Cromarty Snow

Scottish Smolt Data Analysis Report Published

12 Mar 2015

After collation of all available smolt data in Scotland in 2014 with thanks to SFCC members and others, Marine Scotland Science have published the analysis report.

This process represents an example of how locally collected data, when collated and standardised can be utilised to assist in informing national-scale fisheries research.

We are pleased to announce that following the national smolt data collation project entitled: Collation of Available Datasets on Smolt Populations in Scotland to Assess Migration Run Times, Marine Scotland Science have recently published their final report, available here: 

Spatio-temporal variability in Scottish smolt emigration times and sizes.


The project was undertaken under the National Research and Monitoring Strategy for Diadromous Fish (NRMSD): with the overall aim to investigate the potential for interactions between diadromous fish and wind, wave and tidal renewable energy developments. The aim of the smolt analysis was to examine how Scottish smolt emigration times and fish sizes may vary by location and between years.

The key findings are as follows:

  • The start and end of the migration period varied with elevation and over time, but not as a predictable function of geographical location (latitude and longitude).
  • Thus, a single main coastal migration range was estimated for the whole of Scotland as being between day of the year (DoY) 103 and 145 (April 13th -May 25th outwith leap years).
  • Smolt migration begins earlier with increasing distance up river and elevation.
  • Smolt migration is commencing roughly 1.5days earlier in the year per decade.
  • Smolt size varies by site and by year.
  • Across the 20 sites analysed, the % of fish exceeding the 135mm tagging threshold ranged from 0-92%.


In relation to SFCC, the following recommendations were also made: "Future analyses would benefit from central data collation and storage with associated meta-data on collection methods. This would be possible using the existing MSS FishObs database or through additional development of the SFCC database".

SFCC are now looking to draft smolt recording protocols to cater for varied equipment types and research objectives. In addition, use of the Marine Scotland Science FishObs database to act as central storage for all Scottish smolt data is being explored.



Fisheries Trusts and other organisations invested a number of hours and in many cases multiple days in preparing meta and raw data for this project. 

On behalf of Marine Scotland Science we wish to thank the following organisations for their direct involvement:

Ayrshire Rivers Trust

Cromarty Firth Fisheries Trust

Findhorn, Nairn & Lossie Fisheries Trust

Galloway Fisheries Trust

Herriot Watt University / Malcolm Thomson (Orkney)

Inverness College UHI (River Carron)

Kyle of Sutherland Fisheries Trust

Lochaber Fisheries Trust

Outer Hebrides Fisheries Trust

River Annan Trust

Spey Foundation

Tweed Foundation

West Sutherland Fisheries Trust

Wester Ross Fisheries Trust

The SFCC wish to thank Scottish and Southern Energy PLC for support provided to several trap installations reported within this project. In addition, Scottish Natural Heritage should be acknowledged here for their contribution to smolt monitoring activities.

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