Abstract
Reservoirs are artificial ecosystems that modify the hydrological and environmental components nearby. The long-term monitoring of fish assemblages in reservoirs may provide key information to understand how these artificial ecosystems allow fish population fluctuations and identify proper conservation strategies. A sentinel-site approach method assessed changes in fish assemblages in the Feitsui Reservoir (1024 ha) over 14 years, including the periods 2006–2008, 2010–2011, 2016, 2018, and 2020. Fish assemblages, sampled using gill nets, were composed of 38 species (12 families and 8 orders) with Cyprinidae as the dominant family; the fish fauna were dominated by species of the family Cyprinidae (71%) and Cichlidae (20.3%). Principal component analysis and nonmetric multidimensional scaling categorized the assemblages into two groups (cold and warm seasons), and we identified three parameters that were significantly correlated with the season (p < 0.05): SD (R = −0.04), Chl-a (R = 0.01), and algal count (R = 0.19); the algal count was higher in the warm season than in the cold season. The fish assemblage in the cold and warm seasons contained no exclusive taxa, contributing to the dissimilarity between the groups. The fish assemblage for the years before and after 2010 indicated partial overlap between the two groups; S. macrops contributed greatly to the separation of the two periods (>10% each; SIMPER) and O. mossambicus was dominant in assemblage structures after 2010. Our findings show the importance of long-term fish monitoring for the investigation of the effects of nonnative fish species on native fish species composition.
Highlights
The degree of spatial and temporal change in fish assemblage patterns may depend on the magnitude of environmental perturbations
Our findings revealed a mean Secchi disk depth (SD) of 4.09 ± 1.19 m, water temperature (WT) of 24.13 ± 4.75 ◦ C at the surface, turbidity of 2.18 ± 3.36, pH of 7.52 ± 0.56 at the surface, and dissolved oxygen (DO) of 7.65 ± 0.79 mg L−1 at the surface
The results revealed a mean total phosphorus (TP) of 13.20 ± 7.52 μg L−1, Chl-a of 3.81 ± 2.99 μg L−1, and algal count of
Summary
The degree of spatial and temporal change in fish assemblage patterns may depend on the magnitude of environmental perturbations. Long-term fish assemblages studies have suggested that fish groups may transition to new states that eventually stabilize over several decades [7,8,9,10], whereas other processes (e.g., species invasions or dam operation) may cause variations in community structures [11]. Long-term monitoring is indispensable; it allows for an understanding of temporal changes in biodiversity. The longterm monitoring of species assemblage can provide valuable information on the main biotic forces that affect the structure of ecological communities and can enable the detection and assessment of the anthropogenic mechanisms underlying these processes [12,13,14,15]
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