4.6. Elasmobranchs

4.6.1. Desktop Study

  1. Elasmobranchs are a group of cartilaginous fish encompassing sharks, rays and skates. Species reported to occur within the fish and shellfish ecology study area include basking shark, spotted ray, thornback ray, tope shark, small-spotted catshark, spurdog, common skate, thorny skate and cuckoo ray (Coull et al., 1998; Daan et al., 2005; Baxter et al., 2011; Ellis et al., 2012). There are no specific fisheries for these species, however most of these species have commercial value, but not locally to the site boundary. Some of these species have nursery grounds within the fish and shellfish ecology study area (Ellis et al., 2012) and were further discussed in section 4.3.
  2. Basking shark may migrate throughout the fish and shellfish ecology study area and therefore have the potential to be encountered within the site boundary. Basking shark are large, filter feeding fish that are predominantly solitary, but may also occur in aggregations where there is dense zooplankton abundance (Speedie, 1999). Their unique feeding strategy dominates all aspects of their ecology and life history; the basking shark is an obligate ram filter feeder whereby the flow of water across gill rakers within the mouth is controlled by swimming speed (Sims, 1999; Sims, 2008).
  3. Mating has not been observed in basking shark and most likely occurs in deep water with courtship-like behaviour as the precursor, particularly where individuals aggregate in food rich waters (Sims, 2008). Individuals are thought to pair and mate in early summer (Sims et al., 2000) and gestation has been estimated over a range of 12 to 36 months (Parker and Stott, 1965; Sims et al., 2008). As an ovoviviparous species, basking shark bear live young, hatched from eggs within the uterus of the female. Basking shark are a slow growing species with late maturation (at 12 to 20 years of age) and a relatively low fecundity (producing litters of around six pups; Sund, 1943). These characteristics suggest that basking shark would be vulnerable to environmental changes and the population would be slow to recover from any major losses. With a long history of exploitation, this species is listed as Vulnerable on the IUCN Red List globally (Fowler, 2009), and on the European Red List for cartilaginous fish as Endangered (IUCN, 2023). Basking shark are a Scottish PMF.
  4. Basking shark migration routes cover large distances from north Africa to Scotland, using both the continental shelf and oceanic habitats in the upper 50 m to 200 m of the water column (Doherty et al., 2017). Distribution has been shown to be influenced by a range of environmental conditions (Austin et al., 2019). Surface sightings of basking sharks are typically reported where sea surface temperatures range between 15°C and 17.5°C (Skomal et al., 2004; Cotton et al., 2005) where thermal fronts are present (Sims and Quayle, 1998; Jeewoonarain et al., 2000) and where zooplankton is in its greatest abundance (Sims and Quayle, 1998; Sims, 1999). Basking shark have a north to south migration and may be expected to occur within and surrounding the site boundary during August to October and during the return migration in March to June (Doherty et al., 2017).
  5. Twenty-eight basking sharks tagged off Scotland and the Isle of Man in summer months over four years showed an average migration distance of 1,057 km with movements starting in October (Doherty et al., 2017), however, none of the tagged basking sharks migrated to the east coast of Scotland. Due to the migratory behaviour of basking sharks and routes through Scottish waters, basking sharks have the potential to be present within the fish and shellfish ecology study area, however, the majority of basking shark sightings in UK waters are located on the west coast of Scotland (NBN Atlas, 2021).
  6. Common skate are a Critically Endangered demersal elasmobranch (Ellis et al., 2021) found in the North-East Atlantic between 100 m and 1000 m on the continental shelf and slope and around seamounts (FishBase, 2022b). Their large size and life history traits (slow growth, late maturity and low fecundity) has caused them to be highly susceptible to overfishing (Griffiths et al., 2010), with significant decreases in population sizes and distribution range. Their widespread range historically extended from Iceland to north Africa, including the Mediterranean Sea, however, it has been reduced to the British Isles up to Iceland and its presence in the Mediterranean Sea has not been confirmed since records have been attributed to a separate distinct species: the flapper skate Dipturus intermedius (Mendez et al., 2022). Most recently, the majority of sightings around the British Isles were along the west coast of Scotland, the Irish Sea and the English Channel (NBN Atlas, 2021). This is supported by the two distinct populations highlighted in Griffiths et al. (2010), with one occurring in waters off the southern British Isles and around Rockall, and the other occurring in shelf waters along the west coast of Scotland. However, the nursery grounds located in the vicinity of the site boundary suggest that common skate could be present around the site boundary intermittently throughout spring and summer when common skate mate and lay egg capsules, respectively ( Figure 4.6   Open ▸ ; FishBase, 2022b).
