these risks will be mitigated at the Project through the implementation of the INNS Management Plans. Considering the number of consented offshore wind farms in the vicinity of the Proposed Development, the risk of INNS may be higher than in other areas. In addition to this, relatively weak tidal currents in the area may increase the potential for colonisation by some species as larvae are able to settle out of the water column more easily. During site-specific surveys of the Proposed Development, no INNS were observed (see Appendix 22, Annex 22.8).
115. The potential for INNS to out-compete native species and reduce diversity could affect overall resilience and decrease ecosystem functioning (Roberts et al., 2017). The movement of intertidal species into offshore areas has up until recently, been relatively uncommon, generally only occurring around oil and gas installations, the number of which present in the marine environment has historically been far lower than what will be available upon the construction of the many proposed North Sea offshore wind farms likely to be developed over the next few decades (Kerckhof et al., 2011). Increased incidence of lower-trophic level intertidal and subtidal species on and around offshore wind turbines has the potential to affect which species comprise fish assemblages which will in turn, affect the seabird species which can utilise the area during foraging. Around some offshore wind farms fish species richness has been known to increase, in addition to changes to the dominant pelagic fish species (Ybema et al., 2009).

6.5. Mass mortality events

116. Mass mortality events (wrecks) are generally due to severe climatic conditions such as storms (particularly during winter) and results in unexpectedly high numbers of dead or dying seabirds washed up on beaches (Birkhead, 2014; Fort et al., 2015). Prolonged and harsh storms can affect birds’ foraging efficiency and therefore, energy balance, resulting in poor body conditions and potential death (Fort et al., 2015; Mitchell et al., 2020). Wrecks have been documented for years and more frequently across the world (Anker-Nilssen et al., 2016; Camphuysen, 2019; Pashby and Cudworth, 1969; Shepard, 2021). They were found to affect multiple groups of seabirds, such as alcids, shearwaters or petrels, mainly due to their smaller energy reserves (Fort et al., 2015; Glencross et al., 2021), especially along European coasts (Anker-Nilssen et al., 2017; Camphuysen, 2019).
117. The most recent wreck occurred between August and November 2021, when large numbers of auks, particularly guillemots, washed up on coasts across the North Atlantic, including coastlines in the vicinity of the Proposed Development. Autopsies were conducted on 179 carcasses washed up on the UK to determine their age, gender and body condition. All analysed birds were critically emaciated and weighed half their expected body weight, most were young, and no signs of disease such as HPAI were found. As has been documented for previous wrecks, the primary cause of mortality was determined to be starvation (Fullick et al., 2022). As British colonies primarily overwinter in the North Sea, it is thought that the majority of these birds have originated from British colonies. This is supported by the recovery of three ringed guillemot from the east coast of Scotland in the late summer of 2021 (SEAPOP, 2022).
118. Studies including post-mortems have been conducted to understand the potential additional causes of such wrecks, and although oil, plastic, mercury pollution and exhaustion were found, none were considered to be significant enough to cause the death of thousands of birds. Most studies attribute the wrecks to a combination of starvation and exhaustion, relating to poor weather conditions and reduced prey availability (Anker-Nilssen et al., 2017; Camphuysen et al., Heubeck et al., 2011; Morley et al., 2016). Increased extreme weather resulting from climate change could affect prey availability, weakening seabirds before strong winter storms (Camphuysen et al., 1999; 2019; Glencross et al.,2021), thus contributing to the frequency of wrecks occurring.

