Basin Theme: Fish

Over the past 7 years we have been monitoring and evaluating how environmental water is being used to support native fish so that they can breed, grow and move freely. The results are promising…

Fish are an integral component of river ecosystems and have immense cultural, recreational and conservation value.

This web pages pulls together learnings from the past 7 years of studying flows for fish, including:

Snapshot of environmental water delivery in 2020-21
How environmental water benefits native fish
Implications for fish life history processes
Implications for different fish species

Zeb Tonkin, our Fish Theme leader, explains what our work has revealed so far in the introductory video (see right).

Zeb Tonkin, our Fish Theme leader, explains what our work has revealed so far.

Our approach

We use research to investigate how water for the environment can be used to enhance specific parts or processes of the fish life cycle for species like the Murray cod, golden perch and bony herring. We have incorporated these findings into our population models to help environmental water managers more accurately plan when, where and how to deliver flows for fish so that they breed, spawn and, hopefully, successfully add to their numbers.

In collaboration with Selected Areas around the Murray-Darling Basin, we use our long-term monitoring to test our predictions and measure responses to management actions taken by water managers. This enables us to assess what did and didn’t work, so that these actions can be adapted and refined for the next time around.

Electrofishing Wakool River sml — Electrofishing in the Wakool River. Photo Credit: Robyn Watts, Charles Sturt University

What have we learned?

How can water for the environment benefit native fish?

Supports life-history processes

Our assessment of long-term monitoring data on spawning and population size has indicated that environmental water has provided a range of benefits to native fish populations and supported critical life-history processes, such as breeding success, body condition and population growth. For golden perch, environmental water has contributed to increased spawning rates and improved body condition, while for Murray cod environmental water has contributed to increased population growth rates, recruitment and improved body condition. This is a great result because it is providing evidence to inform our understanding of how environmental water is helping maintain, protect and restore native fish populations in the Murray-Darling Basin.

Enables a diversity of fish species

It’s not just the big fish that are benefiting, we’ve also seen improvements in some areas for breeding, recruitment and expanded distributions of smaller species such as Murray-Darling rainbowfish and Australian smelt. These fish are not often thought about, but they are vital for the functioning of a healthy river ecosystem, providing food resources for larger fish, water birds and turtles. It is also important that our rivers have a fish community composition that is mixed with large, medium and small-bodied fish.

Helps fish move

Movement is critical for fish to complete their life cycle, being linked to key life-history processes such as spawning migrations, dispersal from breeding areas or accessing feeding or nursery habitats. We investigated the scale over which these species move and how we can use water for the environment to enhance this. Our latest findings are that for golden perch, movements can occur at large spatial scales, moving hundreds and even thousands of kilometres during their lifetime. These movements to and from breeding and feeding areas, have a major influence on populations in a specific reach or river. Murray cod do not move as much, typically staying within a specific reach or river. For both species, we found a positive association between river flow and these movements, with these results enabling us to quantify how we can influence populations via movement using water for the environment.

Population models developed to inform future management

Population models have now been constructed for Murray cod, golden perch and bony herring. These models enable us to estimate how a population is tracking through time and to forecast what they might look like many years into the future. They do this by integrating the most up to date research on how key life-history processes such as spawning, survival and movement respond to flow management. We can now sit down with water managers and use the models to test a range of management scenarios to help prioritise the best way to deliver water for the environment aimed at achieving long term outcomes for native fish populations.

Volume of Commonwealth water for the environment delivered to Murray-Darling Basin regions (2020-21)

Commonwealth water for the environment is used to support fish life history processes in different regions across the Murray-Darling Basin. Click on different regions on the map to learn how the water was used, and the fish outcomes it was designed to achieve.

