20.7.4.              The Key Predator Species

  1. Volume 2, chapters 9, 10 and 11, provide details on the fish, marine mammals and seabirds which are most abundant in the associated topic Proposed Development study area and are the receptors most likely to be impacted by activities associated with all phases of the Proposed Development. From information on these receptors groups it is possible to ascertain which fish, seabird and marine mammals species are likely to be the key predators in the marine ecosystem in this part of the central North Sea and within the study areas outlined in section 20.1.3.

Piscivorous fish

  1. The key marine predatory fish likely to utilise the marine environment within the Proposed Development array area and Proposed Development export cable corridor are plaice, cod, haddock, whiting, saithe, pollark and European hake. The diet of these species includes small forage such as sandeel, juvenile whiting, juvenile haddock and small flounder. Elasmobranchs which are likely to be present and whose diet will also include small forage fish include tope, spurdog, common skate and rays.
  2. The migration routes of diadromous fish species which also feed on small forage fish, and which are likely to pass through the Proposed Development area during migration (volume 3, appendix 9.1) are sea trout, European eel, sea lamprey, twaite shad, allis shad and Atlantic salmon.
  3. Table 20.19   Open ▸ lists the key predatory fish species and the prey they feed on. This shows that although sandeel, herring, mackerel and sprat are components of most of the key predators’ diets, other fish as well as other benthic fauna are also important in their diet.

 

Table 20.19:
Key Predatory Fish Species and their Prey

Table 20.19: Key Predatory Fish Species and their Prey

 

Marine mammals

  1. The key marine mammal species which are most abundant within and therefore have the potential to be impacted by the Proposed Development are:
  • harbour porpoise;
  • bottlenose dolphin;
  • white-beaked dolphin Lagenorhynchus albirostris;
  • minke whale Balaenoptera acutorostrata;
  • harbour seal; and
  • grey seal.
    1. These species also correspond to the marine mammal IEFs identified in volume 2, chapter 10. The sensitivity of marine mammals to prey availability within the Proposed Development array area and Proposed Development export cable corridor will be affected by how important this area is to the species and how sensitive they are to prey availability. This is discussed further in section 20.7.10.
    2. A summary of the dietary preferences of key marine mammal species within the Proposed Development marine mammal study area is presented in Table 20.20   Open ▸ .

 

Table 20.20:
Diet and Abundances of the Key Marine Mammal Species

Table 20.20: Diet and Abundances of the Key Marine Mammal Species

 

Seabirds

  1. The key seabird species which are most abundant (listed in abundance order) and most likely to be impacted by the Proposed Development (volume 2, chapter 11) are:
  • common guillemot;
  • black-legged kittiwake;
  • razorbill;
  • northern gannet;
  • Atlantic puffin;
  • European herring gull; and
  • lesser black-backed gull.
    1. Seabird species diet and foraging behaviour determine the extent to which individual species can respond to changing prey availability. This is discussed further in section 20.7.10. A summary of the typical feeding strategies and prey species of key seabird species that have the potential to be impacted by the Proposed Development has been outlined in Table 20.21   Open ▸ .

 

Table 20.21:
Diet and Feeding Strategies of the Key Seabird Species

Table 20.21: Diet and Feeding Strategies of the Key Seabird Species

 

20.7.5.              The Key Prey Species

  1. The key fish and shellfish prey species likely to be present within the Proposed Development fish and shellfish study area, within the central North Sea marine ecosystem, are the small shoaling forage fish sandeel, herring, European sprat Sprattus sprattus (hereafter ‘sprat’) and Atlantic mackerel Scomber scombrus (hereafter ‘mackerel’). Volume 2, chapter 9, identified that these four fish species are IEFs, which are species that are considered to be important and could be potentially impacted by the Proposed Development. The abundance of each of these species within the Proposed Development fish and shellfish study area and their relative importance to predators is discussed in the species summaries below.

Sandeel

  1. Sandeel are small eel like fish which feed primarily on plankton of variable size, ranging from small plankton eggs up to larger energy rich copepods found in great abundance in Scotland’s seas (NatureScot, 2022).
  2. There are five species of sandeel found in Scottish waters with lesser sandeel Ammodytes tobianus and Raitt's sandeel Ammodytes marinus being the most commonly recorded species, particularly in the vicinity of the Proposed Development fish and shellfish ecology study area.
  3. As well as being abundant in Scottish waters, sandeel are highly nutritious and are therefore the preferred prey item for many other species of fish, seabirds, seals, whales and dolphins. As they feed on plankton and are eaten by larger marine predators such as cod, harbour porpoise and kittiwake, sandeel represent an important link between the lower and upper levels of the marine food web (NatureScot, 2022).
  4. Lesser sandeel and Raitt’s sandeel are listed as PMFs in Scottish waters and are listed as protected features within the Turbot Bank Nature Conservation MPA, which overlaps within the Proposed Development northern North Sea fish and shellfish ecology study area.
  5. Sandeel have a close association with sandy substrates into which they burrow. They are largely stationary after settlement and show a strong preference to specific substrate types (volume 3, appendix 9.1).
  6. As described in volume 2, chapter 9 and volume 3, appendix 9.1, sandeel have been identified as likely to be present in the Proposed Development array area and Proposed Development export cable corridor, based on historic data and habitat preference. The wider Forth and Tay Scottish Marine Region (SMR) has been known historically to support important sandeel populations. The highest density of this population is focused on the Wee Bankie, however sandeel do range across much of the wider North Sea.
  7. Modelled predicted density and probability of occurrence of sandeel around the British Isles (Langton et al., 2021) and site specific survey of the Proposed Development indicate that much of the Proposed Development Array area is predominantly sandeel preferred habitat. The Proposed Development export cable corridor has a significant patch of unsuitable sandeel habitat which corresponds to an area of largely muddy sediment (see volume 3, appendix 9.1).

