Significance of the effect
Marine fish and shellfish species
127. For sandeel, the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
Diadromous species
Secondary mitigation and residual effect
129. No secondary fish and shellfish ecology mitigation (beyond the designed in measures outlined in section 9.10) is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.
Decommissioning phase
Magnitude of impact
130. Infrastructure left in situ during the decommissioning of the Array (all scour protection and cable protection) will cause permanent subtidal habitat loss. A total footprint of up to 6,786,162 m2 may be left in situ post-decommissioning, due to inter-array cable protection and crossing protection, along with interconnector cable protection, cable crossing protection, and scour protection for moorings and anchors, inter-array junction boxes and OSP jackets. Associated figures are given in Table 9.13 Open ▸ . This represents 0.79% of the site boundary.
131. The impact is predicted to be of local spatial extent, long term duration, continuous and low reversibility. The magnitude is therefore considered to be low.
Sensitivity of the receptor
132. The sensitivity of the fish and shellfish IEFs, for both marine and diadromous species, can be found in the construction phase assessment (see paragraphs 112 to 125) ranging from low (for all marine and diadromous fish and shellfish IEFs, except sandeel) to medium (for sandeel) sensitivity.
Significance of the effect
Marine fish and shellfish species
133. Overall, the magnitude of the impact for marine fish and shellfish, except for sandeel, is deemed to be low and the sensitivity of the receptor is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
134. For sandeel, the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
Diadromous species
135. Overall, the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
Secondary mitigation and residual effect
136. No secondary fish and shellfish ecology mitigation (beyond the designed in measures outlined in section 9.10) is considered necessary because the likely effect in the absence of mitigation is not significant in EIA terms.
Colonisation of Hard Structures
137. Colonisation of hard structures (such as the foundations) may serve as artificial reefs, as these add hard structures to areas typically characterised by soft, sedimentary environments, essentially replicating naturally occurring rocky habitats (Karlsson et al., 2022). Anthropogenic structures on the seabed attract many marine organisms including benthic species normally associated with hard structures (such as the blue mussel (Karlsson et al., 2022) and therefore, may have indirect impacts on fish and shellfish populations through their potential to act as artificial reefs and to bring about changes to food resources (Inger et al., 2009). Karlsson et al. (2022) observed that at the offshore floating Hywind Scotland site, plumose anemones Metridium senile and fan worms Spirobranchus sp. dominated the bottom and mid-section of floating turbines, whilst kept Laminaria sp., other brown seaweeds, and blue mussels dominated the upper 20m to 0 m mean sea level of wind turbines). Additionally, man-made structures may also have direct impacts on fish through their potential to act as fish aggregation devices (Petersen and Malm, 2006). Volume 2, chapter 8 examines this impact from the perspective of benthic subtidal habitats (for example, blue mussels as a habitat type), whereas this assessment looks at the subsequent consequences for fish and shellfish populations.
Operation and maintenance phase
Magnitude of impact
138. Up to 19,270,958 m2 of hard substrate will be installed in the construction phase, though colonisation will not occur until the operation and maintenance phase ( Table 9.13 Open ▸ ). As with ‘Long term habitat loss and disturbance’, this represents up to 2.25% of the total site boundary. Colonisation may also occur on floating structures in the water column. Floating objects in the water column may also be beneficial to some pelagic fish which might display aggregating behaviour for shelter from predators, prey opportunities (particularly if floating objects or objects in the water column become colonised with sessile species), and for schooling companions (Deudero et al., 1999). The impact is predicted to be of local spatial extent, long term duration, continuous and low reversibility. The magnitude is therefore considered to be low.
Sensitivity of the receptor
Marine fish and shellfish species
140. The extent and nature of the colonisation of the hard structures by new species will be determined by the dominant natural substrate character of the fish and shellfish ecology study area (largely muddy sand, sand and slightly gravelly sand). For example, Andersson and Öhman (2010) found that when hard structures are placed on an area of seabed already characterised by rocky substrates, few species will be added to the area but an increase in total hard structures in the environment could sustain a higher abundance of species. However, when hard structures are introduced onto a soft seabed, most of the colonising fish will be those which are associated with rocky habitats (Andersson et al., 2010). These species will replace the original soft-bottom population and form a new baseline species assemblage (Desprez, 2000). However, it was noted by Desprez (2000) that these effects were site-specific and therefore may not necessarily be extrapolated to other offshore wind farms.
