2011 年 17 巻 p. 197-202
We examined whether the usage frequency of low-velocity zone near shoreline by pale chub is changed with increase in thalweg velocity using an experimental flume. We set iron stripped-frictions on one side of the experimental channel to weaken velocity artificially. We divided cross-section of the channel into three equal parts in each of the height and width (nine in total) then recorded which part is used by large-sized (ca. 10cm) and small-sized (ca. 5cm) pale chub after changing current velocity (0, 10, 26, 42, 71 cm/s in the center part). Under low-velocity conditions (≤10 cm/s), most of the fish in both size-classes used the center part. In contrast, under high-velocity conditions (≥ 26 cm/s), small-sized fish moved to the slowest part above the stripped-frictions and large-sized fish moved to the deeper parts with lower currents. These location shifts may be caused by avoidance of high velocity since the shift was explained by the tolerance for current velocity generally calculated as 2 ~ 3 BL (body length)/s. These results suggest that low-velocity zone near shoreline would function as fish habitat, thereby the function is broadly important in the field. Therefore, the low-velocity zone should be considered in the treatment of river bank of nature-oriented river works.
