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Impact Assessment

Description of Baseline Conditions and Cumulative Impact Assessment
Appropriate Assessment
Predicting and Characterising Ecological Impacts
  Confidence in Predictions
  Positive or Negative
  Timing and Frequency
Characterisation of the Change and Impact
Assessment of whether Impacts are Ecologically Significant
  Determining Ecologically Significant Impacts
  Precautionary Principle
  Conservation Status
Presentation of Information and Assessment
Worked Example


5.1 Assessment of impacts on ecological features and resources is required at each of the following stages:

  • in scoping - a broad assessment is needed to provide the basis for selecting those ecological features and resources that will undergo detailed assessment (see Chapter 2);
  • during the evolution of the project to identify:
    • opportunities for preventative management;
    • the need for impact avoidance and mitigation; and
    • opportunities for enhancement;
  • after the mitigation strategies have been fully devised and their likely success considered;
  • after the residual impacts have been assessed if significant negative impacts are still likely; and
  • during construction, operational and decommissioning phases(s).

5.2 The starting point for any assessment is to determine those ecological features or resources within the zone of influence that are of sufficient value to be included in the assessment and are vulnerable to significant impacts arising from the project (see Chapter 4). The rationale for selecting features for inclusion in the EcIA will differ depending on the location, and therefore should be agreed through consultation during scoping. For those ecological features included in the assessment i.e. they have been ‘scoped in’, the next step is to describe:

  • the changes to the baseline conditions likely to arise from the project; and related activities (access, cabling etc); and
  • the resulting impacts.

If, at the scoping stage, these impacts are considered likely to be significant, they should be investigated further and clearly described in ecological terms, before the legal, policy, social or economic implications are considered. Where features are scoped out justifications should be recorded.

5.3 The following guidance is consistent with the EIA Regulations and defines good practice.

Description of Baseline Conditions and Cumulative Impact Assessment

5.4 Assessment of impacts should be undertaken in relation to the baseline conditions within the zone of influence of the proposed development. There are circumstances where a project is likely to be delayed for a significant period of time and therefore there is a need to take account of any clearly identifiable changes to the baseline that can be anticipated. Thus, for example, if construction is programmed for a point five years ahead of the analysis, construction impacts should be assessed against the baseline conditions predicted to occur at that time.

5.5 It is necessary to predict the future baseline conditions with reference to:

  • environmental trends, for example, climate change and coastal processes (including Holocene evolution);
  • cumulative and in-combination effects including completed developments that may affect the zone of influence in the future;
  • conservation objectives for designated coastal and marine sites;
  • any other developments for which planning consent has been granted; and
  • management plans in place for designated sites.

Some relevant information may be available in Strategic Environmental Assessments (SEAs)48, 49, 50 or Sustainability Appraisals (SAs) that have been prepared for plans and programmes and in the ESs of completed or planned developments. It is not appropriate, however, to use long-term climate change impacts to justify judgements that downplay predicted impacts.

5.6 Predicting the future baseline in this way also enables the EcIA to address cumulative and in-combination impacts. This is achieved by assessing the impacts of the proposal in the context of future conditions, including the effects of other projects (see example in Box 11).

5.7 The predicted baseline and approach to assessing cumulative and in-combination impacts should be agreed between all relevant parties during scoping. Close liaison is required between the proponent team and decision makers.

Appropriate Assessment

5.8 EcIA can be either a key component of an EIA or a discrete project in its own right; it is not the same as an ‘appropriate assessment’. Appropriate assessment is the specific decision process undertaken by a ‘competent authority’ where a project affects a Natura 200051 or Ramsar Site and is deemed ‘likely to have a significant effect’. There are subtle differences because the Habitats Directive is designed to ensure that at the end of the assessment process there should be no adverse affect on the integrity of the site i.e. the features for which it was designated. Where impacts are accepted because there are no alternatives and a project is deemed to be necessary for ‘imperative reasons of over-riding public interest’, compensatory measures must be delivered to ensure compliance with the objectives of the Directive. The ‘appropriate assessment’ thereforelooks at the ‘in-combination’ effects of definable projects that are following but have not completed the consents regime, or which have been consented but have not been completed or mitigated/compensated. EcIA and EIA may consider past, unmitigated impacts that may have a bearing upon the impact of new projects, as well as any other ongoing projects that may be relevant. However, there is no statutory requirement for the ultimate outcome to have an ecologically neutral impact and an EcIA cannot be treated as an appropriate assessment because EcIA is not conducted by a 'competent authority’.

5.9 In preparing an EcIA, it is important to bear in mind that the information assembled may be relevant to the completion of an ‘appropriate assessment’. As such, it is in the client’s best interests to make sure that information is compiled in such a way that it can be readily extracted and presented (often as a supplementary annex) as ‘information to inform appropriate assessment’. This part of the EcIA process demands strict quantification of impacts and linkage to the conservation objectives for the protected site. In other words, how do the projects affect the conservation objectives for the protected site?  In this context, traditional assessments of significance cannot be used – there are three clear options which are judgements that can only be made by the Competent Authority in consultation with the SNCOs:

  • there will be no adverse affect on the integrity of a Natura 2000 site; or
  • it cannot be ascertained that there will be no adverse affect on the integrity of a Natura 2000 site; or
  • there will be an adverse affect on the integrity of a Natura 2000 site.

Predicting and Characterising Ecological Impacts

5.10 Having identified the activities likely to cause significant impacts (see Chapter 2), it is necessary to describe the predicted project-related ecological changes and to assess the impact on the valued ecological features. The proponent’s ecologist should expect to liaise with other members of the proponent’s team as the changes to be considered may relate to a wide range of issues such as hydrology, oceanography, water quality, coastal processes, noise, or shipping and navigation.

5.11 The process of identifying impacts should make explicit reference to aspects of the ecosystem’s structure and function on which the feature depends. Some of the elements that may be considered are identified in Box 9. This process is also reflected in the MarLIN sensitivity assessment. It is recommended that habitats and species should be classified in accordance with the Marine Habitat Classification for Britain and Ireland52 so that species and biotope sensitivity and recoverability listed on MarLIN can be used.

5.12 Impacts must be assessed in the context of the predicted baseline conditions within the zone of influence during the lifetime of the development. Predicting the baseline conditions for valued ecological resources should involve consideration of environmental trends and impacts from development activities, as described in Chapter 3 and under the heading of ‘Integrity’ below. This ensures that cumulative and in-combination impacts are properly addressed.