Herring

  1. Herring is a small shoaling forage fish which is a commercially important pelagic fish, common across much of the North Sea. Herring filter feeds on plankton and minute sea creatures, but will also take very small sprats and fry of other fish (British Sea Fishing, 2022).
  2. Herring nursery grounds are also widespread along the east Scottish and Northumberland coastlines (Ellis et al., 2012), with post larvae juveniles up to sub adults that are yet to reach sexual maturity feeding in these areas until migrating to feeding grounds further offshore where they remain until reaching sexual maturity (International Council for the Exploration of the Seas (ICES), 2006).
  3. Herring is an important prey species for larger fish, birds and marine mammals and is listed as a PMF in Scottish waters.
  4. Herring utilise specific benthic habitats during spawning, which increases their vulnerability to activities impacting the seabed. Further, as a hearing specialist, herring may be vulnerable to impacts arising from underwater noise.
  5. Herring deposit eggs on a variety of substrates from coarse sand and gravel to shell fragments and macrophytes, although gravel substrates have been suggested as their preferred spawning habitat. Once spawning has taken place (the peak spawning months being August and September for the Buchan stock), the eggs take approximately three weeks to hatch after which the larvae drift in the plankton (Dickey-Colas et al., 2010).
  6. North Sea herring fall into a number of different ‘races’ or stocks, each with different spawning grounds, migration routes and nursery areas (Coull et al., 1998). North Sea autumn-spawning herring have been divided into three, mainly self-contained stocks — the Buchan, Dogger, and Downs herring groups, which show differences in spawning areas and spawning periods. The Buchan stock which spawn between August and September off the Scottish east coast are most relevant to the Proposed Development.
  7. Herring spawning grounds are most accurately mapped using a combination of herring larval data and sediment particle size analysis (PSA), as recommended by Boyle and New (2018).
  8. Habitat suitability classifications for herring spawning, based on site-specific data (grab sampling undertaken as part of benthic subtidal surveys – volume 3, appendix 9.1), shows that the majority of the Proposed Development fish and shellfish ecology study area has unsuitable sediment for herring spawning, with a small patch of suitable habitat in the north-west section of the Proposed Development array area (volume 3, appendix 9.1, Figure 4.8).
  9. Herring have high intensity nursery areas throughout the Proposed Development fish and shellfish ecology study area, with spawning grounds to the south which overlaps very slightly with the Proposed Development export cable corridor (see volume 3, appendix 9.1, Figure 4.6) and more extensive spawning grounds to the north along the Aberdeenshire coast. The presence of high intensity nursery grounds for herring within the Proposed Development fish and shellfish study area is not supported by outputs from Aries et al. (2014), with predicted aggregations of zero group herring found further inshore (see volume 3, appendix 9.1).

Sprat

  1. Sprat is a small shoaling forage fish which occurs all around the UK and can be found in water depths from a few metres to approximately 100 metres.
  2. Sprat feed predominantly on fish eggs, larvae and plankton (volume 2, chapter 9).
  3. Sprat are a major part of the marine food chain in the North Sea, as they provide a source of food for more or less all predatory fish found in UK waters. They are also an important source of food for marine mammals and seabirds such as gannets and herring gulls.
  4. As described in volume 3, appendix 9.1, sprat have relatively high abundance within the fish and shellfish study area, where thousands of individuals were frequently recorded per hour trawled (volume 3, appendix 12.1). However, the abundances recorded were found to be quite sporadic, with low numbers being recorded frequently. There are no obvious differences in seasonal or age distribution of individuals recorded.
  5. Sprat spawning and nursery grounds (unspecified intensity) coincide with the Proposed Development fish and shellfish ecology study area, with only nursery grounds coinciding with the offshore export cable route (see volume 3, appendix 9.1, Figure 4.5). The presence of sprat nursery grounds within the fish and shellfish study area is not supported by outputs from Aries et al. (2014), with aggregations of 0 group fish seemingly limited to areas further inshore from the Proposed Development array area within the inner regions of the Firth of Forth (see volume 3, appendix 9.1).

Mackerel

  1. Mackerel are small, fast, predatory fish closely related to tuna (Thunnini sp.) which hunt in vast shoals for small fish and sandeel
  2. Mackerel are important prey species for larger fish, birds and marine mammals and are listed as a PMF in Scottish waters (NatureScot, 2020).
  3. Mackerel are migratory and are common throughout the UK, arriving in spring and early summer, when they will feed actively before they migrate to warmer seas in the autumn months to spawn, during which time they will feed little.
  4. Mackerel appear to be arriving in UK waters earlier and leaving later every year, possibly as a result of rising sea temperatures. In some locations around the south of the UK, mackerel are now only absent during the winter months.
  5. They have no swim bladder which means they can change depth rapidly and must keep moving all of the time (British Sea Fishing, 2022).
  6. As described in volume 3, appendix 9.1, recorded abundance of mackerel within the fish and shellfish study area was low during 2020 Q1, however higher abundances were recorded during Q3, and also in Q1 of 2021. This suggests that presence of mackerel in the northern North Sea can vary annually and can be sporadic, as shown by a particular haul capturing over 246,000 mackerel per hour trawled, with other hauls recording very few or no mackerel per hour trawled (volume 3, appendix 12.1).
  7. Mackerel have low intensity nursery grounds which coincide with the majority of the Proposed Development fish and shellfish ecology study area (Ellis et al., 2012), with no spawning grounds identified in the Proposed Development fish and shellfish ecology study area (see volume 3, appendix 9.1, Figure 4.5). Mackerel spawn over summer months from May to August. The presence of mackerel nursery grounds within the fish and shellfish study area is not supported by outputs from Aries et al. (2014), with no modelled observations of 0 group fish on the east coast of Scotland (see volume 3, appendix 9.1).

