Seabirds: strategic ornithological compensatory measures: review

8 Discussion and recommendations

This report has provided an assessment of twelve potential strategic compensatory measures that could be used to compensate for assessed impacts from offshore wind developments following derogation procedure under Article 6(4) of the Habitats Directive. Of these twelve measures, seven were considered in detail for ecological feasibility (section 5). Where measures were less well defined, or where we could not readily identify specific conservation actions, these were considered via scoping reviews (section 6), with one measure assessed via a targeted review (bycatch mitigation). Seven measures were then considered for practical feasibility (section 7). The report has helped clarify some of the key issues that need to be considered when evaluating options for strategic compensation. While we have provided overall assessments of feasibility for measures (see section 1), we caution that the relative ranking of measures is highly dependent on the context in which measures are used (e.g. for which species) and how different criteria or considerations are weighted in decision making.

This report has the following general limitations (these are discussed further below):

• Starting point was a list of measures provided by Scottish Government (see Table 4). While we consider that this includes most measures being discussed in the context of strategic compensatory measures, it is not an exhaustive list of potential options.
• This is a technical review, while it does include wider considerations, especially in the practical feasibility section (see section 7), it does not fully assess issues which are more of a policy or legal nature, e.g. additionality; or sociological or socioeconomic considerations which will be important to consider for some potential measures.
• During the preparation of this report, the full impacts of HPAI on seabird populations was unknown, which is particularly relevant for some of the species most impacted by offshore wind developments (e.g. Gannet). Dedicated HPAI census results were published (Tremlett et al., 2024) during preparation of the final report revision, which limited the extent to which they could be fully integrated. Nonetheless, some edits were made to highlight this).
• It is reliant on the evidence that is available and what could be located for our review.
• In a review covering such a wide suite of measures, we were only able to partially cover some ecological aspects of the measures; e.g. seasonal, regional differences, and different population components (e.g. juveniles vs. breeding adults).
• The scoring used throughout considers measures in terms of their potential for application as strategic compensation (not e.g. as project-level compensation nor as wider conservation measures). The scoring is highly dependent on the criteria used and how these criteria are weighted. As such, the scores provided here should be treated as a guide only and not be considered definitive. For the practical feasibility assessments, we were not able to cover all site-specific aspects which are crucial to feasibility, so would need to be considered if implementing measures as strategic compensation.

The policy and guidance around compensation measures for offshore wind is developing rapidly. Following the Energy Act there is expected to be various legislative and non-legislative (statutory guidance) changes that will affect how compensatory measures are assessed and delivered, including enabling strategic delivery of compensatory measures. However, at the time of this review there was no clear framework or set of criteria for assessing potential strategic compensatory measures (see recommendation 1), so a bespoke approach was taken for the report. This report considers technical and ecological factors which are fundamental to selecting between options. However, the approach to selecting measures is ultimately also dependent on factors that are more of a policy nature, for example, how compensatory measures relate to other policy objectives, e.g. SPA network objectives^[14]. While it is desirable to score and rank potential compensatory measures, the reality is that the choice of the most appropriate is highly context-specific and dependent on how different criteria are weighted. For the systematic reviews of ecological feasibility (see section 5, summarised in (Table 2), we used a standardised scoring approach developed for this report. In theory, this scoring approach makes it possible to directly compare the ecological efficacy scores between measures. However, in practice, due to variation in the evidence available and in the types of measures (see next paragraph), we could not achieve absolutely comparable scores.

Our ability to assess a measure’s ecological efficacy is clearly dependent on the volume of evidence and the relevance of that evidence (how closely the published evidence relates to the proposed compensatory measure). However, the ability to assess measures is not just determined by the volume and relevance of evidence, but also by the type of measure itself. The more indirect measures are fundamentally harder to assess, as the effects on the target seabird species are several steps removed from the compensatory action. These types of measures, that are usually ecosystem-based (e.g. targeting forage fish availability), may require delivery at wide spatial scales or evidence to be collected over many years (even decades), before unequivocal conclusions on their efficacy can be reached.