Box 9:  Some examples of elements of ecological structure and function to consider when predicting impacts.

Available resources
Territory: hunting/foraging grounds; shelter sites; breeding and spawning sites; migration routes and dispersal; stop-over sites.
Food (quantity and quality).
Substrate minerals and nutrients and hydrochemistry.
Light penetration and gaseous resources.
Water movement (for filter-feeding, external fertilisation and larval dispersal).

Oceanographic and physical-chemical processes
Nutrient blooms, prevailing weather patterns (e.g. North Atlantic Oscillation), storm damage and tidal conditions, disease, erosion and sedimentation regimes, deposition and other geomorphological processes, temperature fluctuations, climate change.

Ecological processes
Population dynamics: population cycles; survival rates and strategies; reproduction rates and strategies; competition; predation; seasonal behaviour; dispersal and genetic exchange.  
Algal, microbial and sessile/mobile species dynamics: colonisation; succession; competition; and nutrient-cycling.

Human influences
Aquaculture husbandry, fishing activities, bait digging, shellfisheries, kelp harvesting, culling, excavations, maintenance dredging, port/harbour and other coastal development, coastal defence, water abstraction, flow regulation, land claims, pollution and contamination, use of biocides, introduction of non-native species and genetically modified organisms, noise (sonar, seismic etc.), disturbance from public access and recreation, transport.

Historical context
Natural range and variation over the recorded historical period.
Irregular perturbations beyond the normal range (such as very infrequent storm events).
Historical human influence, e.g. water quality changes, land claim, species exploitation.
Geomorphological evolution.

Ecological relationships
Food webs, predator-prey relationships, e.g. herbivore/planktivore food-source relationships, herbivore/carnivore relationships, adaptation and dynamism.

Ecological role or function
Decomposer, primary producer, herbivore/planktivore, parasite, predator, keystone species.

Ecosystem properties/services
Fragility and stability, carrying capacity and limiting factors, productivity, community dynamics.
Open/closed system.
Numbers in a population or meta-population, minimum viable populations.
Sex and age ratios.
Patchiness and degree of fragmentation.

 Confidence in predictions

5.13 It is important to consider the likelihood that a change or activity will occur as predicted and also the degree of confidence in the assessment of the impact on ecological structure and function. The limitations to certainty should be described and the consequences for confidence in predictions must be stated clearly. A qualitative description may be adequate. Provided limitations are properly recorded, an objectively defined scale based on a stated convention can be used even if the confidence level can only be based on expert judgement, rather than frequency data. Consequently, a meaningful scale in normal language might be: Certain, Probable, Unlikely. Alternatively, based on the fact that the 5% confidence level is conventionally chosen as the lowest limit for acceptable statistical significance in common scientific practice, a four-point scale that might be usefully employed is:

  • Certain/near-Certain: probability estimated at 95% chance or higher.
  • Probable: probability estimated above 50% but below 95%.
  • Unlikely: probability estimated above 5% but less than 50%.
  • Extremely Unlikely: probability estimated at less than 5%.

5.14 The reason for including a confidence level category of 'extremely unlikely' is that some effects may be very improbable, but extremely serious should they occur and hence merit contingency planning. Where doubt exists as to which of two categories of probability best fits the level of professional confidence, the more precautionary level should be cited.

5.15 In most cases, ongoing survey or monitoring may be required to refine predictions or activate mitigation projects.

5.16 When describing changes/activities and impacts on ecosystem structure and function, reference should be made to the following parameters, which are discussed below:

  • positive or negative;
  • magnitude;
  • extent;
  • duration;
  • reversibility; and
  • timing and frequency.

Positive or Negative?

5.17 Is the impact likely to be positive or negative?  Positive impacts merit just as much consideration as negative ones, as international, national and local policies increasingly press for projects to deliver positive biodiversity outcomes. It is however, worth bearing in mind that an impact that raises species diversity may not be a positive impact if the affected biotope is naturally species-poor. It should also be remembered that the SNCOs may not place the same onus on particular outcomes being positive; consequently it would be wise to discuss such assessments with relevant staff in the SNCOs before finalising such judgements.


5.18 Magnitude refers to the 'size' or ‘amount’ of an impact, determined on a quantitative basis if possible. For example, the number of breeding seals likely to be affected by a development; a total loss of intertidal habitat from direct overbuilding; a partial loss of the structure and function of a seagrass Zostera spp. bed due to smothering by sediment. Whilst it may not be possible to provide a quantitative assessment in the latter example, application of some of the following parameters will provide a more accurate understanding of the likely impact.


5.19 The extent of an impact is the full area over which the impact occurs. When the receptor under consideration is the habitat itself, magnitude and extent may be synonymous, but the intensity may vary, especially in the marine environment. It is important to ensure that absolute values are reported, where possible, as these provide the context for subsequent value judgements that may be a matter of debate between the consultancy team and the SNCO advisers.


5.20 The duration over which the impact is expected to last prior to recovery or replacement of the feature should be defined in relation to the ecological characteristics (for example species’ lifecycles) rather than human timeframes. For example, seabed habitats such as sandbanks that are comparatively mobile are likely to recover more quickly from impacts than reefs that support long-lived sessile organisms. Likewise, impacts on long-lived species with a low reproductive rate such as cetaceans could last much longer than effects on shorter-lived fish species.

5.21 The duration of an activity may differ from the duration of the resulting impact caused by the activity. If, for example, construction activities lead to disturbance of a successful breeding bird population and therefore a failure to reproduce during that season, it is possible that the decline in overall numbers will only become apparent as the adults die out and there are insufficient progeny to replace them.


5.22 For the purposes of this guidance:

  • an irreversible (permanent) impact is one from which recovery is not possible within a reasonable timescale or for which there is no reasonable chance of action being taken to reverse it; and
  • a reversible (temporary) impact is one from which spontaneous recovery is possible or, for which effective mitigation is both possible and an enforceable commitment has been made.

5.23 In some instances, the same activity may cause both irreversible and reversible impacts. For example, a causeway or breakwater development may be predicted as nearly certain to cause reversible changes to the distribution of certain fish populations arising from disturbance during construction activities, and will probably cause long term or irreversible changes to sea bed habitats due to subtle hydrodynamic impacts. This is because a ‘tipping point’ has been reached where impacts to the sea bed structure and/or function result in it becoming unable to support the re-colonisation of biotopes previously present. Changes considered irreversible can involve loss of biotopes such as biogenic reef-forming species such as Lophelia, which are unable to re-colonise areas even following project decommissioning.

