Offshore wind - diadromous fish: review - January 2024

1. Introduction

1.1 Overview of this project

This project was commissioned by the Scottish Government, who developed the Sectoral Marine Plan for Offshore Wind Energy in October 2020 (SMP-OWE; Scottish Government, 2020a). The SMP-OWE identified 15 sustainable Plan Options for the future development of offshore wind energy in Scottish waters, with the aim of maximising opportunities for economic development while minimising potential negative impacts on the environment and other marine users (Scottish Government, 2020a). The SMP-OWE is currently undergoing an Iterative Plan Review process.

The 15 SMP-OWE Plan Options are highlighted in Figure 1 alongside the 13 INnovation and Targeted Oil & Gas (INTOG) Exclusivity Agreements. The INTOG Exclusivity Agreements cover small scale innovation projects (<100MW) and offshore wind farms that target electrification of oil and gas installations. These potential INTOG projects are all intending to use floating wind technology and were offered initial Exclusivity Agreements in March 2023 (Crown Estate Scotland, 2023). Throughout this document, these development areas will be referred to as Plan Option Areas (POA).

The planning process for the Sectoral Marine Plan is iterative and includes stakeholder involvement and environmental, social and economic assessments. As part of the Plan and the consenting process, potential impacts on the marine habitats and species (including diadromous fish) must be considered for all POAs. This includes Environmental Impact Assessments which assess the likely significant environmental effects from developments (following the Electricity Works (Environmental Impact Assessment) (Scotland) Regulations 2017 and Marine Works (Environmental Impact Assessment) (Scotland) Regulations 2017).

This report will summarise the most current knowledge in relation to the distribution, movement and abundance of diadromous fish at sea (highlighting 10 focal species), in the context of Scottish offshore wind developments – including both existing projects and future projects that may arise from the ScotWind and INTOG leasing rounds. For the marine distribution and movement of diadromous fish, the spatial focus was on the marine waters of Scotland. It also includes a synthesis of available evidence on potential impacts resulting from offshore renewables on diadromous fish, bringing together information through a literature review and expert panels. Potential impacts were considered across four key categories: sound and vibration, light patterns, electromagnetic fields and novel habitat. The last category included several topics around creation of novel habitat as a wind farm is built, including the creation of physical barriers, predator-prey interactions, community change and disease risk. Most of this work focuses on the offshore arrays, as much less research is available on the potential effects of export cable corridors, especially in inshore areas. The synthesis is followed by a summary of current evidence gaps and recommendations for future research priorities. The report also provides information to be considered for any potential impact to Special Areas of Conservation which may be directly or indirectly impacted by offshore developments.

The aim of this report is to synthesise the current understanding, highlight evidence gaps and provide guidance on the feasibility of addressing evidence needs and the future strategic direction for monitoring and research on diadromous fish in relation to offshore wind farm developments.

1.2 Offshore wind

As the world confronts the challenges posed by climate change and the need to reduce greenhouse gas emissions, the exploration and utilisation of offshore wind energy resources has emerged as a rapidly growing option for ‘cleaner’ energy. The global pursuit of sustainable and renewable energy sources has witnessed an exceptional surge in offshore wind energy as a crucial component of the transition toward cleaner and more environmentally responsible energy systems.

The first offshore wind farm was constructed in Denmark in 1991 (Díaz & Soares, 2020) and since then, there has been significant growth in offshore wind capacity globally. Most of the current offshore wind farms are in Europe, with Asia and America following (Díaz & Soares, 2020). In 2021, Europe had 50% of the world’s offshore wind capacity but this is predicted to decrease to 30% by 2027 – mainly due to growth in China and the United States (International Energy Agency, 2023). Growth has been particularly strong in China, which, for the fourth year running, had the highest rate of offshore wind installations with 17 gigawatts (GW) added in 2021. In comparison, Europe as a whole added 3.3 GW of offshore capacity in 2021 (GWEC, 2022). In the United Kingdom, the entire renewable energy capacity of the country is predicted to increase by 70% between 2022-2027. Additionally, the UK has an offshore wind energy target of 50 GW by 2030 (International Energy Agency, 2023).

The development of offshore wind energy has seen rapid growth in the UK. In addition to the reduction in carbon, it has also led to significant job creation and economic benefits for the country. The UK, and Scotland particularly, has an ideal location on the northwest coast of Europe which exposes it to abundant and consistent wind resources in the North Sea and the Irish Sea. These offshore areas offer some of the best conditions for harnessing wind energy, making them attractive locations for the development of offshore wind farms.

