Longitudinal changes in fish assemblage 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.
Longitudinal changes in fish assemblage were studied in the Ogata River and adjoining tributaries, northeastern Kyushu, southern Japan, in October 2003, and February and August 2004. A total of 18,015 individuals (14 species/subspecies representing 7 families) were recorded at 15 stations, by observers using snorkels. A major fish community transition was apparent from headwater stations with a simple assemblage dominated by amago salmon Oncorhynchus masou ishikawae and Chinese minnow Phoxinus oxycephalus, to downstream stations with more complex assemblages dominated by cyprinid fishes, such as Japanese dace Tribolodon hakonensis and dark chub Candidia temminckii. Multivariate analyses separated the 15 stations into three groups: headwater stations with a salmon/minnow-dominated assemblage (415-820 m altitude), a transition zone with a dace/chub/minnow-dominated assemblage (260-397 m), and downstream stations with a cyprinid-dominated assemblage (232-255 m). The fish assemblage structures were considered to be influenced by longitudinal environmental gradients, being significantly correlated with six environmental variables (topographic type and altitude, and stream gradient, mean wetted width, discharge and minimum daily mean water temperature) showing monotonic changes over the length of the stream investigated (16.3 km). On the other hand, cyprinid population densities did not show such changes, but declined within the transition zone downstream from erosion-control dams, suggesting that such densities were affected by smaller spatial scale factors, including dam-induced habitat degradation.
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