Migratory diversity and growth of Sakhalin taimen Parahucho perryi collected from rivers in northern Hokkaido, Japan

Understanding migratory behavior is a fundamental component of conservation biology. However, the migration ecology of Sakhalin taimen Parahucho perryi , one of the largest salmonids and a landmark species for conservation, remains poorly understood. The lifetime migratory patterns of Sakhalin taimen from rivers in northern Hokkaido that had died due to a heat wave were classified into diadromous and fluvial forms, as revealed by transect analysis of otolith microchemistry. Notably, 2 diadromous individuals had migrated to the sea at the age of 0+ yr and subsequently retired from seaward migration, representing the first empirical evidence of a previously predicted migratory pattern. A hierarchical clustering analysis of maternal origins, based on the otolith strontium:calcium ratios from the core to 80 μm using dynamic time warping analysis, revealed that both post-sea-run migration and post-freshwater residence individuals contribute to offspring production. The migratory patterns revealed a clear difference in the proportion of diadromous forms between the 2 river systems, with a higher occurrence in the Sarufutsu River system, which flows into the Sea of Okhotsk, than in the Teshio River system, which flows into the Sea of Japan. Growth models varied among migratory forms, with diadromous individuals reaching a larger asymptotic fork length than fluvial individuals. These findings suggest that migration to the ocean contributes to size enhancement in Sakhalin taimen. Additionally, the study demonstrated that Sakhalin taimen exhibit diverse growth patterns and migratory behaviors, spanning a wide range of aquatic habitats, from rivers to the ocean, with variations among individuals and river systems.