Collation of Available Datasets on Smolt Populations in Scotland to Assess Migration Run Times

Scottish Marine and Freshwater Science Vol 5 No 6

This project was undertaken in the context of the National Research and Monitoring Strategy for Diadromous Fish (NRMSD) to investigate the potentialfor interactions between diadromous fish and wind, wave and tidal renewable energy developments. By canvassing Scotland’s geographical area, the SFCC believe that the absolute spatial coverage of smolt monitoring locations has been identified. Datasets identified from 13 organisations at 31 locations were requested, resulting in the provision of these datasets. During the project, the fish species scope was expanded to include trout after initially being focused on Atlantic salmon. A total of 126,368 individual fish length measurements and a further separate dataset featuring 292,427 smolt counts were provided. While the majority of smolt trapping was found to occur using rotary screw trap methods, a range of alternative strategies are deployed. Data recording procedures and resolutions were found to vary significantly between organisations and in some cases within organisations. Temporal coverage is also variable with information becoming increasingly limited before 2006. The largest dataset spans 37 years, that of Spey Dam currently operated by Spey Foundation. Out of 31 sites 16 featured individual fish length (1mm) measurements and 2 featured 5mm and 10mm categorical fish length measurements. The remaining 13 datasets were provided as total fish count level observations. 18 of 31 smolt monitoring sites are operated on river main stems, with the remainder on 2nd order tributary rivers. While data are provided in a standard format, considerations relating to crosscompatibility remain specifically around the means by which recordings are made where; fishing did not occur, fishing did occur without the trap being checked, and fishing did occur with the trap being checked resulting in a catch of 0. Strategies for recording the beginning and end of the trapping season also exhibited varied approaches, a caveat which should be considered during further analysis. Further work is recommended to fully quantify the availability of data collected on other fish species captured (while smolt monitoring) and that of river flow and water temperature. Pending analysis by Marine Scotland Science, this collaborative approach may have provided data collected at a local catchment scale, which is also capable of informing research of a national-scale. With 6 organisations reporting the installation of new smolt traps in 2014, the spatial coverage of this dataset will further increase.