Modify flow regimes along regulated rivers (e.g. release water to encourage upstream movements)

Overall effectiveness category Evidence not assessed
Number of studies: 1
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Effectiveness

not assessed
Certainty

not assessed
Harms

not assessed

Calculating overall effectiveness category

Background information and definitions

Regulated rivers are those that have had their natural flow regime altered to meet human demands, often through the construction of dams and other infrastructure (Petts 1999). Altered flows can modify aquatic habitats and decrease connectivity. They may also repel fish such as eels and make migration difficult, particularly at barriers (Liao 2007). The quantity, quality and timing of water flows (‘flow regime’) may be modified along regulated rivers with the aim of reducing these impacts. These modified flows are sometimes referred to as ‘environmental flows’ or ‘e-flows’. Modifications may include releasing water to create seasonal flood pulses, or creating a plunging or streamline flow at barriers (Piper et al. 2012).

For an action that aims to restore the flow regime of rivers to their natural state, see ‘Habitat restoration and creation – Restore natural flow regimes’.

^{Liao J.C. (2007) A review of fish swimming mechanics and behaviour in altered flows. Philosophical Transactions of the Royal Society B, 362, 1973–1993. http://doi.org/10.1098/rstb.2007.2082}

^{Petts G.E. (1999) River regulation. In: Encyclopedia of Earth Science: Environmental Geology. Springer, Dordrecht. https://doi.org/10.1007/1-4020-4494-1_283}

^{Piper A.T., Wright R.M. & Kemp P.S. (2012) The influence of attraction flow on upstream passage of European eel (Anguilla anguilla) at intertidal barriers. Ecological Engineering, 44, 329–336. https://doi.org/10.1016/j.ecoleng.2012.04.019}

Study locations

Key messages

One study evaluated the effects of modifying flow regimes along regulated rivers on anguillid eel populations in inland habitats. The study was in Australia.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Abundance (1 study): One controlled, before-and-after study in Australia found that releasing water from a reservoir into a river during summer resulted in more juvenile shortfin eels moving upstream compared to before the water release or in a regulated control river.

BEHAVIOUR (0 STUDIES)

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 controlled, before-and-after study in 2018 in two rivers in Victoria, Australia (Amtstaetter et al. 2021) found that releasing water from a reservoir in summer resulted in greater numbers of juvenile short-finned eels Anguilla australis moving upstream compared to before the water release or in a regulated control river. During a summer water release, catches of juvenile short-finned eels moving upstream were two-fold higher than 1–2 weeks before the release, and 26-fold higher than in a regulated control river without a summer release (data reported as statistical model results). In summer (February) 2018, water was released over 14 days from a reservoir into a river (peak discharge 81 megalitres/day). Outside of this period, river discharge was regulated at base-flow conditions (<10 megalitres/day). A second regulated river (discharge 2–54 megalitres/day) had no summer water release. Juvenile short-finned eels (<250 mm long) were caught in a fyke net at each of six sites in the treatment river, and three sites in the control river, during the summer water release period (for 96 h) and 1–2 weeks prior (for 72 h). Sampling sites were spaced 250 m apart. Captured eels were counted and released.
Study and other actions tested
Referenced paper
Amtstaetter F., Tonkin Z., O'Connor J., Stuart I. & Koster W.M. (2021) Environmental flows stimulate the upstream movement of juvenile diadromous fishes. Marine and Freshwater Research.

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

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Install preliminary weirs (pre-barrages, check weirs) Action Link	No evidence found (no assessment)	0	Synopsis Link