Why all the fuss about water?
  |  First Published: June 2008

Water levels in streams and lakes, as always, dominate the conversation in this part of the world. And the low water levels are all the more worrying for its effects on native fish and angling in our region.

Native Fish Suffering

Native fish are our first problem. All of our native fish, including golden perch, Murray cod and the few remaining silver perch have the same migration pattern. In spring they move out of the deeper reservoirs where they have been keeping over winter into the feeder streams. They then move progressively upstream as far as they can, searching for food and suitable spawning sites and then move upstream for the summer and back downstream during autumn and early winter.

All of this is reliant on having suitable water flows at the appropriate time of the year. Too little water means the fish aren't tempted to move up or downstream and may even find it physically impossible. They are particularly reluctant to move during periods of intense sunlight and low water levels.

Drought Behaviour

In the past year we have seen a typical drought pattern. In August to November, some of the fish moved up from reservoirs such as Blowering, Wyangala, Googong and Burrinjuck into the feeder rivers, but many decided it wasn't worth the gamble and stayed right where they were, assured of at least a little water over their heads during the summer.

At Blowering they can't get very far because the Jounama Reservoir wall is in the way. At Googong and Wyangala the water levels in the lakes and the Queanbeyan, Lachlan and Abercrombie rivers were so low the fish could only move a short distance.

The Burrinjuck fish on the other hand had three choices: the drought-stricken Yass River, the cold and drought-stricken Goodradigbee River or the more reliable Murrumbidgee River. Most chose the Murrumbidgee but could only manage to navigate a relatively short section because of low flows and so they settled into the first two or three big holes they reached.

All of this meant that the fish populations did not spread very far from their over-wintering location. They stayed together and that meant foregoing some of their spawning opportunities and mixing of gene pools. Secondly, by staying together in limited areas they put extra pressure on local food supplies, some items of which probably were in short supply to begin with. Thirdly, they remained in locations where they were vulnerable and where angling pressure could heavily impact on the population.

How healthy Is This?

All of this is an unhealthy situation. The future survival and wellbeing of any species is dependent on their ability to migrate, to move around in different habitats, to mix with different populations, age and sexual groupings, to feed on a diverse diet and not be too vulnerable to angling pressure.

Unfortunately, drought and a general failure by the authorities to effectively coordinate water management has meant our native fish populations have been in this seriously risky situation for the past seven years. In fact, the only reason we still have populations of fish is because of massive stocking by NSW Fisheries and the ACT Government.

Without begrudging these efforts, this is an artificial, unwieldy, labour-intensive, unhealthy and expensive way of maintaining a fishery. It does little to maintain genetic diversity in the populations and is dependent entirely on the whim of our political masters and the amount of money they allocate to the appropriate government department each year for stocking programs. And every year we run an increasing risk that that money will dry up because of other competing budget demands. Sooner or later, if we are to get off the funding-and-stocking bandwagon we are going to have to find a way for our fish to be able to migrate effectively, to breed naturally and to build and maintain healthy populations.

Current Situation

Currently our native fish are back in the reservoirs seeking the most suitable temperature and oxygen zones in the stratified layers that form during winter. The fish may feed a little or exist on stored body fat and some will do both. They will be hard to catch during this period because they will be lethargic, will stay down deep and will have minimal interest in food. Most anglers will put their gear away and await the return of more active fish in spring, while other will continue to fish on.

Trout Movements

Trout migration and breeding patterns are an interesting contrast to those of native fish. Native fish evolved in a warm, dry, river and ephemeral-lake environment. However, trout evolved in cooler lake and river environments with a more assured year-round water supply. Native fish breed in warm and warming weather, while trout do so during cool and cooling weather.

Currently the brown trout are on the move. They are heading out of the mountain lakes such as Eucumbene, Jindabyne, Tantangara, Tooma, Tumut, Khancoban and Talbingo looking for suitable gravel beds in which to lay their eggs. As the eggs are laid the males will fertilise them and if all goes well, in a month or so the young trout will emerge, feed for a while on the attached egg yolk then swim away as newly independent fish.

There may be a problem with all this, however. Firstly, if the water flows are too low the fish aren't tempted to migrate and secondly they may be unable to pass some of the physical barriers in their way. If they can't get to suitable spawning areas the eggs may be reabsorbed and lost.

The physical nature of the gravel beds where the eggs are laid is also important. The water flowing past the eggs must be silt-free. If a single particle of silt touches the egg and sticks to it, the egg dies. This is a particular concern at Eucumbene. The lake is well below 20 per cent of capacity, which means that much of river is heavily laden with silt. If the browns are silly and travel only a short distance from the lake before laying their eggs they will all be lost in the silt. Conversely, if they show a bit of brainpower and swim for many more kilometres upstream they will find proper, clean gravel beds and can spawn successfully. But are they brainy enough to do that and will there be enough water in the river to facilitate that upstream journey? We are watching the snowfalls and rain events with great interest but also with our fingers crossed. Trout were never renowned for their brainpower, especially when they are sexually excited.

We are looking ahead, too, to August and September when the rainbows have to undertake the same spawning journey. Most anglers regard rainbows as having lesser brainpower than browns but at least at their spawning time there is a greater likelihood of snowmelt putting some flow in the rivers. We will just have to wait and see.

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