142. It is uncertain whether artificial reefs facilitate recruitment into the local population, or if these observations are simply a result of concentrating biomass from surrounding areas (Inger et al., 2009). Evidence demonstrates that the abundance of fish can be greater in the vicinity of foundations than in the surrounding area, which supports the conclusion by Linley et al. (2007) that finfish species were likely to have a neutral to beneficial likelihood of benefitting from introduction of these structures. Increases in species richness were also noted by Coolen et al. (2020), following the introduction of hard structures. Some studies have also shown evidence of increased abundances of small demersal fish species in the vicinity of wind turbine structures, most likely due to the increase in abundance of epifaunal communities which increase the structural complexity of the habitat (e.g. mussel and barnacles Cirripedia spp.) (Wilhelmsson et al., 2006a; 2006b). Some commercially important species including cod and other pelagic species have been recorded aggregating around vertical steel constructions in the North Sea (Andersson, 2011; Wilhelmsson et al., 2006a). Monitoring of fish populations in the vicinity of an offshore wind farm off the coast of the Netherlands indicated that the offshore wind farms acted as a refuge for at least part of the cod population (Lindeboom et al., 2011; Winter et al., 2010). Similarly, horse mackerel, mackerel, herring, and sprat have been found to utilise the new hard structures for spawning, or predation on the newly developed community (Glarou et al., 2020).
143. Contrastingly, post construction fisheries surveys conducted in line with the Food and Environmental Protection Act licence (under the Food and Environment Protection Act 1985) 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). These suggested that any effects, if seen, are likely to be highly localised, site dependent and while of uncertain duration, the evidence suggests effects are not necessarily adverse, although uncertainty does exist surrounding this issue.
144. The greatest potential benefit from the introduction of hard structures is likely to exist for crustacean species, such as crab and lobster, due to expansion of their natural habitats and the creation of additional heterogenous hard structure refuge areas (Linley et al., 2007). Where foundations are placed within areas of sandy and coarse gravelly sediments, this will represent novel habitat and new potential sources of food in these areas and could potentially extend the habitat range of shellfish species such as edible crab, which strongly associate with wind farm foundations (Hooper and Austen, 2014). There is evidence from post-construction monitoring surveys at the Horns Rev offshore wind farm in the North Sea that hard structures are particularly successful for hatchery and nursery grounds for the edible crab, as well as several other species. They concluded that crustacean larvae and juveniles rapidly colonise the hard structures from the breeding areas (BioConsult, 2006). A variety of shellfish IEFs have been identified as being likely to be present within the site boundary (refer to Table 9.12 Open ▸ ).
145. Other shellfish species, such as the blue mussel, have the potential for great expansion of their normal habitat due to increased hard structures in areas of sandy habitat, such as those in the fish and shellfish ecology study area. Krone et al. (2013) found that over a three-year period, almost the entire vertical surface of area of the platform piles had been colonised by three key species blue mussel, the amphipod Jassa spp. and anthozoans (mainly Metridium senile). These three species were observed to occur in depth-dependant bands, attracting pelagic fish species such as horse mackerel Trachurus trachurus and demersal pouting Trisopterus luscus in great numbers. Layers of shell detritus were visible at the base of the foundations due to the mussel populations above and both velvet swimming crab and brown crabs were recorded here. These species were not typical of baseline species assemblage, providing further evidence of localised changes in fish and shellfish assemblages in the vicinity of foundation structures.
146. The colonisation of new habitats may potentially lead to the introduction of INNS (see volume 2, chapter 8 for detailed discussion). With respect to fish and shellfish populations, this may have indirect adverse impacts on shellfish populations as a result of competition. However, no INNS were identified in the fish and shellfish ecology study area during the site-specific benthic subtidal ecology surveys. There is also little evidence of adverse effects on fish and shellfish IEFs resulting from colonisation of other offshore wind farms by INNS. The post-construction monitoring report for the Barrow Offshore Wind Farm demonstrated no evidence of INNS on or around the monopiles (EMU, 2008a), and a similar study of the Kentish Flats monopiles only identified slipper limpet Crepidula fornicata (EMU, 2008b). A study into the spread of INNS by wind farm hard structure colonisation suggested the risk of this occurring was minor, and requires more research to fully understand, with implementation of precautionary built-in measures recommended to prevent spread where possible (Baulaz, et al., 2023). Potential adverse impacts of the introduction of INNS are discussed further in detail in volume 2, chapter 8.
