Fish out of Water

Fish out of water

As the current drought emerges as a defining moment in Australia’s social and agricultural history, it also threatens to be the drought that could wipe out some of our well-loved and iconic riverine species, such as Murray cod, from whole stretches of river. Recovery could take years, decades or may never happen.

Whilst the effects of the drought on our communities, lifestyles and economies are beginning to be widely felt and discussed, the effects of the drought on those whose lives, not just livelihoods, depend on the water in rivers - fish and other riverine animals and plants - has barely rated a mention.

Australia’s animals and plants are adapted to our harsh environmental conditions. This does not mean that they are not severely affected by fires, floods and droughts. On the contrary, these disturbances – in some cases, disasters - can decimate populations. Components of our fauna, however, have evolved in ways that either are able to resist the effects of these extreme natural events or, more commonly, bounce back from them over sometimes astonishingly short times. Indeed, this resilience is a defining feature of our fauna and flora and has become a characteristic of our people too.

Historically, in times of drought, wetlands and lakes dried, and rivers and streams contracted to a series of disconnected pools or disappeared completely (at least, above ground: below ground, rivers will often continue flowing as a result of groundwater). The water quality of these disconnected pools typically deteriorated, food became limited and predation increased. Notwithstanding, these pools were usually the only refuges available for aquatic organisms to wait until rains came and rivers started flowing again. Once the drought broke, pools re-joined, rivers overflowed into wetlands and billabongs and fish and other animals were able to move about, breed and re-populate.

These strategies are highly effective for survival in natural ecosystems and has ensured the continuation of species under seemingly impossible conditions. For more than a century now, however, our rivers and their flows have been dramatically modified to provide year-round water for irrigation, stock and domestic supply. They have also been subject to the ravages of habitat alteration, increased sedimentation, introduced species – such as carp – excess nutrients and intense commercial and recreational fishing pressure. One of the major effects of river modification is the prevention of movement between river reaches, so that fish and other organisms may be less able to find appropriate refuges in times of drought and are less able to re- populate decimated reaches once the drought is over. Also, the way rivers are now regulated means that some never experience low flows during the natural low flow time – which Tom McMahon and Brian Finlayson from Melbourne University call ‘anti-drought’ – whereas others experience drought conditions most of the time. There is one certainty, however: that there will usually be a considerable time lag between the ‘actual’ breaking of the drought – when good rains fall – and the ‘realised’ breaking of the drought – when the rivers receive the runoff from that rain. This is because it takes time and a lot of rain to fill empty dams. Another major issue for fish is that the pools which act as refuges during drought are vulnerable to being pumped dry by landowners or fished out by overly-enthusiastic anglers. Thus, fish and other riverine animals may suffer not only all the stresses associated with being confined to pools during drought, but also the potential that they will have their last bit of water sucked dry, be unable to evade capture by fishers or, if they do survive, be unable to move to areas which have not been so fortunate as to have refuge pools.

But this situation is preventable, through appropriate and sensitive government policy, effective management and public awareness of the problems. We can avoid long- term or permanent damage to our rivers and wetlands and the organisms that inhabit them by recognising the critical nature of the refuges as sources of future populations during droughts and by being active in their management. Through strategies which monitor water quality and intervene where necessary and possible, prevent pools being pumped dry, restrict fishing in key locations, we can at least give the fish a fighting chance. Post-drought strategies are also needed. These may include bans on fishing for many species, no-go areas, re-stocking and specific allocations of water to provide for the requirements of particular species or groups of species.

If the right combination of policy and public awareness and participation is achieved, there is hope that our rivers can ride out this and future droughts. The alternative is an aquatic disaster which those of us working in the field do not dare to think about. With a little cooperation and imagination, however, it is possible that in some circumstances we may even be able to take advantage of this drought to reduce pest species, such as carp and the plague minnow, gambusia. Introduced species such as these may be more vulnerable to drought conditions than natives and it is worth exploring this potential Achilles heel.

The future of the fish and crayfish, the birds, the platypus and turtles and the plants, all of which are important components of riverine ecosystems, is in the hands of the community at large, not just government bureaucrats and managers. Everyone needs to be aware of this looming disaster, talk to local natural resource managers about what they can do, act responsibly in and around rivers during the drought and work to ensure the survival of these things.