Fish And The Drought

[mrmoshe]

Fish and the drought

Thursday, 11 January 2007

Recreational fishers can play a part in preserving fish stocks which are affected by the drought.

Life for fish in drought conditions is very cosy. Less water, fewer places to live, more crowding, says Dr Ben Gawne. That's good news for fisher folk, but only in the short term.

Fish get hungry and keener to take the lures and so fishing may seem better, Dr Gawne observes. A freshwater ecologist, who is a member of the Murray Darling Freshwater Research Centre, he says that over the long term, because the numbers of fish will be reduced by this drought, there will certainly be poorer catches once the drought breaks.

As well, he notes, the small bodies of water that are left have poor water quality with not much oxygen and high temperatures. "It's a very stressful time."

Downstream, the Darling river is drying, contracting to a series of very large and in some cases, very deep pools, says Dr Gawne. This drought is unknown territory he says. Researchers have been looking at these holes and have found some interesting and surprising developments.

The Darling is usually a turbid river with little light penetration, Dr Gawne explains "and so aquatic plants don't grow very well." With no flow, sediments fall out. The still water is clearer and so "aquatic plants are growing now all through some of these pools".

Dr Gawne agrees that our native fish are used to dryer conditions. Before alteration with dams and weirs, rivers would naturally dry up. Northern rivers which aren't regulated still show that pattern, he says. Life in a pool might last a couple of years before rain and flow starts again. The fish hunker down and wait for the next good times. But, he cautions, these are very tough times and not all will survive.

If indigenous species have some immunity, what about introduced species? How do they fare in a drought? Unfortunately, Dr Gawne responds, european carp are "very tough fish." They can be seen them in residual pools, on their sides in the mud -surviving.

Again Dr Gawne makes a comparison with unregulated pools in northern and central Australia. The less regulation, the less carp there are, he states. "So there's something about the way we're managing rivers that seems to give carp a benefit." The MDFRC is a joint venture between CSIRO, the Murray-Darling Basin Commission and La Trobe University. The ecologists are keen to find out what will happen to the carp population as a result of this drought.

Another aspect of ecological balance to consider (which has relevance in drought times), is whether the native murray cod helps to keep invader numbers down. "There is evidence that cod eat young carp," says Dr Gawne, "but once the carp reach a certain size , they have no predators in Australia."

The period when carp numbers first took off in the Murray "coincides with a time when cod numbers where at their absolute lowest." He adds, "We think it's not a coincidence." The recovery of cod numbers seemed to be simultaneous with a reduction in the prevalence of carp. "So it may be that the cod and some of the native birds are also having an impact on the number of carp in the system."

Dr Gawne is keen to get out the message that people have an important role to play in the long term future of our fish stocks. He reiterates that we may pay in the long run for taking the easy fish now. Just as we're all being urged to take personal responsibility for protecting water resources, we can apply the same approach to preserving fish species.

We might think that there's always the ocean if the rivers are unproductive, but Dr Gawne informs us that the drought affects marine fishing as well. Work done up in Queensland shows that productivity of marine fisheries such as shrimp "is intimately linked to the nutrients that are delivered by rivers into the ocean."

The food chain starts with the rivers which dump nutrients into the estuaries. That fuels algae for the invertebrates to snack on, snack in turn for the prawns and then bigger fish. Deficiency of that organic matter coming from inland particularly undermines the survival of young fish in estuaries, which "plummets", says Dr Gawne.

While the work has been specific to Queensland, Dr Gawne believes that the chain would be a general fit.

We can all help ensure the survival of our native fish though to easier times. Recreational fishing can have a big impact because fish are suffering so much, any additional pressure isn't going to help, says Dr Gawne. Target invasive species and leave native species alone, he asks. "If you do catch them, release them."

"Anything that we can do to help the environment survive through this very tough time, I think that there's an obligation on us to try and do it."