  7. Spotted ray are widely distributed across the eastern Atlantic from Morocco to the Shetlands Isles and Norway and were assessed as Least Concern according to the IUCN Red List (Stehmann and Burkel, 1984; Bauchot, 1987; Ellis et al., 2007). The populations in the North-East Atlantic show preferences for inshore waters and shallow continental shelf waters between 8 m and 283 m (Ellis et al., 2005) with higher abundances in shallow waters (up to 100 m). Spotted ray show generational segregation, with juveniles commonly occurring on sandy sediments closer inshore where they feed on small crustaceans and adults occurring further offshore on sand and coarse sand-gravel sediments predating on larger crustaceans and fish (Ellis et al., 2007). Individuals are known to bury themselves to avoid predation and to ambush prey. Sightings of spotted ray concentrate in the Irish Sea and in the southern North Sea (NBN Atlas, 2021). However, with low intensity nursery grounds overlapping the site boundary ( Figure 4.5   Open ▸ ) and records in the fish and shellfish ecology study area, spotted ray are likely to be present within and in the vicinity of the site boundary.
  8. Sightings of spurdog have been recorded around the British Isles with most data from the Irish Sea (NBN Atlas, 2021). Spurdog are listed as Vulnerable on the IUCN Red List (Finucci et al., 2020) and they are a Scottish PMF with a known global distribution in boreal and temperate waters (Ebert et al., 2013). Spurdog dwell in a wide range of habitats both inshore and offshore waters from the surface down to 2,000 m (Cox and Francis, 1997). This species has been targeted and caught as bycatch in artisanal, industrial, and recreational fisheries as its distribution overlaps with intensive fishing activities (Finucci et al., 2020). The population decrease has been accentuated by their aggregation behaviour mostly between pregnant females (ICES, 2018). However, the large scale fishing pressure that targeted spurdog has largely diminished with retention bans implemented in European Union (EU) waters, and the stock was able to recover considerably. Nonetheless, incidental catches continue, and post-release mortality remains high (i.e. 39% for gillnet fisheries) (Rago and Sosebee, 2014; da Silva et al., 2015; Ellis et al., 2017; ICES, 2018). Spurdog are likely to be found within or in the vicinity of the site boundary, especially within the nursery grounds that overlap with the site boundary over the winter months when pups are born (Pawson and Ellis, 2005; Figure 4.5   Open ▸ ).
  9. Tope shark is a species of shark with a global distribution in temperate waters (Compagno, 2005) but is listed as Critically Endangered (Walker et al., 2020). Tope shark is a benthopelagic species occurring on continental shelves and the upper half of continental slopes from shallow inshore to offshore waters up to 826 m (Walker et al., 2006; Wiegmann, 2016; Thorburn et al., 2019). Tope shark often gather in schools, partially segregating by size and sex and sometimes migrate between shallow waters at night to deep waters during the day (Walker et al., 2008). Tope shark is targeted globally for the shark flesh and fins and is caught as by-catch in various fisheries (i.e. industrial, small-scale, demersal, pelagic, gillnet, longline, trawl and hook-and-line) (ICES, 2019; Walker et al. 2020). In addition, tope shark’s low fecundity and late maturity has led to significant stock reductions (e.g. reduction of 76% of the North-East Atlantic subpopulation over 79 years). Implementation of management measures in Europe, including the mandatory release of line-caught tope shark in EU waters has helped maintain the North-East Atlantic population as stable in recent years but extensive movements remain within subpopulations. However, uncertainties remain for the correct identification of tope shark in trawl survey data which can be confused with smooth-hound Mustelus spp. (ICES, 2019). Tope shark have pupping and nursery grounds in shallow waters, protected bays and estuaries where juveniles may remain up to two years (Stevens and West, 1997, Walker, 1999, Walker et al., 2006, Bovcon et al, 2018, McMillan et al., 2018). Figure 4.6   Open ▸ shows the presence of nursery grounds for tope shark adjacent to the site boundary and tope shark are therefore likely present in the vicinity of the site boundary.
  10. Among the other species of elasmobranchs likely to be present within the fish and shellfish ecology study area, angel shark Squatina squatina (Critically Endangered) (Morey et al., 2019) have been observed in the Firth of Forth but are likely to be vagrant, with the majority of sightings in the Irish Sea (NBN Atlas, 2021). The cuckoo ray is widely distributed throughout the North-East Atlantic and Mediterranean Sea. Cuckoo ray, a small bodied species of ray that typically occurs offshore on the continental shelf and slope at depths of 20 m to 500 m and the thorny skate, a Vulnerable demersal species that occurs on the continental shelves and slopes, have been observed in multiple locations in the northern North Sea (NBN Atlas, 2021). Small-spotted catshark and thornback ray are commonly recorded around the British Isles with lower occurrences in the northern North Sea (NBN Atlas, 2021) and porbeagle Lamna nasus, a large pelagic shark species occurring mostly offshore, have been sighted within the fish and shellfish ecology study area.

