Context Habitat fragmentation and its threat to biodiversity, the core of this project, have risen to high prominence on the (inter)national agenda. Hence, the number of conventions, agreements and amendments has grown steadily. In these agreements, the emphasis is put on the need for preserving biodiversity, at the species, subspecies, variety and population levels, because of their ecological, genetic, social, economic, scientific, educational, cultural, recreational and aesthetic value. More specifically concerning freshwaters, the restoration of water quality and hydromorphology of water courses, and the maintenance or restoration of longitudinal and lateral connectivity are central themes of two international directives and decree: the European Water Framework Directive and the Benelux Decree M 96, with deadlines set for 2015 and 2010 respectively. Project description Objectives The disruption of longitudinal connectivity by man-made obstacles and the stocking of fish communities with non-indigenous species or genotypes may threaten the fish fauna of Belgian rivers to various extents. Obstacles impede migrations between habitats that are vital for populations and they may restrict the gene flow between populations, thereby reducing the effective size and genetic diversity of populations and increasing the risk of local extinction. Stocking programmes often involve the introduction of non-indigenous genotypes in native populations. It frequently leads to accidental introductions of non-indigenous fish species and may as such enhance the expansion of alien species. Although stocking programmes lead to the temporal and superficial enrichment of local fish communities or gene pools, they generally result in a loss of biodiversity on a regional or international scale through the homogenisation of communities and the breakdown of genetic differentiation between populations. This project aims at assessing the impact of these factors and provide tools for priorisation and remediation, through a three-step approach: (1) a descriptive field survey including genetic analysis, (2) a study investigating the swimming and leaping capacities of local fish species, (3) and a study of actual migration of fish in the field. Methodology A descriptive field survey of fish diversity in the vicinity of various types of artefacts that are representative of the southern, upland and northern, lowland parts of Belgium will be conducted. It comprises analyses at the fish community level and at the genetic level for target species (brown trout, bullhead, roach, three-spine stickleback) that are representative of river systems and have undergone contrasting histories of restocking. Genetic analyses with hypervariable microsatellites will be conducted on specimens from the field and on stocks used for restocking in order to measure the impact of the stocking and of obstacles on the gene flow. The ecophysiology of movement (swimming and leaping capacity of fish) will be determined under controlled conditions in the laboratory. The critical swimming speed of fish will be measured in respiratory swimming chambers. Theoretical leaping curves will be produced and evaluated in a large flume mimicking a culvert. Energy expenditure associated with swimming and leaping will be determined. Experimental data will be used to develop species-specific predictive models to be validated and evaluated in field situations. Capacities of fishes to cross man-made obstacles will be measured with telemetry (PIT and radio telemetry) in actual field conditions in a section of the river systems under study, both to test the predictions of laboratory models, and to cast light on how the obstacles eventually affect the gene flow. Fishes implied in the telemetry and energy studies will be genotyped to assess their origin and their status in the genetic structure of the population. Interaction between different partners The different partners are very dependent on each others performance and interact during the whole duration of the project. For example, IBW-IN and ULg are responsible for the analysis of fish populations in the chosen model systems in the field: presence, size, condition and sex ratio will be determined and analysed. The physical properties of the barriers will be assessed by RUCA-AWZ. During these same field trips samples will be taken for the genetic analysis, research to be conducted by the KULeuven and the UCL. Fish will also be tagged or provided with telemetry tags which allows to follow fish migration in the field (IBW-IN and ULg), and fish will be taken to the laboratory to assess their swimming and leaping capacities (RUCA-AWZ). The outcome will be a model predicting the capacity of fish species to cross barriers (RUCA-AWZ), which can then be validated by both the results from the tagging expeditions (IBW-IN and ULg) and the genetic analysis (KULeuven and UCL). Expected results and/or products Laboratory and field results will be integrated in order to produce user-friendly tools for predicting the severity of obstacles and stocking practices, and determining the priorities for preservation and remediation. The project will result in (1) extensive datasets that can be used for future research, (2) user-friendly tools (a manual and software) that allow end-users and other stakeholders to assess, mitigate and prevent problems related to fish migration and stocking programmes, and (3) a policy document, where general as well as specific suggestions and advices are formulated to the address of managers, political authorities and decision-makers. Both the Institute for Nature Conservation and the Institute for Forestry and Game Management were partners in this project