7. Role of offshore wind in tackling climate and biodiversity emergencies

119. Offshore wind has the potential to reduce climate change impacts by providing an alternative source of energy generation with lower emissions than traditional methods, which can be used alongside other renewable energy technologies such as solar (Cranmer and Baker, 2020). The addition of offshore wind farms in the marine environment provides solutions towards reaching long and short-term international energy goals (Diaz and Guedes Soares, 2020).
120. In 2020, Europe had a total installed offshore wind capacity of 25GW (WindEurope, 2021). As of the end of 2020, the UK had the highest cumulative capacity of grid-connected offshore wind power in Europe (WindEurope, 2021). This is set to rise with the addition of Round 4 and ScotWind leasing rounds and demonstrates the importance of offshore wind in the UK’s plan to meet net biodiversity gain targets (BEIS, 2020). Investing in offshore wind to provide alternative energy production is desirable, due to the reduced carbon footprint, lower visual impact compared to onshore sites, the relatively high mean wind speed and the higher associated capacity factors (Green and Vasilakos, 2011; Kaldellis and Apotolou, 2017; ORE Catapult, 2021).
121. Currently, positive effects of offshore wind farms are not readily considered outside of the comparison of carbon outputs compared to fossil fuel energy generation. There is potential for further positive effects from offshore wind farms, such as those associated with artificial reef habitats and the rapid implementation of compensatory measures towards a net-gain of biodiversity (RSPB, 2022). Comparison of the potential impacts on marine fauna attributed to climate change with immediate effects from energy generation in the marine environment would be beneficial.). There is a need to understand whole ecosystem responses of climate change and large-scale renewable developments, such as offshore wind, especially given the growth of offshore wind and increasing cumulative impacts. Further research is needed to predict, quantify, and separate possible ecological costs of changes due to climate change from those of large-scale renewable developments (Sadykova et al. 2018).
122. Predictions of ecosystem response to offshore wind and other anthropogenic drivers are limited by the lack of understanding of the drivers of ecosystem functioning, and how they interact collectively at different trophic levels. The majority of research focuses on the relationship between apex predators or commercially important species and their prey, or behaviour of protected species individually, without considering how they interact with other organisms of the same trophic level, or those in other trophic levels. Future research on predator-prey interactions, including PrePARED will improve the understanding of cumulative environmental impacts and benefits from offshore wind farms. The ECOWind project will also address knowledge gaps in how offshore wind expansion interacts with other anthropogenic pressures and affects the marine ecosystem which will be key to inform environmental restoration.

