BiodivERsA: Between Scylla and Charybdis ? managing connectivity for freshwater fish

Whilst freshwater ecosystems make up a relatively small proportion of aquatic ecosystems on the planet, they are disproportionately rich in biodiversity. Yet as sources of freshwater are vital to human societies, they are often subject to anthropogenic pressures. Man-made constructs such as dams, weirs, culverts and even bridges can have severe effects on freshwater ecosystems and the services they provide, changing flow regimes and water chemistry. They can even increase the impact of extreme weather events. As such, restoring connectivity and more stable conditions by removing dams and weirs are important means for improving the functioning of stream-lake networks, and there is a growing inertia behind the movement to remove dams across much of Europe. Yet while dam removal may theoretically restore freshwater waterways, many such human constructs may currently provide barriers for the further dispersal of alien species. Invasive non-native species are a huge threat to biodiversity everywhere, and freshwater ecosystems are nio exception. Many freshwater fish species have been introduced by humans for recreational fishing, or through use as bait, whilst others are simply expanding their range as a warming climate slowly increasing their potential distribution. If barriers like weirs and dams are removed, it may allow these species to colonise new areas and potentially negatively affect native species. This trade-off is not implemented in the national guidelines for water management in most EU countries, and managers lack quantitative tools for exploring the consequences of removing or adding barriers. The overarching aim of this project is therefore to provide a decision support system for the management of connectivity in lake-stream networks. The project is part of a European network through the BiodivERsA program. To this point, the project has focussed on two major aspects of the problem highlighted above, the first being the incorporation of connectivity into species distribution models. The successful incorporation of dispersal constraints as connectivity parameters into species distribution modelling adds valuable statistical power to forecasting species distribution. This allows conservationists to prioritise efforts on waterbodies that are not protected by suitable downstream connections to source populations. However careful selection of dispersal constraints is necessary, as the differences in biology between species of fish means that different waterways will present different levels of difficulty for them when overcoming natural dispersal barriers. The second major focus of the project to this point has been the production of a forecasting framework for the introduction of regionally invasive species. Again, the point here is to identify areas of greater risk for managers, in order to ensure they can prioritise management efforts. We managed to identify areas of concern for six freshwater fish species in southern Norway, using open source data.

Prosjektet har resultert i konkrete oppfølginger hvor videreutviklede data, modeller og verktøy er implementert i annen forskningsaktivitet. Dette gjelder både grunnleggende forskning og anvendt forskning. Sistnevnte gjelder FoU aktivitet knyttet til handlingsplan for fremmede arter og vassdragsforvaltning.

Stream-lake networks are an example of blue infrastructure that are fragmented by grey infrastructure in the form of dams, weirs, culverts, etc. Many man-made obstructions form absolute barriers, with dramatic effects on fish communities and ecosystem services. Restoring connectivity by removing dams and weirs are important means for improving the functioning of stream-lake networks, but may cause the spread of invasive species. This trade-off is not implemented in the national guide lines for the WFD in most EU countries, and managers lack quantitative tools for exploring the consequences of removing or adding barriers.