Guidance Note 6: Guidance to support Offshore Wind Applications - Marine Ornithology Impact Pathways for Offshore Wind Developments

​Published: 2023
Version 1: January 2023

This document is part of a series of guidance notes available on Advice on marine renewables development - marine ornithology.

This guidance note sets out our advice on impact pathways for offshore wind developments.  Please see Guidance Note 1 - Guidance to support Offshore Wind Applications: Marine Ornithology which provides the context within which this guidance note is provided. Check the log of updates in guidance note 1 to ensure the most current version is being followed. We expect each and every developer to adhere to this guidance, including the recommended parameters to provide consistent and comparable results for all Scottish projects to be assessed as an individual project and cumulatively.  This guidance note should be used in conjunction with the Cumulative Effects Framework (CEF).

Please note this guidance was written prior to the development of a NatureScot position on how to account for the ongoing Highly Pathogenic Avian Influenza (HPAI) mortality event within an impact assessment. We are currently developing this advice and will provide updates and guidance when they are available. In the interim please contact [email protected]  should you have any specific queries.

1. Introduction

There are a number of ways in which marine bird species can be impacted by offshore wind developments. In this note we outline the key impact pathways that should be considered as part of the Environmental Impact Assessment (EIA) and Habitats Regulations Appraisal (HRA).

The FeAST tool provides sensitivities of marine bird species to different anthropogenic impacts. We recommend the use of this for identifying relevant literature on impact pathways for each species. The two key impact pathways identified for offshore wind energy are collision risk, when marine birds fly and collide with the rotating turbine blades, leading to direct mortality; and distributional responses such as displacement and barrier effects, which is the effective loss of habitat/barriers to movement resulting in energetic stress to marine birds - which can have consequences on fitness including survival rates and productivity. These impacts can occur at any time of the year. There are a number of other impacts that may also arise from an offshore wind farm development and associated works, including changes to prey distribution, pollution and disturbance due to installation of export cables.

NatureScot Guidance Note 9 - Seasonal periods for birds in the Scottish Marine Environment should be used for breeding and non-breeding season definitions. In order to consider any population consequences arising from distributional changes and estimated collisions, the overall impacts will need to be apportioned by season, between SPAs and other designated sites. For other impacts detailed below these should be considered by season and age class, if appropriate, for each relevant protected site.

We provide specific guidance notes for impact pathways for determining connectivity with marine SPAs and assessing collision risk and distributional responses (displacement and barrier effects). For all other impact pathways, we outline our advice with respect to assessment methodologies below.

2. Consideration of Prey Species

Offshore wind developments may have indirect impacts on marine birds by affecting their prey availability. Impacts to key prey species and their habitats within the wind farm are considered across all development phases alone and in combination with other wind farms in the development area, particularly in areas of importance for foraging seabirds (Wakefield et al. 2017). Breeding density, fine‐scale tracking, and large‐scale modelling reveal the regional distribution of four seabird species.  We recognise most EIA reports concentrate on receptor specific impacts, however increasingly we need to understand the impacts at the ecosystem scale and predator/prey interactions.  Consideration across key trophic levels will enable better understanding of the consequences (positive or negative) of any potential changes in prey distribution and abundance on ornithological interests, and how this may influence population level impacts.  Drivers of change could include habitat loss and potential changes to trophic interactions and community structure and function, including prey species compositional changes e.g., changing from those dependant on sandy substrates to those species favouring rocky substrates.  Consideration of these issues can be included in chapters assessing impacts on benthic interests and fish/shellfish, however we advise that a summary of this is included within the ornithology chapter and that clear links and references be made between the receptor chapters. We also strongly recommend the use of hyperlinks to connect associated assessments for ease of navigating.

3. Cables

It is important to consider the impacts of all cable routes and installation including export, interconnector and array cables, especially if the cable routes or landfall overlap or are in close proximity to designated sites. Additional detailed information on cabling activities and associated vessel movements/sizes, including nature of works, locations, duration and timing, will be required to assess potential impacts on marine birds. There is also a need to consider effects on prey resources, including prey-supporting benthic habitats, for both EIA and HRA for marine SPAs.   For example, closer to land consideration may be needed for the inshore qualifying features such as the diver, grebe and seaduck species many of which demonstrate high or very high behavioural sensitivity to visual disturbance (see e.g. Jarrett et al. 2018 ; Goodship and Furness 2019, Heinänen et al. 2020). Depending on the location of the development, this may be exacerbated by cumulative disturbance from other projects active within the SPA and wider area.

4. Disturbance

There are a number of species that are sensitive to disturbance from both vessel traffic and construction activities (refer to FeAST ). Some species also have particularly vulnerable periods within their annual cycle (for example, flightless moult periods, or any species provisioning young). We therefore require assessment of any associated vessel movements and proximity and timing of any disturbing activities. Noting that vessel routes may go through or be in close proximity to designated sites. We would expect any Vessel Management Plan to include explicit consideration of reducing disturbance to marine birds. Mitigation methods may help reduce these impacts; for example avoiding sensitive times of the annual cycle, avoiding any aggregations of birds on the water and following good practice using principles from the Scottish Marine Wildlife Watching Code.

We acknowledge there is limited evidence available to indicate that significant disturbance from underwater noise is likely (i.e. from noisy pre-construction activities such as high order UXO detonation and geophysical surveys), however it is important to consider the proximity to designated sites.  Mitigation measures necessary to reduce impacts to marine mammals species will help reduce any impacts to diving seabird species in the absence of such evidence. 

5. Cumulative Impacts

The focus and scope of the cumulative assessment (both for the EIA and HRA) should be discussed with NatureScot.  The Cumulative Effects Framework (CEF) will provide the tools that enable this to be undertaken; and should be used when published.

Breeding season

For the breeding season, the colonies affected by a development should be determined (based on MMFR+1SD) then determine all other developments within MMFR+1SD of those colonies.  The cumulative assessment should consider effects from projects within mean-max +1SD foraging range of the designated sites under consideration, based on Woodward et al. (2019).

Non-breeding season

Cumulative assessment in the non-breeding season should include all developments agreed for inclusion in any assessment within the region defined for the species, either by BDMPS or other agreed approach (i.e. for guillemots and razorbills).

There may also be a need to include wind farms located in Scottish and rest of UK (and Irish) waters.  Further discussion and agreement is needed regarding transboundary / cross-border impacts and should be agreed during the scoping process. This can be informed by the HRA screening report and the interim ornithology baseline report. It is likely that impacts will occur to seabird populations that breed outside Scotland as well as to wintering waterbirds that originate outside the UK. The Marine Scotland migratory review, once published, will provide relevant information for considering this.

Start and end times of projects

The CEF requires that the start and end dates of projects are specified. The CEF currently does not allow for habituation, or account for differences between construction years and during operation. We therefore advise that this should follow the start and end of the operation period, noting that should this be amended after consent, but prior to build out. The CEF data store should be updated to ensure other projects have the correct information for their cumulative assessment.

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