20.7.6.              How the Whole Food Chain Operates

  1. The flow of energy moves up the trophic levels of a food chain starting at the bottom level where producers such as phytoplankton and algae in the marine environment make their own food by harnessing the energy of the sun through the process of photosynthesis. The next level in the food chain, the primary consumers such as zooplankton, feed on the phytoplankton to gain energy and energy continues to be transferred up the food chain through each trophic level to the top predators.
  2. Typically, the marine environment follows a ‘wasp-waist’ trophic structure, where mid-trophic level species have lower diversity, compared to high diversity in both high and low trophic levels. These mid-trophic level species play an important role in ecosystem functioning (Rice, 1995). As discussed in section 20.7.5. the main prey species are sandeel, herring, mackerel and sprat. These fish link the lowest trophic levels to the highest (Mackinson and Daskalov, 2007; Fauchald et al., 2011; Lynam et al., 2017).
  3. Phenology plays an important role in how the food chain operates because many species have evolved elaborate behavioural and life history strategies that exploit favourable periods of the year for growth and reproduction and minimise exposure of sensitive life stages to stressful periods (Rubao et al., 2010). Changes in phenology brought about by climate change, can affect the lowest trophic levels, which comprise plankton, and these effects can cascade up the food web and effect mid-trophic level species such as sandeel which can in turn effect top trophic level species such as seabirds (Burthe et al., 2012; Lynam et al., 2017). This is discussed further in section 20.7.8.
  4. Section 20.7.4. described the key fish, seabird and marine mammal predator species and their typical prey species. From this it is possible to see that whilst sandeel, herring, mackerel and sprat are components of most these predators’ diets, they vary in their importance. For example, kittiwake are more reliant on sandeel than the other key seabird species potentially present within the Proposed Development study areas, and therefore will be more sensitive to changes in prey availability and the distribution of sandeel. This is discussed further in section 20.7.10.

20.7.7.              Future Ecosystem Baseline

  1. The EIA Regulations (as defined in volume 1, chapters 1 and 2) require that a "a description of the relevant aspects of the current state of the environment (baseline scenario) and an outline of the likely evolution thereof without development as far as natural changes from the baseline scenario can be assessed with reasonable effort, on the basis of the availability of environmental information and scientific knowledge" is included within the Offshore EIA Report.
  2. In the event that the Proposed Development does not come forward, an assessment of the future baseline conditions has been carried out and has been described within the topic chapters (volume 2, chapters 7 to 11) and are summarised in paragraphs 169 to 173.

Climate change effects

  1. The baseline environment for the physical and biological components of the ecosystem are not static and will exhibit a degree of natural change over time. Such changes will occur with or without the Proposed Development in place due to natural variability. Future baseline conditions would be altered by climate change resulting in sea level rise and increased storminess. In terms of physical processes, this is unlikely to have the effect of significantly altering tidal patterns and sediment transport regimes offshore at the Proposed Development array area. The return period of the wave climates would be altered (e.g. what is defined as a 1 in 50 year event may become a 1 in 20 year event) as deeper water would allow larger waves to develop. There is, however, a notable degree of uncertainty regarding how future climate change will impact prevailing wave climates within the North Sea and beyond.
  2. UK waters are facing an increase in sea surface temperature. The rate of increases is varied geographically, but between 1985 and 2009, the average rate of increase in Scottish waters has been greater than 0.2 °C per decade, with the south-east of Scotland having a higher rate of 0.5°C per decade (Marine Scotland, 2011). A study completed over a longer period of time showed Scottish waters (coastal and oceanic) have warmed by between 0.05 °C and 0.07 °C per decade, calculated across the period 1870 – 2016 (Hughes et al., 2018).
  3. Changes in temperature will affect fish at all biological levels (cellular, individual, population, species, community and ecosystem) both directly and indirectly. As sea temperatures rise, species adapted to cold water (e.g. cod and herring) will begin to disappear while warm water adapted species will become more established. It is also predicted that due to changes in weather patterns, for example increased numbers of spring storms, changes in stratification of water columns and plankton production may occur (Morison et al., 2019). This may cause knock on effect to fish and shellfish species due to changes in food availability for prey species. Climate change presents many uncertainties as to how the marine environment will change in the future; therefore, the future baseline scenario is difficult to predict with accuracy.
  4. The biological environment baseline (including benthic and intertidal ecology, fish and shellfish, marine mammals and seabirds) is not static and will exhibit some degree of natural change over time, even if the Proposed Development does not come forward, due to naturally occurring cycles and processes and additionally any potential changes resulting from climate change and anthropogenic activity. Therefore, when undertaking assessments of effects, it will be necessary to place any potential impacts within the context of the envelope of change that might occur over the timescale of the Proposed Development.
  5. The impact of climate change on harbour porpoise remains poorly understood. Macleod et al. (2005) reported that there has been a decline in the relative frequency of white-beaked dolphin strandings and sightings in north-west Scotland and attributed climate change as a major cause of this decline.