Total Commonwealth environmental water delivered with fish outcomes expected

1,416 GL

of 1,716 GL delivered program-wide

Commonwealth environmental water watering actions with fish outcomes expected

73

of 155 watering actions program-wide

Note: For the purpose of Flow-MER, Locks 1 to 9 are included as part of the Lower Murray Region and Locks 10 to 15 are included as part of the Central Murray Valley.

Legend

Selected Area

Watering actions

Baseflows

Freshes

Bankfull

Overbank

Wetland watering

Learn more about these watering actions

Fish outcomes

Spawning

Survival

Recruitment

Movement

Habitat

Condition

Refuge

Threatened Species

How water for the environment supports fish life history processes

This information is drawn from the Flow-MER Fish Theme Report as part of the 2020–21 Basin-scale evaluation of Commonwealth environmental water. These reports bring together monitoring, evaluation and research findings from long-term data sets and current research. References are provided throughout the synthesis to the original document so you can explore the findings further.

For all references listed in the contents below, please view Basin-scale evaluation of 2020–21 Commonwealth environmental water: Fish

Spawning rates

Water for the environment can contribute to spawning due to its influence on velocity, connectivity between river and wetlands, and connectivity within rivers. For example, for golden perch, positive spawning rates were partially associated with increases in flows 30 days before sampling.

Recruitment

Water for the environment can contribute to the recruitment of native fish by reducing the number of low flow days (pg. vi) which maintains food and habitat sources.

Population growth

Water for the environment can be used to create flow variability which, in turn, can increase population growth. Higher flows benefited bony herring (pg. 18, 30) whereas a decrease in population rate of the Murray cod occurred in low flow days (pg. vii).

Distribution

Water for the environment improved native fish species distribution by supporting hydrological connectivity within and between rivers, wetlands and floodplains, thereby increasing available habitat and food resources, and providing more suitable conditions for fish movement and colonisation (pg. 15, 53).

Body condition

Improved body condition was driven by the reduction in low flow days and an increase in average daily flows. Flow increases can promote fish body condition through increased productivity, availability of food resources and habitat, and connectivity (pg. 39, 40).

Habitat

Water for the environment can increase the habitat availability for small-bodied native fish by being used to inundate off-stream wetlands. This was especially evident in the Murrumbidgee wetlands.

Community composition

Community composition is the measurement of the proportion of a catch that is native. Commonwealth environmental water improved community composition (i.e. the increased proportion of the catch that is native) in the Lower Murray and Goulburn rivers (pg. 18, 22, 33).

How water for the environment benefits different fish species

This synthesised information is drawn from the Flow-MER Fish Theme Reports submitted in December 2022. These reports bring together monitoring, evaluation and research findings from long-term data sets and current research. References are provided throughout the synthesis to the original document so you can explore the findings further.

For all references listed in the contents below, view Basin-scale evaluation of 2020-21 Commonwealth environmental water: Fish

Murray cod

golden perch

Murray-darling rainbowfish

Australian smelt

silver perch

bony herring

Unspecked hardyhead, Murray hardyhead, flathead gudgeon and carp gudgeon

exotic species

Murray cod

Using water for the environment to restore base flows and spring freshes has resulted in significant benefits for Murray cod. These results demonstrate the importance of using water for the environment to fill the gaps in flow hydrographs altered by river regulation. The other important factor to consider is that populations of Murray cod are recovering from the hypoxic blackwater events in 2016-17 (pg. vii) and this has had an impact on the outcomes.

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Outcomes

Improved recruitment in most areas with the greatest improvement in the southern Basin.
Increased adult abundances in several Selected Areas (Edward/Kolety–Wakool; Goulburn, Lachlan, and Murrumbidgee River System) (pg. 15, Section 3.3.1).
Enabled spawning in most years in all Selected Areas (pg. vii).
Improved population growth rate in adults in most areas (Goulburn River, Lachlan River System and Lower Murray River) (pg. vii, 18), although the growth rate decreased during low flow days (pg. vii).
Improved distribution in some years in most Selected Areas (pg. vii, 18, 28).
Improved body condition at all Selected Areas monitored (all except Warrego-Darling) and increased the average daily flows in some years (pg. vii, 18, 32).