Developing an approach that allows decisions to be made following a sound scientific basis based in ecological theory, while acknowledging the uncertainty on the specific outcomes from a given compensatory measure, is likely to be necessary to develop some broader ecosystem-based measures. Here, it will be useful to learn from approaches developed in restoration ecology (see e.g. Palmer et al. (2016)), where ecological theory is applied to guide restoration initiatives but where confident predictions on specific outcomes cannot be formed. In these cases, we will often need to rely on projections or forecasting, rather than evidence from existing trials, to make anticipatory predictions (Mouquet et al., 2015), because until certain novel or wide scale measures are applied, we will not be able to observe their effects directly. While a predictive approach may allow consideration of a wider suite of potential compensatory measures than if limited to those that have been empirically tested (i.e. trialled in some way), it is important to consider accuracy in predictions (Beckage et al., 2011; Elliott-Graves, 2019). However, when used appropriately, predictive models can have a useful role in informing policy and management decisions (Sutherland and Freckleton, 2012). This issue is, in part, mirrored by uncertainty in predicting the effects of offshore wind developments. Some of the thinking that has been developed for accounting for this uncertainty (Searle et al., 2023b) may be useful to apply also in the context of how we assess compensatory measures and apply adaptive management.

For a measure to lead to a compensatory response it must have a positive effect on one or more demographic rates (e.g. adult survival or productivity). When selecting amongst alternative options for compensatory measures it is important to consider the ecological context, both of the impacted population and of what the effect is that is triggering the need for compensation (e.g. whether it is collision mortality or loss of habitat). For example, if adult mortality is the key effect (e.g. from collision mortality) leading to a requirement for compensation, then the most effective compensatory measures will usually be those measures that reduce some other source of adult mortality. However, there is potential for measures not directly countering such effects to also function as compensation. For example, a measure that boosts productivity could allow a population to withstand higher mortality rates.

Climate change adds an additional complexity, as even if we are able to demonstrate that a certain measure is effective at the current time, or that it has been in the past, we cannot necessarily be confident that it will continue to be in future as ecosystems change. For example, the North Sea is currently experiencing fundamental shifts in its ecology with shifts in zooplankton communities having potential for cascading effects at higher trophic levels (MacDonald et al., 2015; Lindegren et al., 2017; Olin et al., 2022). Recent studies have predicted profound changes in UK breeding seabird populations over the coming decades due to climate change (Searle et al., 2022; Davies et al., 2023). The theory and practice of how we consider this threat in conservation decision-making is still developing (see e.g. Hirsch and Long (2021)). While there has been work to consider options for conserving seabirds in the face of climate change (Pearce-Higgins et al., 2021; Hakkinen et al., 2022), there has been less consideration in terms of how we develop conservation and restoration measures that are resilient to and/or remain effective as conditions change. We recommend that this is considered when developing compensatory measures (see recommendation 5) including considering how we can make better uses of predictive approaches (see above).

Coordinated delivery of multiple measures can potentially increase the effectiveness of individual measures and thus increase overall confidence that measures will deliver the desired compensatory effect. For example, improving nesting habitat may only have limited effects on productivity if breeding success is limited by foraging conditions. Therefore, where possible, when designing strategic compensatory measures, consideration should be given to delivering a suite of measures (potentially some as compensation and others for wider nature restoration/enhancement purposes).

We provide the following recommendations for further work around strategic compensatory measures for seabird populations:

1. When considering a specific measure, consider the recommendations included within the corresponding report sections.

2. Developing guidance for how strategic compensatory measures should be assessed, including key criteria to consider (see also, recommendation 3).

3. For more indirect measures, including those acting at a wider ecosystem scale, we recommend that a decision-making framework is developed for how such measures can be evaluated. This framework would support developing a better understanding on how to link these measures to population level responses for the target seabird populations. Without this, it will rarely be possible to have confidence that such measures can deliver as compensation by helping support coherence of the network for the impacted feature species. This framework would include policy and technical aspects and would help inform on research and adaptive management. For example, selection of appropriate proxies (e.g. prey availability) for use in adaptive management where the ultimate effects (e.g. seabird productivity) cannot be realistically related directly to the compensatory measure. Note these proxies would only be appropriate where there is confidence that there is a link between the proxy and the ultimate effect and that all key ecological factors have been considered (e.g. increasing forage fish may not increase prey for seabirds if they are outcompeted by predatory fish). Applying path analysis and structural equation modelling approaches (Garrido et al., 2022) could be beneficial here.

4. For many potential categories of compensatory measures (e.g. habitat management at breeding colonies) there has been a lack of detailed work to scope out what specific conservation actions could be delivered as compensation. This report includes a scoping section from some of these potential measures (see section 6), but many areas would benefit from their own dedicated reviews and research, including field trials.

5. Developing an integrative approach to compensatory measures that accounts for, and works to support, adaptation in seabird populations to the impacts of climate change.

This report has demonstrated that there are multiple conservation measures that have potential to be applied as strategic compensation for offshore wind impacts. However, all the measures considered had varying challenges to overcome if they were to be developed as strategic compensation. This report has mapped out some of these issues and provided recommendations on how these can be addressed.