Vattendragsrestaurering i teorin och fiskinventering i praktiken : en litteratur respektive metodstudie

Sammanfattning: Running water-pathways have played an important roll in Sweden and frequently been manipulated. One profound change was made during the period of logging when streams were cleared from obstacles as big boulders, sharp bends and side-streams. Dams and different constructions gave control of the stream water and the streams became channel-like with a homogen structure. This interference gave problems for many fish populations and resulted in a shortage of feeding habitat, over-wintering habitat, spawning habitat, unnatural flow regimes, sedimentation, unnatural temperature fluctuations. Many of these historical changes of the watersheds are now subjects for restoration, ie., bring back the streams to what we believed it was before the change. However, what once existed in terms of complexity is now gone and difficult toreplace. To make the best of forthcoming restoration it is recommended that managers: • Have a plan with a clear goal, how to get there and following-up procedure, • See the whole stream as an ecological system with all its habitats, • Use everything from big boulders (> 1m³) to pebbles and sand to make the restoration more heterogenic and sustainable, • Build construction with bigger boulders in its base to withstand ice and spring flood. A smaller angle between boulders and the water suface also puts less strain on the construction, • Include the brinks in the restoration to create a more natural environment where debris in the stream over time can make the habitat more homogenous. Monitor stream changes and do follow-up studies in restored streams so effects can be evaluated. With following-up procedures on the recovery process(es) after a restoration we most easily learn to do restorations better in the future.In Sweden electro-fishing is the most common monitoring method in small streams. Electro-fishing is well documented and works well but has some drawbackswhere other methods may be a good alternative. In this study snorkelling and angling were compared with electro fishing in a small stream in northern Sweden, Tolkijoki 50 km ENE of Gällivare, during year 2000, 2001 and 2002. Electro-fishing seems to be the best method to use in streams less then < 8 m in width with a maximum depth of 1 m. However, angling in deeper sections gave larger graylings showing that some species and large fish may be underestimated when electro-fishing. Low visibility may cause small fish (0+) to be underestimated using electro-fishing. Angling, on the other, overestimated the proportion of larger fish in an area. For snorkelling the visibility has to be 3 meters or more. The temperature and time of year also affect the results. Temperature under 4°C effect electro-fishing negatively since this method is less efficient at lower temperatures. Snorkelling gets less effective under 15ºC and gives constantly poor results under 10°C. Both low and high temperatures make fish more passive and may effect the results from angling. During my survey the water temperature never exceeded 10ºC. This may explain why the electro-fishing did not result in a single wounded fish. Angling caused wounds so some fish (7,5 % of all caught) were observed bleeding. Angling in water with good visibility made it possible to see when fish took the bait which made it possible to minimize the numbers of deep hookings.