The Cod Story

The Flooding Has Begun
Wanda the cod lies motionless in the deep pool of the River Murray. She is 105 years old and weighs almost 100 kgs. She is almost as big as a cod can grow. Wanda is waiting. She knows that the increased currents and cool fresh waters flowing across her gills are the first signs of flood. She knows her river and the ancient entrance to the Darling anabranch.

The new waters come from two sources. The Murray River receives its rejuvenating flows from the springtime snow thaw and rains from the snowy mountain ranges in southern NSW and Victoria. It is clean and cold. Quite different from the warmer waters of the Darling where fine soluble clays make the water milky in colour but alive with nutrients. These water arrive later than those in the Murray for their origins lie north in the extensive southern blue mountains and channel country of southern Queensland. They are born from the summer and autumn monsoonal season of northern Australia taking some months to cross three states and reach her.

Wanda is waiting for the convergence of these slow moving waters to fill the rivers and anabranches beyond their limits and to spill out across the floodplains. It is the process of rejuvenation for the rivers and the floodplains and is crucial to the diversity of life that has evolved from thousands of years of such events.

The waters rise, the milky Darling River mingles with the cooler and clearer waters of the Murray. The channel capacities are exceeded. The water spills over the bank. The flooding has begun.

A Changing Environment
Unlike the past, the flooding is now becoming more infrequent, less significant and the waters are changing with the effects of human agriculture and activity. Wanda has seen much change. She now shares her river with the introduced European carp, redfin and the mosquito fish released to eat mosquito larvae. The carp too were released for weed control in other waters and have now found their way into many important waterways. While they compete for food and muddy the waters, for Wanda they are an additional foods source. The waters have also changed. They stay at a more constant level. The weirs and locks now hold back the water. Upstream of locks the water slows and pools.

The fine sediments destined for floodplains and the ocean are released and the river floor is muddy and devoid of plant life. Her seasonal movements are more restrictive as she tries to negotiate the river regulation structures. She can sense the increasing salinity and cannot escape the foreign taste of phosphorus and other agricultural wastage. In her time she has seen the reduction and disappearance of many long time friends. And while the gentle chatter of paddle steamers has been replaced over the years by the graceful movement of houseboats the peace is regularly interrupted by the deafening and threatening pass of ski boats. These are no longer the tranquil and capricious waterways of the past. Much change is for the worse. She must make the best of every rejuvenation opportunity.

The Journey Upstream
Wanda moves to the mouth of the anabranch just like her mothers before her. It is the gateway to their breeding lands and it is time. She pushes upstream leaving the noisy and compounded water of the Murray behind her. The waters of the anabranch are warm and sweet. Others move forward with her, other murray cod of all sizes, yellow belly, and silver brim.

Long necked turtles move excitedly around her as they chase down the small shrimp. Water rats play in the shallows. Their water repellent fur keeping them buoyant and agile. Their focus is shrimp and freshwater mussels, and the cod are focussed on them.

Wanda does not stop for the easy feed. She is pushed to find traditional nesting grounds while the water stays and anyway, she knows that the highly prized yabby will soon be available as the waters slowly soak into the clay landscape and awaken them from their deep mud hibernation. They will be easy prey for Wanda as they clean the old mud from their shells, sift for nutrients in the rich floodwater, change into a larger shell as they grow, then mate and hatch a myriad of young before the retreating waters signal their return to the deeper cooler mud until the next life giving flood.

On offer too will be the tasty burrowing frogs fresh from their muddy hide outs and easy to catch as they compete for space and are engrossed in the processes of mating and breeding. Food for the cod and other animals will be plentiful. She continues her journey. She feels the current getting stronger and knows that this event is significant and lasting. She pushes on and on along the winding ancient waterway, through timber obstacles, through the warmer shallows and over the deeper holes where the cold water sits unable to break free and join the faster moving warmer, nutrient rich floodwaters. While she does not miss the risks of being speared and caught by the Traditional Barkindji people she no longer sees the Koori children frolicking and searching for mussels in the shallow waters and sandbars or hears the gentle movement of canoe and paddle on the surface above her. She pushes on. The excitement and activity around her confirms the event and commits her to her destiny.

