Diversity and site occupancy of fish communities
Altogether 30 bony fish taxa and one lamprey were identified in the 189 reservoir samples (Table 4, Figure 2). Across the dataset (i.e. all reservoirs and seasons), no fish were detected in nine pelagic and two littoral samples. Six taxa were detected in all reservoirs and seasons, and another 14 taxa were consistently detected in the same reservoir in summer and autumn. Conversely, six taxa were only detected in one sampling campaign (Table 4). Seven taxa were categorised as non-native and others were sorted in six IUCN categories from Extinct, Critically Endangered, and Vulnerable, to Least Concern (Table 4).
Římov possessed the most taxa whereas Klíčava had the lowest number of taxa (Figure 3). In all reservoirs, significantly more taxa were detected in late autumn compared to summer (t2 = 12.124, p = 0.007) (Figure 3). The Spearman’s rank correlation coefficient between site occupancy and gillnet score for each taxon was statistically significant for all sampling campaigns (Figure 5, p ˂ 0.05). The rho correlation coefficients were higher in summer than in late autumn, but this was not statistically significant due to low sample size (t2 = 1.981, p = 0.186).
More taxa per sample were detected in the main inflows than in the side tributaries (GLMM: F3,6 = 6.458, p = 0.026) and in the main reservoirs (GLMM: F3,177 = 11.918, p ˂ 0.001). Differences in the number of taxa between samples from the reservoirs and the side tributaries were not significant (GLMM: F3,177 = 0.327, p = 0.806) (Figure 3). In the main body of the reservoirs, the number of taxa was significantly different between localities showing an increasing trend from the dam to the tributary (GLMM: F3,171 = 14.473, p ˂ 0.001). Moreover, the in-reservoir habitats differed in the number of taxa with highest diversity in the littoral zone (GLMM: F12,162 = 2.128, p = 0.017) and without a significant seasonal effect (GLMM: F3,171 = 0.946, p = 0.420) (Figure 2, 3). The Bray–Curtis dissimilarity indices were significantly different between habitats (GLMM: F5,723 = 21.104, p ˂ 0.001) and seasons (GLMM: F1,722 = 27.689, p ˂ 0.001) (Figure 4).