147. Marine fish and shellfish ecology IEFs in the fish and shellfish ecology study area are deemed to be of low vulnerability, and local to national importance (recoverability is not relevant to this impact during the operation maintenance phase). The sensitivity of the receptor is therefore, considered to be low.
Diadromous species
148. Diadromous species that are likely to interact with the fish and shellfish ecology study area are only likely to do so by passing through the area during migrations to and from rivers located on the east coast of Scotland, such as to rivers with designated sites, with diadromous fish species listed as qualifying features, as presented in Table 9.11 Open ▸ . In most cases, it is expected that diadromous fish are unlikely to utilise the increase in hard structures within the fish and shellfish ecology study area for feeding or shelter opportunities as they pass through the Array.
149. There is the potential for impacts upon diadromous fish species resulting from increased predation by marine mammal species within offshore wind farms and both Atlantic salmon and sea trout have been identified as having the potential to migrate through the site boundary. Tagging of harbour seal Phoca vitulina and grey seal Halichoerus grypus 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 foundations. However, a further study using similar methods concluded that there was no change in seal behaviour within the offshore wind farm (McConnell et al., 2012), so it is not certain exactly to what extent seals utilise offshore wind developments and effects may be site-specific. It is possible that if seals do utilise offshore wind developments as foraging areas, diadromous fish species may be impacted by the increased predation in an area where predation was lower prior to development. It is, however, unlikely that this would result in significant predation on diadromous species. Research has shown that Atlantic salmon smolts spend little time in the coastal waters, and actively swim in away from natal rivers making their way to feeding grounds in the north soon after maturation (Gardiner et al., 2018a; Gardiner et al., 2018b; Newton et al., 2017; Newton et al., 2019; Newton et al., 2021) (see volume 3, appendix 9.1 for further detail on Atlantic salmon migration). Due to the evidence that Atlantic salmon tend not to forage in the coastal waters of Scotland, they are therefore at low risk of impact from increased predation from seals and other predators in the fish and shellfish ecology study area as their presence in the region will be transitory.
150. Sea trout may be at higher risk of increased predation from seals than Atlantic salmon due to their higher usage of coastal environments. Given that sea trout are typically more coastal than Atlantic salmon, greater abundance would be expected further inshore than compared with the offshore waters of the site boundary (approximately 80 km offshore). Sea trout are generalist, opportunistic feeders with their diet comprising mainly of fish, crustaceans, polychaetes and surface insects with proportion of each of these prey categories varying dependent on season (Rikardsen et al., 2006; Knutsen et al., 2001). Due to the potential for increase in juvenile crustacean species and other shellfish species, which are possible prey items from sea trout, it is possible that foraging sea trout may be attracted to the hard structures introduced by installation of the Array. This attraction could in turn lead to increased predation of seal species upon sea trout species. However, there is little evidence at present documenting an increased abundance of sea trout around foundations (increases in fish abundance tend to be hard bottom dwelling fish species), therefore the effect of increased prey items attracting sea trout has not been recorded, to date. Given that it is unlikely that sea trout will spend time foraging around the foundations, there is a low risk of impact from increased predation from marine predators in the fish and shellfish ecology study area.
151. The low risk of impacts on diadromous fish species extends to the freshwater pearl mussel, which is included in the diadromous species section, as part of its life stage is reliant on diadromous fish species including Atlantic salmon and sea trout.
152. Most diadromous fish species are deemed to be of low vulnerability, high recoverability and national to international importance. The sensitivity of the receptor is therefore, considered to be low.
153. Atlantic salmon are deemed to be of low vulnerability, high recoverability and national to international importance. The sensitivity of the receptor is therefore, considered to be low.
154. Sea trout are deemed to be of medium vulnerability, high recoverability and national to international importance. The sensitivity of the receptor is therefore, considered to be low.
Significance of the effect
Marine fish and shellfish species
155. Some fish and shellfish species may benefit from the colonisation of hard structures, whereas others (more likely to be less mobile, demersal species associated with soft sediment habitats), may be adversely affected.
