Research project: The impact of tide gates on fish migration - Dormant

Diadromous fish migrate between essential habitats in salt and fresh water to complete their lifecycles. Delay at obstacles can increase predation risk and energy expenditure prior to extensive migrations, calling for mitigation measures to be implemented. Despite their abundance worldwide, the impact of tide gates on diadromous fish is currently unknown, identifying a requirement for research.

Acoustic and PIT telemetry were used to assess the impact of tide gates on the migration of critically endangered European eel and locally declining abundances of sea trout between essential spawning and maturation habitats. Mitigation measures that aimed to improve successful passage and decrease migratory delay were also studied to assist fisheries management in tide gated rivers.

Tide gates are used in estuaries worldwide for land reclamation, flood prevention and insect control. Tide gates form a temporal barrier to fish movement, closing during the flood tide to preclude brackish water from moving upstream and opening during the ebb to discharge freshwater. When tide gates are open, the size of aperture, hydraulic conditions, absent tidal cues, abrupt salinity and temperature gradients, and the presence of overhead cover may cause further physical or behavioural barriers to fish migration. In association with the Environment Agency and the Interreg IVB Living North Sea Project, this study used acoustic and passive integrated transponder (PIT) telemetry to assess the impact of tide gates on the migration of diadromous fish, specifically the critically endangered European eel, Anguilla anguilla, and sea trout, Salmo trutta, between essential spawning and maturation habitats. Delayed movement past such structures can increase predation risk and energy expenditure prior to extensive migrations. The influence of novel modifications to tide gates such as flapped and un-flapped orifices, also known as pet doors, on fish migration were also investigated.