From the mighty Murray cod to the beloved Golden perch, some of our favourite native species have enjoyed the benefits of learnings gathered from the Flow Monitoring, Evaluation and Research program (Flow-MER).

The program uses 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. They incorporate these findings into 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 addition, they also use long-term monitoring in collaboration with Selected Areas around the Murray-Darling Basin to test predictions and management actions, so that they can see what did and didn’t work, and then refine these actions the next time around.

The Commonwealth Environmental Water Holder (CEWH) has been responsible for delivering e-water throughout the basin and tracking its outcomes through Flow-MER, which has been running for the past 7 years.

What is e-water?

E-water (or environmental water) is used to maintain the health of rivers, wetlands and floodplains. As agriculture, industries and communities have grown over time, water use has increased dramatically – as much as 50% of natural flows are removed from the river in some locations. E-water seeks to mimic the flows that once occurred naturally prior to development of industry.

Water is allocated to federal and state environmental water holders across the Basin, who make decisions about when, where and how much water is released for the environment, and with measurable environmental outcomes in mind.

What have we learned?

How can water for the environment benefit native fish – a short summary

Supports life-history processes

Our assessment of long-term monitoring data on spawning and population size has indicated that water for the environment 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 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 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 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 kilometers 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. In the future we are really excited to be able to sit down with water managers and use the models to test a range of management scenarios which will help prioritise the best way to deliver water for the environment aimed at achieving long term outcomes for native fish populations.

Murray cod. Illustration by Nina Rupena
Golden perch. Illustration by Nina Rupena

We know that e-water is a key factor in supporting the recovery of native fish species across the basin. However, the research by the Flow-MER fish teams helps us to be more specific and measured when evaluating the outcomes.

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