8. Future for seabirds: predicted climate change impacts

123. Under predicted climatic conditions, global ocean temperatures are expected to rise, with studies in the North Sea predicting an increase of approximately 3⁰C by 2100 (Schrum et al., 2016), in addition to other changes such as increased acidification and frequency of extreme weather events (Mitchell et al., 2020). Projections indicate rising ocean temperatures may alter marine food webs, including the quality, availability, and diversity of prey available to seabird populations (Mitchell et al., 2018) as previously discussed in section 6.1. The availability of phytoplankton to higher trophic level species supporting seabirds may be reduced with increased ocean acidification (Riebesell et al., 2013, Richier et al. 2014), possibly compounded by increased incidence of species targeting phytoplankton such as jellyfish, caused by increased ocean acidity, eutrophication and overfishing (Brotz et al., 2012; Báez et al., 2022).
124. Many seabird species occupy thermal niches, with preference for warmer or colder waters affecting the ability for species to cope with changes to ambient conditions. Seabird species favouring cooler water, such as puffin, kittiwake, great black-backed gull and herring gull are predicted to have an adverse response to climate induced increased water temperature (Searle et al., 2022), with a projected 67.9% decline in the abundance of puffins in the UK estimated (Johnston et al., 2013). Forecasting models predict that populations and distributions of seabird species such as kittiwake and auks, could be greatly reduced as a result of increasing sea temperature around the UK (Mitchell et al., 2020; Sadykova et al., 2020).
125. Climate change may cause large scale shifts in seabird distribution. In the North Sea, a northwards shift has been predicted for guillemot and razorbill, in addition to more substantial differences between summer and winter densities (Searle et al., 2022). Changes to the European range of UK seabirds are predicted to occur, with a decline in range expected for 65% of UK breeding seabird species (Russell et al., 2015). For guillemot, the future distribution in Europe is projected to overlap only 54-62% with the current distribution, and only 41% for razorbill (Huntley et al., 2007; Russel et al., 2015). Distributional changes linked to climate change predicted that several species such as Leach’s storm petrel Oceanodroma leucorhoa and some skua species could be extinct as breeding species in the UK by 2100 (Huntley et al., 2007; Russell et al., 2015). Huntley et al. (2007) also predicted that the Forth and Tay region will become climatically unsuitable for kittiwake, puffin and razorbill by 2100. Many seabird species are faithful to their breeding colonies potentially constraining their capacity to redistribute or expand their range in response to climate change (Mitchell et al., 2020).
126. Sadykova et al (2020) predicted the spatial trends of predators and prey species around the UK in 2050 under climate change scenarios. This study used Bayesian hierarchal joint models with integrated nested Laplace approximation (INLA) to predict future spatial density distributions of predators, including guillemot, kittiwake and gannet, and the prey species sandeel and herring. Gannet and guillemot were overall projected to increase in overlap with sandeels. Kittiwake were predicted to decrease in their spatial overlap with sandeel and herring which are key prey for the species. However, these models must be interpreted with caution, as they will more accurately reflect losses than they will gains, since the future projections are not constrained by the presence (or lack) of suitable breeding sites and sediment type for prey. They also do not consider the potential for increased inter- and intra- specific competition resulting from these shifts in spatial distribution.
127. As discussed in section 6.1.2, predicted northward shifts of lower trophic level species with climate change are likely to underpin changes in distribution of many seabird species in the North Sea (Lynam et al., 2017; McGinty et al., 2021). SST and salinity affect phytoplankton and zooplankton productivity, which can cascade along the food web through trophic mismatch and changes to prey availability due to mixing of the water column (Force et al., 2015; McGinty et al., 2021), possibly leading to less efficient energy and carbon transfer up to higher trophic levels (Lewandowska and Sommer, 2010). For some seabird species, such as kittiwake, spatial overlap with prey species is predicted to decrease by around 50% by 2050 (Sadykova et al., 2020). 
128. The European range of herring gull and lesser black-backed gull is projected to be reduced and to shift northwards, with their southern-most extent becoming climatically unsuitable (Huntley et al., 2007; Russel et al. 2015). Consequently, within the UK, gull populations have been generally predicted in to increase in response to warming climates in the UK, primarily related to their availability of prey (Johnston et al., 2021).
129. As discussed in section 6.1, the breeding success of many seabird species has been linked to primary consumer availability (Carroll et al., 2015), with the location of many seabird colonies in the North Sea correlated with areas of high zooplankton abundance (Fredriksen et al., 2013). Weaker, later stratification and lower SST has been associated with higher breeding success in kittiwake colonies across the UK, including at the Isle of May and St Abbs Head NNR (some of the closest monitored populations to the Proposed Development) (Carroll et al., 2015). Under climate change, stronger and earlier stratification is predicted, which contributes to a predicted 37.3% and 32.2% decline in breeding success for kittiwake at the Isle of May and St Abbs Head NNR, respectively, by 2070-2099 (Carroll et al., 2015). Puffin and kittiwake are expected to experience declines in productivity to the projection period of 2070-2099 and are unlikely to be able to increase their foraging range to compensate (Searle et al., 2022). The same is true for great black-backed gull across the same period. Searle et al (2022) predicted a decrease in population size, whereas Sadykova et al (2020) had greater uncertainty in their predictions, from -13.0 to +4.6% by 2050. Gannet productivity is expected to increase (Searle et al., 2022), which may be attributed to their flexibility in prey species and foraging strategy and the large predicted spatial overlap with potential prey species (Davies, 2012; Sadykova et al., 2020).  
130. Comparing the adverse effects of climate change and the presence of offshore wind farms on seabirds is challenging, due to the dynamic, complex nature of marine ecosystems (Scott, 2022). Whilst there is potential for adverse effects from offshore wind farms, adverse ecological effects relating to climate change are predicted to increase but may be reduced by renewable energy and have an overall positive effect on ecosystem health (Figure 8.1 ;Scott, 2022). In order to ensure the future of seabirds, a holistic, ecosystem-based approach is required, with a suite of restoration measures to address habitat modifications, disruption to food webs, remove invasive species and HPAI (RSPB, 2022). Reducing the pace and magnitude of climate change effects is an important factor in a holistic approach, with offshore wind development considered a key part of the solution (European Commission, 2020; ORE Catapult 2021; RSPB, 2022; Scottish Government, 2021).