4.6.2. Site-Specific Surveys

  1. No basking shark were recorded during the 24 months of aerial surveys undertaken for marine mammals and birds for the site boundary (refer to volume 3, appendix 11.1, annex D).
  2. No elasmobranch species were recorded during the 2022 site-specific survey (grab/DDV or epibenthic beam trawls) within the site boundary (refer to volume 3, appendix 8.1, annex A). In the wider fish and shellfish study area, a single cuckoo ray was recorded during a 2011 epibenthic trawl for the Seagreen Alpha and Bravo project (now referred to as Seagreen 1 and Seagreen 1A) (Seagreen Wind Energy Ltd., 2012).

4.7. Diadromous Fish

  1. Diadromous fish are species that migrate between freshwater and seawater. These are grouped into anadromous species, which live in the sea and migrate to freshwater to breed, and catadromous species which live in freshwater and migrate to sea to breed. On the east coast of Scotland, there is potential for diadromous fish to migrate through the fish and shellfish ecology study area to reach or to leave Scottish rivers. During migration, diadromous fish may migrate through the site boundary during certain times of the year (NBN Atlas, 2021).
  2. The northern North Sea is home to diadromous fish species which move between the sea and freshwater at different stages of their life cycle. Atlantic salmon and sea trout are two commercially important diadromous fish species found in the North Sea. Sea lamprey Petromyzon marinus, river lamprey Lampetra fluviatilis, European eel Anguilla anguilla, allis shad Alosa alosa, twaite shad Allosa fallax and sparling Osmerus eperlanus are also known to occur in the region. Brook lamprey Lampetra planeri are also recorded in the fish and shellfish ecology study area, although as a purely freshwater species, this species migrates between downstream river habitat to upstream areas to spawn and are therefore not considered further in this report as they are unlikely to interact with the Array.
  3. No site-specific surveys have been undertaken within the site boundary to support the impact assessment on diadromous fish species, nor were they undertaken at other offshore wind projects in the fish and shellfish ecology study area (Berwick Bank, Seagreen 1 and 1A, Neart na Gaoithe, or Inch Cape Offshore Wind Farms). Therefore, a precautionary approach has been taken when characterising the baseline for diadromous species. It has been assumed that the eight species mentioned in paragraph 114 may be present within the fish and shellfish ecology study area during key migration periods. Due to uncertainties in the migration routes and foraging areas and times for diadromous fish, it is also assumed that all relevant species have the potential to occur within the area year-round.
  4. All species described in paragraph 113 are considered individually below with their likely presence within the site boundary defined and whether they are considered as IEFs for the fish and shellfish ecology assessment of effects. For example, some species (e.g. river lamprey) remain coastal during their time in the sea and are unlikely to migrate through the site boundary. Diadromous species presence in the fish and shellfish ecology study area and within the site boundary will vary throughout the year with presence likelihoods dependent on the key migration periods presented in Table 4.6   Open ▸ .
Table 4.6:
Overview of Life Histories for Diadromous Fish Relevant to the Fish and Shellfish Ecology Study Area

Table 4.6: Overview of Life Histories for Diadromous Fish Relevant to the Fish and Shellfish Ecology Study Area

 

