A dry season streamflow reconstruction of the critically endangered Formosan landlocked salmon habitat

This study presents a 259-year (1750–2008 CE) reconstruction for October to February (ONDJF) standardized streamflow index of the Chichiawan Stream, the sole habitat of the critically endangered Formosan landlocked salmon (Oncorhynchus formosanus) remaining natural population. The reconstruction was based on the earlywood ring-width variations of Taiwan Douglas-fir (Pseudotsuga wilsoniana), using ensemble empirical mode decomposition for chronology development. Results showed that a higher average ONDJF streamflow in the 1968–2008 period was positively associated with a wider Taiwan Douglas-fir earlywood ring. During that period, the average ONDJF streamflow was related to the Pacific Decadal Oscillation and El Niño-Southern Oscillation development. Spectral analysis indicated that the reconstructed index had significant peaks around 2∼7 years and less significant peaks around 20–35 years. Based on the derived and reconstructed indices, most of the average ONDJF streamflow between 1750 and 2008 was within the normal range. Furthermore, there was no statistical evidence to suggest that the flow regime of the last few decades had changed, which refuted the speculation that the dry season streamflow natural variability in the 1960s and 1970s might have contributed toward the critically endangered status of Formosan landlocked salmon. The results of this study will be useful for developing short- to mid-term strategies to protect the endangered species and manage water resources.