Fish passage efficiency and fish behavior analysis in the vertical slot fishway using the PIT telemetry technology

Abstract: Passive integrated transponder (PIT) has been extensively applied as one of the important telemetry technologies for fish behavior monitoring in recent years. It is necessary to evaluate the fish passage efficiency (FPE) for the survival of tagged fish (especially the juvenile individuals), further to determine the reading efficiency of the PIT system before application. In this study, PIT equipment (Oregon RFID, United States) was selected to estimate the passage efficiency in a vertical slot fishway of Angu Hydropower station on the Dadu River in China. One of the typical fishways was also constructed in Southwest China, which was 289.0 m long, 2.5 m wide with a slope of 1.5%, and a vertical slot of 0.3 m. The fish behaviors and the FPE were determined to clarify the effects of PIT tags on the juvenile survival and the reading abilities of those tags on the vertical slot of the fishway. A total of 212 individuals of juvenile fish from two species (i.e., Hemibarbus labeo, Onychostoma sima) were tagged with HDX tags (Half Duplex, 12 mm long) via the body cavity implanting. Besides, six receiving antennas (2.0 m long and 0.4 m wide, matching the size of the vertical slot) were manufactured and separately installed in the fishway, including the entrance and exit, two turning channels, and two typical straight channels. An array of PIT systems was established using the synchronization control of the six antennas and HDX readers via a control computer. The surgical wounds of the tagged individuals were entirely recovered after five to seven days with a survival rate of 79.17%. The detection sections of six receiving antennas were ranged from 10 to 60 cm during the different periods of observations, due to the electromagnetic interferences from the ambient noise. Moreover, a total of 169 tagged individuals with a total length ranging from 9.70 to 26.60 cm were released in the river near the fish entrance from May 18-26, 2017. After 192 h detection, 81 tagged individuals entered the fishway and fourteen swam out of the fishway from the exit, including one individual swam back to the fishway. The passage durations of H. labeo swam through the fishway ranged from 1.46 to 17.38 h with an averaged value of 9.0 h; the passage durations of O. sima ranged from 11.50 to 162.38 h with an averaged value of 50.06 h. The passage duration of H. labeo was significantly shorter than that of O. sima, possibly due to the different swimming abilities of the two species. Moreover, fish cannot find the guiding flow under complicated hydraulic conditions, leading to the persistent movements in the turning channels. Both species presented much higher staying duration (more than 40 h for all individuals detected) in both turning channels of the fishway, compared with the remaining channels. The attracting efficiency and the FPE of the fishway were ultimately determined to compare the individuals entered the fishway and individuals swam out of the fishway with the individuals released in the river. The attracting efficiencies of H. labeo and O. sima were 44.44% and 48.87%, respectively, while the FPEs were 11.11% and 7.52%, respectively. Therefore, the attracting efficiency and the FPE for the target fish species were 47.93% and 8.28%, respectively, indicating no significant difference in both species. Therefore, the PIT technology can be successfully applied for the fish behaviors and the FPE determination of juvenile fish in the vertical slot fishway. Nevertheless, the reading efficiency of the PIT system and the periods of dam operation were covered to underestimate the FPE, due to the limits in the durations of observations. Further studies are also required for the improvements to realize the accurate evaluation of passage efficiency.