Users should refer to Jackson et al. (2025) for full details of the NEPS 2023 survey design. In brief, the survey is an unequal probability Generalised Random Tessellation Stratified (GRTS) survey design with a panel design for survey over time and oversamples. The target population encompasses all rivers that are accessible to Atlantic salmon, where there are registered fisheries and where sampling by wading and electrofishing is possible. The survey had 54 separate strata, including SACs and index monitoring sites. Sample site selection is weighted towards rivers where higher juvenile salmon densities were expected, based on the salmon benchmark model predictions from Malcolm et al (2019a), with a targeted minimum distance of 75 metres between sites. Sample numbers reflected scientific requirements, available resources, and an expectation of oversample requirements based on previous surveys and practical considerations.
The survey design was generated using R version 4.2.0 (R Core Team, 2022) and spsurvey version 5.3.0 (Dumelle et al., 2023).