Seasonal abundance and the re-establishment of iwana charr Salvelinus leucomaenis f. pluvius after excessive sediment loading by road construction in the Hakusan National Park,central Japan

Synopsis Seasonal abundance and the re-establishment of stocks of iwana charr, Salvelinus leucomaenis f. pluvius were studied in the Jadani Stream, Hakusan National Park, central Japan, between 1984 and 1989 after the introduction of a moratorium on fishing. Stream conditions were severely damaged by dumped materials from the construction of a mountain road between 1967 and 1977. The densities of iwana increased markedly in the upper reaches and slightly in the middle reaches of the stream and showed marked seasonal fluctuations over the study period. Data shows that the iwana has a high potential reproductive capacity under degraded stream conditions. However, the population density of iwana remained low in the lower reaches, where the stream conditions were more severely damaged not only by construction of the mountain road but also abstraction of water for hydro-electric generation. We review also the state of native iwana and problems relating to its conservation in Japan.