Reconstructing Sakhalin Taimen Parahucho perryi Historical Distribution and Identifying Causes for Local Extinctions

The Sakhalin taimen Parahucho perryi is an endangered salmonid with a natural range limited to the Russian Far East and Japan. We constructed a classification tree to determine the environmental factors shaping the historical global distribution of this species and then predicted its potential geographic range. The distribution was most strongly influenced by a spatial autocorrelation term, indicating that it is highly contiguous. Large drainage basins with low topographic relief and large floodplains had a higher probability of taimen occurrence. The boundary of the global distribution was delineated by mean monthly precipitation within the range of 54–96 mm. The presence of Sakhalin taimen was predicted in many drainage basins where it has never been recorded. We also modeled the status of 48 taimen populations in Japan, where it was possible to classify them into three categories: currently stable (7), endangered (5), and extinct (36). The most significant factor differentiating the 12 extant populations from the 36 extinct populations was mean annual air temperature, the extant populations being distributed exclusively in areas where the air temperature is below 5.2°C and agricultural development is minimal. The extant populations were found in drainages with significantly lower elevations and a smaller percentage of farmland compared with drainages where populations have been extirpated. The presence of lagoons was a common characteristic of the drainages with the 7 stable populations, suggesting that lagoons represent critical refugia for the species. The implications of this study for taimen conservation are discussed.