20.7.8.              Exisitng Pressures on Prey Species

  1. Before assessing the potential effects of the Proposed Development on prey species at an ecosystem level, it is important to understand the existing pressures on prey species.
  2. As described in volume 3, appendix 20.1, the North Sea is one of the most anthropogenically impacted marine ecosystems (Halpern et al., 2015; Emeis et al., 2015). Small, shoaling forage fish in mid-trophic levels experience top-down pressure from commercial fisheries (volume 3, appendix 20.1, Figure 4.1), whilst bottom-up processes driven by temperature, have dominated changes to planktonic groups since the 1960s. These pressures propagate up and down the food chain, with mid-trophic fish linking the pressures between the upper and lower trophic levels (Lynam et al., 2017).
  3. 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). In the past, sandeel have been commercially important, targeted by industrial fisheries in the North Sea for their oil and use as an animal feed and fertiliser. Despite being highly managed, the majority of sandeel stocks have experienced severe declines, thought to have been brought about by a combination of overfishing and the effects of climate change (Nature Scot, 2022).
  4. As described in volume 3, appendix 9.1, in the early 1990s there was a substantial industrial sandeel fishery on the Wee Bankie, Marr Bank and Berwick Bank sandbanks. In 2000, this industrial sandeel fishery was closed in response to concerns that the fishery was having a deleterious effect on sandeel stocks within the Forth and Tay (SMR).
  5. After the Forth and Tay SMR sandeel fishery closed, high levels of recruitment, combined with a lack of any significant fishing activity resulted in an immediate and substantial increase in the biomass of sandeel on the Wee Bankie sandbank. However, since 2001, sandeel biomass has steadily declined to levels that were similar to those observed when the sandeel fishery was active (Greenstreet et al., 2010). More recently sandeel stocks have recovered leading to an increase in sandeel fishing adjacent to the closed area. However, ICES recently stated "The escapement strategy [by which sandeel stocks are managed] is not sustainable for short-lived species unless the strategy is combined with a ceiling (Fcap) on fishing mortality" (ICES, 2022).
  6. As described in volume 3, appendix 9.1, herring is a commercially important pelagic fish and has a relatively large fishery; the most recently published figures (2020) for herring in the North Sea (ICES Area IVa to IVc) landed by Scottish vessels was 46,742 tonnes with a value of £26,078,000 (Scottish Government, 2020a).
  7. Herring stocks in the North Sea crashed as a result of overfishing in the latter part of the 20th century. Although there has since been a recovery, active management is required to prevent a recurrence (Dickey-Collas et al., 2010). A herring recovery plan to reduce fishing mortality was implemented in 1996 for the North Sea and was revised in 2004. Although this was considered generally successful, it was not as successful for those herring stocks found in the northern North Sea. A ban on discards for pelagic fisheries such as herring commenced on 1 January 2015.
  8. The prey species present in the marine ecosystem within which the Proposed Development occurs, are also an important food source for larger fish. For example, plaice, cod, haddock, whiting, saithe, tope and spurdog all include prey forage fish species in their diet such as sandeel, herring, sprat and mackerel. Additionally, diadromous fish species which migrate between the sea and freshwater are also likely to feed on these species. Volume 2, chapter 9, identified the following diadromous species are likely to migrate through the Proposed Development fish and shellfish ecology study area: Atlantic salmon Salmo salar, sea trout salmo trutta, European eel Anguilla anguilla, sea lamprey Petromyzon marinus, twait shad Alosa fallax and allis shad Alosa alosa.
  9. As described in volume 3, appendix 20.1, 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).
  10. Declines in abundance and quality of mid-trophic level-species, such as forage prey species, have been linked to multiple factors, including rising sea surface temperature (SST), changes in stratification and alterations in the North Atlantic Oscillation (Johnston et al., 2021).
  11. The ability of fish species to move in response to temperature varies depending on a range of factors, including their physiological capacity to acclimatise and respond to the change as well as their degree of geographical attachment or how their prey respond. Where a species has a strong geographical attachment, the result can be a localised decline in species (Wright et al., 2020).
  12. As described in volume 3, appendix 20.1, sandeel are one of the most important trophic links between plankton and predators in North Sea ecosystems; however, climate driven changes to phytoplankton and zooplankton 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). Factors such as rising SST may have altered the phenology, abundance and distribution of many species, with a switch in the dominant zooplankton species in the North Sea and northwards shift in distribution for multiple fish species such as sandeel and sprat (Burthe et al., 2012).
  13. Climate change impacts on sandeel will be influenced both directly through their metabolic rate and indirectly via their planktonic prey (MCCIP, 2018).
  14. Changes in temperature can have a large impact on the metabolic rate of sandeel, which can in turn affect the success of their reproduction and increase their mortality rate (NatureScot, 2022). Increased temperatures have been observed to cause inhibited gonad development in sandeel, which means warmer seas can delay the spawning time and lead to reduced reproductive success (Wright, Orpwood and Scott, 2017). Adult sandeel feed on zooplankton 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).
  15. A key factor in sandeel larval success is synchrony between the larval hatching times and the spring zooplankton bloom. Through impacts on gonad development, warming is expected to lead to later larval hatch times and earlier zooplankton blooms, resulting in a decrease in zooplankton available for sandeel to feed upon and a reduction in sandeel growth and survivorship, leading to low recruitment (Réginer, Gibb and Wright, 2017).
  16. The life cycle of sandeel ties them to sandy sediments of a particular grain size which they burrow into at night and during the winter months. This means that their ability to move and redistribute to new suitable habitats in response to rising sea temperature relies on larval distribution (Macdonald et al., 2015).
  17. Herring are also constrained as demersal spawners, by their requirement to spawn at specific locations, depositing their sticky eggs on coarse sand, gravel, small stones and rocks (Wright et al., 2020).
  18. Additionally, there is an increasing body of research into the effect of ocean acidification on fish physiology and early survival (Wright et al., 2020). As described in volume 3, appendix 20.1, climate change is 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 (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).

