Transactions of the American Fisheries Society 140:1–13, 2011 C  American Fisheries Society 2011 ISSN: 0002-8487 print / 1548-8659 online DOI: 10.1080/00028487.2011.544999 ARTICLE Reconstructing Sakhalin Taimen Parahucho perryi Historical Distribution and Identifying Causes for Local Extinctions Michio Fukushima* National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506, Japan Hiroto Shimazaki Kisarazu National College of Technology, Kiyomidaihigashi 2-11-1, Chiba 292-0041, Japan Peter S. Rand Wild Salmon Center, 721 Northwest 9th Avenue, Suite 280, Portland, Oregon 97209, USA Masahide Kaeriyama Graduate School of Fisheries Science, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido 041-8611, Japan Abstract 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. Identifying the geographical range of a species, potential threats to the species, its preferred habitats, and areas at risk of future exposure to these threats are crucial to the conservation of imperiled species (Richter et al. 1997; Gustafson et al. 2007; Williams et al. 2007). This has been poorly done for aquatic species, however, because the distributions are not easily ob- served and most local extirpations of such species have gone *Corresponding author: michio@nies.go.jp Received January 13, 2010; accepted September 2, 2010 unnoticed by humans. Unless we understand the species’ cur- rent and historical distributions and causes for past extirpations, we will be much less likely to achieve success in our conserva- tion actions such as reintroduction of the species into currently unoccupied historical ranges (Williams et al. 2007). Owing to their ability to adapt to changing conditions and mi- grate into nearby river systems through the marine environment, 1