HYDROPOWER AND CONNECTIVITY IN INLAND RIVERS

The primary objective of RIVERCONN has been to provide new knowledge about ecological and evolutionary consequences of reduced and/or loss of ecological connectivity in large inland rivers. The project has so far published six scientific papers, and two papers are currently in review. RIVERCONN has contributed to increased knowledge about the ecological significance of migrations in European grayling and brown trout, differences between the two species and the effects of fragmentation and dysfunctional fish passages. How critical is it to maintain fish migrations in large inland rivers? This question has been discussed in the Glomma river system and other inland rivers for many years since the river sections between the hydropower dams include all vital habitats as spawning, feeding and overwintering areas. RIVERCONN has shown that maintenance of partial migration systems are important in order to both preserve life history variation and maintain fish production in regulated rivers. RIVERCONN has shown that grayling fry drift downstream after hatching and emergence from the gravel. In river sections with high water velocities, grayling fry can drift many kilometers. This phenomena is probably an important driving force for migrations later in their life. Drift of fry from the spawning areas makes it possible to utilize feeding and nursery areas downstream spawning areas. The results from the RIVERCONN-project point out that it is important to consider fish migrations and habitat demands in a life-span perspective. The terms "life-span migrations" and "compensatory migrations" are relevant when describing grayling and trout migrations in large inland rivers. RIVERCONN has compared migrations of grayling and trout in un-fragmented river sections with the timing of migrations in fishways, and this has revealed a mismatch between the opening times of the fishways and the timing of migrations in the river. Both grayling and trout start the migrations earlier in the spring than previously assumed, already in April. Often, the fisways are not open until end of May / beginning of June. Especially for the grayling, it is critical to pass fishways in the spring because it is a spring spawner. The fishways in many inland rivers are so-called pool-and-weir fishways (also termed "Salmon ladders"). In this type of fishways, the fish has to jump from pool to pool and it is now general knowledge that this fishway type is not suitable for grayling, trout and other inland fish species with lower swimming capacity than Atlantic salmon. As a direct consequence of the finding in the RIVERCONN-project, instructions for the opening and closing times of fishways in the Glomma river are worked out and the possibilities to modify pool-and-weir fishways to make them more suitable for e.g. grayling and trout will be assessed as a part of the SAFEPASS-project (ENERGIX, NFR). The RIVERCONN project has also shown that long migrating grayling have higher individual growth rates than more stationary individuals. Hence, although there is a cost associated with migrations, migrating individuals seem to increase their fitness compared to stationary individuals. Genetic studies have revealed differences in the population structure between grayling and trout in the Gudbrandsdalslågen river system. Grayling shows no genetic structuring in river sections between natural migration barriers, whereas the opposite is the case for trout. This may be caused by differences in early life history between the two species, with grayling drifting from spawning areas after emergence and hence possible lack of homing behavior. Both species may migrate over quite long distances and expel large variation in life history strategies. RIVERCONN has contributed to address current challenges associated with fish migrations in regulated rivers, and the findings in the RIVERCONN-project are followed up in other research projects and by both environmental authorities and the hydropower industry.

The implementation of the EU Water Framework Directive (WFD) requires preservation or improvements of the ecological status in large rivers developed for hydro electrical purposes. RIVERCONN is designed to address key R&D challenges required to achieve Go od Ecological Potential (GEP) or Status (GES) according to WFD in regulated rivers. This is obtained by investigating evolutionary and resilience consequences following reduced or lost connectivity caused by hydropower installations. The primary objective is to provide new and fundamental knowledge to disentangle criteria to assess GEP and GES by investigating ecological and evolutionary consequences following connectivity change experienced by grayling and brown trout in large regulated rivers. Secondary objectives are to 1) establish basic knowledge on the effects of fragmentation inflicted by hydropower dams on ecosystem functionality on grayling and trout, 2) define life history variations, species-specific responses and genetic signatures for the sam e species in natural and fragmented sections of the rivers, 3) evaluate the impact from genetic and evolutionary changes during a century-long stocking program on the resilience capacity of a trout population, 4) assess dam passage efficiency for both spe cies in two fishways and 5) to operationalize and expand the GEP/GES-concept in the context of balancing society?s costs and benefits regarding preservation of connectivity for grayling and trout and maintenance of sufficient hydropower production. It is anticipated that the project findings will meet major demands from management authorities in the process of defining GEP and GES in heavily as well as less modified river basins. Furthermore the knowledge will be useful in the process of revisions of disc ontinued hydropower licenses and evaluating plans for new hydropower installations and rearmament of existing installations.