Timing and Frequency

5.24 Some changes may only cause an impact if they happen to coincide with critical life-stages or seasons (for example, the fish breeding or migration season). This may be avoided by careful scheduling of the relevant activities, e.g. by the implementation of an EAP that specifies important constraints in relation to the timing of works.

5.25 The frequency of an activity and hence the resulting impact should also be considered. For example, there may be occasions when a single person walking a dog will have very limited effect on nearby waterfowl using wetland habitat. If, however, numerous walkers subject the waterfowl to frequent disturbance, then feeding success may be significantly reduced. In extreme cases the birds could be permanently displaced. Conversely, at Bathside Bay, Harwich the exclusion of visitors in advance of port development work, led to a significant increase in bird usage. Other possible examples include usage of near-shore waters by kite-surfers, which on their own may be insignificant but will be highly significant if numbers increase. Regular passage of vessels through waters used by diving ducks and fish-eating birds may be a further example. Equally, disturbance may take place seasonally (rafts of sea ducks in winter) or weekly e.g. recreational impacts at the weekend.

Characterisation of the Change and Impact

5.26 In order to characterise the likely change and impact, it is necessary to take into account all the above parameters. Take, for example, the construction of a marina that would involve capital dredging of the benthic habitat totalling 4,600 m2. Confidence in describing this change is high, based on the developer’s plans. However, the impact of this loss on the structure and function of the surrounding habitat is less certain. The quality and extent of the habitat that will potentially be lost and the habitat surrounding the affected area both require assessment. This will help to determine if the surrounding habitat is similar in community composition to the habitat that will be lost, if it is of a viable size and how it may be affected by any smothering or other effects of the dredging activity. Mitigation to minimise the impacts of the dredging on the surrounding habitat can be suggested.

5.27 If the habitat that is to be lost through the capital dredging is similar to the surrounding habitat, research can indicate a time-frame over which communities of the dredged habitat may recover (if the substrate conditions have not been irreversibly altered). It may be a number of years before the community assemblage resembles the baseline condition, assuming no maintenance dredging takes place.

5.28 Box 10 gives an example of the way in which setting the baseline enables effective assessment of cumulative effects.


5.28 The dynamics of the marine environment, together with the current level of knowledge of impact pathways, sometimes makes it necessary to evaluate the potential risk of a particular hazard occurring, for example this might be the case for:

  • an oil spill arising from transfers between ships;
  • the introduction or spread of invasive species, (see 7.22);
  • an unusual siltation event caused by rarely experienced wave and tidal conditions;
  • an erosion event linked to changes in substrate morphology;
  • an oil rig fire, or leakage; or
  • a windfarm structure failure.

5.30 In each example, the impact of the hazard may be high whilst the likelihood of such an event is low. Assessment of such situations depends upon analysis of risk comparing the evidence for such an event occurring with the evidence for its potential impact. Within the analysis consideration should be given to measures that may be used to minimise the potential for risk. Risk management of this nature, with a clear audit trail that explains the assumptions is an essential component of the assessment, providing reassurance both to the client and to the competent authorities.

Box 10:  Example scenario for setting the baseline and assessment of cumulative impacts

The scenario
An EIA for a proposed extension to an existing port facility within an estuary is under development. The extension will involve the removal of an area of inter-tidal mud and dredging of sub-tidal mud, both areas are out-with, but adjoin, a site designated for its national value. Expansion of another port in the same estuary is currently underway.

The approach to setting the baseline and considering cumulative impacts should be agreed as a result of discussion between the competent authority, the SNCO and any other relevant agencies. It is likely to include consideration of the following:

Predicting the Baseline

  • the agreed conservation objectives (if any);
  • trends affecting the baseline condition of inter-tidal habitats, e.g. sea-level rise, climate change or anticipated changes in the level of disturbance caused by the increased traffic generated by the visiting public;
  • predicted impacts arising from the current port expansion, as reported in the EIS; and
  • predicted (but yet to occur) effects from completed port-related projects, e.g. long-term erosion of inter-tidal habitats expected to occur as a consequence of the original port, acting together with the inter-tidal habitat erosion predicted to occur as a consequence of the proposed port expansion.

Considering cumulative impacts
The changes arising from the project should be described in the context of the predicted baseline e.g. the current port expansion project is likely to include capital dredging, which together with environmental trends and predicted (but yet to occur) effects from completed projects, will change the estuary’s morphology. This predicted situation is the baseline against which any changes arising from the capital dredge for the new project should be assessed, such as changes to the hydraulic processes that act on the inter-tidal habitats.

Assessment of whether Impacts are Ecologically Significant

Determining ecologically significant impacts

5.31 Legislation and policy guidance require significant negative or positive impacts to be distinguished from one another, although there is little guidance on how this distinction should be made (see Box 11). Where no conservation designations apply, significance can be evaluated by using the proportional extent of an affected site, or relating impacts to likely changes as a result of climate change. However, where projects affect designated sites this is not the case. For example, the loss of foreshore might be equated to the likely level of loss to sea level rise over a particular time frame and therefore it might be argued that the impact was insignificant in the context of sea level rise. Alternatively, a loss of extent may be quoted as a percentage of the overall extent and might therefore be regarded as insignificant. Both of these examples fail to take account of the process of designated site selection and the conservation objectives issued by the SNCOs and are therefore inappropriate.

5.32 Importantly, the concept of SSSI (in the UK) has been to secure boundaries around tightly defined interest features and consequently they represent the minimum necessary to maintain the scientific interest. Furthermore, the conservation objectives will normally consider ‘no loss of extent (subject to natural change)’ as the underpinning principle for conservation. Consequently, impacts need to be compared against a defined baseline, rather than a wider timeframe or spatial consideration. Where impacts affect a coastal location, the impact of climate change and sea level rise may have been recognised through the preparation of a Coastal Habitat Management Plan (CHaMP)53 that takes account of the impact of sea level rise and coastal squeeze and negates the contention that the habitat will be lost anyway.

Box 11: Determining Ecologically Significant Impacts


The term ‘significant’ has meaning in terms of both the EIA Regulations and the Habitats Regulations. There are substantial differences between its usage in these two contexts and this frequently leads to confusion. Significance in the context of the Habitats Regulations is used as a coarse filter to establish the overall scale of the impact and whether a possible pathway for an effect can be identified.   

