3.1 Habitat conditions
The first and second axes of PCA explained 28.98% and 19.18% of the habitat variances, respectively. Impoundments had higher water width, water depth, and lower current velocity and substrate coarseness than free-flowing segments (Figure 3). PERMANOVA showed that habitat conditions significantly differed between the impoundments and free-flowing segments (R2 =0.13, P <0.001). However, PERMDISP showed that habitat heterogeneity (i.e., average distance to median) did not significantly differ between the two habitat types (ANOVA like permutation F =0.89, P >0.05) and that of the impoundments (2.31 ± 1.09 [mean ± standard deviation]) was slightly higher than that of the free-flowing segments (2.11 ± 1.08 [mean ± standard deviation]).