Scotland has set ambitious renewable energy targets, aiming to significantly reduce its carbon emissions and transition to cleaner energy sources. These goals include plans to achieve net-zero carbon emissions by 2045, through substantially increasing the use of renewable energy relative to non-renewable energy sources (Scottish Government, 2023a). Offshore wind energy plays a crucial role in achieving these targets. This is ahead of the UK target which is to achieve net-zero carbon emissions by 2050 (Scottish Government, 2023a).

Currently there are 40 operational offshore wind farms in UK waters, in addition to 11 that are under construction or consented. Out of these, Scotland has six operational wind farms and nine under construction or consented (Scottish Government, 2020a; Woodward et al., 2023). In Scotland, offshore wind developments are guided by Sectoral Marine Planning. The purpose of sectoral marine planning for offshore wind is to identify sustainable sites for future development through provision of spatial strategy for the seabed leasing process in Scottish waters (Scottish Government, 2020a). Seabed leasing in Scotland is managed by Crown Estate Scotland. The published operational offshore wind farms produced over 2,729 GWh of energy in 2021 (Scottish Government, 2023b). ScotWind leasing round results were announced in January and August 2022 with 20 projects given seabed Option Agreements. Of these, 14 are proposed floating structures, securing Scotland’s role at the forefront of this technology. The ScotWind leasing round has the potential capacity of 27.6 GW of production. Further planned developments include 13 sites through the INTOG leasing round, which has potential capacity of 5.5 GW (Offshore Wind Scotland, 2023). Most of the existing offshore wind developments and the Sectoral Marine Plan Option Areas for Scottish offshore wind farms are on the east coast of Scotland, although there are some ScotWind Option Agreements in northern and western locations as well.

While the benefits of offshore wind farms through their contribution to reducing carbon emissions is clear, there are concerns that they might have negative impacts on habitats and species that interact with them. Offshore wind turbines are a relatively new development and therefore research into the potential impacts is still limited. Potential impacts on birds are relatively well known and include displacement and collision mortality (Furness et al., 2013). There has been comparatively less research on fish and particularly diadromous fish, likely due to the challenges of monitoring them. However potential impacts include disturbance, behavioural changes and injury due to construction activities or noise.

1.3 Diadromous fish

Diadromous fish are species that undertake regular migrations between freshwater and marine environments as part of their life cycle. These migrations allow fish to access different habitats for feeding, growth and reproduction. There are two main types of diadromous fish; anadromous fish that spawn in the freshwater and migrate to the marine environment for better growth, and catadromous fish that spawn in the marine environment and migrate to freshwater where they mature. Diadromy is an adaptive life history strategy that allows exploitation of different habitats, often leading to higher reproductive success and survival. However, migrations, particularly long-distance ones, introduce the individual to increased risk. These potential risks include increased energy expenditure, potential to interact with novel predators and novel parasites, as well as physiological challenges (due to the transition between fresh and saltwater).

Many diadromous fish species have seen severe declines in their populations over the last few decades (Costa-Dias et al., 2009; Mota et al., 2016; Waldman & Quinn, 2022). This is due to a variety of reasons including climate change, habitat degradation, overfishing and migration barriers. Obstruction to migration in the form of barriers is a particularly significant factor globally, especially in Europe where it has been estimated that there are over 1.2 million instream barriers (Belletti et al., 2020). Similar declines have been seen in Scotland, with clear decreases in populations of Atlantic salmon and anadromous brown trout for example (Adams et al., 2022). A recent reclassification of the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species categorised global populations of Atlantic salmon (Salmo salar) as “Near Threatened” (Darwall, 2023) with salmon populations in Great Britain categorised as “Endangered” (Darwall & Noble, 2023) (IUCN Red List). Nunn et al (2023), using the IUCN Red List of Threatened Species categories and criteria, assessed native UK fish populations and categorised European eel (Anguilla anguilla) and allis shad (Alosa alosa) as “Critically Endangered”, Atlantic salmon as “Endangered” and twaite shad (Alosa fallax) as “Vulnerable” in Great Britain. For fish populations that are already at risk, any additional pressures, such as an offshore wind farm, may have significant effects and are therefore important to consider when developing future projects.

This review focused specifically on the following 10 diadromous fish species: Atlantic salmon (Salmo salar), anadromous brown trout (Salmo trutta), three-spined stickleback (Gasterosteus aculeatus), European eel (Anguilla anguilla), river lamprey (Lampetra fluvialis), sea lamprey (Petromyzon marinus), European flounder (Platichthys flesus), European smelt (Osmerus eperlanus), allis shad (Alosa alosa) and twaite shad (Alosa fallax) (Table 1).