Install nature-like fishways

Overall effectiveness category Evidence not assessed
Number of studies: 3
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Effectiveness

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Background information and definitions

Nature-like fishways are channels built around barriers in rivers with the aim of facilitating fish passage. They are designed to closely mimic the natural conditions of rivers and streams, e.g. with plants, rocks and meanders, offering fish a potentially safer and unobstructed route around obstacles such as dams, weirs, or hydropower plants (Thorncraft & Harris 2000). Nature-like fishways are likely to be most effective when there is a consistent and steady flow of water (O’Connor et al. 2015).

For other actions that may help eels to move past barriers, see ‘Install bypass systems alongside exclusion devices’, ‘Install siphon fish passes, ‘Install baffled fish passes’, ‘Install pool-and-weir fish passes’, ‘Install pool-and-orifice fish passes’, ‘Install weirs with notches’, 'Install vertical-slot fish passes’, ‘Install rock-ramp fish passes’, ‘Install fish elevators/lifts’, ‘Install fish locks’, ‘Install preliminary weirs (pre-barrages, check weirs)', ‘Install climbing structures for fish’, ‘Install airlift fish passes’ and ‘Install fish passes (type not specified)’.

^{O’Connor J., Mallen-Cooper M. & Stuart I. (2015) Performance, operation and maintenance guidelines for fishways and fish passage works. Technical Report No. 262. Arthur Rylah Institute for Environmental Research, Department of Environment, Land, Water and Planning, Victoria, Australia. https://www.ari.vic.gov.au/__data/assets/pdf_file/0024/39453/ARI-Technical-Report-262-Performance-operation-maintenance-guidelines-for-fishways-and-fish-passage-works.pdf}

^{Thorncraft G. & Harris J. (2000) Fish passage and fishways in New South Wales: a status report. Office of Conservation NSW Fisheries, Sydney Cooperative Research Centre for Freshwater Ecology Technical Report 1/2000.}^{https://ewater.org.au/archive/crcfe/freshwater/publications.nsf/8116917c22b76d58ca256f120027bb83/7b50f33602c685f2ca256f0f0014b3e6/$FILE/Fish%20Passage.pdf}

Study locations

Key messages

Three studies evaluated the effects of installing nature-like fishways on anguillid eel populations in inland habitats. Two studies were in Sweden and one was in Germany.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (0 STUDIES)

BEHAVIOUR (3 STUDIES)

Use (3 studies): Two of three studies in Germany and Sweden found that a nature-like fishway at a hydropower station was used by around half of tagged European silver eels to migrate downstream. The other study found that a nature-like fishway and canoe pass at a hydropower station were used by low numbers (2%) of migrating 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

A study in 2014–2016 in a river near Bonn in Germany (Økland et al. 2017) found that a nature-like fishway and canoe pass at a hydropower station were used by low numbers of European silver eels Anguilla anguilla to migrate downstream. In two experiments, a nature-like fishway and canoe pass were used by 2 of 91 (2%) and 3 of 74 tagged eels (4%) that were tracked passing the power station. The remaining eels passed via a spillway gate or ice gate (36–54 eels, 49–59%), a surface bypass via a rack and debris flushing channel (20–22 eels, 24–27%) or a vertical-slot fish pass (7–9 eels, 8–12%). In 2014 and 2015, silver eels were captured in the river (134–136 eels/year, 60–112 cm length), fitted with radio tags, and released 10 km upstream of the power station. Stationary receivers were placed at migration routes past the power station, including a nature-like fishway and adjacent canoe pass (eels using the fishway or canoe pass could not be differentiated). Tagged eels were recorded passing the power station from October 2014 to July 2015 and October 2015 to May 2016. 
Study and other actions tested
Referenced paper
Økland F., Teichert M.A.K., Havn T.B., Thorstad E.B., Heermann L., Sæther S.A., Tambets M. & Borcherding J. (2017) Downstream migration of European eel at three German hydropower stations. Norwegian Institute for Nature Research (NINA) report, 1355.
A study in 2014–2015 in a river in Falkenberg Sweden (Calles et al. 2021; same study site as Kjærås et al. 2023) found that a nature-like fishway at a hydropower station was used by almost half of tagged European silver eels Anguilla anguilla to pass a hydropower station during downstream migration. Over two years, 26 of 59 tagged eels (49%) used a nature-like fishway to pass a hydropower station. The other tagged eels used a bypass channel next to a turbine intake with a bar rack (27 eels, 46%) or failed to pass the hydropower station and remained in the reservoir (3 eels, 5%). A 'large' nature-like fishway was created in 2013 by modifying the main river channel at one of two powerhouses at a hydropower station. A bypass channel was installed next to a turbine intake with an angled bar rack at a second powerhouse. In each of two years, 30 migrating silver eels captured 13–70 km upstream of the hydropower station were tagged and released at dusk either immediately upstream (during four nights in September 2014) or 24 km upstream (during three nights in September–October 2015). Eels were tracked passing the hydropower station using an array of eight antennas. One eel was not detected due to tag failure.
Study and other actions tested
Referenced paper
Calles O., Elghagen J., Nyqvist D., Harbicht A. & Nilsson P.A. (2021) Efficient and timely downstream passage solutions for European silver eels at hydropower dams. Ecological Engineering, 170, 106350.
A study in 2017 in a river in Falkenberg, Sweden (Kjærås et al. 2023; same study site as Calles et al. 2021) reported that a nature-like fishway at a hydropower station was used by more than half of tagged European silver eels Anguilla anguilla to migrate downstream. The nature-like fishway was used by 52 of 90 eels (58%) to travel downstream. Of those, 24 eels (27%) passed over weirs to access the fishway, and 28 (31%) through a hydraulic entrance. The remaining 38 eels (42%) used a bypass channel alongside a rack to pass the hydropower station. Passage time was significantly higher for eels using the fishway than the bypass (see paper for details). In 2013, a nature-like fishway was installed at one of two powerhouses at a hydropower station. Eels could enter the fishway over concrete weirs or through a hydraulic entrance. A bypass channel was installed next to a turbine intake with an angled bar rack at a second powerhouse. On 23–25 September 2017, downstream-migrating silver eels (98 eels, 64–100 cm long) caught in four traps, located 13–17 km upstream of the hydropower station, were tagged and released 20 km upstream. Eels were tracked passing the hydropower station using 33 hydrophones.
Study and other actions tested
Referenced paper
Kjærås H., Baktoft H. & Silva A.T. (2023) Three‐dimensional migratory behaviour of European silver eels (Anguilla anguilla) approaching a hydropower plant. Journal of Fish Biology, 102, 465-478.

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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This Action forms part of the Action Synopsis:

Eel Conservation in Inland Habitats

Related Actions

Actions	Effectiveness	Studies	Category
Install nature-like fishways Action Link	Evidence not assessed	3	Synopsis Link
Install siphon fish passes Action Link	Evidence not assessed	4	Synopsis Link
Install weirs with notches Action Link	No evidence found (no assessment)	0	Synopsis Link