Reaching The Breeding Grounds
After her long trip she is here. The stream floor has changed but she knows it is the place. She waits for the cover of the evening sunset shadows and moves out of the anabranch onto the floodplain - She has reached the ancient breeding ground at Tona Station. Wanda pushes cautiously onto the new ground. Bubbles are still rising from the ground as the air is purged from parched cracked clays. The bubbles tickle her stomach. She nudges through plants that are not found in the river but will die due to inundation. The dense tangles of lignum and goosefoot slow the waters reducing their energies and releasing the fine particles of clay and nutrient onto the wetland floor. These floodplains are the kidneys of the rivers and streams. She navigates by current to find the pathway. When the waters recede this precious nutrient resource will rejuvenate the plant and animal life in the floodplains dryland phase. On Tona station this crucial vegetative barrier still remains and performs its vital function. For many other floodplains this cleansing tool has been lost to grazing and clearing. In these areas the water is no longer cleansed and the floodplain no longer adequately rejuvenates.

For Wanda her floodplain is different. Her requirements are still met. The red gums are still there, not only along the banks of the anabranch but out onto the floodplain marking the boundary of floodways and ephemeral lakes where the processes of the flood continue in the trapped water long after the high water event has gone. Lignum and goosefoot is joined by the river cooba wattle and share this area with red gums.

Lines of young red gums and black box saplings signal the successful replacement of species and mark the new flood lines on a changing landscape. The process is still intact. On the wider floodplain the magnificent black box tree dominates where the denser vegetation of the riverbank and floodways give way to sparse trees and open plains of smaller and colourful plants. The pigface opens its flower in the hot afternoon sun to display its brilliant purple haze across the landscape as the ruby saltbush dries its prized sweet seed pod. Their time is short. The floodwaters move slowly but deliberately towards them. The rich dark clay soils consuming huge volumes of water as it wets, expands and seals. It will take time but the waters will be all consuming to the plants basking in the floodplain sunlight.

A Time to Breed
Wanda is searching. She needs to build her nest as large male cod begin to arrive and court her. Many males will court her, swimming around her, rubbing against her and competing for the right to fertilise her eggs. The floodplain floor is littered with timber for her nest. She is lucky. Many floodplains across Australia are now devoid of fallen timber. It has been progressively harvested for firewood. Where fires have destroyed much of this nesting resource the harvest of ancient red gums and the loss of small saplings through grazing of introduced animals may see the continued loss of this important material. For Wanda there are ample nesting materials. She selects the right site. A large red gum branch rehydrated from its parched and dry existence before flooding and submerged in a gentle eddy. She begins her building; pushing and fanning with her tail until a depression is excavated. Her maternal systems have reacted and her belly is beginning to swell with the development of thousands of eggs known as roe.

From her nest site she feeds well. The yabbies have arrived from their muddy homes, cleaned themselves and the delicacy is ready for the taking. Carp, yellow belly and brim are also making the best of the flood and present easy snacks throughout the day.

But it is night time that the symphony of life explodes. Large bogong moths fall infrequently into the water. The humid stormy nights have generated their hatching and mating activities. They vibrate on the water surface trying to escape the hold of the water. Wanda knows this feeling and knows the sweet snack it provides. In the moonlight she sees the flickering of clouds of bats as they skim through the trees above the water catching insects in their wings like a ball into a baseball glove. She can hear the muffled and busy pitch of their radar and incessant croaking of frogs whose numbers have swelled to make the best of the opportunity. The mopoke calls its name amidst the constant hum of mosquitoes and cicadas. The noise is deafening.

Soon it is time to lay her eggs. The male cod gather, waiting to release their sperm over the nest of eggs. She lays. A frenzy of cod pass over and about the nest until their job is done. The eggs are fertilised. The species is perpetuated. Wanda's work is done. A selected male will guard the site until the eggs have hatched and the young move off to build their own story of survival and reproduction. The water currents have slowed, the flood has peaked. Time is of the essence for all creatures to complete their roles and responsibilities before they are pushed from the floodplains and dryness comes again.

The Waters Recede
Gently the waters begin to drain from the floodplain. Many more will return to the anabranch and rivers than escaped. Many have fallen prey. The giant red gums have drunk their fill transpiring hundreds of litres of moisture back into the sky daily to support the hydrological cycle and future rains. The waters returning to the main stream are cleansed of their silt and nutrient load, leaving it behind to generate a rich array of plant and animal life. By now many creatures have prospered. The pelican and spoonbill have raised two clutches of young, the yabbies have grown, mated and bred and now prepare themselves again for the long wait in the deep mud below. Many have been eaten but many young have been born to replace the old. The frogs too are preparing for their underground retreat.

All have benefited - the water rat, the eagles, the tortoise, the snake, the goanna, the bat. The crescendo of life is over until next time.

The Cycle is Complete

Story by Samantha Walters