Anadromous fishes, especially Pacific salmon and other salmonids (Onchorhynchus spp.) are one of the important vectors for transporting marine nutrients to the freshwater and terrestrial ecosystems. Pacific salmon return to natal stream to spawn and die. Their carcasses affect the nutrients cycling, stream productivity, and forest food-webs in given watershed. Despite the long history of salmon fisheries in northern Japan, ecology surrounding salmon carcasses has long been neglected, it is necessary to describe the variations of ecology in different localities because natural salmon runs are recovering for this decade in Hokkaido, northernmost island of Japan. Retention devices inside the channel are important for increasing availability of resource subsidies around riparian area. In this study, we delineated the retention structure of salmon carcasses in each channel unit (pool, riffle) and measured turnover rates of carcasses to clarify the function of each structure. Retention structure was classified as follows; 1) stone obstacle, 2) bank, 3) under-cut bank, 4) vegetative obstacles (woody debris, branch, root), 5) riverbed. Each carcass was labeled to track its movement and decomposition from September to December, 2011. In forested small stream, vegetative obstacles played a significant role in carcass retention at both channel units.