A fish counter network for monitoring Scottish salmon stocks

Appendix B

Method and approach undertaken for 2021 field study of fish counter sites in Scotland

Site Identification Exercise

The site identification exercise involved identifying criteria that would make a river, and then a (potential) counter site, suitable for use in a national context. The focus was on identifying sites suitable for counting fish using resistivity and optical systems. This was done by obtaining information from national and local stakeholders, online searching and the extensive use of mapping and Geographic Information Systems (GIS).

The Rivers and Fishery Trusts and District Salmon Fishery Boards entered information to a GIS mapping tool (hosted by the Scottish Fisheries Coordination Centre (SFCC)) based on their knowledge of potential locations for counters. The tool also included information from the Scottish Environment Protection Agency (SEPA) on known obstacles to migration and was set to focus on those less than 5 km from the coast (since a weir with a fish pass can make a good location for a counter).

Following a desk-based assessment of the available information, including discussions with local stakeholders, 28 potential sites were selected to visit to gauge more fully their suitability for inclusion in a national fish counter network.

Prioritisation Exercise

There are several features that would make a fish counting site suitable for use in assessing salmon stocks. It was recognised that not all these features are essential and for those that are not, there needed to be a trade-off between what is ideal and what is practical and/or available.

Accordingly, prioritising rivers where new counters may be installed was an iterative process, with some of the following steps being visited more than once:

• Mapping existing counters and identifying any not currently providing data to the Marine Directorate, but which may be suitably located for use in the national network
• Mapping assessed areas and identifying rivers of interest as being Special Areas of Conservation (SAC) under the European Habitats Directive (92/43/EEC)
• Seeking knowledge of where local managers are developing plans to install counters and identifying whether sites may be suitable for the network
• Mapping obstacles on main stem rivers within 5 km of the sea
• Seeking input from local stakeholders to identify potential locations and for local knowledge on sites
• Identifying suitable locations where there would be local support for maintaining and operating a new counter
• Examining fish catch records for the reliability of returns and the numbers of fish caught. As robust data on the numbers of salmon caught on the river are required to model the relationship between count and catch, rivers with very few catches or incomplete recent catch records were excluded from the selection process
• Site visits for visual assessment of suitability. Visits assessed both the location (how far from mouth of a river), form and condition of existing structures (weir, natural feature) to assess the potential to attach a fish counter successfully.