Basin Theme: Fish

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

Key Learnings

E-water Delivery

Learning by Species

Knowledge Catalogue

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

This webpage pulls together our learnings so far, including:

A snapshot of water for the environment delivery in 2020-21
How water for the environment 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, 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. This enables us to assess what did and didn’t work, so that we can then refine these actions 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 water for the environment has provided a range of benefits to native fish populations, supporting 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 body condition. This is a great result because it provides evidence to inform our understanding of how water for the environment 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 the 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 mixed fish community composition, with large, medium and small-bodied fish.

Helps fish move

Movement is critical for fish to complete their life cycle, as it the key to 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 water for the environment can be used 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. The models 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

Please note: For the purpose of the Flow-MER Program, 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.

Learn More

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 page 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.

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.

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.