Where a likely significant effect on a Natura 2000 site is identified (and, in the UK, as a matter of policy, Ramsar sites are included) an ‘appropriate assessment’ is required to determine whether or not there will be an adverse affect on the integrity of a European site; if this cannot be determined then further tests must be satisfied before a project is consented.

Significance in the context of the EIA Regulations is used to describe the relative importance of impacts on any feature of importance, regardless of the application of the Habitats Regulations.

Application within EcIA

An ecologically significant impact is an impact that has a negative, or positive, effect on the integrity of a site or ecosystem and/or the conservation objectives for habitats or species populations within a given geographical area. In this way significant impacts are distinguished from other, lesser (and, in the context of EIA, unimportant) effects. The concept of integrity is elaborated in paragraph 5.37 et seq.

It is important to establish the geographical scale of predicted impacts so that the extent to which a project potentially conflicts with nature conservation legislation or policy can be identified and its significance determined.

The geographical scale at which a predicted significant impact will occur is determined by the value of the feature(s) affected (see paragraph 4.4 et seq.). So a predicted significant impact on a feature of interest of an SPA would be a significant impact at a European level. If the feature affected was a population or habitat of, say, regional importance, then the assessment would conclude that it would be a predicted significant impact on a feature of county importance.

The assessment should focus on the highest level of importance of a feature whilst recognising that it is also of interest at other levels.

In addition, there may be habitats or species populations present within the site that do not form part of its designated interest features, but are still important in their own right. These should be identified as features and potential impacts upon them assessed in a way that is commensurate with their value.

5.33 The value of any feature that will be significantly affected is used to identify the geographical scale at which the impact is significant. This value relates directly to the consequences, in terms of legislation, policy and/or licensing and development control at the appropriate level. So, a significant negative impact on a feature of importance at one level would be likely to trigger related planning policies and, if permissible at all, generate the need for development control mechanisms, such as planning conditions or legal obligations, as described in those policies.

5.34 If an impact is not significant at the level at which the resource or feature has been valued, it may still be significant at a more local level e.g. the presence of pink sea fans Eunicella verrucosa, which are protected at a national level may mean that the overall value of the resource is greater than current designations imply.

5.35 During the assessment process, the magnitude of an impact upon a site or ecosystem may be found to be lower than had been originally anticipated. In some cases, it may be lower than the threshold that would trigger concern about overall negative impacts according to the agreed conservation objectives. Nonetheless, there may still be impacts on features that are of specific, if more localised, interest whose conservation status may be affected. For example, whilst a particular impact may not be considered to have a significant negative effect on the conservation objectives set for an SPA, it may be found to be likely to have a significant impact on the conservation status of a population of non-qualifying species (that is of national or local value).

5.36 In summary, if there is likely to be a significant impact on an ecological feature, the consequences, in terms of development control, policy guidance and legislation, will depend on the level at which it is valued. Where avoidance cannot be achieved in the first instance, significant impacts on features of ecological importance should be mitigated (or compensated for) in accordance with guidance derived from policies applied at the scale relevant to the value of the feature or resource. Any significant impacts remaining after mitigation (the residual impacts), together with an assessment of the likelihood of success of the proposed mitigation, are the factors to be considered against ecological objectives (legislation, policy and development control) in determining the application.

5.37 There may be conditions or legal agreements attached to a consent to ensure the delivery of the proposed mitigation. The commitment of the proponent to such arrangements will influence the assessment of the likelihood of success of the mitigation.


5.38 To determine the possibility of a significant effect on a site or ecosystem it is necessary to understand whether the changes arising from the project are likely to influence baseline conditions of the site or ecosystem. It is then necessary to establish whether these changes are likely to weaken or strengthen the integrity of that system. The lack of information on many marine ecosystems and understanding of the effects of many marine developments need to be taken into account when assessing significance. Advice on the use of the concept of integrity is given below.

5.39 The term ‘integrity’ has a long lineage in the ecological literature. This concept evolved to deal with ecosystems and networks of protected sites, and can be applied to sites that can reasonably be considered to represent an ecosystem. It is also used here to indicate the conditions required for an ecosystem to continue functioning in its characteristic form. This interpretation should also take account (where appropriate) of the ecosystem services that are provided, particularly those that buffer the effects of human activities or naturally occurring extreme events on key receptors e.g. natural coastal zones areas that provide protection from flooding. It is important to note that the marine environment differs from the terrestrial in that the impact pathways and ecosystem linkages are often much stronger but sometimes less clearly defined or understood. As a result it is recommended that clear distinctions are made when assessing impacts to the integrity of ecosystems and protected sites (or both).

5.40 The EC Habitats Directive and associated national regulations, require that development shall normally not be permitted when it will negatively affect the 'integrity' of such sites. In this case, a particular definition of site integrity is provided in the UK Government circular:  biodiversity and geological conservation – statutory obligations and their impact within the planning system54 and in the equivalent Welsh (TAN 5)55 and Scottish guidance56 as follows:

'The integrity of a site is the coherence of its ecological structure and function, across its whole area, that enables it to sustain the habitat, complex of habitats and/or the levels of populations of the species for which it was classified.'

5.41 A protected site that achieves this level of coherence is considered to be at favourable condition when it is judged to be meeting established conservation objectives. It may be necessary to expand the parameters under consideration when looking at the wider ecological impacts of a project - i.e. not just at a protected area.

5.42 For protected sites, a key measure of integrity is the extent to which its conservation objectives are being met. Where they are being met, a site is considered to be in favourable condition, this should not be confused with favourable conservation status a term in the Habitat Directive; a term which is yet to be defined.

5.43 Outside protected areas it is unlikely that conservation objectives exist or that there is a definition of what would constitute favourable condition or the baseline condition. The development of an agreed baseline should, therefore, require engagement between the project team, relevant external specialists (e.g. SNCO staff), to consider the:

  • extent of the habitats present;
  • composition of particular assemblages and the degree to which these fit into more widely used descriptions of biotopes;
  • assemblages or age classes; and
  • scarcity of assemblages or degree to which they are re-creatable.

Where the above information is not available, agreement will need to be reached on the data to be gathered for specific habitats and species, including how it is to be collected and over what time period.

5.44 In the marine environment it is very difficult to define clear site boundaries; interaction with a wider zone of influence is thus likely. Therefore, it is very unlikely that the impacts on integrity can be evaluated without considering functions and processes acting outside the site’s formal boundary. Thus any predictions should always consider wider ecosystem processes.