20.7.9.              Effects of the Proposed Development on Prey Species

  1. This section assesses the impacts of the Proposed Development on prey species and any impacts on physical processes which may impact prey species indirectly by altering their availability to food sources such as plankton and zooplankton.
  2. Information to support this assessment has been taken from the relevant receptor topic Offshore EIA Report chapters. Each assessment of an impact focuses on the prey species most vulnerable to the impact to explain the maximum adverse scenario without repeating all the detail from the original receptor topic chapter. For example, where sandeel and/or herring are the most sensitive prey species to a given impact, details are provided for these species only.

Potential impacts on prey species

  1. Volume 2, chapter 9, identified that the following potential impacts as a result of the Proposed Development could result in positive/negative effects on fish and shellfish ecology:
  • temporary habitat loss/disturbance;
  • increased suspended sediment concentrations (SSC) and associated sediment deposition;
  • injury and/or disturbance to fish and shellfish from underwater noise and vibration;
  • long-term subtidal habitat loss;
  • EMFs from underwater electrical cabling; and
  • colonisation of foundations, scour protection and cable protection.
    1. Of these potential impacts, the first five were assessed as having minor adverse effects on marine fish (including prey species), which would not result in a significant change to prey species populations. A summary of the assessment of these impacts is provided in the following sub-sections.
    2. The final impact, colonisation of foundations, scour protection and cable protection, has the potential to affect numbers of prey species and predators and so is described in more detail, drawing on the findings of volume 2, chapters 8, 9 and 10.
Temporary habitat loss/disturbance
  1. As discussed in volume 2, chapter 9, in general, mobile fish species are able to avoid areas subject to temporary habitat disturbance. Of the key prey species, sandeel and herring are most sensitive to temporary habitat loss because they spawn on or near the seabed sediment. However, the assessment concluded that sandeel populations would recover quickly from any adverse effects following construction and due to the limited overlap of seabed disturbance with suitable herring spawning habitat in the Proposed Development fish and shellfish study area, there would be minor effects on herring and sandeel, which are not significant in EIA terms.
Increased SSC and associated sediment deposition
  1. As stated in volume 2, chapter 9, the prey fish species most likely to be affected by sediment deposition are sandeel and herring because they spawn on the seabed. However, sandeel eggs are likely to be tolerant to some level of sediment deposition, due to the nature of re-suspension and deposition within their natural high energy environment. Therefore, effects on sandeel spawning populations are predicted to be limited. Sandeel populations are also sensitive to sediment type within their habitat, preferring coarse to medium sands and showing reduced selection or avoidance of gravel and fine sediments (Holland et al., 2005). However, modelled sediment deposition levels are expected to be highly localised (within metres) and at very low levels (less than 10 mm).
  2. It has been shown that herring eggs may be tolerant of very high levels of SSC (Messieh et al., 1981). Any deposited sediment which could result in smothering would be expected to be removed quickly by currents (i.e. within a couple of tidal cycles) with a very small amount of sediment deposition being forecast. Furthermore, there is a relatively limited amount of suitable sediments for herring spawning and the mapping of the core herring spawning habitats are well outside the Proposed Development fish and shellfish ecology study area, which would also limit the potential for effects on herring spawning.
Injury and/or disturbance to fish and shellfish from underwater noise and vibration
  1. As discussed in volume 2, chapter 9, injury and/or mortality for all prey fish species is to be expected for individuals within very close proximity to piling operations. However, this is unlikely to result in significant mortality due to soft start procedures allowing individuals in close proximity to flee the area prior to maximum hammer energy levels.
  2. Behavioural effects are expected over larger ranges. Herring are known to be particularly sensitive to underwater noise and have specific habitat requirements for spawning which makes them particularly vulnerable to impacts associated with construction related increases in underwater noise. However, noise modelling indicated minimal overlap of mapped underwater noise contours with core herring spawning grounds, and where there is an overlap, the noise levels are considerably lower than levels expected to result in behavioural effects.
Long-term subtidal habitat loss
  1. As discussed in volume 2, chapter 9, long-term habitat loss will occur within the direct footprint of wind turbine and OSP/Offshore converter substation platform foundations, associated scour protection and cable protection (including at cable crossings) where this is required. However, the area of habitat loss equates to a small proportion (0.7%) of the Proposed Development fish and shellfish study area. Of the prey fish species, sandeel are particularly sensitive to this impact because they have specific habitat requirements (i.e. sandy sediments) for spawning and for burrowing in at night and through the winter. Whilst sandeel were assessed to have medium sensitivity to this impact, given the relative small area potentially impacted (0.7%), significant effects are not predicted.
  2. Herring are also sensitive to this impact due to their demersal spawning requirement; however herring were assessed as having low sensitivity due to the limited suitable spawning habitat overlapping with the Proposed Development fish and shellfish ecology study area.
EMFs from electrical underwater cabling