4.7.1. Atlantic Salmon

  1. Atlantic salmon are an Annex II species under the Habitats Directives and are designated as a qualifying feature of Special Areas of Conservation (SACs) including European sites in Scotland, with some European sites located within the fish and shellfish ecology study area (such as the River Dee SAC and the River Tay SAC). Atlantic salmon are also defined as a PMF in Scotland for the marine life cycle and an Annex III species under the Bern Convention (for the freshwater life cycle). Atlantic salmon populations have seen a rapid decline across Scotland in the last 25 years (Youngson et al., 2002).
  2. Atlantic salmon are of considerable cultural and conservation importance (Hindar et al., 2010). Atlantic salmon are subject to many pressures in Europe both in marine and freshwater environments, including pollution, the introduction of non-native salmon stocks, physical barriers to migration, exploitation from netting and angling, physical degradation of spawning and nursery habitat, and increased marine mortality (ICES, 2017; Cefas, 2019b).
  3. Since 2016, as a result of the Salmon Conservation Regulations, Atlantic salmon caught in coastal waters have to be released. This was implemented to prevent the killing of Atlantic salmon in coastal waters and estuaries to protect stocks that were in poor conservation status.
  4. Atlantic salmon are considered a Priority Species under the UK Post-2010 Biodiversity Framework. The species is known to be a relatively large bodied fish that can be encountered in clean and healthy rivers throughout the UK. Like other salmonid species, the Atlantic salmon spends most of its life at sea, returning to spawn in the same stretch of river or stream in which they was born (natal river).
  5. Adult Atlantic salmon spawn in Scottish east coast rivers and after the ova mature to fry and then parr, the smolts migrate to the sea. After one to three years at sea, adults migrate, usually, to their native river. Various cues are involved during their return migration; in earlier phases, sun position and Earth’s magnetic field seem to play a role in oceanic orientation (Hansen and Quinn, 1998). Tidal phase and time of day have also been suggested as important factors for their upstream migration (Smith and Smith, 1997). Migration upstream of estuaries have also been observed to be nocturnal, occurring during ebb tides (Smith and Smith, 1997). In the final phase of the upstream migration, olfactory cues direct Atlantic salmon up the river (Hasler and Scholz, 1983). For smolts migrating downstream, migratory activity has been identified to be associated with night time while daytime was utilised more for prey detection and predator avoidance (Hedger et al., 2008). East coast Scotland post-smolts, once in the North Sea, are transported by water currents towards northern Norway and then into the Norwegian Sea (Holst et al, 2000; Jonsson et al., 1993). Further evidence from Scottish Atlantic salmon (i.e. from Aberdeenshire Dee, Tay and North Esk rivers) recaptured in Greenland and Faroe Islands waters showed that smolts emigrated west to feed and grow (Malcolm et al., 2010).
  6. This is further supported by recent evidence from the Moray Firth (Newton et al., 2017; Newton et al., 2019; Gardiner et al., 2018a) which suggests that smolts migrating from their rivers in the Moray Firth head directly across the North Sea relatively rapidly. It is thought that this route, rather than moving in a coastal direction upon leaving their natal rivers, allows them to take advantage of east flowing currents which cross the North Sea. This fast progress away from the coast limits exposure to predators occurring close to the coast; it also reduces the potential for interaction with marine renewables developments (including offshore wind). Similar evidence of a rapid easterly migration out into the North Sea has also been shown for the River Dee in Aberdeenshire (Gardiner et al., 2018b). Therefore, it could be assumed that smolts from other east coast rivers (e.g. Tay, Forth and South Esk) would move in a similar fashion.
  7. Malcolm et al. (2015) used metadata to assess the timing of smolt emigration across Scotland. This suggested that most fish leave rivers between mid-April and the end of May. These results do not include the period spent by smolts in the coastal environment after leaving their native rivers. There was also evidence that smolt emigration is becoming earlier (by around 1.5 days per decade over a period of around 50 years).
