Scottish Marine and Freshwater Science Volume 5 Number 6: Collation of Available Datasets on Smolt Populations in Scotland to Assess Migration Run Times

4. Discussion

To gain a national summary of smolt monitoring efforts the SFCC was able to canvass the fisheries network including non- SFCC member Fisheries Trusts and District Salmon Fishery Boards. The SFCC member network were also able to assist in identifying further smolt monitoring locations operated by external organisations or individuals. In total 30 different fisheries organisations or other bodies were contacted, resulting in the identification of 16 organisations collecting smolt trap monitoring data, and the remaining 14 confirming that they are not currently undertaking smolt trapping activities. Out of those collecting smolt monitoring data, 13 organisations were deemed to have data relevant to the project aims. Within the time frames, a total of 31 individual monitoring sites were identified and could be made available for collation.

River main-stem monitoring locations were identified in the project specification as being of particular importance in the context of national modelling of smolt emigration timings. The datasets provided feature around one half main-stem and one half 2 ^nd order tributary level coverage.

Meta-data questionnaires were utilised to ascertain a range of information including the research question(s) targeted by the installation. The relationship of these efforts to each respective fisheries management plan has also been presented. Capture efficiency is quantified for the majority of locations using a range of methods and further work is recommended if MSS require a comprehensive assessment of these calibration methods. Data is provided firstly on Atlantic salmon and emigrating trout with some data also included on other fish species captures. Further work is required to fully collate data gathered during smolt trapping on other fish species. Several flow and temperature datasets are provided in the context of improving our understanding of the relationship between discharge, temperature and smolt migration run timings. Associated environmental data communicated in the meta-data questionnaire returns also indicated a significant data resource requiring further exploration.

Temporal resolution was found to vary with the longest being a 37 year count dataset. Individual fish length measurement data was not available for all 13 sites and temporal resolution of individual fish length datasets appeared to be limited before 2010. Trapping strategies vary with cost-effective solutions being utilised in several catchments and the hydro power sector also providing mobile and fixed strategies contained within hydro power infrastructure. While the SFCC believe that this project contains the absolute number of sites in Scotland, within the current sites it is noted that there are datasets from certain years that were not able to be collated within the project timescales.