5.45 In determining whether there is likely to be an effect on the integrity of a site or ecosystem, the answers to the following questions should be considered.

  • Will any site/ecosystem processes or key characteristic be removed or changed?
  • What will be the effect on the extent, structure and function of component habitats?
  • What will be the effect on the average population size and viability of component species?
  • What will be the effect on the capacity of the site/ecosystem to buffer the effects of extreme natural events or pollution arising from human activities?

This should be in the light of the overall questions:

  • For protected sites/species: are the projects likely to move the condition of the site/species towards or away from favourable condition; and/or
  • For ecosystems: are the projects likely to result in an adverse ecosystem response?

5.45 When assessing potential impacts on sites with international and national designations, integrity should be considered in relation to the published citations and the conservation objectives. Conservation objectives for sites within the marine environment in the UK are defined within statutory advice from the SNCOs given under Regulation 33 of the Habitats Regulations (1994). In some cases, there are 'criteria features', 'attributes', 'measures' and 'targets' against which likely changes can be assessed (see e.g. Wheeldon 200357).

5.46 Many ecosystems have a degree of resilience to perturbation that allows them to tolerate some biophysical change before the fundamental ability of the site or ecosystem to support characteristic habitats or species populations is compromised. Clearly there will sometimes be an element of doubt as to whether the change is sufficient to cause such changes as described in 5.45 above. This should be reflected in assigning confidence levels to the predictions. Mitigation measures may then be proposed to increase the level of confidence in that prediction, even when a negative effect on integrity is not predicted.

Precautionary Principle

5.47 Where there is doubt, and it cannot be proven that a negative impact will not arise, a precautionary approach (see SNIFFER 2006) should be adopted and a negative effect on integrity predicted. This is required for sites, species and habitats protected under the EC Birds and Habitats Directives. Case law such as the Waddensea judgement (cockle fishery) C-127/02 reinforces the need to establish certainty that a negative impact will not arise.

5.48 For beneficial effects that may result in the creation of new sites or ecosystems, or intervention to restore degraded examples, the concept of site integrity is equally applicable. The intervention must be sufficiently robust as to sustain the new level of value created in all reasonably predictable scenarios.

Conservation Status

5.49 As indicated above, the extent to which a project may have an effect should be determined in the light of its expected influence on the integrity of a protected site or ecosystem. The integrity of protected sites is considered specifically in the light of the site’s conservation objectives. Beyond the boundaries of sites with specific nature conservation designations and clear conservation objectives, in line with approaches taken in UK BAP and MARLin, it is recommended that the concept of ‘conservation status’ is used.

5.50 The EC Habitats Directive (Article 1, sections (e) and (i)) provides a helpful definition of conservation status for habitats and species. This guidance uses slightly modified versions of these definitions so that evaluation of conservation status can be applied to habitats or species within any defined geographical area:

  • for habitats, conservation status is determined by the sum of the influences acting on the habitats and its typical species that may affect its long-term distribution, structure and functions as well as the long-term survival of its typical species within a given geographical area; and
  • for species, conservation status is determined by the sum of influences acting on the species concerned and inter-relationships that may affect the long-term distribution and abundance of its populations within a given geographical area.

5.51 Conservation status should be evaluated for a study area at a defined level of ecological value. The extent of the area used in the assessment will relate to the geographical level at which the feature is considered important.

5.52 In some cases, (e.g. for BAP species and habitats) there may be an existing statement of the conservation status of a feature with formal objectives and targets. Most species or habitats will not be described in this way and in such cases the conservation status of each feature being assessed should be agreed with the relevant SNCO.

5.53 When assessing potential effects on conservation status, the same reasoning should be applied as set out above in relation to conservation objectives. The known or likely trends and variations in population size should be considered. The level of ecological resilience, or the level likely to exist, in terms of the quality of physical and biotic conditions, that would permit the given population of a species or area of habitat to continue to exist at a given level, or continue to increase along an existing trend, should also be estimated.

5.54 A significant positive impact could be defined as one that prevented or slowed an existing decline as much as one that permitted a population or habitat area to increase.

Presentation of Information and Assessment

5.55 It is important to remember that the EcIA and EIA will usually be assessed by the SNCOs (as statutory consultees) who will be asked to provide an opinion to the competent authorities. Their advice is crucial to the competent authority and can be instrumental in the subsequent progress of a project. A list of the competent authorities and statutory consultees for Ireland is given in section 4 of the EPA guidance on EIA.

5.56 The statutory agencies will focus on ensuring the assessment is transparent and contains sufficient information to assist in the determination of the ecological changes that may arise. The use of unquantified assessment terms (insignificant, minor, significant, etc) without clear definitions will prevent the application of judgement and the principles developed within the agency concerned to the case. This invariably leads to delay as clarification is sought. It is in the proponent’s best interests for these data to be presented clearly and straightforwardly, even if they do suggest that there may be an impact of a magnitude that gives rise to concern. This is because public inquiries in which the predicted impacts are challenged can be costly, involve considerable delay, and undermine confidence in the project proceeding.

5.57 Where projects relate to a statutory site that is affected by sea level rise and coastal squeeze, it is tempting for assessors to factor in the impact of these processes and to argue that losses to a development would have happened anyway over a longer timescale and therefore the impact is less pronounced than it would otherwise have been. This approach is not advisable because the impact is immediate; it reduces the available habitat and takes the site away from favourable condition, and will be regarded unfavourably by the SNCOs and other conservation bodies, which can be expected to vigorously challenge the approach.

5.58 The process of evaluation is an important precursor to determining those impacts that can be mitigated and those that require compensatory measures (particularly in accordance with the Habitats Directive). Experience shows that the early identification of robust and defensible mitigation and compensatory measures is greatly facilitated if a relationship based on clarity and openness is established with statutory advisors and key stakeholders from the outset.

Worked Example

5.59 A worked example considers the application of the Guidelines to a project to develop an offshore wind farm.

5.60 A commentary provides the background to the analysis of the overall significance on integrity and conservation status of feature (that might be suitable for the main text of the ES), with a Table giving a summary of the analysis.

Worked Example – Offshore Wind Farm

Note: The worked example provided below, whilst intended to be as realistic as possible, is fictitious and for illustrative purposes only. Its aim is to show the general principles of how the approach to EcIA recommended in these Guidelines might be applied in practice. The actual values of various parameters and the conclusions reached could differ in a real situation; other parameters could be relevant and other research findings brought to bear. 