156. Overall, for the IEF species listed in Table 9.12 Open ▸ , the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be low. At worst, the effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms, though could be minor beneficial for some species. This is likely to be a conservative prediction as there is some evidence (although with uncertainties) that some fish and shellfish populations are likely to benefit from introduction of hard structures.
Diadromous species
Secondary mitigation and residual effect
158. No secondary fish and shellfish ecology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.
Underwater noise from piling and UXO clearance impacting fish and shellfish receptors
160. The following scenarios were investigated through site specific underwater noise modelling:
- single piling – wind turbine anchor piles (3,000 kJ);
- single piling – OSP jacket foundation piles (4,400 kJ);
- two concurrent piling events – wind turbine anchor piles (3,000 kJ); and
- two concurrent piling events – wind turbine anchor pile (3,000 kJ) and OSP jacket pile (4,400 kJ).
161. Underwater noise modelling was undertaken related to the MDS as outlined in Table 9.13 Open ▸ with the detail of the assessment provided in volume 3, appendix 10.1.
Construction phase
Magnitude of impact
162. The installation of wind turbine anchors and OSP foundations may lead to injury and/or disturbance to fish and shellfish species due to underwater noise during piling within the fish and shellfish ecology study area. The MDS ( Table 9.13 Open ▸ ), considers the greatest impact from underwater noise on fish and shellfish IEFs, based on the greatest hammer energy. This scenario is represented by the installation of up to 265 semi-submersible floating foundations, with up to six anchors per foundation and one 4.5 m diameter pile per anchor (1,590 piles) for wind turbines, and up to three large and 12 smaller jacket foundations (total 216 piles) for OSPs, with all piles installed via impact piling.
163. For wind turbines, piling was assumed to take place over a period of up to eight hours per pile with up to eight piles installed in each 24 hour period. OSP foundations will take place at an average of three piles over 24 hours (maximum duration of up to eight hours per pile) with up to eight piles installed in each 24 hour period. A maximum duration of 1,728 hours of piling activity, over a maximum of 72 months, may take place during the construction phase, based on the maximum duration of the piling phase.
164. Underwater noise modelling was undertaken for both single piling and concurrent piling (i.e. piling at more than one location simultaneously). To ensure a precautionary assessment, modelling of a concurrent piling scenario based on a 3,000 kJ hammer energy for the foundation piles and 4,400 kJ hammer energy for the OSP jacket piles has been undertaken, alongside single piling scenarios, using the maximum 4,400 kJ hammer energy for the OSP jacket piles. These are discussed further below in relation to injury impacts with relevant contours also presented and discussed in the context of potential behavioural impacts on fish and shellfish ecology receptors.
165. UXO clearance (including detonation) also has the capability to cause injury and/or disturbance to fish and shellfish IEFs. Clearance will be completed prior to the construction phase (pre-construction). The MDS ( Table 9.13 Open ▸ ) assumes clearance of 15 UXOs within the site boundary, with a maximum of 698 kg NEQ. The UXO clearance campaign will involve subsonic combustion with a single donor charge of up to 0.025 kg NEQ for each clearance event, and up to 0.5 kg NEQ to neutralise residual explosive material at each location. Total duration of UXO clearance campaigns is eight days, with up to two detonations within 24 hours.
166. To understand the magnitude of noise emissions from piling and UXO clearance during construction activity, underwater noise modelling has been undertaken considering the key parameters summarised above. Further, implications of UXO on fish injury are discussed in paragraphs 173 to 183. Compared to piling, UXO detonations will be single, isolated events of very short duration; as such, potential behavioural effects upon fish and shellfish will be extremely short lived and reversible.
Sensitivity of the receptor
168. The following sections apply to both marine fish and diadromous fish species.
169. Underwater noise can potentially have an adverse impact on fish species ranging from physical injury/mortality to behavioural effects, with focus given to the impacts on herring and cod, as well as a range of other species identified as IEFs. Peer reviewed guidelines have been published by the Acoustical Society of America (ASA) and provide directions and recommendations for setting criteria (including injury and behavioural criteria) for fish. These guidelines (Popper et al., 2014) provide the most relevant and best available guidelines for impacts of underwater noise on fish species (see volume 3, appendix 10.1).
