Cardross Lakes

By Nick Thorne, August 1996

I represented NFA at a workshop held in Mildura on Monday 15th July 1996 to discuss and make recommendations about the future management of the Cardross Lakes system.

The Cardross Lakes are a series of natural and artificial depressions that have been used as drainage basins and to control salinity by the local irrigation schemes.

Recently the local water authorities have changed from using open channels to a system of pipelines to distribute the water.

With the open channel system it has been the practice over the last sixty years or so to discharge excess water into the drainage system and to empty the channels into Cardross Lakes at the end of the irrigation season.

With the introduction of the pipeline and changes in irrigation practice to reduce drainage water, inflows into Cardross Lakes has been substantially reduced.  Today, water levels are dropping.

Into this scenario came the discovery of the Southern purple-spotted gudgeon Mogurnda adspersa in the system in 1995 (this fish is officially listed as endangered, presumed extinct in Victoria, with the last previously recorded specimen collected in 1935).  As a result of this discovery a survey was conducted by Fisheries scientist Tarmo Raadik in February '96 and again in June which found that this system has the most diverse assemblage of fish species of any lake in Victoria.

Victorian Flora and Fauna Guarantee Act (FFG) listed species found or know to be present:

• Southern purple-spotted gudgeon Mogurnda adspersa
• Murray hardyhead Craterocephalus fluviatilus.
• Eel tailed catfish Tandanus tandanus.
• The Broad-shelled tortoise Chelodine expansa.
• Murray cod Maccullochella peelii peelii (this was not actually captured in the survey due to the sampling methods used which were targeting smaller species, but is known to be present due to stocking for angling purposes.)

In addition to the FFG listed species the following were found:

• Western carp gudgeon Hypseleotris klunzingeri
• Golden perch Macquaria ambigua (as with Murray cod, these were not actually captured but are known to be present due to stocking).
• Bony Herring Nematalosa erebi
• Flat headed gudgeon Phylypnodon grandiceps
• Dwarf flat-headed gudgeon Phylypnodon spp. nov.
• Australian smelt Retropinna semoni
• Freshwater shrimp Paratya australiensis
• Common yabby Cherax destructor
• Murray prawn Machrobrachium australiense
• Short-necked tortoise Emydura kreffi
• Common Long-necked Tortoise Chelodina longicollis

Present in relatively low abundance were the exotic fish: gold fish, carp, gambusia and redfin.

The meeting started with a number of briefings to provide suitable background to the attendees.  Tarmo Raadik gave an excellent presentation about what is in the lakes, the significance of that and basically covered the biological issues involved.  Tony Sheedy from Sinclair Knight Merz, the consultants engaged by the North West office of the Department of Natural Resources and Environment (DNRE) to examine Cardross Lakes, reported on the hydrology of the system and presented their recommendations for the long term management of the system in accordance with their terms of reference.  Chris Stoltz from the Sunraysia Rural Water Authority presented his slant on things and Owen Lloyd from the First Mildura Irrigation Trust explained the history of the drainage scheme and recent changes of practice to reduce drainage outflows and over all water consumption.

In my opinion, the work done by the consultants was severely flawed as a result of grossly inadequate and inappropriate terms of reference.  The models that they created, however, should prove useful in determining the results of possible courses of action.  I believe that they did the best under the circumstances, but there are serious questions about the motives of those who engaged them.

During the meeting the Australian Conservation Foundation representative Tim Fisher and myself backed up by a number of other people including NFA member Colin Mansell representing the Far West Anglers Association, took a very strong stand on the need to provide an immediate influx of water to raise the levels above the base of the of the cumbungi which is essential for the survival of the purple-spotted gudgeon.  At present, levels are 1.5 to 2 m below this.  The gudgeon should hang for a time at this level, but the problem is now critical.

The meeting became quite energetic at times and I got the distinct impression that the local DNRE people had not even considered that we would go so strong on the need for an immediate large release of water into the system.

We have placed the DNRE area manager on notice that we expect prompt action to fix the problem. It remains to be seen what happens, but I can't see how he can afford now to continue to do nothing about the immediate problem of low water levels in the lakes. If nothing happens in the next few weeks, expect to see NFA and the ACF making a big noise about it!

I will give a full briefing on this issue, plus any developments between now and then at the August meeting.