The Project

The application considered in this example relates to a project to develop an offshore wind farm with a capacity of approximately 450 MW. In common with many such applications the project takes the form of an envelope i.e. an area of sea and seabed within which the development is proposed. Specific details of the design will be confirmed when and if consent is granted and subject to a more detailed design exercise. Nevertheless, for the purposes of EIA it has been agreed that likely development scenarios will include either 90 x 5 MW turbines or 150 x 3 MW turbines. The latter is more likely as it is unclear that a commercial case can be made for the use of 5 MW turbines. It is also considered that, from an ecological perspective, many smaller turbines represent the worst-case scenario (more disturbance, greater footprint, etc.). On this basis the EcIA is based on the 150-turbine scenario. The 3 MW turbines proposed are likely to have a maximum (to tip of blade) height of no more than 130 m.

Four cables (export cables) will be installed to connect the wind farm to the onshore electricity-generating network.

Scoping Issues for an Offshore Wind Farm

The categories of potential ecological effect arising from offshore wind farms are likely to include:

  1. Loss of benthic habitat arising from the installation of turbines foundations and scour protection.
  2. Habitat and species disturbance arising from the installation and operation of export and other cabling.
  3. Changes to coastal processes resulting in changes to the distribution and composition of sediment types.
  4. Noise arising from construction activities and to a lesser extent in operation.
  5. Disturbance from construction activities.
  6. Disturbance arising from the operation and maintenance of the wind farm.
  7. Pollution from accidental release of fuels/oils during construction and during operation.
  8. Effects on migratory species.

Loss of habitat is likely to be restricted to the turbine locations around the masts.
Temporary disturbance would be along the export cable route, which may extend for some distance inshore, including inter-tidal areas. The potential impacts of 1 and 2 would be on benthic habitats, fish spawning and foraging for birds.

Coastal process effects could manifest over a large region – the extent of which may need to be modelled. There is potential for effects to offshore and coastal sediments and these changes could affect benthic habitats and associated species.

Noise from construction vessels can result in disturbance to bird populations and marine mammals within the wind farm and within access routes. Noise, particularly from piling operations, has the potential to cause lethal and sub-lethal effects to fish, marine mammals and birds and these effects can occur over many kilometres.

During operation, maintenance vessels can disturb bird populations and marine mammals within the wind farm and within access routes.

Operational wind farms may cause ongoing disturbance to bird populations, with some species likely to avoid turbine structures. Some species are also at risk of collision with turbine blades. Electromagnetic fields around export cables have the potential to affect elasmobranchs.

There is some risk of pollution during construction from the release of fuels, oils and sediments (during piling) and during operation from the leakage of oil from turbines or off-shore substations.

Setting the baseline

The scope of the EcIA will, therefore, need to include consideration of the effects arising from the construction, operation and decommissioning of the wind farm and its export cables over a typical lifetime of at least 25 years. These effects may impact upon water quality, benthic habitats and species, inter-tidal habitats, fish populations, marine mammals and birds. The zone of influence will vary for each, but will extend from the immediate location of the turbines and export cables (e.g. habitat loss) to areas many kilometres from the wind farm site (e.g. coastal processes and noise) and the baseline will need to reflect this.


Benthic habitat surveys (sidescan sonar and grab sampling) indicate that the wind farm area comprises infralittoral mobile clean sand with sparse fauna (SS.SSa.IFiSa.IMoSa). This biotope comprises medium to fine sandy sediments and typically supports an impoverished fauna. This is a widespread biotope around England that occurs at various locations on the east coast (including Spurn Head and The Wash), the Sussex coast, Start Point (Devon), the Bristol Channel and Morecambe Bay; it is less widely recorded in Scotland, Wales and Ireland. SS.SSa.IFiSa.IMoSa forms part of the Subtidal Sands and Gravel (previously Sublittoral Sands and Gravel) priority habitat listed under the UK Biodiversity Action Plan (BAP).

The surveys indicate that in places SS.SSa.IFiSa.IMoSa grades to SS.SBR.PoR.SspiMx (previously CMX.SspiMx) ‘Sabellaria spinulosa on stable circa-littoral mixed sediment’. This biotope is found in the subtidal and lower intertidal/sublittoral fringe and in places S. spinulosa forms biogenic reef structures that support a diverse community of epifauna and infauna. It has a wide but restricted distribution throughout the north-east Atlantic, especially in areas of turbid seawater with high sediment loads. However, records are restricted to the east coast (south of Whitby) and south coast (no further west than Weymouth) of England; it has also been recorded from several locations on the Welsh coast. Biogenic reef is a habitat type listed on Annex I of the EC Habitats Directive and is a priority habitat under the UK BAP. Discussions with relevant experts and SNCO indicate that this biotope is rare within the region where the wind farm is proposed and that the reef is sufficiently extensive to qualify as a SAC (but is not classified as a candidate SAC). Some parts of the area have been proposed for inclusion in the Natura 2000 network.

Boat-based and aerial surveys indicate the presence of 56 species of birds, including lesser black-backed gulls, which were recorded throughout the year. A literature search and discussions with the SNCO indicate that birds recorded within the proposed wind farm area are likely to include breeding birds from a coastal SSSI. The breeding population of lesser black-backed gulls (~400 pairs) is an interest feature of the SSSI.


Protection Status

Conservation Status



Subtidal features




BAP priority habitat



SS.SBR.PoR.SspiMx (Biogenic reef)

Annex 1

cSAC interest feature
BAP priority habitat

Very restricted






Lesser Black-backed Gulls

General protection under WCA

SSSI interest feature

Common and widespread


Impact assessment

For the purpose of this section, two potential impacts arising from the wind farm example are considered in detail. The first relates to habitat disturbance on the SS.SSa.IFiSa.IMoSa and SS.SBR.PoR.SspiMx biotopes. The second is the operational impact of potential collision mortality on the breeding population of lesser black-backed gulls.

Feature 1:  Habitats


Surveys, initially comprising side-scan sonar and grab analysis both conducted over a coarse sampling grid, have confirmed the presence of the SS.SSa.IFiSa.IMoSa biotope and its spatial extent. It is also known, from historical data (> 5 years old) and side scan sonar that biogenic reefs formed by S. spinulosa are present, although the extent and precise location of individual reefs is less well understood.

