Impact of tide gates on diadromous fish migration in the UK

• Main Author: Wright, Gillian Victoria
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: Anguilla anguilla; European eel
• Online Access: https://eprints.soton.ac.uk/376995/; https://eprints.soton.ac.uk/376995/1/G%2520Wright%2520PhD%2520Thesis%25202014.pdf

Anthropogenic structures fragment river connectivity, impeding the migration of diadromous fish between essential habitats. Tide gates are used worldwide primarily for flood protection and land reclamation by closing under hydraulic pressure during the flood tide and opening when head differential is sufficient during the ebb. Although tide gates are known to decrease fish species richness, abundance, and movement, their impacts on the migration of ecologically and socioeconomically important diadromous fish in terms of passage efficiency and delay have not been reported elsewhere. Acoustic and passive integrated transponder telemetry revealed that passage efficiencies of upstream migrating adult brown trout, Salmo trutta (92%), and downstream migrating juvenile sea trout smolts (96 - 100%) and adult European eel, Anguilla anguilla (98%), were high at top-hung tide gates in two small English streams. However, these fish experienced delay at the gates (adult brown trout, median = 6.0 h; sea trout smolts, mean = 6.5 and 23.7 h; eels, mean = 66.2 h) when compared to migration through unimpeded reaches. The percentage of time the gates were closed and mean angle of opening were positively related to delay in both species and life stages. Diel periodicity also influenced delay for smolts and eels, which were more active at night. For adult trout, water temperature was positively associated with delay. Upstream and downstream water temperature and salinity were influenced by the temporal operation of the gates. Orifices installed in the gates did not mitigate delay for adult or juvenile trout. For adult eels, delay was decreased when an orifice was operational, although this coincided with more eels first approaching the gates when open, higher tides and greater saline intrusion upstream of the gates. When gates were open, fish would not pass immediately through, indicating the potential influence of a behavioural avoidance component. To examine the effect of hydrodynamics created by top-hung tide gates with different ...