Publication (Media): FISHING FOR ANSWERS

Publication Type:	Media Release
Publication Name:	FISHING FOR ANSWERS

Reference Information

Lynne Sealie (2001) FISHING FOR ANSWERS - Feb 21 2001, CRCFE, Canberra - Media Release.

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The following article looks at some of the issues concerning the health of the Murray-Darling river system and discusses some of the research initiatives being employed to combat river degradation and restore balance to our fish populations.

FISHING FOR ANSWERS
Estimates suggest that between two and five million Australians participate in recreational fishing making it one of our most popular pastimes, it is an activity that makes no distinction between age, sex or ability. Maintaining healthy rivers and fish is vital if we are to continue to enjoy this pastime. The fishing fraternity is only too aware of the need to monitor our fishing resources both on a recreational and a commercial level.

The level of community concern and interest in river health is high, but there remains a lack of information about the status of native fish communities and the rivers that sustain them.

The health of a river has direct implications for the number and variety of fish species that live within it. Recreational fishers are aware of the declining numbers of many of our native fish species including Murray cod, golden perch and trout cod.
The Murray cod, once bountiful in the River Murray is now a rare catch in many parts of the Murray-Darling river system. And while some anglers are able to catch this fish in key habitats, their catch may misrepresent the true status of fish populations. While some populations of Murray cod can support fisheries in some areas, it is
clear that populations of this ‘flagship’ species are patchy and dangerously low.

A survey of NSW rivers1 carried out between 1996-1998, failed to catch one Murray cod in the lower reaches of the river Murray where the species once thrived. The survey gave researchers much needed information on the status of native fish and the rivers that support them. It also identified the extent to which alien pest species such as carp have invaded our rivers.

Fish communities were sampled at sites representing the main freshwater ecological regions and river types in NSW. Intensive sampling with five different fishing gear types (including electrofishing) occurred four times over two years at 80 sites.
A total of 50, 438 fish (representing 55 species) were recorded, 39 species were native and six were introduced. While the number of native species is still high, it was the absence of some key native species and the over abundance of some introduced species such as carp, redfin, perch, gambusia, goldfish and trout that is of concern to researchers.

In fact, native fish constituted only twenty percent of total fish catch from regulated rivers in the Murray region. This was less than half that found in the Darling region.

Researchers at the Department of Natural Resources Victoria (DNRE) through the Cooperative Research Centre for Freshwater Ecology (CRCFE) and NSW Fisheries are piecing together some of the reasons behind the decline in fish numbers. The more we understand about what is causing this decline the better equipped we are to prevent further loss and ultimately restore numbers to a healthy and sustainable level.

The effects of invasive species, such as carp, salinisation, disruption to water flow due to dams and the almost seasonal occurrence of algal blooms due to increasing nutrient loads are well publicised events that are negatively impacting on our waterways and affecting our fish.

Reviving our rivers through research

A less well understood but equally damaging phenomenon is the removal of snags (de-snagging) from our lowland rivers. Snags are branches that fall into the stream and lodge on the bottom of the riverbed. The reason snags are important to river health is complex. They are part of an intricate food web, involving algae, fungi, insects and large invertebrates such as crayfish, platypus and a range of large native fish.

Snags have been described as the “coral reefs” of lowland rivers and support a greater abundance of aquatic organisms than any other part of the river. They also provide roosting sites for birds, turtles and platypus.

De-snagging commenced in the 1850’s and continued into the 1980’s removing over three million of these ecological goldmines.

The importance of snags to fish survival is becoming clearer as research reveals more about fish movement and biology. David Crook, a PhD student with the CRCFE based in Albury is mapping the position of snags and using radio transmitters to track the movement of fish, giving researchers a picture of life beneath the surface.

One of the outcomes of this research has been the discovery that golden perch use the snags as shelter spots in turbulent streams. He also discovered perch, like cats, keep coming back. When displaced several kilometres from a snag, the fish repeatedly returned to the same snag within 4 days.

Snags not only provide shelter to fish but also provide sites for egg laying, often the only hard surface available in some of our lowland rivers. River blackfish lay their eggs in the safety of hollow logs, while other fish lay sticky eggs that attach to the hard surface of snags.

The Murray Cod is thought to use snags as staging posts as it journeys hundreds of kilometres to spawn. Cod also migrate long distances after flooding and use the snags as shelter, thus avoiding the deepest and fastest part of the river.
Murray cod numbers have been in decline for many years and the removal of snags is seen as one of the contributing factors.

To the recreational fisher, snags may at times appear a hazard to boats and lines. However, streams with snags are likely to have higher numbers of fish and invertebrates than those without. Unless we are able to restore snags there is likely to be a continuing decline in the abundance of our native fish and any attempts to reintroduce fish to our rivers may be severely compromised.

Scientists at the CRCFE are involved in a number of research projects aimed at restoring snags to lowland rivers. Three hundred snags have now been replaced in a section of the Murray River between Yarrawonga and Cobram and monitoring will continue to determine how ‘re-snagging’ affects local fish numbers.

The recreational fisher experiences first hand the impact of poor river management,
and the CRC for Freshwater Ecology is striving to provide the scientific basis upon which sound management decisions can be made to improve the health of our rivers. Research focuses largely on the Murray-Darling system, the largest river system in Australia, supplying water for industry, agriculture and domestic consumption.

The maintenance of a clean, sustainable water supply with a healthy balance of fish and other aquatic species is vital to the future of river health and ultimately, human health and enjoyment.

1. Fish and Rivers in Stress, The NSW Rivers Survey.
NSW Fisheries Office of Conservation, Cooperative Research Centre for Freshwater Ecology and
NSW Resource and Conservation Assessment Council
Ed. J. Harris and P. Gehrke
Oct. 1997

For more information on the CRC
Visit our website at:
http://freshwater.canberra.edu.au

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