I specialize in fieldwork-based research on animal ecology and conservation biology by investigating the life history and population processes of aquatic organisms. I study aquatic ecosystems that span from rivers to the ocean by observing mainly salmonid fishes. Salmonids that live in aquatic ecosystems are suitable subjects for conservation biology because their adaptation to cold water makes them susceptible to the effects of global warming and because their nursery habitats are affected by human disturbance, such as hatchery programs, introduced trout, and riverine artificial structures (e.g., dams). In addition, salmonids are a suitable subject for conservation genetics because the ongoing release of farmed individuals from fisheries and recreational fishing causes genetic disturbance.
Life-history studies: I focus on the mechanisms that cause variation in life history traits and population fluctuations by using a comprehensive approach that combines observed data with theory building and testing using mathematical models. I would like to continue to develop and conduct research on the evolutionary mechanisms of animal reproductive strategies and life-history diversity (e.g., migration, growth, sexual dimorphism, egg size, age at maturity, size at maturity). Many animal species have two alternative life histories: migratory and non-migratory. Much research has been done on the evolutionary mechanism of migratory polymorphisms in salmonids, especially from the perspective of understanding the ultimate factors that cause animals to migrate, and I have been interested in this research myself. In the future, I intend to devote my research life to understanding and elucidating the integrated response of life history traits and population dynamics to unintended selection induced by human activities (e.g., fisheries-induced evolution) and changes to the environment. I would like to contribute to the conservation of biodiversity and the realization of sustainable social and economic activities.
Conservation ecology: One of my main areas of research is the ecological risk to native fishes of damming and invasion of non-natives and farmed conspecific. My field data shows that small populations isolated in the areas upstream of dams are becoming extinct, thus reducing genetic diversity; through numerical simulations of population dynamics, I have shown that the risk of extinction increases for decades after a dam has been constructed. My long-term data also showed that introduced trouts drive declines in native salmonid through interspecific competition. I also conduct applied research on population dynamics and biodiversity-conscious resource management for fisheries. To advance future technology for aquaculture in fisheries, I proposed the importance of measures that eliminate the concern of "domestication" (the genetic transformation of wild fish) and support sustainable fisheries by balancing artificial propagation and natural reproduction.
