Modelling fish dispersal in catchments affected by multiple anthropogenic pressures

The colonisation of rivers by fishes is directly linked to abiotic habitat conditions but often impaired by dispersal abilities of fishes and movement constraints such as barriers. Despite the relevance of dispersal, comprehensive knowledge and in particular quantitative information or models on fish dispersal in rivers considering fish populations as differently mobile consisting of stationary and mobile components has not been available yet. The first part of this thesis provides the first comprehensive compilation and quantitative analysis of freshwater fish movement while considering each fish population consisting of differently mobile specimens. Main objectives of the study were to determine movement distances of stationary and dispersal relevant mobile components of fish populations and identifying determining factors for dispersal distances. The review yielded 160 empirical datasets from 71 studies on the movement of 62 riverine fish species which were evaluated, completed and analysed in a standardised way based on refitted leptokurtic probability-densitiy functions (dispersal kernels). A share of one third and two thirds emerged as a general pattern of the mobile and stationary component of a fish population, respectively. Moreover, four variables were identified primarily determining dispersal distances: fish length, aspect ratio of the caudal fin, river size and time. In the second part of the thesis, the novel fish dispersal model FIDIMO is introduced. FIDIMO provides a tool for predicting and simulating spatio-temporal patterns of fish dispersal in dendritic river networks considering movement barriers with a real integration of GIS. The fish dispersal model FIDIMO links conceptual considerations on dispersal modelling with empirically observed leptokurtic fish movement patterns and the strengths of geographically explicit modelling in Free and Open Source GIS. In the third part of the thesis, FIDIMO was applied for modelling dispersal of multiple fish species in an anthropogenically impacted North-German river catchment. A main objective of the study was to disentangle and quantify the single and joint contributions of habitat suitability, dispersal constraints and network fragmentation (barriers) on the distribution patterns of 17 fish species. The results show significant positive effects of both, local-scale habitat quality and speciesspecific dispersal ability on the distribution of river fishes, whereas no significant effect of barriers influencing the presence of a species could be found. Furthermore, over longer time periods the importance of dispersal decreased in favour of habitat suitability becoming relatively more relevant in determining species’ presence. Overall, this thesis contributes to an improved understanding of fish dispersal abilities and patterns and points out its importance in the colonisation of river networks. Moreover, the presented dispersal model FIDIMO allows predicting spatiotemporal colonisation patterns and estimating time lags in fish response to river rehabilitation and changed network connectivity, predicting temporal patterns of (invasive) species spread and estimating maximum distance between stepping stone habitats. Based on the findings, it can be emphasised that the prioritisation of connectivity measures (e.g. opening new suitable habitat patches) and the restoration of stream reaches might be most efficient if the spatial arrangement of source populations, their position in relation to barriers and the dispersal ability of fishes are considered.