Construction Impacts

1 Direct habitat loss

1.1 Proposed activity and its duration biophysical change and relevance to receptor in terms of ecosystem structure and function

Turbine foundations would be installed within SS.SSa.IFiSa.IMoSa biotope, but not within an area known to support biogenic reef. The construction of turbines is expected, to result in the loss of an area of the SS.SSa.IFiSa.IMoSa biotope beneath turbine foundations and the associated scour protection. However, the area affected is not considered likely to significantly damage the ecosystem structure and function.

1.2 Characterisation of unmitigated impact on the feature

Habitat loss arising from the installation of turbine foundations is likely to be restricted to the immediate area of the foundation pile and scour protection (comprising rock armour). The habitat loss associated within each turbine is unlikely to extend over more than 300 m2. As 150 turbines are proposed, the total area affected is unlikely to exceed 4.5 ha. (Out of a total wind farm area of 12,000 ha). Habitat loss is a long-term effect, it will persist until the turbine structures are removed (a 25 year operational lifetime is predicted for the wind farm).

1.3 Rationale for prediction of effect on integrity (of a site or ecosystem) or conservation status (of a habitat or population)

As sublittoral sands and gravels are widespread both within the proposed wind farm area and more widely within Britain, the extent of habitat loss arising from this wind farm construction is considered to be very small at geographical scales.

1.4 Significance without mitigation and confidence in assessment

Although the effect of habitat loss arising from turbine construction is long term (at least 25 years), a significant negative effect is not predicted due to the very small proportion of this habitat affected.

1.5 Mitigation, enhancement and compensation

Although a significant effect is not predicted it is considered good practice to limit the extent of habitat loss arising from construction.

1.6 Residual significance (confidence)

It is certain that the habitat loss arising from turbine construction will not be significant.


2 Habitat disturbance (abrasion and physical damage)

2.1 Proposed activity and its duration, biophysical change and relevance to receptor in terms of ecosystem structure and function

The operation of, and activities associated with, jack-up barges used in turbine erection and the installation of inter-array electrical cables during construction have the potential to cause disturbance to habitats. The use of high pressure water jets to assist in the burial of inter-array cables is known to cause the temporary liberation of sediments, which may disperse over nearby areas of habitat causing smothering. The extent of ‘jetting’ is not known in advance, but previous experience shows that it tends to be only occasionally required.

Four cables are proposed, which will be installed sequentially. These export cables from the wind farm will pass through an area where biogenic reefs are known to form. The preferred installation method, ploughing, has the potential to cause direct structural damage to the reefs.

2.2 Characterisation of unmitigated impact on the feature

The extent of any effect arising from construction of the wind farm turbines is not known but it is expected that disturbance will be restricted to localised damage and abrasion of benthic fauna in the area immediately adjacent to turbine foundations. In light of the extent of similar habitat recolonisation, recovery is, however, likely to be rapid and any effect will be fully reversible in the short-term.

The extent of any sediment plume arising from jetting activities is unlikely to extend over more than several hundred square metres and is expected to persist for a timeframe measured in hours rather than days.

The disturbance to the habitat from installing the four proposed export cables will, based on previous experience, be restricted to a corridor of no more than 40 m (10 m maximum per cable). Approximately 1 km of the cable route passes through an area known to support the SS.SBR.PoR.SspiMx community, although the extent of biogenic reef within this area is unknown.  Installation of the cables will cause damage to any biogenic reef present. Based on experience in similar developments, these effects are probably reversible but only in the long-term with localised damage expected to persist for several years.

2.3 Rationale for prediction of effect on integrity (of a site or ecosystem) or conservation status (of a habitat or population)

The following are extracts from the Habitat Action Plan (HAP) for Subtidal Sands and Gravel (

‘Sand and gravel habitats are subjected to a variety of anthropogenic factors including the influence of pollutants in riverine discharge and physical disturbance by fishing and aggregate dredging activities. The latter two factors probably have the greatest influence on the organisms that inhabit sand and gravel substrata...
Many species inhabiting highly perturbed and mobile sediments are relatively unaffected by fishing activities or other anthropogenic physical disturbance. However, large bodied, slow growing fauna such as bivalves are sensitive to fishing disturbances and their populations may be slow to recover. Biogenic reefs and sedentary worm beds may be particularly vulnerable to trawling activity.

In summary, the biotope is less sensitive to short-lived mechanical impacts than those arising from repeated disturbance or pollution.

In contrast the SS.SBR.PoR.SspiMx biotope is considerably more sensitive to even small scale physical disturbance. For example, MarLIN ( indicates that: S. spinulosa reefs are particularly affected by dredging or trawling and in heavily dredged or disturbed areas an impoverished community may be left (e.g. SS.SCS.CCS.Pkef) particularly if the activity or disturbance is prolonged. However, it is likely that reefs of S spinulosa can recover quite quickly from short term or intermediate levels of disturbance as found by Vorberg (2000) in the case of disturbance from shrimp fisheries and recovery will be accelerated if some of the reef is left intact following disturbance as this will assist larval settlement of the species.

On this basis it is considered that the SS.SSa.IFiSa.IMoSa biotope is resilient to disturbance effects of low magnitude and can be expected to recover quickly from direct habitat damage and sediment deposition of the magnitude envisaged here. It is probable that the predicted effects on this community arising from habitat disturbance would be insignificant. Biogenic reefs, however, are considerably more sensitive to disturbance which impacts on their physical structure. It is considered probable that damage to reefs arising from cable installation could negatively affect the conservation status of this feature.

2.4 Significance without mitigation and confidence in assessment

The effects of disturbance arising from the installation of turbines and inter-array cables will be temporary and very limited in their spatial extent. It is anticipated that the community affected by this disturbance will rapidly recover from these disturbance effects. A significant negative effect from turbine installation and inter-array cabling is not, therefore, predicted.

A significant negative effect on biogenic reefs, arising from export cable installation, at the international level is probable. The physical disturbance caused by the cable installation process is reversible but only in the long-term. As this is an interest feature of a cSAC, the likelihood of such an effect is sufficient to trigger the requirement for an ‘appropriate assessment’.

2.5 Mitigation, enhancement and compensation

Although no significant impacts arising from the installation of turbine foundations and inter-array cables have been identified, it is considered good practice to minimise the extent of any unnecessary habitat disturbance. On this basis it is recommended that the extent of jetting used during inter-array cabling is constrained to those areas where it is essential.

A detailed survey of the proposed export cable route which passes through the SS.SBR.PoR.SspiMx community will be undertaken using remote video surveying techniques to identify the location of individual biogenic reefs. The cable route will be modified to avoid these features.