Figure 8.1.  The ecological effects of climate change (represented in red) are increasing rapidly with time but is reduced by renewable energy. The comparative magnitude of effects from renewable industry in today’s climate is indicated in green (Scott, 2022).

131. As presented in this technical report, there is extensive evidence that climate change both directly and indirectly is having wide scale impacts on seabirds across the North Sea. Few studies have attempted to rank the significance of pressures on seabirds. Dias et al (2019) concluded that 20.5% of global seabirds are exposed to climate change impacts, compared with just 2.2% for energy production and mining, of which offshore wind is only one component. In the Forth and Tay region, auks and kittiwake are predicted to be particularly vulnerable to the impacts of climate change, both independently and in combination with other anthropogenic pressures ( Table 8.1   Open ▸ ; Burthe et al., 2014).

8.1. Assessment of anthropogenic pressures on key seabird species

132. The impacts on seabird populations due to changes such as climatic and prey availability (discussed in sections 5.1 and 6.1), outbreaks of HPAI (section 5.4) and mass mortality events such as experienced for auks in winter 2021/22 (section 6.1) could increase in severity and frequency. The development of offshore wind farms, such as the Project, is anticipated to make a significant positive contribution to reducing greenhouse gas emissions, contributing to reducing climate change impacts (section 7; Figure 8.1 ;Scott, 2022). Possible increases in prey availability around offshore wind farms may lead to decreased commuting and foraging time for seabirds, in addition to decreased stratification of the water column in the immediate vicinity of wind turbines, the opposite of which is predicted under current climatic predictions (De Deominicis et al., 2018; Scott, 2022).
133. The vulnerability of seabird communities in the Forth and Tay region to offshore wind development and climate change was considered by Burthe et al. (2014), together with a range of other threats including the indirect effects of commercial fisheries, disturbance, and pollution. Colony and at-sea seabird demographic data for 1980 – 2011 and SST data were analysed to understand seabird species vulnerability to climate change and to generate an index of population concern. Vulnerability to other threats was assessed qualitatively. The results of this study for the key seabird species present within the Proposed Development are summarised in Table 8.1   Open ▸ . The information presented in Burthe et al (2014) is supported by the literature review of the impacts of threats on seabirds in the previous sections of this report.

Table 8.1: A summary of the vulnerability of key seabird species to anthropogenic threats, their population status and the index of concern which takes into account the magnitude of vulnerability to the threats, the number of threats they are vulnerable to, their population status and their conservation status (Burthe et al., 2014).

8.1.1.    Gannet

134. Burthe et al. (2014) concluded that gannets were less vulnerable to climate effects, than the effects from fisheries and offshore wind farms. Gannets are predicted to be buffered from climate change effects due to their wide range of prey types, ability to forage long distances from the colony, and the ability to dive into the water column and so have access to prey at wider depths (Hamer et al., 2001; Johnston et al., 2021). Gannet at Bass Rock, near the Proposed Development, predominantly feed on sandeel and mackerel (Lewis et al, 2003), both of which are thought to be in decline in the North Sea, potentially due to climate change (Burrows et al., 2019; Clausen et al., 2017; Jansen et al., 2012; MacDonald et al., 2019). The ability of gannets to consume diverse prey types may allow them to exploit other species which currently occur in the area, or warm-water species such as horse mackerel which may increase in dominance with climate change (Burrows et al., 2019). They may also be able to take advantage of strong winds during adverse weather, making them more resilient to storms (Lane et al., 2019). This is consistent with Burthe et al. (2014), who concluded that gannet in the Forth and Tay area are highly resilient to climate change ( Table 8.1   Open ▸ ). Despite their vulnerability to displacement from offshore wind and fisheries, overall gannets were also predicted to be of low population concern to anthropogenic threats (Burthe et al., 2014). Additionally, there were no gannet bycatch offshore of the east cost of mainland Scotland, suggesting this is not a common threat to gannets specifically in the Proposed Development (Northridge, Kingston and Coram, 2020). 