  8. Migration of Atlantic salmon smolts through the Cromarty Firth and into the Moray Firth was tracked in a study undertaken for Beatrice Offshore Windfarm Ltd. by Glasgow University (BOWL, 2017). The study results indicated an eastwards migration of the tagged fish along the southern coast of the Moray Firth. Results also showed the majority of fish to remain predominantly within the upper 1 m of the water column during migration. Mortality of smolts was considered mainly attributable to predation and there was a strong relationship between group survival, early migration and group size.
  9. Between 2018 to 2021, a tagging study was conducted on juvenile Atlantic salmon and sea trout migrating from the River Dee and River Don, which are located in Aberdeenshire (in the north of the fish and shellfish ecology study area) (River Dee Trust and MSS, 2023). Atlantic salmon were found to travel at an average speed of 0.45 m/s from the river mouths to around 4 km offshore, before dropping to 0.24 m/s between 4 to 20 km offshore (River Dee Trust and MSS, 2023). Individuals mostly swam within the top 3 m of the water column and swam in an easterly direction in the first 4 km, before following a south-easterly trajectory. This pattern was consistent over the three years of the study, suggesting that this is a regular migratory route and that Atlantic salmon must make a northerly course adjustment at some point in their migration to reach higher latitude feeding grounds in the Norwegian Sea (River Dee Trust and MSS, 2023). The authors concluded that this easterly and south-easterly migratory trajectory suggests that Atlantic salmon could be present in offshore areas of the North Sea (River Dee Trust and MSS, 2023).
  10. The wild Atlantic salmon total catch from rod fishing reported 42,204 individuals in 2022, the fourth lowest record since the start of the statistics on salmon fisheries in Scotland by Marine Scotland in 1952 (Scottish Government, 2023). This is an increase from the 35,693 recorded in 2021 (Marine Scotland, 2022a), but still supports the population declines of Atlantic salmon in Scotland. Most of the catch data (97%) in 2022 are salmon caught by rod fisheries with 95% of the catches released. Other fishing methods (e.g. net and coble or fixed engine fisheries) accounted for 2% or less (Scottish Government, 2023). For retained catch data, rods accounted for around 74% while net and coble fisheries accounted for 26%. Historically, between 1952 and 2022, total rod catches of Atlantic salmon increased until its peak in 2010 and sharply declined since then to the current historic low.
  11. Using rod catch data from relevant Scottish east coast rivers (Marine Scotland, 2022a), trends in Atlantic salmon populations in the fish and shellfish ecology study area can be highlighted. Data from 2021 on the number of fish caught in each of the following rivers have been collated in Figure 4.17   Open ▸ for the Tweed, Teith, Tay, South Esk, and Dee. It should be noted that data for 2022 were not available at the time of writing. The five year average between 2017 and 2021 of Atlantic salmon caught by rods has also been provided. Figure 4.17   Open ▸ demonstrates that Atlantic salmon migrate to and from east coast Scottish rivers. Therefore, migrating smolts or returning adults are likely to pass through the site boundary during migration periods. This is consistent with assumptions made for Seagreen 1 and 1A and Berwick Bank Offshore Wind Farms (Seagreen Wind Energy Ltd., 2012, SSER, 2022).
  12. During their oceanic phase, Atlantic salmon are thought to use chemoreceptor in coastal waters to locate their natal river and electromagnetic fields (EMFs) during offshore migrations (Gill and Bartlett, 2010). However, Atlantic salmon being a pelagic species, the effects would be mostly perceived in shallower waters away from the location of the site boundary (Snyder et al., 2019).
  13. Atlantic salmon and sea trout are host species for the freshwater pearl mussel Margaritifera margaritifera during their larval stage from late summer before they settle on the riverbed. Freshwater pearl mussel are strict freshwater species and have seen population declines. Amongst the factors that threaten their populations is the decline in salmonid stocks. Therefore, the impacts to Atlantic salmon and sea trout can directly affect the populations of freshwater pearl mussel.