  1. As discussed in volume 2, chapter 9, and the Berwick Bank Wind Farm Marine Protected Area Assessment (SSER, 2022b), the presence and operation of inter-array, interconnector and offshore export cables within the Proposed Development fish and shellfish ecology study area may result in emission of localised EMFs which may affect some fish species. It is common practice to block the direct electrical field (E) using conductive sheathing, meaning that the EMFs that are emitted into the marine environment are the magnetic field (B) and the resultant induced electrical field (iE). Fish species (particularly elasmobranchs) are able to detect applied or modified magnetic fields. However, the rapid decay of the EMF with horizontal distance (i.e. within metres) minimises the extent of potential impacts. A study investigating the effect of EMF on lesser sandeel larvae spatial distribution found that there was negligible effect on the larvae (Cresci et al., 2022), and a further study concluded the same for herring (Cresci et al.,2020). Overall, the assessment concluded the effect on all fish species (including prey species) would not be significant.
Colonisation of foundations, scour protection and cable protection
  1. Volume 2, chapters 8 and 9 discussed how the introduction of infrastructure within the Proposed Development array area and Proposed Development export cable corridor may result in the colonisation of foundations, scour protection and cable protection. Since these hard structures are added to areas typically characterised by soft, sedimentary environments, the resulting change of habitat type acts like an artificial reef and the impact is known as the ‘reef effect’.
  2. The reef effect has the potential to adversely affect existing biological soft sediment communities but also have some potentially beneficial effects on the marine ecosystem.
  3. A review by Degraer et al (2020) explained the process by which wind turbine foundations are colonised, and the vertical zonation of species that can occur. Installation of an offshore wind farm is typically followed by rapid colonisation of all submerged parts by biofouling organisms. Vertical zonation can be observed on wind turbine foundations with different species colonising the splash, inter-tidal, shallow and deeper subtidal zones. In general, biofouling communities on offshore installations are dominated by mussels, macroalgae, and barnacles near the water surface, essentially creating a new intertidal zone; filter feeding arthropods at intermediate depths; and anemones in deeper locations (De Mesel et al., 2015). Colonisation by these species will likely represent an increase in biodiversity and a change compared to if no hard substrates were present (Lindeboom et al., 2011).
  4. As stated in volume 2, chapter 8, this may produce some potentially beneficial effects such as:
  • an increase in biodiversity and individual abundance of reef species and total number of species over time, as has been observed at the monopile foundations installed at Lysekil research site (a test site for offshore wind-based research, north of Gothenburg, Sweden) (Bender et al., 2020);
  • structural complexity of the substrate may provide refuge as well as increasing feeding opportunities for larger and more mobile species; and
  • a higher food web complexity associated with zones where high accumulation of organic material is present such as soft substrate or scour protection, suggesting potential reef effect benefits from the presence of the hard structures, as was observed in a study of gravity based foundations in the Belgian part of the North Sea (Mavraki et al. 2020).
    1. Colonisation of the wind turbine foundations, associated scour protection and cable protection may have indirect adverse effects on baseline communities and habitats due to increased predation on, and competition with, the existing soft sediment species. These effects are difficult to predict, especially as monitoring to date has focused on the colonisation and aggregation of species close to the foundations rather than broad scale studies.
    2. Some studies (De backer et al. 2020; Hutchison et al 2020; Apem, 2021) have also shown that the installation and operation of offshore wind farms has a negligible impact on the soft sediment environments. For example:
  • De Backer et al. (2020) found that eight to nine years after the installation of C-power and Belwind offshore wind farms (offshore Belgium) the soft sediment epibenthos underwent no drastic changes; and the species originally inhabiting the sandy bottom were still present and remained dominant in both wind farms;
  • a review of monitoring from Block Island wind farm in the United States showed no strong gradients of change in sediment grain size, enrichment, or benthic macrofauna within 30 m to 90 m distance bands of the wind turbines (Hutchison et al., 2020); and
  • the most recent benthic post-construction monitoring data of wind turbine foundations from Beatrice offshore wind farm (APEM, 2021) found foundation colonisation of wind turbines has resulted in zonation on the foundation itself but had little influence on the sedimentary habitat below.
    1. As described in volume 2, chapter 8, the maximum design scenario of habitat creation due to the installation of jacket foundations, associated scour protection and cable protection associated with inter‑array cables, OSPs/Offshore convertor substation platforms, interconnector cables and offshore export cables equates to 0.70% of the Proposed Development benthic subtidal and intertidal ecology study area. This value is likely an over estimation of habitat creation as it has been calculated assuming the foundations were a solid structure. In reality the jacket foundations will have a lattice design rather than a solid surface, which would result in a smaller surface area. It is expected that the foundations and scour and cable protection will be colonised by epifaunal species already occurring in the benthic subtidal and intertidal ecology study area (e.g. tunicates, bryozoans, mussels and barnacles which are typical of temperate seas).
    2. The Firth of Forth Banks Complex (FFBC) MPA overlaps with the Proposed Development array area and Proposed Development export cable corridor and therefore some habitat creation and colonisation of hard structures will occur within the FFBC MPA (SSER, 2022b). Based on the maximum design scenario for the Proposed Development, new habitat for colonisation equates to 0.13% of the FFBC MPA.
    3. As discussed in volume 2, chapter 8, where scour and cable protection are deployed, use of smaller rock sizes, where reasonably practicable at the time of operation and maintenance, may facilitate the colonisation of rock protection by epifaunal species typical of coarse sediment which are found within the Proposed Development export cable corridor. Previous studies have shown that for artificial hard substrate to be colonised by a benthic community similar to that of the baseline, its structure should resemble that of the baseline habitat as far as reasonably practicable (Coolen, 2017). The addition of smaller grained material to scour/cable protection may therefore be of some benefit to the native epifaunal communities (Van Duren et al., 2017; Lengkeek et al., 2017).
