Epsilon Archive for Student Projects

Abstract

Is it necessary to build fishways at all artificial migration barriers to restore and sustain bio-diversity? Hydropower plants have often been built at places where a difference in height has been used to gain more power, leading to the hypothesis that many hydropower dams have been built at natural migration barriers. How are Swedish running waters (not large rivers) assessed with respect to historical passability for fish at natural migration barriers and dams? How does one study a specific location with respect to the historical passability for different fish species?
The methodologies that are evaluated in this thesis are relevant and specific information from a habitat mapping from Värmland County, where 2 903 km waterways already have been surveyed. The evaluation in this thesis has been made on various types of artificial migration barriers, to find out whether natural migration barriers have been replaced by artificial migration barriers. A detailed study was made on a hydropower plant in a tributary to the Västerdalälven River, Horrmundsvalla. Several different methods were used to investigate the historical passability for different fish species. The methods consisted mainly of historical information and DNA analysis of brown trout (Salmo trutta L.) upstream and downstream of the waterfall, Horrmundsvallafallet.
Field surveys of Swedish waters are often done with the use of “habitat mapping” (or Jönköpingsmodellen). My conclusion after evaluating this habitat mapping, is that the current mapping methodology gives an unclear result with respect to historical passability for different fish species. The most likely reason to this unclarity is the design of the protocol template used in the habitat mapping. In the protocol template, one can choose whether it is a natural or artificial barrier to migration. There is however, no question in the template that can be used to indicate the historical passability for different fish species. I therefore propose to change the protocol template, with the aim that historical passability for different fish species also can be commented.
Historical information indicates that brown trout have not been able to pass Horrmundsvallafallet, though some sources refer that eels (Anguilla Anguilla) have been able to pass. However, this must be very unlikely when one reflects the biological conditions and life cycle of eels. Bream (Abramis brama) are the fish species that dominate the lake upstream Horrmundsvallafallet. However, it is not likely that bream have been able to colonize Lake Horrmunden through Horrmundsvallen on their own, given the breams physiological capac-ity and watercourse morphology.
The DNA analysis of trout populations upstream and downstream of Horrmundsvallafallet showed that the difference in the FST (genetic difference between the two populations) was 0.023. The difference in FST could be interpreted as that both populations initially (prior to
1960 when the hydropower plant was built) belonged to the same population, but after that have been isolated. The explanation for why the FST value was so low could however be due to the stocking history of trout in the lake upstream of the two populations. If one should conduct an investigation of historical passability based on DNA analysis it is important to check and examine the historical stocking or transfers of fish in the water systems of interest.
In summary, I conclude that Horrmundsvallafallet was a total natural migration barrier to all existing fish species prior to human impact of the watercourse. Historical information is important for assessing historical passability for fish species. However, one should be careful and judge the credibility or plausibility degree of historical sources that are used. The habitat mapping done by the County Administration Board of Värmland indicates that natural migration barriers occur at hydropower dams. The share is difficult to determine today given that Habitat Mapping methodology does not reflect historical passability. Despite the shortcomings of the methodology, over 5 % of hydropower dams could have been built by a historically definitive natural migration barrier for trout.