Ecological and genetic study on Lethentron japonicum of which biomass is remarkably dicreasing

为了阐明北极七鳃鳗在溪流生活期种群数量急剧减少的原因和影响，进行了幼虫和上游迁徙成虫的生态野外研究，并对石卡里河种群进行了种群遗传分析。结果表明，河床上的软泥量和落叶枯枝落叶中大量的碎屑对七鳃鳗幼体的高成活率起着重要作用。此外，研究还发现，水深对上游迁徙的七鳃鳗成鱼的产卵成功有重要影响。微卫星DNA分析结果表明，石家河种群的遗传多样性近年来呈下降趋势。在此基础上，我们提出了一些溪流环境的改善方案，以恢复七鳃鳗的种群数量。

To elucidate the cause and effect of highly decreased population size of the Arctic lamprey, Lethenteron japonicum in the stream life period, the ecological field research for larvae and upstream migrating adults, and population genetic analysis of the Ishikari River populations were carried out. As a result, it was made clear that both the soft mud quantity on the stream bed and the abundance of detritus originated from the litter of fallen leaves played an important role for high survival of lamprey larvae. In addition, it was found that the water depth was important for spawning success of upstream migrating lamprey adults. The results from microsatellite DNA analysis showed the genetic diversity of Ishikari River populations decreased in recent years. On the basis of these results, we proposed some improvement plans of stream environments to restore the population size of this lamprey species.