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The poster and the following information were originally presented at Wild Trout IX in 2007 but not published at the time due to an intention to publish the full results in a peer-reviewed journal.An earlier version of this poster which included the results for just two fish was published on Zenodo in 2015 at https://zenodo.org/records/30826 Introduction Ferox trout are brown trout (Salmo trutta) which despite inhabiting the nutrient-poor water of a large oligotrophic freshwater highland loch have grown big enough to switch to a primarily piscivorous diet of Arctic charr (Salvelinus alpinus) (Campbell 1979). This trophic switch is associated with rapid growth and extended longevity – ferox can grow to over 1m in length and live for over twenty years (Campbell 1979). The main aim of the study was to investigate the summer (May-September) movements of ferox trout in their natural habitat. Methods Site Loch Garry is an oligotrophic freshwater loch situated 406 m above sea level in the Grampian mountains. Lying at the bottom of a steep-sided glacial valley the loch is 4.2 km long, with a maximum width of 0.5 km and maximum depth of 34.4 m. It has a surface area of 1.67 km2. Tagging All fish were caught by trolling a dead Arctic charr behind a boat (Greer, 1995). When hooked, each fish was played with care. Upon recovery in a large fine mesh keep-net each fish was anaesthetised, measured and tagged. Tags were attached externally in a pannier arrangement next to the dorsal fin. Each fish was then returned to the keep net, to recover for a minimum of 20 minutes, before being released from the shore as close to the original capture site as possible. Fish The horizontal summer movements of three ferox trout (Fish1-3) were tracked using radio and acoustic tags (Table 1). Their horizontal position was recorded using a handheld GPS whenever weather and work commitments permitted. In addition, the vertical movements of five ferox (Fish4-8) were recorded every 15 minutes using data storage tags (Table 1). Analysis All analyses were performed using ArcGIS 8.3 and R 2.5.1 (R Development Core Team 2007). Home ranges were estimated using the Minimum Convex Polygon (MCP) method (Worton 1987). To control for statistical non-independence (Swihart and Swade 1985) the data were analyzed using mixed models with autoregressive errors (Pinheiro and Bates 2000). Results Horizontal movements The dominant swimming pattern was to move slowly and undertake frequent changes in direction. All three ferox had home ranges that extended over much of the loch (0.78-1.10 km2). The tracks for Fish2 and Fish3, which included their positions during darkness, indicated that both fish tended to move closer to shore at night (p < 0.05). Vertical movements The DST data indicated that Fish4-8 tended to remain in the top 5 m of the water column but undertook frequent dives to depths of 5 m to 20 m. At night all five fish became less active (p<0.05) and, with the exception of Fish8, tended to be recorded higher in the water column (p<0.05). Discussion The results indicate that during the summer months, ferox trout cruise through the top 5 metres of Loch Garry undertaking frequent changes in direction and dives to 20 m. At night the fish become less active and move into shallower water closer to the shore. We suggest that the ferox dive during the day to hunt Arctic charr in the deeper water but at night become less active to conserve energy. Acknowledgements We thank Scottish and Southern Energy, Wild Trout Trust and Turftech International Ltd for their support and Iain Malcolm for comments. References Campbell, R.N. (1979). Ferox trout, Salmo trutta L., and charr, Salvelinus alpinus (L.), in Scottish lochs. Journal of Fish Biology 14, 1-29. Greer, R. (1995). Ferox trout and Arctic charr: a predator, its pursuit and its prey. SwanHill Press, Shrewsbury, UK. Pinheiro, J.C. and Bates, D.M. (2000). Mixed effects models in S and S-PLUS. Springer Verlag, New York. R Development Core Team (2007). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.R-project.org. Swihart, R.K. and Slade, N.A. (1985). Testing for independence of observations in animal movements. Ecology 66, 1176-1184. Worton, B.J. (1987). A review of models of home range for animal movement. Ecological Modellling 38, 277-298.