1. Marine Scotland, Freshwater Laboratory, Faskally, Pitlochry, Perthshire PH16 5LB, Scotland, UK
2. Department of Mathematics and Statistics, University of Strathclyde, Glasgow G1 1XH, Scotland, UK
3. Marine Scotland, Freshwater Laboratory, Inchbraoch House, South Quay, Ferryden, Montrose, Angus DD10 9SL, Scotland, UK
4. The Tweed Foundation, Drygrange Steading, by Melrose, Roxburghshire TD6 9DJ, Scotland, UK
5. The Spey Research Trust, 1 Nether Borlum, Knockando, Morayshire AB38 7SD, Scotland, UK