Figure 4.17:
Marine Scotland Catch Data for Rod Caught Atlantic Salmon (2017 to 2021)

Figure 4.17 Marine Scotland Catch Data for Rod Caught Atlantic Salmon (2017 to 2021)

4.7.2. Sea Trout

  1. Sea trout are known to be found in rivers, streams and lakes, often preferring cold and well oxygenated waters. Sea trout spawn in rivers and streams that have swift currents, which are usually characterised by the downward movement of water into gravel, favouring large streams and mountainous areas that have adequate cover resulting from submerged rocks, undercut banks, and overhanging vegetation (Fishbase, 2021a). While there is limited information regarding sea trout migration patterns, the information available suggests preferences are primarily limited to inshore and local waters within the marine environment (Malcolm et al., 2010). Sea trout are listed as a Scottish PMF during the marine part of their life cycle.
  2. The wild sea trout total catch from rod fishing reported 14,509 individuals in 2022 the fourth lowest record since the start of the statistics on sea trout fisheries in Scotland by Marine Scotland in 1952 (Scottish Government, 2023). This is an 11% increase upon the 12,636 individuals recorded in 2021 (Marine Scotland, 2022b). Most of the catch data (91%) in 2022 are sea trout caught by rod fisheries with 87% of the catches released. Other fishing methods (e.g. net and coble or fixed engine fisheries) accounted for 5% or less per method. For retained catch data, rods accounted for around 64% while net and coble fisheries accounted for 13% and 23% respectively. Historically, between 1952 and 2022, total rod catches of sea trout showed a general decreasing trend (Scottish Government, 2023).
  3. Using rod catch data from relevant Scottish east coast rivers (Marine Scotland, 2022b), trends in sea trout populations within the fish and shellfish ecology study area can be highlighted. Data from 2020 on the number of fish caught in each of the following rivers have been collated in Figure 4.18   Open ▸ : Tweed, Tay, South Esk, and Dee. It should be noted that these are the most recent available data at the time of writing. The five year average between 2016 and 2020 of sea trout caught by rods has also been provided. Figure 4.18   Open ▸ demonstrates that sea trout migrate to and from east coast Scottish rivers. Therefore, migrating smolts or returning adults are likely to pass through the site boundary during migration periods. This is consistent with assumptions made in Seagreen 1 and 1A and Berwick Bank Offshore Wind Farms (Seagreen Wind Energy Ltd., 2012: SSER, 2022).
  4. However, as described in paragraph 125, a recent tracking study provides insight into migratory routes for juvenile sea trout from the River Dee and the River Don (River Dee Trust and MSS, 2023). In this study, between 2018 and 2021, sea trout remained in the nearshore environment to a greater extent than Atlantic salmon and exhibited a range of different migration strategies. These included freshwater migration only (potamodromous; 18% of individuals), from freshwater to estuaries (semi-anadromous; 37%), and migration from freshwater to marine environments (anadromous; 45%) (River Dee Trust and MSS, 2023). Anadromous sea trout tended to stay between 4 km from the shore, and within the top 3 m of the water column. The authors suggested that sea trout from the River Dee and River Don are less likely to be present offshore than Atlantic salmon (River Dee Trust and MSS, 2023).

Figure 4.18:
Marine Scotland Catch Data for Rod Caught Sea Trout (2016 to 2020)

Figure 4.18: Marine Scotland Catch Data for Rod Caught Sea Trout (2016 to 2020)


4.7.3. European Eel

  1. European eels are classified as Critically Endangered (IUCN, 2023) and are a Scottish PMF during the marine part of their life cycle. European eel dwell in a range of benthic habitats from streams to shores, rivers, lakes, and ultimately migrate to the Sargasso Sea to spawn. Eel larvae are brought to European waters by the Gulf Stream and transform into glass eel, followed by elvers which migrate up estuaries around the Scottish coast, colonising rivers and lakes. Sexually mature eels leave the river and migrate to sea, covering great distances during their spawning migration (5,000 km to 6,000 km) (Fishbase 2021b). European eel may migrate in the vicinity of or through the site boundary and therefore, given their critically endangered status, will be considered as an IEF.

4.7.4. Sea Lamprey

  1. Sea lamprey are anguilliform (or eel-like) jawless fish found primarily in estuaries and easily accessible rivers, and are parasitic on a number of fish species and other marine fauna. Sea lamprey is the largest of the lamprey species found in the UK. Sea lamprey are anadromous (JNCC, 2021a) and spend most of their adult life at sea. Like other lamprey species, sea lamprey requires clean gravel for spawning, preferably in warm waters, and marginal silt or sand for the burrowing of juveniles (ammocoetes). Spawning of sea lamprey coincides with the warmer spring temperatures in Scottish rivers (refer to Table 4.6   Open ▸ ) (JNCC, 2021a).
  2. Sea lamprey’s natural range has declined in the UK due to river pollution and barriers to migration (such as dams and weirs) but they remain widespread in UK rivers up to Scotland with a northern limit at the Great Glen (JNCC, 2021a). Sea lamprey are Annex II species on the Habitats Directive and are the primary reason or qualifying features for some designated sites on the east coast of Scotland (refer to section 4.7.8). They are also listed as a Scottish PMF during the marine part of their life cycle. However, there is limited information on the distribution and behaviour of sea lamprey in marine waters (Hume, 2017). While it is possible that migration routes may overlap with the site boundary, considering the distance to the nearest SAC (i.e. 128.58 km to Tweed Estuary SAC), the presence of sea lamprey within or in the vicinity of the site boundary is unlikely and sea lamprey are not considered as IEFs.

