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Impact of tide gates on diadromous fish migration in the UK

Impact of tide gates on diadromous fish migration in the UK
Impact of tide gates on diadromous fish migration in the UK
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 aperture sizes, wild sea trout smolt behaviour was observed by video cameras in an experimental flume at night. Avoidance responses occurred within an average of 1.4 fish body lengths upstream of the gate. Fish were more likely to exhibit avoidance (switch in orientation from negative to positive rheotaxis, increased tail beat frequency and/or retreat upstream) in the vicinity of a model gate with a smaller angle of opening and passage aperture.

Overall, top-hung tide gates delayed the migration of diadromous fish, potentially increasing energy expenditure and predation risk. Delay was not decreased by orifices. Modifying or replacing top-hung tide gates with designs that allow them to open wider and for longer could reduce migratory delay and improve the environmental conditions that cause behavioural avoidance.
tide gate, diadromous, telemetry, trout, eel, passage efficiency, delay
Wright, Gillian Victoria
98c6aa2b-d857-4fb7-89db-76bd6af182cb
Wright, Gillian Victoria
98c6aa2b-d857-4fb7-89db-76bd6af182cb
Kemp, Paul
9e33fba6-cccf-4eb5-965b-b70e72b11cd7

Wright, Gillian Victoria (2014) Impact of tide gates on diadromous fish migration in the UK. University of Southampton, Engineering and the Environment, Doctoral Thesis, 227pp.

Record type: Thesis (Doctoral)

Abstract

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 aperture sizes, wild sea trout smolt behaviour was observed by video cameras in an experimental flume at night. Avoidance responses occurred within an average of 1.4 fish body lengths upstream of the gate. Fish were more likely to exhibit avoidance (switch in orientation from negative to positive rheotaxis, increased tail beat frequency and/or retreat upstream) in the vicinity of a model gate with a smaller angle of opening and passage aperture.

Overall, top-hung tide gates delayed the migration of diadromous fish, potentially increasing energy expenditure and predation risk. Delay was not decreased by orifices. Modifying or replacing top-hung tide gates with designs that allow them to open wider and for longer could reduce migratory delay and improve the environmental conditions that cause behavioural avoidance.

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More information

Published date: October 2014
Keywords: tide gate, diadromous, telemetry, trout, eel, passage efficiency, delay
Organisations: University of Southampton, Water & Environmental Engineering Group

Identifiers

Local EPrints ID: 376995
URI: http://eprints.soton.ac.uk/id/eprint/376995
PURE UUID: b8ffac11-ad1e-4487-8b6d-69242503ec4a
ORCID for Paul Kemp: ORCID iD orcid.org/0000-0003-4470-0589

Catalogue record

Date deposited: 07 Jul 2015 10:55
Last modified: 06 Jun 2018 12:42

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