170. The Popper et al. (2014) guidelines broadly group fish into the following categories according to the presence or absence of a swim bladder and on the potential for that swim bladder to improve the hearing sensitivity and range of hearing (Popper et al., 2014):
- Group 1: Fishes lacking swim bladders (e.g. elasmobranchs and flatfish). These species are only sensitive to particle motion, not sound pressure and show sensitivity to only a narrow band of frequencies;
- Group 2: Fishes with a swim bladder but the swim bladder does not play a role in hearing (e.g. salmonids and some Scombridae). These species are considered to be more sensitive to particle motion than sound pressure and show sensitivity to only a narrow band of frequencies;
- Group 3: Fishes with swim bladders that are close, but not connected, to the ear (e.g. gadoids and eels). These fishes are sensitive to both particle motion and sound pressure and show a more extended frequency range than Groups 1 and 2, extending to about 500 Hz; and
- Group 4: Fishes that have special structures mechanically linking the swim bladder to the ear (e.g. clupeids such as herring, sprat and shads). These fishes are sensitive primarily to sound pressure, although they also detect particle motion. These species have a wider frequency range, extending to several kHz and generally show higher sensitivity to sound pressure than fishes in Groups 1, 2 and 3.
171. Relatively few studies have been conducted on impacts of underwater noise on invertebrates, including crustacean species, and little is known about the effects of anthropogenic underwater noise upon them (Hawkins and Popper, 2016; Morley et al., 2013; Williams et al., 2015). There are therefore no injury criteria that have been developed for shellfish, however, these are expected to be less sensitive than fish species and therefore injury ranges of fish could be considered conservative estimates for shellfish species (risk of behavioural effects are discussed further below for shellfish).
172. An assessment of the potential for injury/mortality and behavioural effects to be experienced by fish and shellfish IEFs with reference to the sensitivity criteria described above is presented in turn below.
Injury
173. Table 9.19 Open ▸ summarises the fish injury criteria recommended for pile driving based on the Popper et al. (2014) guidelines, noting that dual criteria are adopted in these guidelines to account for the uncertainties associated with effects of underwater noise on fish.
Table 9.19: Criteria for Onset Injury to Fish Due to Impulsive Piling (Popper et al., 2014)a
a Relative risk (high, moderate, low) is given for animals at three distances from the source defined in relative terms as near field (N; i.e. 10s of metres), intermediate (I; i.e. 100s of metres), and far field (F; i.e. 1000s of metres); Popper et al. (2014).
174. The full results of the underwater noise modelling are presented in volume 3, appendix 10.1. To inform the assessment for fish and shellfish ecology receptors, predicted injury ranges associated with the installation of one 4.5 m diameter pile have been presented. The metrics presented are for cumulative sound exposure level (SELcum) for moving fish and static fish ( Table 9.20 Open ▸ ), and SPLpk ( Table 9.21 Open ▸ ). This modelled scenario resulted in the greatest predicted injury ranges and therefore forms the focus of the assessment for injury, noting that in most cases, the maximum hammer energy would not be reached during piling.
175. For the cumulative SEL metric, the injury ranges presented indicate that injury may occur out to ranges of tens to a few hundred metres, based on the MDS (e.g. mortality ranges for the 3,000 kJ hammer energy of 15 m to 50 m for fleeing receptors and 328 m to 1,460 m for static receptors; see Table 9.20 Open ▸ ). Practically, the risk of fish injury will be considerably lower due to the hammer energies being lower than the absolute maximum modelled, through soft starts. The expected fleeing behaviour of fish from the area affected when exposed to high levels of noise and the soft start procedure, which will be employed for all piling mean that it is likely that those fish species which flee from a noise source will have ample time to vacate the areas where injury may occur prior to noise levels reaching that level.