4.7.5. River Lamprey

  1. The river lamprey has a similar body shape to the sea lamprey and inhabit coastal waters, estuaries, and accessible rivers. While some populations reside permanently in freshwater, the species is normally anadromous, and pollution or obstacles can hinder their migration (JNCC, 2021b). River lamprey live on hard bottoms or as parasites attached to larger fish such as cod and herring with spawning taking place in pre-excavated pits in riverbeds. River lamprey are widespread in UK rivers up to Scotland with a northern limit at the Great Glen and the populations in the UK are considered of conservation importance at European level (Hume, 2017). Like sea lamprey, river lamprey are also listed as Scottish PMFs during the marine part of their life cycle. Due to their preference for estuarine and nearshore coastal waters, it is unlikely that river lamprey will be found within the site boundary and are therefore not considered as IEFs.

4.7.6. Allis and Twaite Shad

  1. The two shad species are very similar in appearance and are hard to distinguish. They both belong to the herring family (Clupeidae) and the only reliable way of differentiating the two species, apart from allis shad being usually bigger, is the number of gill-rakers (JNCC, 2021c).
  2. The habitat requirements of twaite shad are not decisively understood, however they are known to return to rivers from the sea to spawn in spring ( Table 4.6   Open ▸ ). On the River Usk and the River Wye, twaite shad are known to spawn at night shallow areas near deeper pools, in which the fish congregate. The eggs are released into the water column, sinking into the interstices between coarse gravel/cobble substrates (JNCC, 2021c). Recruitment yield is usually greater during warm years. The majority of adults (75%) generally die after spawning, and pollution, overfishing and migration obstacles have caused population declines (JNCC, 2021c). No spawning stocks of twaite shad are found in Scotland.
  3. The allis shad also has poorly understood habitat requirements in freshwater. It grows in coastal waters and estuaries, spending most of its adult phase in the marine environment, but migrates into rivers to spawn, swimming up to 800 km upstream in continental Europe. Adults spawn at night with the eggs released into the current where they settle among gaps in gravelly substrates. Shallow gravelly areas adjacent to deep pools are thought to represent optimal spawning habitat (JNCC, 2021d). The majority of the adults die after spawning and migration obstacles are a major cause of population declines as well as pollution and overfishing. There is no clear spawning site in Scotland but there is probably a spawning population in the Solway Firth (Maitland and Lyle, 2001).
  4. Both species have limited research surrounding their freshwater life cycle phases which has subsequently resulted in scarce understanding of their spatial ecology during the species marine life-phases (Davies et al., 2020). These species are considered unlikely to be found in significant numbers within the vicinity of the site boundary, however they are considered as IEFs to ensure a precautionary approach.

4.7.7. Sparling (European Smelt)

  1. Sparling or European smelt are known to inhabit estuaries and large lakes, spending much of their life in the estuarine zone, with short incursions into the littoral zone. Sparling have been evidenced to enter rivers to spawn on both sandy and gravelly substrates, predominantly in fast flowing waters of lake tributaries or shallow shores of lakes and rivers (Fishbase, 2021c). Sparling are listed as Scottish PMFs during the marine phase of their life cycle. Due to their preference of inhabiting estuarine waters upon entering the marine environment, it is unlikely that sparling will be found within and in the vicinity of the site boundary and are therefore not considered as IEFs.

4.7.8. Freshwater Pearl Mussel

  1. The freshwater pearl mussel is an endangered species of freshwater mussel and is included with diadromous fish as per standard EIA approach due to its reliance on salmonids during the first year. Freshwater pearl mussels are similar in shape to common marine mussels but grow much larger and live far longer. They can grow as large as 20 cm and live for more than 100 years, making them one of the longest- lived invertebrates (Skinner et al., 2003). These mussels live on the beds of clean, fast flowing rivers, where they can be buried partly or wholly in coarse sand or fine gravel. Mussels have a complex life cycle, living on the gills of young Atlantic salmon or sea trout, for their first year, without causing harm to the fish (Skinner et al., 2003). Freshwater pearl mussel is fully protected under Schedule 5 of the Wildlife and Countryside Act 1981 (as amended) and is also listed on Annexes II and V of the Habitats Directive and Appendix III of the Bern Convention. The conservation status of the species is reflected in its listing as Endangered on the IUCN Invertebrate Red List. While there is no potential for direct impacts on this species from the site boundary (as this is an entirely freshwater species), indirect impacts may occur due to effects on their host species (i.e. Atlantic salmon and sea trout) during their marine phase.