Radio‐tagged adult grayling Thymallus thymallus(n = 22), monitored from mid August to mid December 1999 in the River Kuusinkijoki, Finland, shifted by the end of September (water temperature 10·0–14·5° C) from riffle sites to deeper and slower pool sites 0·7–1·6 km up‐ or downstream. In early winter (c. 0° C water temperature), eight of 13 fish still under study made a further shift into new pool sites, possibly triggered by ice formation. The summer range of grayling in the riffles was smaller (mean ± s.d. length: 75 ± 146 m) than the autumn range (99 ± 46 m) in the pools, but gross daily movements were equally short in both the seasons (18 ± 34 m and 15 ± 7 m, respectively). In late summer, adult grayling preferred water depths 80–120 cm and mean velocities >40 cm s−1. In autumn, the preferred ranges were 100–240 cm and <30 cm s−1, respectively. Substratum was mainly boulders in the summer sites, and gravel or pebbles in the autumn sites.
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Document Type: Regular Paper
Finnish Game and Fisheries Research Institute, Kainuu Fisheries Research and Aquaculture, Manamansalontie 90, FIN-88 300 Paltamo, Finland and
Fortum Service, P. O. Box 10, 00 048 Fortum, Finland
Publication date: 01 May 2004