Publication (Media): NATIVE FISH NEED UNTAMED RIVERS

Publication Type:	Media Release
Publication Name:	NATIVE FISH NEED UNTAMED RIVERS

Reference Information

Watson, Garth (2000) NATIVE FISH NEED UNTAMED RIVERS - Feb 21 2000, CRCFE, Canberra - Media Release.

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NATIVE FISH NEED UNTAMED RIVERS
Garth Watson

Our inland rivers support far fewer native freshwater fish than at the turn of the century. In fact, over half of the native fish in the Murray-Darling Basin (MDB) are 'threatened', and five species are in danger of extinction.

Attempts to turn this situation around have included restocking programs, which have had limited success in some areas. But merely returning populations to some 'critical size' will do little if the forces which decimated native fish, in the first place, are still prevalent.

Benefits and Competing Demands

The Murray-Darling Basin covers just over 1 million square kilometres, or 14% of Australia, incorporating four states and one capital territory. Weirs, and other river regulation structures, have made the Basin extremely significant in terms of agricultural activites. Valued at $8.56 billion a year, the basin produces 41% of Australia’s total gross agricultural production. To achieve this, irrigated agriculture uses just over half of all water used in Australia but amazingly irrigation practices in the Basin occupy less than 1% of the nations land.

This is enormous removal of river though, water comes at a cost. As the Basin's resources have been over-used, degradation of both land and water have resulted. Issues of water quality such as salinisation and algal blooms have become alarmingly apparent while native fisheries have plummeted in the face of rising populations of introduced fish species such as carp.

Native fish in the Basin

Since the construction of weirs and dams, there has been a rapid decline in both the numbers and distribution of native fish, while introduced species now dominate most of the Basin. Records at the Euston Weir, Murray River, have shown silver and golden perch to have declined 94 per cent and 74 per cent respectively in numbers in the 50 years up to 1992. High conservation status is given to many native fish now as they diminish in both numbers and where they are found.

The Basin currently has some 50 species of fish recorded. Of these, 26 are native and are found entirely within the Basin. There are several species which spend the majority of their life at sea, and are only regarded as Basin fish as they venture into the lower Murray at certain times in their life cycles. These are essentially marine or estuarine. This means that the 11 introduced species comprise around 30% of the truely interior fish in the Basin.

An Experiment with Environmental Flows

An ambitious program is underway that addresses the impacts of changed river flows to fish populations. The Cooperative Research Centre for Freshwater Ecology (a co-operative seven-year venture involving several state and federal research institutions and natural resource agencies) is mid-way through a long-term research project on the Campaspe River, northern Victoria. It will study the response of fish to an experimental change in flows that better resembles natural river flow conditions. It has become the largest scale, long term and intensive experiment of its kind.

Less regulation/more natives

The Campapse River flows into the Murray at Echuca and is highly regulated for irrigation purposes through Lake Eppalock. Natural winter flows are held back in the storage for artificial spring/summer releases. So tailored are these flows for irrigation that little water makes it to the Murray. Holding back winter flows and releasing them over spring and summer is thought to be largely responsible for the rivers woeful native fish populations.

Native fish populations of the nearby Broken River, don't appear to be suffering to the same extent as the Campaspe River. Interestingly, it is far less influenced by river regulation and continues to hold more interest for the angler, with a more diverse range of native species known to spawn in the river.

This fits with the current scientific claims that river regulation is destroying our native fish populations and giving introduced species such as carp, a strangle hold in our inland river systems.

Once a fine fishing spot

The Campaspe actually has excellent habitat for fish in terms of snags and fallen trees. It was once renown as one of the states best spots for Macquarie Perch. Between 1925 and 1935, the Kyneton and Malmsbury Angling Clubs boasted bags of Macquarie perch up 1.8 kg. Only 10 years later perch were scarce. Soon after, Murray cod would also become rare.

The river had begun to choke from poor land practices that caused erosion and siltation of the many larger pools. With fish habitat diminishing the river had just about had its day until the completion of Lake Eppalock, in the late 1960s, sealed its fate. At the same time, introduced fish were reported on the increase, especially from about 1945 onwards. Attempts at restocking have produced little result, even though the effects of siltation have now been largely turned around.

Too much, too little, too late?

