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Fish that undertake juvenile migration pass through habitats that vary in mortality risk. The ability to identify regions of persistently low survival would improve fishery management. We conducted a field study combined with predictive modeling of survival in downstream migrating juvenile sea lamprey using a new micro-acoustic telemetry tag designed for implantation into small, slender-bodied fishes. Detection data were collected from eight receivers placed across a coastal riverine–wetland–lake complex. Juvenile sea lamprey initiated downstream movement near nautical twilight, stopped frequently, and were more likely to move during high river discharge. Estimated survival was highest in the riverine reach, declined through the river–wetland complex, and dropped precipitously in the drowned rivermouth lake. However, the high transmission rate and resulting short battery life of the microtransmitters (as configured) likely resulted in missed detections in the lower reaches. Simulation analyses suggested survival estimation could be improved by increasing the number of tagged lamprey and staggering release locations. We offer practical recommendations for the use of this new transmitter in field studies with small anguilliform fish. [ABSTRACT FROM AUTHOR]

Global climate change, species invasion, and human activities such as the construction of hydraulic facilities are contributing to the worldwide degradation of fish stocks. As a pivotal environmental factor that affects fish migration and population distribution, the low‐velocity flow has not drawn enough attention despite its extensive presence in various ecoregions.To understand the behavioural profiles of fish in low‐velocity flow, we examined the motility and swimming performance of two representative cyprinids, grass carp (GC, Ctenopharyngodon idella) and silver carp (SC, Hypophthalmichthys molitrix), under the combined effect of different flow velocities and illuminance ranges.The two species were exposed to two flow velocities (0.15 and 0.25 m/s) and three illuminance ranges (100.0–0.9 lx, 300.0–2.5 lx, and 700.0–4.9 lx). A novel behavioural metric, composed of light preference, swimming speed, rheotaxis index (RI), swimming stability (SS), and the probability of moving forwards/backwards over a certain distance (PMf‐0.1 and PMb‐0.1), was developed to fully characterise the motion strategy of fish.By analysing the individual distribution in light gradient, we confirmed the scototaxis of GC and found the oscillating light preference in SC that changed from 84.41–10.18 to 6.00–2.08 lx and disappeared with increasing illuminance. The RI and SS increased at the fast flow velocity (0.25 m/s) for both species, and SC was more forward‐prone and more stable than GC. Despite the fluctuating light preference, the higher illuminances heightened the RI and SS in SC, while in GC, higher illuminances inhibited the SS and had no impact on the RI. The results of PMf‐0.1 and PMb‐0.1 indicated that a higher flow velocity could facilitate the temporary upstream swimming in both species, while illuminance could only promote the same effect in SC.Finally, our study proposed possible manoeuvres in fine‐scale spatio‐temporal scenarios such as attraction flow and non‐traditional passages and provided valuable insights into fish community dynamics, laying the groundwork for alleviating the threat from invasive species and for future fish population recovery. [ABSTRACT FROM AUTHOR]

The effect of the fish body on the source level and beam pattern of an acoustic fish tag signal was investigated through laboratory experiments and an analytical method. In laboratory experiments, the source level and beam pattern were measured in both a tag-only group and a tag-in-fish group. In the analytical method, both forward and backward scattering were calculated by assuming the acoustic tag was a point source and the swimbladder was an air-filled prolate spheroid. The mean source level of five tested tags decreased by ∼4 dB after implantation in fish bodies, which is important for designing fish migration studies using acoustic telemetry. [ABSTRACT FROM AUTHOR]

Abstract: A micro-acoustic Doppler velocimeter (ADV) was used to measure three-dimensional mean velocity and turbulence characteristics in a full-scale culvert with spiral corrugations. The culvert was set up in a test bed constructed to examine juvenile salmon passage success in various culvert types. The test culvert was 12.2m long and 1.83m in diameter and set at a 1.14% slope. The corrugations were 2.54cm deep by 7.62cm peak to peak with a 5° right-handed pitch. Cross-sectional grids of ADV measurements were taken at discharges of 0.028, 0.043, 0.071, 0.099, 0.113, 0.227, and 0.453m3/s at nine locations. In the uniform flow region, the centerline velocity profiles were consistent with fully rough turbulent flows and the friction factor was independent of Reynolds number and was very close to theoretical results. Secondary flow induced by the spiral corrugations caused asymmetries in the velocity and turbulence distributions creating a reduced velocity zone (RVZ) on the right side of the culvert as seen looking upstream, which small fish could utilize to aid their upstream passage. Velocity and axial components of turbulence in the RVZ were found to be much less than in mid-channel or on the left of the culvert, and the difference became greater at increased flow rates. In addition, cross-stream and vertical velocity components within the RVZ were small relative to the downstream axial component, while lateral and vertical turbulence intensities were comparable to the axial component. Observations from a concurrent fish passage study showed that more juvenile fish migrate through the right side of the culvert within the RVZ. [Copyright &y& Elsevier]