    4. Additionally, the designed in measures regarding the suitable implementation and monitoring of cable protection will ensure that no more than the declared amount of new hard substrate habitat is created and that any buried infrastructure remains so and does not impede upon the surface sedimentary habitat (volume 2, chapter 8, Table 8.16).
    5. Volume 2, chapter 8, concluded that although the sensitivity of benthic ecology IEFs to this impact was high, the magnitude of the effect would be low and therefore overall, the effect on benthic ecology was not predicted to be significant in EIA terms.
    6. The Berwick Bank Wind Farm MPA Assessment Report (SSER, 2022b), concluded that whilst the installation of hard structures will result in the loss of some sedimentary habitat directly below it and with a small radius around it, the remaining sedimentary habitat will not be continually degraded and will largely remain unchanged as a result of the introduction and colonisation of hard substrate. There may be some benefits for species which prefer hard substrates as a result of the reef effect, but this is unlikely to affect species which inhabit the offshore subtidal sands and gravels. The Applicant is committed to engaging in discussions with Marine Scotland and the Statutory Nature Conservation Bodies (SNCBs) to identify, and input to, strategic benthic monitoring of the colonisation of hard structures and impacts to surrounding soft sediments across wind farms off the east coast of Scotland, if available and proposed by Marine Scotland.
    7. As discussed in volume 2, chapter 9, the introduction of hard substrates can have indirect and direct effects on fish as follows:
  • indirect effects on fish through the potential of the reef effect to bring about changes to food resources; and
  • direct effect on fish through the potential to act as fish aggregation devices.
    1. The colonisation by epifauna of the foundations, scour, and cable protection, may result in an increased availability of prey species, which in turn may lead to increased numbers of fish and shellfish species utilising the hard substrate habitats.
    2. As discussed in volume 2, chapter 9, hard substrate habitat created by the introduction of wind turbine foundations and scour/cable protection are likely to be primarily colonised within hours or days after construction by demersal and semi-pelagic fish species (Andersson, 2011). Continued colonisation has been seen for a number of years after the initial construction, until a stratified recolonised population is formed (Krone et al., 2013). Feeding opportunities or the prospect of encountering other individuals may attract fish aggregates from the surrounding areas, which may increase the carrying capacity of the area (Andersson and Öhman, 2010; Bohnsack, 1989). The dominant natural substrate character of the Proposed Development fish and shellfish ecology study area (e.g. soft sediment or hard rocky seabed) will determine the number of new species found on the introduced vertical hard surface and associated scour protection as follows:
  • hard structures on an area of seabed already characterised by rocky substrates, results in few new species but may sustain a higher abundance (Andersson and Öhman, 2010); and
  • hard structures on a soft seabed, may result in increased diversity of fish normally associated with rocky (or other hard bottom) habitats, (Andersson et al., 2009). A new baseline species assemblage will be formed via recolonisation, and the original soft-bottom population will be displaced (Desprez, 2000).
    1. However, it was noted volume 2, chapter 9, that the longest monitoring programme conducted to date at the Lillgrund offshore wind farm in the Öresund Strait in southern Sweden, showed no overall increase in fish numbers although redistribution towards the foundations within the offshore wind farm area was noticed for some species (i.e. cod, eel and eelpout; Andersson, 2011). More species were recorded after construction than before, which is consistent with the hypothesis that localised increases in biodiversity may occur following the introduction of hard substrates in a soft sediment environment. However, there is uncertainty as to whether:
  • artificial reefs facilitate recruitment in the local population; or
  • the effects are simply a result of concentrating biomass from surrounding areas (Inger et al., 2009).
    1. Linley et al. (2007) concluded that finfish species were likely to have a neutral to beneficial likelihood of benefitting, which is supported by evidence demonstrating that abundance of fish can be greater within the vicinity of wind turbine foundations than in the surrounding areas, although species richness and diversity show little difference (Wilhelmsson et al., 2006; Inger et al., 2009).
    2. Volume 2, chapter 9 also noted that, in contrast, post construction fisheries surveys conducted in line with the Food and Environmental Protection Act (FEPA) licence requirements for the Barrow and North Hoyle offshore wind farms, found no evidence of fish abundance across these sites being affected, either beneficially or adversely, by the presence of the offshore wind farms (Cefas, 2009; BOWind, 2008) therefore suggesting that any effects, if seen, are likely to be highly localised and while of uncertain duration, the evidence suggests effects are not adverse.
    3. As described in volume 2, chapter 9, diadromous species that are likely to interact with the Proposed Development fish and shellfish ecology study area are only likely to do so during migration when passing through the area to and from rivers located on the east coast of Scotland. In most cases, it is expected that diadromous fish are unlikely to utilise the increase in hard substrate within the Proposed Development fish and shellfish ecology study area for feeding or shelter opportunities, due to the limited time they are likely to be in the area. Therefore, the reef effect is not anticipated to effect diadromous fish species numbers or behaviour. There is potential for impacts upon diadromous fish species resulting from increased predation by marine mammal species within offshore wind farms. Tagging of harbour seal and grey seal around Dutch and UK wind farms provided significant evidence that the seal species were utilising wind farm sites as foraging habitats (Russel et al., 2014), specifically targeting introduced structures such as wind turbine foundations. However, a further study using similar methods concluded that there was no change in behaviour within the wind farm (McConnell et al., 2012), so it is not certain to what extent seals utilise offshore wind developments and therefore effects may be site-specific.
