Install baffled fish passes

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Two studies evaluated the effects of installing baffled fish passes on anguillid eel populations in inland habitats. Both studies were in the UK. 

COMMUNITY RESPONSE (0 STUDIES) 

 

POPULATION RESPONSE (0 STUDIES) 

 

BEHAVIOUR (2 STUDIES) 

  • Use (2 studies): Two studies in the UK, both at the same location, found that a baffled ‘Larinier’ fish pass, along with ‘trough-type’ elver passes, were used by 82% of tagged yellow European eels1 to travel upstream and 4% of tagged European silver eels to travel downstream.  

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A study in 2013–2015 in a river in Suffolk, UK (Piper & Wright 2017; same experimental set-up as Piper et al. 2018) reported that a baffled Larinier fish pass and two ‘trough-type’ elver passes were used by European yellow eels Anguilla anguilla to bypass a hydroelectric power turbine when migrating upstream. Results are not based on tests of statistical significance. Fifty of 56 tagged yellow eels (89%) that approached the hydropower station passed through the fish passes to travel upstream (separate results not reported for fish pass type). Most adult (yellow and silver) eels (82%, number not reported) migrating downstream passed by a lock instead of the fish passes (percentage/number not reported). Of eels that approached the passes, the average delay before passing was 1.8 hours. In March 2013 to March 2014, yellow eels were captured, tagged, and released either upstream (74 eels) or downstream (216 eels) of a hydroelectric power turbine in a river. In addition, 127 actively migrating silver eels were captured, tagged and released upstream in autumn 2013 and 2014. Antennas were installed to monitor eel movements through a baffled Larinier fish pass (see Piper et al. 2018 for details) and two ‘trough-type’ elver passes (details not provided). 

    Study and other actions tested
  2. A study in 2013–2015 in a river in southeast England, UK (Piper et al. 2018; same experimental set-up as Piper & Wright 2017) found that a baffled fish pass at a hydropower station was used by low numbers of silver and yellow European eels Anguilla anguilla to travel downstream. Over two winters, five of 122 silver eels (4%) migrated downstream through a baffled fish pass. The other eels passed through an 'Archimedes' screw turbine (29 eels, 24%), a navigational lock (84 eels, 69%), or returned upstream (4 eels, 3%). The fish pass was also used by yellow eels to travel downstream (4 eels) and upstream (3 eels). In 2012, a 'Larinier' super active baffled fish pass (9.3 m long, 0.7 m wide, 15° slope, 100 mm baffle height) was installed next to an 'Archimedes' screw turbine. A navigational lock (with open gates) was located in an adjacent channel. In November–January 2013/2014 and 2014/2015, silver eels captured 5 km upstream of the hydropower station were radio-tagged and released (30–67 eels/year). In the second winter, 30 tagged silver eels were also released 30 m upstream of the hydropower station. In April–September 2013 and March–July 2014, yellow eels captured in the river were tagged and released 100 m upstream (total 74 eels) and downstream (total 216 eels) of the hydropower station. Eels were tracked using radio antennas from April 2013 to March 2015, and with imaging sonar from November to March 2015. 

    Study and other actions tested
Please cite as:

Cutts V., Berthinussen A., Reynolds S.A., Clarhäll A., Land M., Smith R.K. & Sutherland W.J. (2024) Eel Conservation in Inland Habitats: Global evidence for the effects of actions to conserve anguillid eels. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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Eel Conservation in Inland Habitats

This Action forms part of the Action Synopsis:

Eel Conservation in Inland Habitats
Eel Conservation in Inland Habitats

Eel Conservation in Inland Habitats - Published 2024

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