4. Baseline Characterisation

4.1. Fish and Shellfish Ecology Study Area

4.1.1. Desktop Study

  1. This section provides an overview of the fish and shellfish assemblages found within the fish and shellfish ecology study area. This review primarily covers fish species and communities from regional datasets including other offshore developments within the area, with some additional information on shellfish species and communities. A more detailed characterisation of key shellfish species in the fish and shellfish ecology study area, including species of commercial importance, is presented in section 4.8.
  2. The fish and shellfish ecology study area is based upon a 100 km buffer zone around the site boundary within the northern North Sea, extending inshore to encompass the Firth of Forth. This area also includes much of the Forth and Tay and North East Scottish Marine Regions (SMRs); the Forth and Tay SMR is discussed in section 4.2.
  3. The North Sea can be divided into three areas with associated fish assemblages defined by depths contours and broad biogeographical patterns: shelf edge and northern North Sea, central North Sea, and southern and south-eastern North Sea (Callaway et al., 2002). The northern North Sea and central North Sea fish assemblages differ significantly to the southern and south-eastern North Sea, largely due to the depth profile and water temperature differences (Teal, 2011).
  4. Many fish and shellfish species of commercial importance are present within the North Sea and thus the fish abundances are dependent on fishing pressure. Many commercial and non-commercial species also hold high ecological value as prey items for other marine species (e.g. birds and marine mammals, and other fish species).
  5. A range of biotic and abiotic factors are involved in the determination of fish distribution. Abiotic factors include water temperature, salinity, depth, local scale habitat features and substrate type, and biotic factors include predator-prey interactions, inter- and intra-specific competition and anthropogenic parameters such as marine and coastal infrastructure and commercial fishing intensity.
  6. The site boundary is situated in ICES area IVb, and within the south-east of the northern North Sea (Marine Scotland, 2022d). The fish assemblage in the fish and shellfish ecology study area includes demersal, pelagic, diadromous and elasmobranch species. Demersal species in the area include cod Gadus morhua, haddock Melanogrammus aeglefinus, whiting Merlangius merlangus, plaice Pleuronectes platessa, lemon sole Microstomus kitt, ling Molva, saithe Pollachius virens and sandeel. Pelagic species include herring, mackerel Scomber scombrus and sprat Sprattus sprattus. Elasmobranchs (i.e. sharks, skates and rays) are also likely to be present in the vicinity of the site boundary and the wider fish and shellfish ecology study area. Species such as spotted ray Raja montagui, thornback ray Raja clavata, tope shark Galeorhinus galeus, small-spotted catshark Scyliorhinus canicula, spurdog Squalus acanthias, thorny skate Amblyraja radiata and cuckoo ray Leucoraja naevus, among others, have been observed in the fish and shellfish ecology study area (Coull et al., 1998; Daan et al., 2005; Baxter et al., 2011; Ellis et al., 2012).
  7. Dominant shellfish species in the northern North Sea include pink shrimp Pandalus borealis, Nephrops, edible crab Cancer pagurus, king scallop Pecten maximus, European lobster Homarus gammarus, brown shrimp Crangon crangon, velvet swimming crab Necora puber, queen scallop Aequipecten opercularis, cockle Cerastoderma edule, mussel Mytilus edulis, common whelk Buccinum undatum (referred to as whelk hereafter), and squid (Loliginidae spp. and Ommastrephidae spp.). The distribution of lobster and crab species is highly dependent on habitat/substrate type due to habitat preferences and relatively low mobility.
  8. The IBTS is a historic time series of trawl surveys in the north-east Atlantic and Baltic Seas. IBTS trawl data gathered between 2019 and 2023 have been interrogated to ascertain the most commonly recorded species and to identify whether major components of the species assemblage have shown variation within the last five years (ICES, 2022a). Data from IBTS survey area 3 have been used as they are the most spatially relevant to the fish and shellfish ecology study area ( Figure 4.1   Open ▸ ). The most commonly recorded relevant species (i.e. those considered fish and shellfish ecology receptors) between 2019 and 2023 during the IBTS were haddock, herring, whiting, common dab Limanda limanda, Norway pout Trisopterus esmarkii, sprat, Raitt’s sandeel Ammodytes marinus, lesser sandeel Ammodytes tobianus, grey gurnard Eutrigla gurnardus, European common squid Alloteuthis subulata and long rough dab Hippoglossoides platessoides (ICES, 2022a). At least nine of the overall top ten species listed above have comprised the top ten species within each survey year between 2019 and 2023, with mackerel replacing European common squid in 2022 and Nephrops replacing Raitt’s sandeel in 2023 (ICES, 2022a). These results, based on 712 hauls within the northern North Sea over a five year period, show a high level of temporal consistency for the major components of the targeted fish and shellfish assemblage, suggesting that these species are a good indicator of characteristic species within the fish and shellfish ecology study area.
  9. IBTS data for 2021, 2022 and 2023 showed low abundances of cod, with only tens of individuals, mostly juveniles of age class 1 or 2, recorded per hour trawled. Plaice also showed low abundances within the northern North Sea, with IBTS data indicating abundances of tens individuals regularly recorded per hour of trawling (ICES, 2022a). No obvious differences in abundance associated with season or age distribution of individuals was observed in the 2021 to 2023 data.
  10. Herring abundances within the IBTS are high, with thousands of individuals recorded per hour trawling. Herring abundance is also seasonal, with higher numbers of individuals evident in catches at the end of the year (Q3) than at the start of the year (Q1). The IBTS data showed a marked increase specifically in adult herring abundance during Q3, which supports existing literature on herring spawning seasons, as the influx of adult herring individuals in Q3 coincides with the spawning season (refer to section 4.4 for further information) (ICES, 2022a).
  11. Average recorded abundances of mackerel were low during 2022 and 2023 Q1 in comparison with 2021 Q1, however higher abundances were recorded during Q3 (2022 only). 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 (ICES, 2022a).
  12. Sandeel, which are a crucial forage fish for many other species, are one of the most abundant species in the North Sea, accounting for approximately 25% of fish biomass (Christensen et al., 2013). Raitt’s sandeel featured in the top ten species recorded between 2019 and 2022, although it’s worth noting that a full year of survey data for 2023 is not yet available, therefore the overall composition of most abundant species may change following further sampling in Q3 into Q4 (ICES, 2022a). Further information on sandeel is provided is section 4.5.
  13. Sprat have relatively high abundance, where thousands of individuals were frequently recorded per hour trawled. However, similar to mackerel, the abundances recorded were found to be quite sporadic, with low numbers being recorded frequently. While there are no obvious differences in seasonal distribution of individuals recorded, a decrease in abundances of age five fish was recorded in 2021 and 2022 (ICES, 2022a).
  14. Whiting are highly abundant within the northern North Sea. IBTS data for 2021, 2022 (Q1 and Q3) and 2023 (Q1) showed abundances as high as 8,000 individuals per hour trawled. Notably, juvenile whiting (up to two years old) were, on average, the highest abundances recorded in Q1 and Q3 trawls (ICES, 2022a). Whiting is one of the most widespread and numerous species found in the North Sea but is also found across the North-East Atlantic and other European seas (Cefas, 2001). Whiting are most commonly found in depths of 30 m to 100 m, predominantly on mud and gravel bottoms, but also on sand and rock where whiting feed on crustaceans, small fish and molluscs. After the first year, whiting migrate further offshore (FishBase, 2022a).
  15. Many of these fish and shellfish species have high ecological value as prey species for marine mammals and seabirds (e.g. sandeel, herring, mackerel and sprat) as well as being of high importance for commercial fisheries (e.g. European lobster, edible crab, king scallop and squid) (refer to volume 3, appendix 8.1).