    4. Research has shown that Atlantic salmon smolts spend little time in coastal waters, and instead are very active swimmers in coastal waters, making their way to feeding grounds in the north quickly (Gardiner et al., 2018a; Gardiner et al., 2018b; Newton et al., 2017; Newton et al., 2019; Newton et al., 2021). Due to the evidence that Atlantic salmon tend not to forage in the coastal waters of Scotland, it is unlikely that they will spend time foraging around wind turbine foundations and therefore are at low risk of impact from increased predation from seals and other predators (volume 2, chapter 9).
    5. Sea trout may be at higher risk of increased predation from seals than Atlantic salmon due to their higher usage of coastal environments. Sea trout are generalist, opportunistic feeders, with their diet including crustaceans as well as smaller fish species. Due to the potential for increases in juvenile crustaceans and other shellfish species from colonisation of the hard structures introduced by installation of the Proposed Development, it is possible that foraging sea trout may be attracted to the hard substrates. This attraction could in turn lead to their increased predation by seal species. However, there is little evidence at present documenting an increased abundance of sea trout around wind turbine foundations. Further, the Proposed Development fish and shellfish ecology study area is situated in an area of high sandeel abundance, and it is likely that sandeel will make up a considerable proportion of sea trout diet when in the marine environment (Svenning et al., 2005; Thorstad et al., 2016). Sandeel species are unlikely to be associated with wind turbine structures due to habitat preferences (discussed in volume 3, appendix 9.1) and therefore sea trout may be less likely to be attracted to increased prey availability colonised on hard substrates, when there is an abundance of prey species which is not associated with the installation of hard substrate (volume 2, chapter 9).
    6. Sea lamprey are parasitic in their marine phase, feeding off larger fish and marine mammals (Hume, 2017). As such it is not expected that they will be particularly attracted to structures associated with offshore wind developments. However, this is not certain, as there is limited information available on the utilisation of the marine environment by sea lamprey (volume 2, chapter 9).
    7. In volume 2, chapter 9 overall, the impact “colonisation of foundations, scour protection and cable protection from the Proposed Development” on diadromous fish was assessed as negligible to minor adverse significance.
    8. As discussed in volume 3, appendix 20.1, 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 Proposed Development is close to four offshore wind farms in the Forth and Tay area: Seagreen 1 and Seagreen 1A Project to the north, Inch Cape to the north‑west and Neart na Gaoithe to the west.
    9. As stated in volume 2, chapter 8, colonisation is likely to only occur on new infrastructure and not extend far beyond the infrastructure because the benthic communities colonising the hard structures are unlikely to be suited to the sedimentary habitats which the Proposed Development is largely composed of. Impacts from the colonisation of hard structures are predicted to be localised to the individual projects and therefore neither stepping stone effects or significant cumulative effects are anticipated.
    10. As discussed in volume 2, chapter 10, higher trophic levels, such as marine mammals, are likely to profit from locally increased food availability and/or shelter and therefore have the potential to be attracted to forage within an offshore wind farm array area. However, still relatively little is known about the distribution and diversity of marine mammals around offshore anthropogenic structures. Species such as harbour porpoise, minke whale, white-beaked dolphin, harbour seal and grey seal have been frequently recorded around offshore oil and gas structures (Todd et al., 2016; Delefosse et al., 2018; Lindeboom et al., 2011). Acoustic results from a T-POD measurement within a Dutch wind farm found that relatively more harbour porpoises are found in the wind farm area compared to the two reference areas (Scheidat et al., 2011; Lindeboom et al., 2011). Authors of this study concluded that this effect is directly linked to the presence of the wind farm due to increased food availability as well as the exclusion of fisheries and reduced vessel traffic in the wind farm (shelter effect). However, as discussed above in volume 2, chapter 10, different studies on marine mammals’ use of offshore wind farm structures return different results. Whilst there is some mounting evidence of potential benefits of man-made structures in the marine environment (Birchenough and Degraer, 2020), the statistical significance of such benefits and details about trophic interactions in the vicinity of artificial structures and their influence on ecological connectivity remain largely unknown (Petersen and Malm, 2007; Inger et al., 2009; Rouse et al., 2020, McLean et al., 2022; Elliott and Birchenough, 2022).
    11. In summary, the direct and indirect impacts of the Proposed Development on prey species will largely result in temporary and highly localised effects which are reversible, with a return to baseline conditions anticipated to occur shortly after the cessation of construction activities. As discussed in section 20.6.9, Table 20.12   Open ▸ , the individual impacts on fish and shellfish were assigned a significance of negligible to minor as standalone impacts. As described in volume 2, chapter 9, cumulative impacts arising from the Proposed Development together with other projects and plans were predicted to result in effects of negligible to minor adverse significance (not significant in EIA terms) upon fish and shellfish IEFs within a 25 km buffer of the Proposed Development fish and shellfish ecology study area.
    12. The impact 'colonisation of foundations, scour protection and cable protection' has the potential to lead to localised increases in fish species through potential reef effect. However, the assessment of effects concluded any increases would be localised and did not conclude that the Proposed Development would lead to a significant increase in prey species. Sandeel, for example require specific sediment habitat conditions and are therefore unlikely to be attracted to the hard structures of offshore wind farm infrastructure.