1Tochigi Prefectural Fisheries Experiment Station, Tochigi 324-0404, 2Freshwater Fisheries and Environment Division, National Research Institute of Fisheries Science, Nagano 386-0031, 3Department of Ocean Sciences, Tokyo University of Fisheries, Tokyo 108-8477, 4Department of Aquatic Biosciences, Tokyo University of Fisheries, Tokyo 108-8477, Japan
We investigated the seasonal changes in number, dispersal and growth of juvenile Japanese charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou masou in the Karatakisawa Stream, a small tributary of the Kinu River in central Japan. 873 (81.4%) of a total 1073 charr caught by monthly sampling from 1993 to 1995 were age-0, and 241 (98.8%) of a total 244 salmon were age-0. Most of the newly emerged age-0 salmon were caught in the spring of 1995. They shifted downstream, and the number of fish decreased markedly by early summer. The number of the age-0 charr caught at any sampling from any month did not decrease until the end of autumn, although the distribution of the age-0 charr shifted downstream. In contrast, of a total 387 age-0 fish captured by samplings in the adjacent Kinu River in 1995, 356 (92.0%) were salmon, whereas only 31 (8.0%) were charr. These results suggest that small tributaries play an important role as nursery habitats, especially for Japanese charr.