Gravel bed spawning grounds are essential for the reproduction of salmonids. Such spawning grounds have been severely degraded in many rivers of the world because of river regulation and erosive land use. To reduce its effects on salmonid reproduction rates, river managers have been restoring spawning grounds. However, measures of effectiveness are lacking for the restored spawning sites of brown trout (Salmo trutta).In this study, two methods were used to restore gravel bed spawning grounds in the Moosach River, a chalk stream in Southern Germany: the addition of gravel and the cleaning of colmated gravel. Seven test sites were monitored in the years 2004 to 2008, focussing on sediment conditions. Furthermore, brown trout egg survival and changes in the brown trout population structure were observed.Both gravel addition and gravel cleaning proved to be suitable for creating spawning grounds for brown trout. Brown trout reproduced successfully at all test sites. The relative number of young-of-the-year brown trout increased clearly after the restoration. Sediment on the test sites colmated during the 4 years of the study. In the first 2 years, highly suitable conditions were maintained, with a potential egg survival of more than 50%. Afterwards, the sites offered moderate conditions, indicating an egg survival of less than 50%. Conditions unsuitable for reproduction were expected to be reached 5 to 6 years after restoration.
This review provides a summary of knowledge on two-way fish migration of salmonids and eels past hydroelectric plants in Europe. On the basis of a summary of international literature, general designs and recommendations for best practices for fish-pass facilities are provided. The review is part of the Norwegian SafePass project, which focuses on Atlantic salmon, brown trout, grayling and European eel. According to recent international recommendations, many existing European fishways for upstream migration do not have an optimal design. This is especially evident for denil and pool-and-weir fishways in inland areas with species such as grayling and brown trout. Based on the review, we generally recommend (1) using ramps, nature-like channels and vertical-slot fishways for these species and (2) reducing water drop between the pools in pool-and-weir fishways and reducing energy dissipation compared with the design of traditional Atlantic salmon ladders. There are few well-functioning passages for downstream migration of fish in Europe and significant progress has been made in the past decade to improve technology and knowledge. Several international studies have shown that physical structures, such as fine-mesh trash racks with alternative escape routes and bypass arrangements, provide >90% passage efficiency for downstream migration, especially for brown trout and salmon, and have, in recent years, shown good results also for silver eels.
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