Since a fish's total environment is defined by the water in which it lives, the characteristics of that water will affect a fishs ability to survive and reproduce. Native fish are well adapted to natural river flows that include high winter and very low summer levels. Regulation has reversed this, while typically adding cold releases from storages in summer, which hinders egg development and spawning in some species.

The key to reversing the damage to native fish will involve restoring some of the more extreme conditions that rivers would exhibit if dams were absent. By taming the big wild rivers we have 'damned' the plight of our native fish. Researchers at the CRCFE believe that the knowledge they generate from this experiment will enable a turning around for dwindling populations of native fish.

How will they do it?

To test the theories, Lake Eppalock will be operated so that it releases water to better resemble what would naturally occur if the weir was not present. Now this is a big ask given the river is regulated for important irrigated industries. But an agreement was arrived at that will not compromise existing commitments. Consequently, researchers can only experiment with an 'environmental flow' outside the irrigation season, and only then after the lake is in excess of a pre-determined safety level.

Water will be now be available at a time when regulation has previously caused the river to stop flowing! Certainly this will enable the movement of big fish through shallow sections but something even more important is emerging. Evidence now suggests that sustained higher river levels are important in the development of eggs and providing fish with the conditions they need leading up to spawning.

What are we catching?

When you're fishing with a rod, the size of your catch definitely matters, but when catching fish for research, we go after the little ones too! The mere presence of fish larvae indicates that fish are spawning. Crucial to understanding fish survival is where they spawn, why and for how long. Comparing the Campaspe and Broken rivers before and after the flow change will give invaluable knowledge to the future management of regulated rivers.

Four years of intensive fishing trips along the Campaspe have confirmed what most local anglers could already tell you, introduced fish dominate. In fact refin and carp comprise approximately 80% of the total weight of adult fish caught. Adult Golden Perch on the other hand contributed only 14% but even this seems to reflect annual stockings since there has been little evidence of Golden Perch spawning in the last three years. So far, the Broken River has a greater range of native fish than the regulated Campaspe although introduced fish, especially carp, are in abundance. Species such as cod, golden perch, river blackfish, rainbowfish and a galaxid species have been recorded.

Just whether native fish spawn, regardless of conditions, but don't go on to survive in the Campaspe is a question in focus. But should they prove to at least spawn, then any small increase in survival will greatly enhance adult populations in the river since they lay so many eggs.

Fish Food - washed away or high and dry?

The other main area of study is the aquatic insects and other invertebrate 'fish food' that are affected by changes in flow, as their survival will directly influence fish populations in the river. Snags are a major habitat for invertebrates in lowland rivers. Consequently, the work also concentrates on the communities of insects that live on snags, especially shrimp.

In upper reaches of the Campaspe, irrigation flows cause constantly high river flows, while in the lowest reach, water levels remain low all year restricting the availability of submerged snag habitat. This seems to explain the lower numbers of shrimp found when compared with the Broken. Irrigation flows can raise and lower river levels rapidly immediately below the weir giving some bugs little chance of escape and survival .

Outcomes

While it is impossible to regulate rivers entirely for environmental purposes, changing the way water is released will be crucial to encouraging our native fish to recover. Otherwise we are left with restocking programs can be expensive and inefficient. This grand experiment will contribute to answering the big question of how much water, for how long and when. By releasing flows at times when the river often stops, and researching native fish flow requirements during spawning, the same volume of water may be released in a way that gives natives a fighting chance.

The CRCFE is a government initiative with funding from the Environment Australia and the Land and Water Resources and Research Corporation. For further information call Garth Watson at the CRCFE Albury, 0260 582 300.

Slides

Slide 1: (Photo: G. Watson)
Slide 2: Locality map. (Photo:P. Humphries).

Slide 4: Larval flat-headed gudgeon and redfin indicate spawing adults in the Campaspe River. (Photo:P. Humphries).
Slide 5: Larval Murray cod in the Broken River, indicates spawning adults. (Photo:P. Humphries).

Slide 7: 'Fyke' nets are left overnight to catch larger fish. (Photo: G. Watson)
Slide 8: This 1.2kg yellowbelly was a more rare catch for the Campaspe. (Photo: G. Watson)

Slide 10: It's not often you get this close. (Photo: G. Watson)

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