176. For peak pressure noise levels when piling energy is at its maximum for the foundation pile installation ( Table 9.21 Open ▸ ) mortality and recoverable injury to fish may occur within approximately 266 m to 414 m of the piling activity (lower estimate for Group 1 fish species, higher estimate for Groups 2, 3 and 4 species). The potential for mortality or mortal injury to fish eggs would also occur at distances of up to 414 m ( Table 9.21 Open ▸ ). When piling for OSP foundations (i.e. maximum hammer energy of 4,400 kJ; Table 9.22 Open ▸ ), greater injury ranges are predicted (e.g. mortality ranges of 25 m to 425 m for fleeing receptors and 855 m to 3,380 m for static receptors based on the cumulative SEL metric; Table 9.22 Open ▸ ). Underwater noise modelling using the peak SPL metric showed a similar pattern with mortality and recoverable injury to ranges of up to 615 m to 1,055 m for the maximum hammer energy of 4,400 kJ. For eggs and larvae, the mortality range is also 1,055 m for the 4,400 kJ hammer energy ( Table 9.23 Open ▸ ).
177. Based on the two noise criteria (SEL and SPL), injury will occur in the range of tens to hundreds of metres ( Table 9.20 Open ▸ to Table 9.23 Open ▸ ), with the injury ranges larger for the greater hammer energy of 4,000 kJ for OSP jacket pile installations. However, these are maximum energy scenarios, which, in most cases, will not be reached. Additionally, injury ranges at the start of each piling sequence will be much smaller than the maximum scenario due to soft starts; at 660 kJ for OSP foundations and 450 kJ for foundation piles.
Table 9.20: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Fleeing and Static Fish
Table 9.21: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Peak SPL Metric
Table 9.22: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Cumulative SEL Metric for Moving and Static Fish
Table 9.23: Potential Injury Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Peak SPL Metric
178. Construction may occur utilising two pile installation vessels operating concurrently. The potential cumulative SEL injury ranges for fish due to impact pile driving of piles are modelled as following the same piling plans with all phases starting at the same time. For injury, the MDS is that of two adjacent piles, separated by a distance of 950 m due to the maximal overlap of noise propagation contours leading to the maximum generated noise levels. Conversely, for disturbance the maximum separation between two piling locations would lead to the larger area ensonified at any one time and therefore the greatest disturbance (discussed further below).
179. Injury ranges for concurrent piling of OSP jacket pile installation at 4,400 kJ and foundation piles at 3,000 kJ at each site are given in Table 9.24 Open ▸ . The peak metric will remain the same as the single installation case. For all other piling scenarios, injury ranges would be smaller; the full range of modelled scenarios are given in volume 3, appendix 10.1. As expected, these show that for this precautionary cumulative piling scenario, injury ranges are similar or slightly larger than the single piling scenarios for fleeing fish, but considerably larger (e.g. double the ranges) for static fish receptors.
Table 9.24: Potential Injury and Disturbance Ranges for Concurrent OSP Jacket Pile Installation at 4,400 kJ and Wind Turbine Foundation Pile at 3,000 kJ Based on the Cumulative SEL Metric for Fleeing and Static Fish
180. Underwater noise modelling has also been undertaken for UXO clearance/detonation. The criteria used in this underwater noise assessment for explosives are given in Table 9.25 Open ▸ following Popper et al. (2014). There are no thresholds in Popper et al. (2014) in relation to eggs and larvae in terms of sound pressure.
Table 9.25: Criteria For Injury To Fish Due To Explosives (Popper et al., 2014)b
b Note: Relative risk (high, moderate, low) is given for animals at three distances from the source defined in relative terms as near field (N; i.e. 10s of metres), intermediate (I; i.e. 100s of metres), and far field (F; i.e. 1000s of metres); Popper et al. (2014).
181. Underwater noise modelling was undertaken for a range of orders of detonation, from a realistic maximum design case high order detonation to low order detonations (e.g. deflagration and clearance shots) to be used as mitigation to reduce noise levels. Table 9.26 Open ▸ details the injury ranges for fish of all groups in relation to various orders of detonation. The method of low order has been committed to ( Table 9.13 Open ▸ ) and as such will be the dominant method of UXO clearance, although higher order detonations may also occur if low order is not successful or unintentionally as part of the low order process.
182. The predicted injury ranges for low and high order disposal order detonations of UXOs are presented in Table 9.26 Open ▸ and demonstrate the effectiveness of the low order methods to reduce the risk of injury to fish and shellfish ecology receptors (i.e. injury ranges of tens of metres for low order, but up to 930 m for high order detonations).
Table 9.26: Potential Impact Ranges for Low Order, Low Yield, and High Order UXO Clearance Activities, Based on Injury Criteria in Table 9.25 Open ▸