Figure 4.1:
Areas Surveyed in the North Sea IBTS (Source: ICES, 2013)

Figure 4.1: Areas Surveyed in the North Sea IBTS (Source: ICES, 2013)

 

4.1.2. Site-Specific Surveys

  1. As outlined in section 3.3, epibenthic beam trawl sampling was conducted at ten locations within the benthic subtidal ecology survey area ( Figure 3.1   Open ▸ ).
  2. A total of 16 fish species were observed in the epibenthic trawls, with long rough dab being the most abundant followed by plaice, common dab, Norway pout, Raitt’s sandeel, lemon sole and grey gurnard. Other species recorded in lower abundances were pogge Agonus cataphractus, poor cod Trisopterus minutus, haddock, cod, transparent goby Aphia minuta, sand goby Pomatoschistus minutus, scaldfish Arnoglossus laterna, Lotidae spp. and Argentinidae spp. (refer to volume 3, appendix 8.1, annex A). Other common species known to occur within the fish and shellfish ecology study area may not have been identified through site-specific surveys within the site boundary due to the sampling method. Epibenthic trawls do not target pelagic species or large demersal species due to their low headline height and ground contact, and slow towing speed, however these have been fully characterised via desktop data sources, including survey data from the IBTS. Shellfish recorded during site-specific surveys (including trawl surveys) are discussed in section 4.8.
  3. Fish species observed in DDV or caught in grab samples within the site boundary are listed Table 4.1   Open ▸ .

 

Table 4.1:
Notable Fish Species Recorded in DDV/Grab Samples

Table 4.1: Notable Fish Species Recorded in DDV/Grab Samples