The impacts that environmental factors brought to the population of the Formosan landlocked salmon are discussed in this paper and the evidence results indicate that the air temperature and typhoon have taken negative effect during past 15 years. Under the population simulations, without considering the environmental factors, it is clear that the population growth rate tends towards a steady state in the long run. On the contrary, the population would be in decline or suffer the extermination while we consider those factors.

An ecosystem always involves some implicit relations between habitat environment and inhabitants, whose reciprocal links can not be identified easily. Three sets of ecological monitoring data were analyzed in this study, including coral reef, algae (Thalassia hemprichii Aschers) in Kenting National Park, and Formosan landlocked salmon (Oncorhynchus masou formosanus) in the basin of Chichiawan Stream. Two data-oriented analysis techniques, which are Habitat Evaluation Procedure (HEP) and Group Method of Data Handling (GMDH), were applied to retrieve the embedded patterns from these data sets. Eventually, for each data set, a forecasting model based on the technique of combined forecasting were developed, which is to integrate the results from HEP and GMDH, for improving the overall modeling precision. The results of this study show that the data-oriented analyses, such as HEP and GMDH, are useful for finding valid information from the ecological data. Furthermore, the combined forecasting technique can really improve the performance of model prediction even for the ecological research. In order to acquire the most important habitat environmental factors affecting the inhabitants, this study also performed sensitivity analysis of the models. The contributions of this study are to identify effective knowledge for future ecological research and to provide reasonable suggestions for formulating conservation strategy.

Atlantic salmon (Salmo salar) are found in a range of locations along Sweden's coastline, but Sweden's largest lake, Vänern, also harbors a population of salmon; the rare freshwater migratory form. The majority of the salmon in Lake Vänern migrate upstream in River Klarälven in order to spawn, where they are assisted by humans through the "trap and transport" method to get past Klarälven's eight hydropower dams, which otherwise constitute definite obstacles to upstream migration. When the salmon later migrate downstream to Lake Vänern they receive no assistance and experience a high mortality rate as they are partially forced to swim through the turbines. The wild salmon population today includes over 1000 spawners annually, an increase from <200 in the 196os, but far below historic records of over 10,000 spawners.  This report therefore aimed to investigate the population growth rate and extinction risk for the salmon in Klarälven, both in the current situation and with passages installed past the hydropower plants, and in doing so answer the questions 1) How large is the population growth rate and risk of extinction for today’s population of salmon in Klarälven over the course of 100 years? and 2) How would passage solutions past the hydropower plants in Klarälven affect the population growth rate and risk of extinction for today’s population of salmon in Klarälven over the course of 100 years? These questions were answered by running a population viability analysis in the program Extinction Vortex, which allows the programming of model populations and the manipulation of parameters to test different scenarios. The scenarios that were tested were 1) Scenario 1: Today's method with trap and transport and total lack of passages, 2) Scenario 2: Trap and transport continues, and downstream passages are installed past all eight power plants, and 3) Scenario 3: Upstream and downstream passages are installed past all eight power plants and trap and transport ceases. The results of the vulnerability analysis did not show any risk of extinction for the next 100 years, but a long-term negative trend for the salmon in Klarälven using today's method was seen. However, the development became significantly more positive for the salmon in Klarälven when the installation of downstream passages was simulated, but after that not significantly more positive when the installation of upstream passages was simulated as well. This result provided answers to the research questions and based on them it could be concluded that even though the salmon in Klarälven are not under any acute threat at the moment, and that there may be other fish populations in other regulated streams and rivers that would benefit more from environmental adaptation, measures need to be taken also in Klarälven, to ensure the long-term conservation of the unique freshwater migrating salmon that inhabit the area. / Laxen (Salmo salar) förekommer på flera håll längst Sveriges havskuster, men även Sveriges största insjö Vänern hyser en population av lax; den sällsynta sötvattensvandrande formen. Majoriteten av Vänerlaxarna migrerar upp för att leka i Klarälven, där de assisteras av människan genom metoden ”trap and transport” som tar dem förbi Klarälvens åtta vattenkraftverk vilka annars utgör definitiva vandringshinder. När laxen sedan ska ta sig tillbaka ner till Vänern får de ingen assistans, i stället tvingas de delvis simma genom turbinerna med stor dödlighet som följd. Laxpopulationen idag består av över 1000 lekande fiskar varje år, en ökning från <200 individer på 1960-talet, men långt under historiska siffror på över 10 000 lekande laxar. Detta arbete syftade därför till att undersöka populationsutvecklingen och utdöenderisken för Klarälvslaxen, såväl i nuläget som vid en installation av passager förbi kraftverken, och genom detta besvara frågeställningarna 1) Hur stor är populationsutvecklingen och utdöenderisken för dagens population av Klarälvslax över kommande 100 år? och 2) Hur skulle passagelösningar förbi vattenkraftverken i Klarälven påverka populationsutvecklingen och utdöenderisken för dagens population av Klarälvslax över kommande 100 år? Dessa frågeställningar besvarades med hjälp av en sårbarhetsanalys i programmet Extinction Vortex, som tillåter uppbyggandet av modellpopulationer och manipulation av parametrar för att testa olika scenarier. Scenarierna som testades var 1) Scenario 1: Dagens metod med trap and transport och total avsaknad av passager, 2) Scenario 2: Trap and transport fortsätter samt nedströmspassager installeras förbi alla åtta kraftverk, och 3) Scenario 3: Upp- och nedströmspassager installeras förbi alla åtta kraftverk och trap and transport upphör. Resultatet av sårbarhetsanalysen visade inte på någon utdöenderisk kommande 100 år, men en negativ trend för Klarälvslaxens långsiktiga populationsutveckling med dagens metod. Utvecklingen blev dock signifikant mer positiv för Klarälvslaxen vid den simulerade installationen av nedströmspassager, och ännu något stabilare när även uppströmspassager installerades. Detta resultat gav svar på frågeställningarna, och utifrån detta kunde slutsatsen dras att trots att Klarälvslaxen inte befinner sig under något akut hot för närvarande, och att det kan finnas andra fiskpopulationer i andra vattendrag som är i mer akut behov av miljöanpassning, så behöver åtgärder komma på plats även i Klarälven, för att säkerställa det långsiktiga bevarandet av den unika sötvattensvandrande Klarälvslaxen.