Contents of this page

The environment

Water management

Land management

Environmental sustainability

Energy management

The climate

The environment

The 14 ha of aquaculture ponds is located on a 130 ha block of natural tropical savanah forested land. The map coordinates are 120 ⁰ 42' 20” S and 130 ⁰ 57' 35” E and Google Earth provides high definition views of the farm and surrounding country. 100 ha of this land has been left in its natural state and is home to a huge diversity of tropical wildlife and vegetation. The neighboring land has also been left in its natural state and as aerial views can testify there is little sign of human habitation or disturbance of the landscape for miles and miles around the property.

The estuary from where the farm obtains water for its ponds is lined with saltwater mangrove forests that are up to a kilometer wide. The estuary remains navigable for large seagoing boats for some kilometers upstream from the farm. Often schools of dolphins can be seen in the river, visiting from the sea and chasing the myriads of fish that live in this mangrove lined fish haven.

Water management

In fish farming good water quality means healthy fish. Of all the water quality parameters, the most important is the amount of oxygen in the water. This is important because the fish need oxygen to survive. Some fish species such as the tarpon which often lives with barra have the ability to take in air and so can survive in water with no oxygen. Barramundi however do not have this ability so it is vital to ensure that the oxygen content of the water is always maintained at a safe and healthy level. On our farm, each pond has its own oxygen monitoring system which works continually day and night. This system is linked to a series of switches that turn on aerators in the ponds when the oxygen levels begin to drop. These aerators mix air into the water, thereby maintaining oxygen at a safe level for the fish. Have a look also at the section on Energy Management.

Land management

The 320 acre section of land on which the farm is located is managed to maintain its biodiversity, to minimise erosion and to control weeds. Biodiversity is maintained by keeping about 200 acres in its natural state. The major portion of this natural bushland is ironwoods, eucalypts and acacias with grevillia, cycads and sand palms in the understorey. Early dry season “cold burning” is employed every 2^nd or 3^rd year to keep fuel loads minimised to avoid harmful bushfires later in the dry. Erosion is controlled by maintaining a ground cover of natural grasses on the cleared sections of the land. This ground cover of natural grasses is managed by slashing to ensure maximum retention of natural grasses and maximum retardation of early wet season weeds. Dangerous weeds include mission grass and most importantly, gamba grass. Gamba is a real hazard in the Top End and must be killed off with weed spray (glyphosate).

Environmental Sustainability

Given the need to run a sustainable business, farmers are by necessity very keen indeed to look after their local environment. After all, it is the environment that allows them to produce fish. If the water was of poor quality, for example, then the fish would be under stress and the risks of them getting sick and not surviving through to harvest would be unacceptable to the business. Farmers therefore are very careful to ensure that the water remains in as good condition as possible. At the ARDA-Tek farm, we manage our water in such a way as to ensure that the quantity of water going from the farm back to the river is kept to minimum. We do this by operating our ponds to allow the development of all sorts of life including small fish, prawns and most importantly, worms. All these animals help to cycle the waste from the fish and keep the pond and the water healthy. The fish and prawns, once they reach a size acceptable to the barra (about 1 inch) are eaten by the barra and so provide them with supplemental food. The worms are the most valuable of the natural recycling resources on the farm and ARDA-Tek is working closely with the NT Museum and with Charles Darwin University and NT Fisheries to research exactly how these creatures manage to recycle the pond waste in such an amazing way. What do the worms do and how do they do it? The worms build up in numbers in the pond after we do the intial seeding at the beginning of the crop. The worms take about 5 months from seeding juveniles to beginning to reproduce. Since the crop cycle is about 18 months this gives the worms plenty of time to proliferate to large numbers in the pond. The highest biomass of worms we have measured in our ponds is about 1.2 kg per sq meter, or 12 tonnes per ha.

The adult worms burrow down to more than 30 cm into the soil. Once the worms reach a certain population level in the pond, they begin to have a major impact on the pond ecology. Exactly what this level is remains a question for the scientists but our observations suggest that at around 0.5 kg per sq meter the worms really start cleaning up the pond. The results of the work by the worms is that all sludge from the pond bottom is cleaned up, so that when the crop is finally harvested, and the pond drained, there is simply no sludge in the pond. How do the worms perform this miracle? This question is currently being examined by the researchers, and, we'll keep you posted! 

Click here for a recent Poster Presentation on these worms by Dr Chris Glasby from Northern Territory Museum. This worm has been described by Dr Glasby as a new species, Marphysa fauchaldi (Glasby and Hutchings 2010) or the barra bloodworm.

Energy management

Electricity and fuel are major costs on the farm and must be managed carefully to ensure that the cost does not become excessive and also to ensure that power is not being wasted. There are many ways to waste power on the farm and ARDA-Tek is constantly reviewing its energy usage to ensure wastage is kept to an absolute minimum. In general terms we balance up the amount of water that we pump through the ponds with the primary productivity that we extract from the ponds. This allows us to minimise both water usage and energy usage. This can be achieved because the pond has the ability to produce its own oxygen through the activity of the algae in the pond. The key is to reach a stable balance between the algae and other organisms in the pond including bacteria, benthic organisms (including our worms), zooplankton and of course the barramundi. The result is that we can achieve our farming objective with only about 1% water exchange per day, which means that through effective management we have minimised our environmental footprint.

Electric power is expensive in the NT, because the NT has a small population and we use gas fired turbines. Gas is more expensive than coal, but has about half the carbon emissions. The result of this expensive power is that we must continually monitor and improve efficiencies of our power usage. Voltage drop, power factor and motor efficiency must all be managed. If voltage drops, then the amp draw of the equipment increases and this results in increased use of electricity and higher power bills. Much of the electrical equipment on the farm is 3 phase induction motors. On our farm we have almost 100 of these, mainly 4 kw in size. These motors need to run at close to their max efficiency in order to get optimum power factor. If the amp draw is less than the max for the motor then power factor drops away. As power factor falls away from PF = 1 then the amount of power that the supplier must provide to the farm increases. This is bad for the environment, because the power generation plant must burn more fuel. So in order that our environmental credentials remain amongst the worlds best, we take every effort to maintain our power factor close to unity, even though at this time at least, there is no economic motive to do this.

The climate

The Top End climate is defined by the Wet (October to April) and the Dry (April to September). The build-up (October to December) is the hottest, most humid and most uncomfortable time of year with frequent violent thunder and lightning storms. The monsoons start usually around the end of December and the weather becomes cooler with the frequent cloud cover and rain. Monsoons also bring the threat of cyclones which can throw off very heavy rain with floods and general inconvenience such as washed out roads and bridges. Once we are into April and May, the wind changes to the east and south and the nights are cool for the next few months, while the days are hot but dry and not uncomfortable. September is interesting on our farm: we always look forward to it with apprehension because it is the month that the biting flies hatch in their millions. This hell lasts only for about 3 weeks, then its over, but it certainly is memorable!