Influence of weirs and a fish pass on home range and use of spawning sites of adult brown trout Salmo trutta fario L. in the River Nebel
Summary: In the river Nebel adult brown trouts mostly stayed at the same place out of spawning season (November/ December) Frequently fish moved in a range of 100 m, occasionally, however, in a range of 500 m. Thus, out of reproduction the weirs of the river Nebel did not limit movement activities within the home range. Extensive movements up to 12,000 m across the existing weirs, resulted in a loss of animals of the upstream population. During the spawning season within October/November (on average 41 days) all suitable spawning habitats downstream the weir Kölln were used. Often spawning sites were used repeatedly; this was connected with an increased spawning mortality. Due to a fish ledder the density of spawning females downstream the weir was reduced. About 20 to 30 % of the adults from the river downstream the weir crossed the ledder. Thus, they contributed to the reproduction success of the total population.