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The University of Southampton

Research project: Fish passage upstream over gauging structures

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Assessing the effectiveness and efficiency of a new design of fish pass for eel and lamprey.

River infrastructure designed to impound water has reduced longitudinal and lateral river connectivity, impeding the movement of fish between essential habitats. Historically, fish passage research has tended to focus on a limited number of taxa (e.g. salmonids) and swimming modes (e.g. sub-carangiform). More recently research has begun to assess the ability of weaker swimming species (e.g. eels and lamprey, anguilliform locomotion) to pass in-river barriers, and develop specific fish passes to facilitate their movement over barriers to migration.

At ICER, the ability of eels and lampreys to pass a range of barriers, their behaviour when doing so, and the efficiency of anguilliform specific passes are being assessed.

Gauging structures are common features of modified rivers. High velocities, vertical drops and high levels of turbulence are all common hydraulic features associated with gauging structures. As such, they can impede the upstream migration of weaker swimming fish species.

To improve passage, taxonomically specific fish passes have been developed that utilise distinct physical and behaviour adaptations. Eel specific fish passes rely on the ability of eels to climb slopes using surface irregularities. As such, numerous substrate types have been developed to facilitate this behaviour. One such substrate is a brush like material that consists of clusters of bristles (usually synthetic), set at regular intervals, protruding from a flat board. These ‘bristle passes’, when used in a traditional configuration (orientated horizontally with water flowing through) can pass a large size range of eels over long distances.

The same technology is now being utilised as a cheap and hydraulically unobtrusive modification to low-head gauging structures in the UK to facilitate the upstream passage of anguilliforms. However, in contrast to previous applications, the bristle passes are orientated vertically and attached directly to the side of the gauging structure in the main flow. As such, their current effectiveness for eels, there original target species, and for other anguilliforms is in question. On-going research at ICER is examining the passage efficiency of this new design of bristle pass, in addition to other passage substrates, using a 2.4m long Crump weir installed in a large internal recirculating flume. To date, passage efficiency tests have been conducted on European eel and upstream migrant adult river lamprey.

Fish passes full view
Fish passes full view
Fish passes side view
Fish passes side view

Related research groups

International Centre for Ecohydraulic Research
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