Variation

The predicted effects of Commonwealth environmental water in the southern Basin could inform the monitoring and management of Murray cod in the northern Basin, where data are more limited due to a single Selected Area site, the Gwydir River System. The Gwydir is subject to cold-water pollution that likely overrides the effects of Commonwealth environmental water. Monitoring over the period shows a decrease in recruitment and distribution of Murray cod in the Gwydir River System (pg. 24). This is an area requiring further research over more sites in the north.

Water for the environment actions

Supplemented the natural spring pulses which contributed to the early life stages (pg. vi, 15).
Supported hydrological connectivity (river base flows maintained), reducing the number of low flow days and increasing the average daily flows. (pg. 31)

Notes for environmental water managers

Recruitment varied between each area, with the low flows identified as the most dominant variable affecting recruitment (pg. 25, 26). However, the range of responses of Murray cod recruitment to Commonwealth environmental water potentially reflects the complex range of hydrological conditions the species relies on.
There were some impacts on population growth rates, such as fish death events, extensive dry conditions and low flows that cannot be ameliorated by using water for the environment alone (section 4.3.4 pg. 39; section 4.3.8 pg. 41; section 4.3 pg. 36; included as a hypothesis in metrics on pg. 54).

Golden perch

Using water for the environment to provide high flows during spawning and restoring hydrological connectivity has resulted in significant benefits for golden perch. These results demonstrate the importance of using water for the environment to fill the gaps in flow hydrographs altered by river regulation.

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Outcomes

Enabled spawning and increased spawning rates in most areas, including the Goulburn River, Lower Murray River, Lachlan River System and Murrumbidgee River System (pg. vi, viii, 18)
Supported recruitment in the Warrego River. Although, there was limited evidence of successful recruitment in other areas (pg. vi, vii)
Increased population growth of golden perch in the Lachlan River System (pg. 18)
Improved distribution in some years in most Selected Areas (pg. vii, 18, 28)
Improved body condition (Goulburn, Lower Murray and Murrumbidgee River System) in some years (page. vii, 18)

Variation

Overall decreased abundance in the Edward/Kolety–Wakool and Lachlan river systems due to fish deaths or emigration (pg. 39)

Water for the environment actions

Higher flows during the spawning period (large fresh events and overbank flows) provided the conditions required for increased spawning rates. These increases were partially associated with increases in flows 30 days before sampling (pg. vi, viii).
Enabled hydrological connectivity, reducing the number of low flow days, and increasing the average daily flows.

Notes for environmental water managers

Given that golden perch recruitment is often associated with high flows or flood events when productive floodplains may be inundated, limited successful recruitment may reflect the prevalent low flows and dry conditions and/or the limited Commonwealth environmental water contribution to large flows and overbank flows at the Selected Areas (pg. vii, 49).
Some impacts on population growth rates, such as fish death events, extensive dry conditions and low flows may not be ameliorated by water for the environment alone (section 4.3.4 pg. 39; section 4.3.8 pg. 41; section 4.3, pg. 36; included as a hypothesis in metrics on page 54).

Murray-Darling rainbowfish

Using water for the environment to deliver flows from spring to autumn contributed to Murray-Darling rainbow fish recruitment and distribution. These results demonstrate the importance of restoring specific flow components rather than simply ‘topping up’ existing flows.

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Outcomes

Improved recruitment as a result of the reduction in the number of low flow days (pg. vi, 38). This includes increased recruitment of 100% in the Murrumbidgee river system, up to 400% in the Lower Murray River and Edward/Kolety–Wakool river system, and 100% in the Goulburn River.
Improved distribution in some years in the Goulburn River, Lower Murray River, and to a lesser extent in the Edward/Kolety–Wakool, and Murrumbidgee River systems (pg. vii report and page 18, pg. 28, page 39. Selected Areas identified from Appendix I, Table I.3 page 92).

