National Electrofishing Programme for Scotland (NEPS) 2023: status of juvenile Atlantic salmon and brown trout populations

Conclusions

Evidence based fisheries management requires robust information on population processes, status, pressures, and the likely efficacy of different management actions. Juvenile assessments are one of the main information sources required to inform and guide freshwater fisheries management, providing catch independent data that can be applied across a wide range of spatial scales depending on resources. These data become increasingly important as management focus shifts from commercial fisheries to recreational fisheries and species conservation, as most practical management action is undertaken in freshwater and at sub-catchment scales.

Before NEPS, information on the status of salmonids in freshwater was generally poor. Data collection methods varied between regions and within regions over time. Few catchments had good spatial or temporal coverage (Malcolm et al., 2019). Further, data collection often used timed or single-pass methods without calibration, and lacked a formal survey design, potentially resulting in biased data that could result in misleading assessments of status and understanding of change (Glover et al., 2019). Without comparable sampling methods and survey designs it was difficult to compare between regions (Millar et al., 2016) or to scale assessments across larger spatial scales (Alexandre et al., 2024). This constrained understanding of the status of salmonids in freshwater, hindered practitioners from identifying underperforming areas and reduced opportunities for targeting appropriate management action except in the most extreme and evident of circumstances (e.g. major barriers).

The concepts underpinning the NEPS juvenile assessment framework were developed as a collaboration between the Scottish Government Marine Directorate, fisheries trusts and boards, Nature Scot and SEPA following a major review of Wild Fisheries Management in Scotland (Thin et al., 2014). It provides a combination of clearly documented sampling methods, a formal survey design, and peer reviewed analytical and modelling approaches to harmonise data collection at a national scale, providing robust assessments of status and trends in juvenile abundance. These data can support a wide range of evidence and reporting requirements, including policy development, local management, Habitat Regulations and Water Framework Directive reporting. If the NEPS sample frame were extended, this could support new monitoring requirements such as the Sea Lice Risk Assessment Framework. If further extensions were made to the analyses, this could allow assessment of other freshwater fish species (e.g. European eel), more granular assessments of stocks within river systems (e.g. spring vs. later running salmon) or improved site-wise assessments incorporating the effects of local habitat.

As the NEPS datasets have grown they also become increasingly powerful for identifying the effects of pressures. Pressure metrics can be included alongside spatial habitat data in regression models. This could help to identify some of the dominant pressures in freshwater and also clarify the nature of pressure - response relationships. This information could be used to improve management and regulatory decisions and target remedial action where necessary.