Modeling the impact of dam removal on the Formosan landlocked salmon in the context of climate change

Dam removal is analyzed as a conservation strategy for the Formosan landlocked salmon Oncorhynchus masou formosanus, a critically endangered species whose last refuge is the Wuling basin in central Taiwan. In a previous study, a stochastic age-structured simulation model was developed and used to assess the effectiveness of removing four dams in increasing salmon abundance in Kaoshan Stream in the context of climate change. Three check dams remain intact in Chichiawan Stream and one of its tributaries. In this study, the model is recalibrated for these regions and simulates the removal of each of these dams. Model analysis suggests that the combined effect of dam removal and climate change decreases the effectiveness of dam removal while increasing the negative impact of climate change on abundance. A simple graphing technique is presented for comparing the predicted impact of the removal of each dam under consideration. The model predicts that removing the dam in Chichiawan Stream has the largest potential for increasing the 2035 abundance, but only under narrow conditions of climate change and effectiveness of dam removal. The potential benefit from removing one of the tributary dams is smaller, but the conditions for reaching closer to its potential are less restrictive. This type of analysis is useful for dam removal management decisions regarding habitat restoration.