National Adult Salmon Sampling Project

1. Background

Sampling of individual adult salmon is used to collect information on the size, sex and age of the fish. This information feeds directly into the stock assessments used for national and international management of Scottish salmon. Sampling of individuals can also provide information on their condition, while examination of scale samples allows their growth history to be investigated.

In Scotland, and other countries, scale samples were historically collected from commercial netting but most of these fisheries have closed in recent years. Due to a lack of sampling information, it has been necessary to assume that there have been no changes in age or size of salmon returning to Scotland since 2018. This is clearly unrealistic given previously documented long-term shifts in the size and demography of salmon in Scotland (Bacon et al. 2009; Todd et al. 2008; Todd et al. 2012) and more widely in the North Atlantic (Bal et al. 2017; ICES 2023). To fill this data gap the options for using existing rod fisheries and targeted scientific sampling as a source of biological information on returning adult salmon were investigated.

During 2021-2023, a national adult salmon sampling programme was developed by the Marine Directorate, Fisheries Management Scotland and local District Salmon Fisheries Boards and Trusts. The objectives of the programme were:

• To trial different approaches to obtaining biological data on adult salmon (length, weight, age) and to see what approaches to obtaining samples worked in different settings.
• To inform the design of any future adult sampling programme for use in stock assessments.
• To provide information on the size, sex and age of adult salmon that could be used to inform future stock assessments.