Variation

Decreased distribution in the Gwydir River System (pg. 24; 92).

There is a higher level of uncertainty with this result and further investigation is needed. See the report for information on modelling methods and assumptions

Water for the environment actions

Delivery of flows from spring to autumn contributed to recruitment. It also demonstrated the need to provide flows that restore specific flow components rather than simply ‘topping up’ existing flows, where low flows were the most dominant variable affecting recruitment of these species (pg. 25, 26).
Improved distribution by supporting hydrological connectivity, thereby increasing available habitat and food resources – and providing more suitable conditions for fish movement and colonisation (pg. 39).
Low flows were the most dominant variable affecting recruitment of these species (pg. 25, 26).

Australian smelt

Using water for the environment to deliver flows from spring to autumn contributed to Australian smelt recruitment and distribution. These results demonstrate the importance of restoring specific flow components rather than simply ‘topping up’ existing flows.

Learn More

Outcomes

Improved recruitment in most Selected Areas (all except Gwydir and Warrego-Darling) driven by the reduction in the number of low flow days (pg. vi, 24).
Improved distribution in some to most years in the Goulburn River, Lower Murray River, the Edward/Kolety-Wakool, Lachlan and Murrumbidgee river systems (pg. vii, 18, 28) This includes increases across all years of 60% in the Lachlan river system and 150% in the Murrumbidgee river system (pg. 28).

Water for the environment actions

Flows delivered from spring to autumn contributed to recruitment. It also demonstrated the need to provide flows that restore specific flow components rather than simply ‘topping up’ existing flows.
Improved distribution by supporting hydrological connectivity which increased available habitat and food resources, providing more suitable conditions for fish movement and colonisation (pg. 39)

Silver perch

Environmental water has contributed to spawning of the silver perch through enabling connectivity and flow velocity variation. However, analysis of silver perch is complicated by sparsity of data for this species.

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Outcomes

Helped enable spawning to occur in Goulburn River, Lower Murray River and Murrumbidgee River System (pg. 15)

Water for the environment actions

Delivered water to enable connectivity within and between rivers.
Enabled flow velocity variation and connectivity that positively contributed to creating the conditions required for spawning (pg. 15).

Note for environmental water managers

The analysis of silver perch spawning was complicated by the sparsity of data for this species. This meant it was difficult to identify direct effects of water for the environment. The primary challenge is that there are no Selected Areas in the main spawning and recruitment reaches for silver perch, which occurs in the mid-Murray River between Torrumbarry and Euston weirs (Mallen-Cooper and Stuart 2003). Fortunately, a monitoring program (spawning and recruitment) has begun in this reach, the results of which will provide important information over the coming years.

Bony herring

The delivery of water for the environment enabled flow variability and hydrological connectivity that improved population growth and distribution of the bony herring.

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Outcomes

Improved the population growth rate in some years in the Lower Murray River, the Murrumbidgee, Gwydir, Lachlan and Edward/Kolety–Wakool river systems. (pg. 18, 30)
Improved distribution in some years in most Selected Areas, particularly the Goulburn River, Lower Murray River and Murrumbidgee river system. (pg. vii, 18, 28)

Variation

Decreased distribution in the Gwydir River System (pg. 18, 24)
Variable impact on abundance at most areas, due to fish deaths or emigration. (pg 59, 75)

There is a higher level of uncertainty with this result and further investigation is needed. See the report for information on modelling methods and assumptions.

Water for the environment actions

Provided flow variability that improved population growth.
Supported hydrological connectivity which was linked to improvements in distribution due to increasing available habitat and food resources – and providing more suitable conditions for fish movement and colonisation (pg. 39).

