Habitat use by newly emerged fry of red-spotted masu salmon (Oncorhynchus masou ishikawae) in a mountain stream, northeastern Kyushu, southern Japan
2015
Kimoto, K. (Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Saiki, Oita (Japan). Fisheries Research Division) | Kagehira, M. | Azechi, K. | Nagasawa, K.
The habitat use of newly-emerged fry of red-spotted masu salmon (Oncorhynchus masou ishikawae) was studied on a channel-unit scale in the Ogata River, northeastern Kyushu, southern Japan from January to March in 2007-2009. Fry abundance was investigated by snorkeling along both banks and the habitat components (channel-unit type, water depth, velocity, vegetation cover, width-depth ratio and distance from spawning redds) assessed in 56 consecutive sections of the lower distribution area of the species in the river. The number of fry per section was positively associated with channel-unit type near the riffles but negatively related to water depth near the banks and distance from spawning redds. Fry were strongly associated with channel-units near the riffles in their lower distribution area, probably because of the profitable microhabitat (low water-velocity habitats adjacent to a fast current, thereby ensuring high energy efficiency, were common in the upper distribution area but were restricted to the marginal area of riffles in the lower area). It is also suggested that fry moved downstream from profitable channel units which lacked profitable microhabitat. Therefore, for maintaining sustainable reproduction and effective stock enhancement of the species in the lower distribution area, it is important to create profitable microhabitats within channel-units near the riffles, thereby balancing the abundance of fry with the carrying capacity of suitable habitats.
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