Fish and fisheries research to inform ScotMER evidence gaps and future strategic research in the UK: review

FF.09: Accurate spatial -temporal patterns of spawning activity by marine fish species

Review of current knowledge

The importance of spawning areas and the need to minimise impacts on fish species during this key period of their life cycle is widely recognised as part of marine policy and marine plans developed in the UK (UK MPS 2011, The Scottish Government 2015, MMO 2014c, Welsh Government 2019 and DAERA 2018).

Existing knowledge on fish spawning around the UK has been compiled into key publications which consolidate data from various surveys and cover a comprehensive range of species:

• Fisheries Sensitivity Maps in British Waters (Coull et al 1998); and
• Spawning and nursery grounds of selected fish species in UK waters (Ellis et al 2012).

These publications provide a comprehensive review of the broad distribution of grounds and timing of spawning for a range of fish species and are widely used to inform impact assessments in support of MRE projects and other offshore activities.

As the spawning grounds identified in Coull et al (1998) are based on historic research, in some instances they may not be representative of recent trends in the distribution of fish species and preferred spawning grounds. Similarly, the information in Ellis et al (2012), whilst based on more recent data, is also subject to limitations due to the variable amount of ichthyoplankton (fish egg and larvae) data available for different regions and different species. Therefore, where available, for species for which regular survey work is undertaken in key spawning areas (e.g. International Herring Larvae Survey (IHLS)), data from more recent survey results is often analysed and used to further inform impact assessments. It should be noted, however, that limitations associated with survey coverage, annual variability and the wide survey grid used for sampling in the IHLS and other surveys which inform Coull et al (1998) and Ellis et al (2012), mean that it is not always possible to characterise the relative importance of discrete, localised sea areas as spawning grounds for fish species.

The difficulty in ascertaining the level of spawning activity and key spawning periods at the spatial scale of individual MRE projects, has resulted in the need to implement broad temporal and/or spatial restrictions during the construction phase (i.e. piling restrictions) and monitoring requirements as part of consent conditions for many projects. In addition, in some cases, fish spawning surveys have been undertaken as part of the EIA baseline characterisation with a view to reducing uncertainty prior to consent.

Piling restrictions and conditions on monitoring with regard to fish spawning have often being focused on herring. In a recent study, Boyle et al (2018) reviewed licence conditions across offshore wind farm projects in the UK and identified 19 offshore wind farm projects with conditions related to spawning herring. Other species of particular concern with regard to impacts on spawning associated with MRE projects in the UK to date, include gadoids, particularly cod, and flatfish species (Dover sole, plaice).

In order to minimise consenting risks and current uncertainty in the assessment of potential impacts of MRE projects on fish, there is a need to improve our understanding of the distribution and timing of spawning for key fish species. Whist information gathered through survey work will continue to improve the evidence base in this respect, additional approaches, including the use of modelling tools to predict spawning distribution and intensity should be given due consideration. More detailed information on this topic is provided below under "Evidence Gap FF.10: Essential fish habitat".

In addition, for species with high substrate specificity such as sandeels or spawning herring, the potential to develop detailed sediment maps identifying the extent of suitable areas to support these species during critical periods should be explored. Standard sediment suitability criteria for these species have been developed for the marine aggregate sector (Reach et al 2013, Latto et al 2013), and are increasingly used to inform assessments for other industries, including in EIAs for MRE projects. Spatial information on sediment suitability in combination with data on the distribution of early life stages would facilitate the mapping of more accurate spawning grounds for these species.

Next steps in research

As described above, whilst broad information on the spatial distribution and timing of spawning for key fish species is already available, this is often not sufficient to accurately identify the relative importance of areas occupied by MRE projects as spawning grounds and the timing when spawning may take place in these areas. This has resulted in the need to implement wide restrictions during the construction phase and monitoring requirements as part of consent conditions for many MRE projects.

In order to address this knowledge gap and assist in reducing uncertainty, the development of spawning mapping tools which take account of up-to-date data and that allow higher resolution mapping, both in spatial and temporal terms, is strongly recommended. For species with specific seabed suitability requirements for spawning (i.e herring, sandeels), these mapping tools would benefit from the integration of information on sediment characteristics.