Note for environmental water managers

Low flows were the most dominant variable affecting recruitment of these species (pg. 25, 26)
Some impacts on population growth rates, such as fish death events, extensive dry conditions and low flows may not be ameliorated by water for the environment alone (section 4.3.4 pg. 39; section 4.3.8 at pg. 41; section 4.3, pg. 36; included as a hypothesis in metrics on page 54).

Unspecked hardyhead, Murray hardyhead, flathead gudgeon and carp gudgeon

Small-bodied fish species benefited from the use of water for the environment to inundate off-stream wetland habitats.

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Outcomes

Increased population of small-bodied native fish (pg. vi, 15).
Increased distribution of small-bodied native fish (pg. vi, 15).

Variation

Decreased distribution of carp gudgeon in some areas. (pg. 24)

Water for the environment actions

Inundation of Murrumbidgee wetlands facilitated hydrological connectivity and increased habitat availability.
Specific flow components, especially winter base flows and summer flows to maintain habitat availability and water quality, as opposed to top-up flows, were important for many native fish species (pg. 48)

Note for environmental water managers

Low flows were the most dominant variable affecting recruitment of these species (pg. 25, 26)

Exotic species

The use of water for the environment can both benefit and inhibit exotic species, with variations recorded in populations of common carp and in the distribution of eastern gambusia.

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Outcomes

Increases in population of the common carp (with enhanced recruitment pg. 24), particularly in the Gwydir, Lachlan and Murrumbidgee river systems.
The distribution of eastern gambusia varied across areas, with decreased distributions in some Selected Areas (pg. 28, 29, 36), while others saw some increases in some years.
Population growth rate of common carp decreased in the Goulburn River, Lower Murray River and Murrumbidgee river system (pg. 30,36).

Water for the environment actions

Planning of environmental water needs to consider impacts on exotic species as well as native species.

Fish outcomes at Selected Areas

There are 7 Selected Areas where Flow-MER work is undertaken, and some of the data synthesised here is drawn from work in these Areas. Environmental water contributed to several outcomes in each Selected Area as shared below:

Increased recruitment rates for Murray-Darling rainbow fish, Australian smelt, and Murray cod.
Expanded distribution for the Murray-Darling rainbowfish, Australian smelt and Murray cod.
Increased population growth rate for Murray cod.

Increased likelihood of spawning for golden perch.
Increased recruitment rates for Murray-Darling rainbow fish, Australian smelt, and Murray cod.
Expanded distribution for Murray-Darling rainbow fish, Australian smelt, bony herring and Murray cod.
Increased population growth rate for Murray cod.
Increased body condition for Murray cod and golden perch.
Increased proportion of catch that was native.

Expanded distribution for golden perch.
Increase population growth rate for bony herring.
Increased body condition for Murray cod.
The Gwydir River System also showed some negative outcomes for some species, including a decrease in recruitment and distribution of Murray cod, and decreased distribution of Murray-Darling rainbowfish. With lower numbers of monitoring sites in the northern Basin, there is a higher level of uncertainty with these results and further investigation is needed. Please see the report for information on modelling methods and assumptions.

Increased recruitment rates for Australian smelt and Murray-Darling rainbowfish
Expanded distribution for Australian smelt
Increased population growth rate for Murray cod and golden perch.

Increased likelihood of spawning for golden perch
Expanded distribution for Murray-Darling rainbow fish, Australian smelt and Murray cod
Increased population growth rate for Murray cod and bony herring
Increased body condition for Murray cod
Increased proportion of catch that was native.

Increased likelihood of spawning for golden perch
Increased recruitment rate for Murray-Darling rainbow fish and Australian smelt
Expanded distribution for Australian smelt, bony herring and Murray-Darling rainbow fish
Increased population growth rate for bony herring and Murray cod
Increased body condition for Murray cod.

Knowledge Catalogue

For more information on how Commonwealth environmental water has benefited fish, you can explore the webinars and articles below. The Flow-MER Fish Theme reports are also available.