Offshore wind - diadromous fish: review - January 2024

2. Methods

2.1 Literature review

A review of the published literature (peer-reviewed and grey) was undertaken using traditional literature searches. Peer-reviewed literature was searched through Web of Science and other scientific literature search engines (e.g. GoogleScholar). Accessing the "grey" literature (e.g. existing mitigation documentation, accounts of species distributions, etc.) was done through GoogleScholar and governmental websites.

Information was mainly gathered on diadromous fish in Scotland and the UK. Where no information was available for this geographical area, studies from elsewhere in Europe or the world were reported for context. For the sections focusing on potential impacts on diadromous fish associated with offshore renewables, the literature review first focused on the 10 focal diadromous fish species, however where no or very little information was available the search was expanded to other similar fish species or to other relevant fish studies. Information about the spatio-temporal distribution, movement and abundance of these species was summarised and assessed for scientific rigour by considering methodology, sample size and analysis approach. The information about species’ spatio-temporal distribution, movement and abundance resulting from the review was then linked with identified potential impacts of marine renewables.

2.2 Expert panel workshops

In addition to the literature review that identified clear evidence gaps in all researched topics, further information was gathered through a series of expert panels. These panels were also used to assess the quality (breadth of coverage) of the literature review and to identify any missing literature (especially grey literature).

There were five expert panels held: one focused on the distribution of diadromous fish in Scottish waters and four focused on the potential impacts of offshore renewables (Sound, Electromagnetic fields, Light pattern changes and Novel habitat and associated effects). Potential experts for each panel were identified through authorship in key papers and this included experts from both academic and government backgrounds. While most experts were UK-based, some were invited from North America.

Five workshops were undertaken:

• Study species distribution – 28 June 2023
• Sound and Vibration – 15 June 2023
• Light Patterns – 28 June 2023
• Electromagnetic Fields – 18 July 2023
• Novel habitat (physical barriers, predator-prey interactions and disease) – 29 June 2023

An outline of the broad aims and objectives of the whole project was presented, putting the workshop into context. Following this, the results from the literature review were presented with specific key publications highlighted. A discussion of the results of the literature review followed and notes taken by the project team. Attendees at the workshops were requested to highlight thoughts or comments on the review as it was presented to encourage round table discussions and exploration of knowledge gaps within the scientific knowledge. In addition to providing key information from expert scientists from specific fields, these workshops also served as a quality check for the literature review.

2.3 Identification of key evidence gaps and recommendations for future research

Following the literature review and the expert panels, many evidence gaps were identified in the available research for marine distribution, migration routes and the potential interactions with offshore wind farms for diadromous fish. Based on this, a suggested list of potential future studies to address these evidence gaps was created through discussions within the project team and steering group. These studies highlight questions and areas of science that have been noted to currently lack evidence. For each evidence gap, the priority of answering the questions was ranked and a steer provided on the appropriate methodology needed to answer each question where possible. However, providing a clear methodology for all questions was not possible. The spatial and temporal scales required were noted and possible challenges of delivering such studies identified.

Recommendations for future research have been made which represent the authors’ view on important evidence gaps. The applicability of each study question and design to each of the 10 focal species was considered and recommendations made on which species studies should focus on.

2.4 Special Areas of Conservation

Special Areas of Conservation (SAC) support habitats and/or species which form part of the Annexes of the Habitats Directive (Council Directive 92/43/EEC). In Scotland and in the context of this review, this extends to Atlantic salmon, sea lamprey and river lamprey, which are recognised as features of SACs. Allis shad and Thwaite shad are recognised features, but currently do not contribute to any SAC designation in Scotland. Freshwater pearl mussels (Margaritifera margaritifera) are also features of SACs in Scotland. Freshwater pearl mussels use salmon and trout as hosts during their early development (glochidia, juvenile stages of mussels attached to the gills of host Salmo species) and may be indirectly impacted by offshore development through changes to the host population. In Scotland, Atlantic salmon and trout are both hosts for freshwater pearl mussels (Clements et al., 2018), this makes the Scottish populations distinct compared with other geopolitical regions, where mussels appear to use one or other of the Salmo host species.

There are 17 SAC sites across Scotland for which Atlantic salmon are a feature, six SAC sites for sea lamprey, six SAC sites for river lamprey and 19 SAC sites for freshwater pearl mussels (summarised in Table 4).

NatureScot is the statutory nature conservation adviser to the Scottish Government. As part of the Environmental Impact Assessment (EIA) scoping phase for individual offshore wind proposals, NatureScot provides scoping advice. However, there is currently limited knowledge available on the distribution and behaviour of Atlantic salmon, sea lamprey or river lamprey in the marine environment. This contrasts with other species, for example seals, for which their distribution and behaviour in marine waters and connectivity to individual SACs is reasonably well understood. This inability to understand connectivity to and within individual rivers to an offshore wind farm currently prohibits an informed assessment of the potential impact on individual SAC site integrity.

These issues of understanding spatial and temporal distribution of the 10 focal diadromous fish species in the marine environment and whether or not there are potential key impact pathways from offshore renewables developments, have been a key driver in commissioning this report. One potential key source of information is the “Salmon and Sea Trout fishery statistics: 1952 - 2021 season - reported catch by district and method” data (available via Salmon and sea trout fishery statistics: 1952 to 2022 season - reported catch by district and method). These data have been summarised in Appendix 1.

2.5 Summarising current projects investigating the migration routes and space use of diadromous fish in the UK

To contribute to identifying evidence on the distribution, movement and abundance of diadromous fish at sea, a list of ongoing and recently completed projects on this topic in the UK waters was compiled (up-to-date as of December 2023). This information was mainly gathered through the project team’s professional network which covers academic institutions, governmental organisations and NGOs. For each project, information was gathered on study questions, methodology, participating organisations, timelines and geographical focus. This information was compiled initially as an Excel spreadsheet and is provided in the appendix of this report.