2.6 Residual significance (confidence)

It is certain that the effects of turbine installation in areas that do not support biogenic reef would not be significant.

It is certain that the effects of the installation of export cables in areas that do not support biogenic reef would not be significant. If detailed surveys are undertaken and biogenic reefs are avoided during the installation of export cables then the effect of construction disturbance is unlikely to be significant.


Feature 2:  Lesser black-backed gulls

Surveys of the proposed wind farm area indicate occasional use of the site during the breeding season by lesser black-backed gulls. A maximum monthly count of 20 individuals was recorded during a two-year programme of boat surveys, and approximately 25% of all observations were recorded at rotor height (assumed to be between 30 – 150 m above sea level).

Construction Impacts

3 Collision mortality

3.1 Proposed activity, duration of activity, biophysical change and relevance to receptor in terms of ecosystem structure and function

The installation of wind turbines has the potential to be an additional mortality factor for bird populations due to collision with turbine blades; the risk arises when birds fly within the rotor swept area. The project is for 150 turbines in the vicinity of a breeding colony of lesser black-backed gulls (< 10 km). Any birds of this species observed within the wind farm (particularly during the breeding season) are assumed to form a part of the breeding population that is an interest feature of the adjacent SSSI.

3.2 Characterisation of unmitigated impact on the feature

Collision risk modelling (using a method agreed with the SNCO and with appropriately cautious assumptions) indicates that approximately 0.30 – 0.50 birds per year can be expected to collide with turbine blades (it is assumed that any bird colliding with a turbine blade will die). Although there are uncertainties in the collision risk modelling undertaken (including, but not limited to, assumptions about avoidance rates) precautionary assumptions have been agreed with the SNCO and other consultees. In light of these assumptions it is considered that the upper value in this range is the maximum rate of mortality likely to arise during operation.

3.3 Rationale for prediction of effect on integrity (of a site or ecosystem) or conservation status (of a habitat or population)

Without application of methods such as Population Viability Analysis (PVA) it is not known to what extent the breeding population of lesser black-backed gull can sustain additional levels of mortality. It has been agreed, with the SNCO and other consultees, that any impact not increasing adult mortality by more than 1% of the existing background mortality rate can be considered to be insignificant. Wanless et al (1996) indicates that annual adult survival is 93%, which implies a background mortality rate of about 56 birds within a population of 800 (i.e. 400 pairs), therefore, a predicted mortality rate arising from collision of greater than 0.56 birds per year would be considered to be significant.

3.4 Significance without mitigation and confidence in assessment

The predicted annual mortality rate arising from collisions with turbines is less than the threshold agreed with the SNCO and it is considered that it is probable that the impact would not be significant at the national (or any other) level.

3.5 Mitigation, enhancement and compensation

No options for mitigation have been identified.

3.6 Residual significance (confidence)

It is probable that there would not be a significant impact on the lesser black-backed gull arising from collision mortality.


Vorberg, R. (2000). Effects of shrimp fisheries on reefs of Sabellaria spinulosa (Polychaeta). ICES Journal of Marine Science, 57, 1416-1420.

Wanless, S., Harris, M.P., Calladine, J. & Rothery, P. (1996). Modelling responses of herring gull and lesser black-backed gull populations to reduction of reproductive output: implications for control measures. Journal of Applied Ecology, 33, 1420–1432.

Feature 1:  Habitats


Characterisation of unmitigated impact on the feature

Significance without mitigation and confidence level

Mitigation and Enhancement

Residual significance and confidence level

Construction impacts





Direct habitat loss

Turbine and scour protection construction will result in the long-term (>25year) loss of approximately 4.5 ha of the SS.SSa.IFiSa.IMoSa biotope.

Habitat loss is considered to be insignificant in the context of the availability of similar habitat within the wider area at all geographical scales: certain.

None required, but it is considered to be good practice to restrict unnecessary habitat loss to a minimum.

Certain not to have a negative effect on the conservation status of this biotope and therefore not significant.

Habitat disturbance (abrasion and physical disturbance)

The operation of jack-up barges is expected to cause localised abrasion and damage to benthic fauna (associated with SS.SSa.IFiSa.IMoSa biotope) around turbine structures.

Sediment plumes generated by jetting of inter-array cables may cause localised smothering of benthic fauna (associated with SS.SSa.IFiSa.IMoSa biotope).

Installation of export cables may cause abrasion and damage of biogenic reef within a 40 m wide corridor.

Habitat disturbance arising from the operation of jack-up barges is considered to be insignificant in the context of the availability of similar habitat within the wider area and the potential for rapid recolonisation of affected areas at all geographical scales: certain.

Smothering arising from jetting operations is considered to be insignificant in the context of the availability of similar habitat within the wider area and the potential for rapid recolonisation of affected areas at all geographical scales: certain.

A significant negative effect on biogenic reefs, arising from export cable installation, at the international level is probable.

None required for disturbance arising within the wind farm, but it is considered to be good practice to restrict unnecessary habitat disturbance to a minimum.

A detailed survey of the proposed export cable route which passes through the SS.SBR.PoR.SspiMx community will be undertaken using remote video surveying techniques to identify the location of individual biogenic reefs. The cable route will be modified to avoid these features.

It is certain that the effects of turbine installation in areas that do not support biogenic reef would not be significant.

It is certain that the effects of the installation of export cables in areas that do not support biogenic reef would not be significant.  If detailed surveys are undertaken and biogenic reefs are avoided during the installation of export cables then the effect of construction disturbance is unlikely to be significant.

 Feature 2:  Birds


Characterisation of unmitigated impact on the feature

Significance without mitigation and confidence level

Mitigation and Enhancement

Residual significance and confidence level

Operational impacts





Collision mortality

Collision risk modelling indicates that the operation of the wind farm will result in an increase in mortality within the lesser black-backed gull population of approximately 0.30-0.50 birds per year.

The predicted annual mortality rate arising from collisions with turbines is less than the threshold agreed with the SNCO and it is considered that it is probable that the impact would not be significant at the national (or any other) level.

No options for mitigation have been identified.

It is probable that there would not be a significant impact on the lesser blacked-backed gull arising from collision mortality at any geographical scale.

Depending on the length of the delay, it may result in the requirement for re-surveys or further surveys, in which case the relevant SNCO should be contacted to establish any need for such surveys on a case-by-case basis.

Note, however, that any particular trend does not justify early destruction of a particular block of habitat, thus exacerbating the trend.