Sampling was undertaken between April and September, annually between 1997 and 2019. 2010 features only data from mainland west coast fisheries trust regions (which includes some inner islands). Each sampling event aims to catch at least 30 fish of either post-smolt and/or finnock life stage.
Once caught fish are anaesthetised using neutral-buffered MS222 (100 mgl-1) with the water poured through a 100µm sieve to catch any lice detached during the anaesthetising process. Fork length (to the nearest mm) was recorded during this process. For counting of lice, fish are placed in water against a light background with the number of lice present on the fish and the life cycle stages of the lice recorded as one of the following three categories:
Category 1: Early stages-attached copepodids and chalimus.
Category 2: Mobile stages: pre-adults and adults including mature males and non-ovigerous females.
Category 3: Gravid stages: ovigerous females.
Further details on sweep netting method can be found at https://www.sfcc.co.uk/assets/files/SFCC%20Sweep%20Netting%20Protocol.pdf

Column headings
“site” contains the sampling site name
"region" contains the wider region within which sampling sites are situated
“date” contains the date that sampling point was undertaken
“length” contains the fork length in mm of the individual sea trout
“lice_stage” contains the sea lice life cycle stage. Either "copepodid_chalimus", "preadult_adult" or "ovigerous_females"
“count” contains the number of sea lice of the specified class on the fish

Acknowledgements
This work was funded by Marine Scotland, and managed by Marine Scotland Science and Fisheries Management Scotland. Sampling was carried out by employees of the district fisheries trusts with the help of volunteers as required.