Jonathan D. Bolland | Search USGS

USGS2023

Tracking anadromous fish over successive freshwater migrations reveals the influence of tagging effect, previous success and abiotic factors on upstream passage over barriers

Predicting and mitigating the impact of anthropogenic barriers on migratory fish requires an understanding of the individual and environmental factors that influence barrier passage. Here, the upstream spawning migrations of iteroparous twaite shad Alosa fallax were investigated over three successive spawning migrations in a highly fragmented river basin using passive acoustic telemetry (n=184). More fish approached and passed barriers in the lower river reaches than further upstream, with the median cumulative weir passage time (IQR) of 4.6 (1.8 - 9.2) days representing 18% of their time in river. Returning fish in their second year had significantly higher weir passage rates than in their tagging year, with passage rates also positively influenced by previous passage success. Higher water temperature and river level also had positive impacts on passage rates. Lower weir passage rates by newly tagged individuals suggests that reliance on within-year passage estimates in telemetry-based barrier impact assessments could result in conservative results, while higher passage rates of previously successful versus unsuccessful individuals suggests a conserved motivation and/or inherent ability to pass barriers.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2019

Comparison of attraction, entrance and passage of downstream migrant American eels (Anguilla rostrata) through airlift and siphon deep entrance bypass systems

Downstream migrating anguillid eels face many barriers including turbines and pumps at impoundments for water abstraction, power generation and water level control, when attempting to exit the freshwater catchment to reach spawning grounds. Multiple eel species worldwide are facing different levels of endangerment and alleviating the impacts of barriers to migration is essential to allow completion of the life cycle. Deep bypass systems with entrances located near the riverbed hold some promise for increased effectiveness compared to traditional downstream guidance and bypass facilities with entrances near the surface, as eels typically occupy the bottom of the water column. Here we evaluate two deep entrance bypass designs; an airlift (the Conte Airlift) and a conventional gravity siphon of the same entrance dimensions. Tests were performed using migratory silver-phase American eels ( Anguilla rostrata ), at night, in a simulated forebay environment. Passage performance was monitored over a 3 h test period using both PIT (passive integrated transponder) tag and video recording equipment. Entrance velocity was fixed at 1.2 m s −1 in each of 8 test runs with cohort size fixed in six runs at 14 and in two runs at 42. Test eels readily located, entered and passed both bypass designs. Differences in performance metrics between the airlift and siphon were not statistically significant ( P > 0.05) with linked mean values of 74.5%, 90.5% and 100%, respectively. Eel length did not affect passage speed ( P > 0.05) or slip ratio, i.e., the measured eel velocity relative to fluid velocity. The slip ratio was, however, greater in the siphon than in the airlift ( P < 0.01) within identical vertical upflow sections of the test equipment. Siphon slip ratios in the upflow vertical section were comparable to those established for the horizontal and downflow sections. Fish density did not affect attraction and passage through the airlift or siphon. No mortality or signs of injury were observed on any of the test eels through a 48 h post-test observation period. Both airlift and siphon downstream bypass systems show promise as effective technologies for protection of downstream migrating eels at a variety of water diversion or hydroelectric sites that pose threats of impingement, entrainment, and turbine mortality.

Massachusetts↗