8.1.2.    Guillemot

135. Burthe et al. (2014) concluded that guillemots were vulnerable to both climate effects, and anthropogenic threats; particularly disturbance. Votier et al., (2005) estimated a decline in guillemot populations with climate change from a weak association between guillemot and forage fish abundance and SST change, and from increasing stormy weather events at Skomer Island, Wales, and so may not be representative of the response of guillemot in the vicinity of the Proposed Development. Lahoz-Monfort et al. (2011) concluded that previous guillemot abundances could be partially explained by climate indicators (the North Atlantic Oscillation and SST).
136. Guillemot population abundance have been closely linked with the success of their prey species in a number of studies, both in the North Sea (e.g. Rindorf, Wanless and Harris, 2000; Frederiksen et al., 2006; Burthe et al., 2012) and further afield (e.g. Barrett and Erikstad, 2013; Erikstad et al., 2013; Lauria et al., 2012). Therefore, it is likely that the response of guillemot to indirect climate change effects, such as increasing SST, will be underpinned by their diet and the success of their prey (Johnston et al., 2021). As pursuit divers, guillemot are able to forage at a range of depths, which may make them more resilient to changes in prey availability and to climate change effects (Furness and Tasker, 2000; Johnston et al., 2021). In approximately the last 20 years, a shift from sandeel to sprat and herring has been observed in breeding guillemot at the Isle of May, which is located in the Firth of Forth (Wanless et al., 2018). This may be evidence of the ability of guillemot in the Firth of Forth area to adjust their target prey species in response to changing prey availability. However, guillemot are also vulnerable to storm events and are frequently are seen as part of wrecks (see Section 6.4 Mass Mortality Events). The combined impact of reduced prey availability from climate change and increased frequency of storms could lead to an increase of mortalities in guillemot, and an increase in wrecks featuring this species (Camphuysen et al., 2019; Harris and Wanless, 1996; Newell et al., 2015). Guillemots are also vulnerable to anthropogenic threats, including oil spills and fisheries bycatch ( Table 8.1   Open ▸ ; Burthe et al., 2014; Votier et al., 2005), which may be more significant pressures on abundances than those relating to climate change (Johnston et al., 2021).  

8.1.3.    Herring gull and lesser black-backed gull

137. Burthe et al., (2014) concluded that herring gull and lesser black-backed gull are less vulnerable to climate change than other threats. These gull species have been considered together here, due to the similarity of how they are affected by climate and anthropogenic pressures.
138. Whilst herring gull have been in decline and lesser black-backed gull populations have been unstable, it is predicted they will increase in Scotland in response to climate change pressures, because of their adaptability and generalist feeding nature (Burthe et al., 2014; Johnston et al., 2013; Johnston et al., 2021). However, management of fisheries discards and landfill, which have previously been important food sources for gulls, in the Forth and Tay region may be further detrimental to the foraging success of these species moving forward. Declines are also likely attributed to culling events, with 150,000 herring gull and lesser black-backed gull estimated to have been killed between 1970 and 1985, including 41,000 herring gulls on the Isle of May (Coulston, 2015). In Scotland, a licence has been required since 2010; however, there is limited information publicly available about licenced culls. However, an increase in lesser black-backed gulls in the 1990s on the Isle of May has been attributed to cessation of gull control measures (JNCC, 2021e). Both species are able to use urban environments for nesting, which makes them more resilient to nest failure relating to an increase in storm and flooding events, and increased competition for suitable nesting habitats, as well as pressures from coastal urbanisation (Balmer et al., 2013; Rock and Vaughan, 2013). The estimated decline in Scotland has coincided with distributional trends away from coastal areas towards inland and urban sites in both species (Balmer et al., 2013; JNCC, 2021d), where they may be more likely to be culled. Burthe et al., (2014) concluded that both species have high sensitivity to pressures from wind farms. Given the sensitivity of herring gull and lesser black-backed gull to the availability of human food sources, fisheries discards, disease and INNS, the success of populations in the Forth and Tay region may be more significantly influenced by these pressures than climate change (Burthe et al., 2014; Johnston et al., 2021).