Following Yangtze River protection policies, many small dams have been removed. Using the Heishui River as an example, we compared food web structures among areas affected by dams (DAs), areas from which dams were removed (DRAs), and natural reference areas (NRAs) using stable isotopes and a Bayesian mixing model. NRAs had balanced basal carbon sources; DAs relied on periphytic algae (43.6%) and POM (23.5%); and DRAs were dominated by periphytic algae (50.8%), with terrestrial inputs lower in both DAs and DRAs. NRAs showed a compressed food chain (1.89–2.23). DAs exhibited an extended but inverted structure, with benthivorous fish (3.00) surpassing carnivores, perhaps reflecting the accumulation of sedimentary organic matter under the lentic conditions created by damming. DRAs expanded the vertical dimension, with carnivorous fish reaching the highest level (3.70). DAs had the fewest nodes (16) but the highest connectance (0.492). DRAs showed the most nodes (20), highest linkage density (4.00), lowest connectance (0.421), and lowest trophic redundancy, indicating functional differentiation. NRAs had an intermediate number of nodes (17) and the lowest linkage density (3.41). These findings indicate that small dam removal altered basal resource use, triggered food web reorganisation that increased the trophic position of carnivorous fish, and enhanced topological complexity, although terrestrial energy inputs in DRA remained below natural levels.

To investigate the group behavioral characteristics of Schizothorax wangchiachii during the spawning period, we used acoustic telemetry to track 10 mature individuals (4 females, 12 males) in a semi-controlled stream section (28.1 m × 5.8 m) simulating natural spawning microhabitats from 23 to 26 January 2024. By integrating trajectory similarity analysis and wavelet transform, we examined the aggregation patterns and activity rhythms during natural spawning events. The population formed two relatively stable subgroups, with significantly shorter inter-individual distances during the day (1.69 ± 0.72 m) than at night (2.54 ± 0.85 m, p < 0.01). Aggregation behavior exhibited a dominant ultradian rhythm of 16.5 h, with stable clustering between 09:00 and 16:00 (spawning window: 13:40–14:20) and dispersal from 19:00 to 00:00. Group activity followed a decreasing-then-increasing trend, with higher nighttime activity. Males were more active than females (F = 51.89, p < 0.01); female activity peaked on the spawning day and was influenced by reproductive progression, while male activity was mainly driven by diel rhythms (p < 0.01). A weak positive correlation was found between active time and inter-individual distance in both sexes (r = 0.32, p < 0.05), indicating reduced activity when aggregated. These findings provide insight into the temporal coordination and spatial regulation of reproductive behavior under semi-controlled conditions. However, due to the short monitoring period and experimental setup, caution is warranted when generalizing to the full reproductive season or fully natural habitats.