Author(s): Maria Alp; Celine Le Pichon; Laurence Tissot; Alain Alric; Axel Guillemin; Sylvie Tomanova; Nicolas Poulet
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Abstract: Brown trout (Salmo trutta) is an emblematic European fish species living primarily in well -oxygenated cool streams. As for other salmonids, reproductive migrations of mature trout individuals are well -known, but also diel and seasonal movements of earlier life stages have been repeatedly reported. It suggests that the species may be sensitive to the degree of functional connectivity of streams throughout its life -cycle and this potentially at different spatio-temporal scales. Moreover, in upstream areas, where trout most frequently occur, populations are often confronted with hydropower-related alteration of stream continuity through presence of dams, weirs or water flow diversion. While observations of movement through stream networks have been regularly documented for brown trout, many questions remain open. What are the frequency, and spatial scale of dispersal events occurring over a year? How big is the proportion of population involved and how synchronized is migration? What are the main environmental drivers or triggers of dispersal at different life stages? Clarifying these questions is an important prerequisite for evaluating the influence of stream connectivity on trout population dynamics and taking efficient measures for preserving the species. We present results of a multi-annual field study, conducted on the Neste d’Oueil, a second -order mountain stream with natural hydrological regime located in the French Pyrenees. About 1900 juvenile and adult trout individuals were marked with pit-tags between 2014 and 2017. Our study design included recordings of fish movements by three fixed antennae combined with regular mobile antennae surveys at two spatial scales: 500 m (monthly) and 1.5 km (yearly). Together with yearly population electrofishing sampling providing biometric data, this resulted in a highly complementary data set, wel l resolved both in space and time. We use these data to analyze phenology, trajectories, extent and direction of movement, make quantitative estimates of home range extents and explore dispersal behavior types for different life stages, in particular, juve nile trout. We analyze the relationship of these patterns to temperature and discharge as well as mesohabitat and obstacle distribution within the study area. Finally we discuss the results of this work in the light of population persistence in streams but also in the perspective of improvement of stream connectivity for the species.
Year: 2018