WATER QUALITY IN AUSTRALIA
80% of current Australian farmed prawn production occurs adjacent to the World Heritage-listed Great Barrier Reef Marine Park. The prawn farming industry in the Great Barrier Reef Region is a highly profitable, but small agriculture sector, which has potential to expand considerably without impacting on water quality.
As the Great Barrier Reef is an international icon, and is reported to be under threat from overfishing and climate change, it is important that land-based industries invest in technology and farm practices to minimise potential impact on reef water quality. A recent study by the Australian Productivity Commission highlighted the environmental leadership of the Australian prawn farming sector.
The largest anthropogenic source of Nitrogen to Queensland east coast rivers is that associated with sediment loss from grazing which is estimated at 18,018 tonnes per year (55.78% of the total anthropogenic input). Other sources are 8,800 tonnes per year (27.24%) from canelands, 3,502 tonnes per year (10.84%) from fertiliser applied to agricultural land other canelands, and 1,928 tonnes per year (5.97%) from sewage. Inputs of Nitrogen to the Queensland east coast from prawn farming are estimated at 52.6 tonnes per year which is 0.1% of the annual anthropogenic Nitrogen input to Queensland east coast rivers.
The largest anthropogenic source of Phosphorous to Queensland east coast rivers is that associated with sediment loss from grazing which is estimated at 5,544 tonnes per year (65.02% of the total anthropogenic input). Other sources are 1,300 tonnes per year (15.25%) from canelands, 878.1 tonnes per year (10.30%) from fertiliser applied to agricultural land other canelands, and 1,928 tonnes per year (9.36%) from sewage. Inputs of Phosphorous to the marine system from prawn farming are estimated at 6.6 tonnes per year which is 0.00006% of the anthropogenic P inputs to Queensland east coast rivers.
Since European settlement, sediment input to Great Barrier Reef catchments has increased 3.8 times to 28 Megatonnes per year. Sediment input from prawn farming contributes 1,314 tonnes per year or approximately 0.0004% of the annual anthropogenic sediment input to Great Barrier Reef catchments.
Owing to the spatial scale of farming, the regulatory environment and high standard of farming practices, negative impacts (e.g. large scale mangrove destruction) are not necessarily occurring in Australia.
WATER TREATMENT
Waters released from a prawn pond may contain nutrients, algae and clay particles which occur naturally in ocean waters.
Recent changes to Australian policy requires water to be cycled through a settlement pond, where most of the clay particles settle out. In this picture you can see four large settlement ponds on the right of screen through which all used water circulates and settles. Nitrogen and phosphorous attach to the soil particles, and thus settlement can lead to significant reduction in solid and dissolved loads. Any algae which may be in the pond water, occurs naturally in the area, and is introduced into the farm in intake water. Some algae species are encouraged to grow in prawn ponds as they are a natural, high energy and nutritious feed for the prawns.
Many Australian farms recirculate water as routine practice. Partial recirculation helps minimise fluctuations in water quality (salinity, turbidity, nutrient load) and reduces the risk of introducing pathogens from the wild. However partial recirculation is not suited to all farms. Farms have variable requirements depending on a range of factors including quality of intake water, location in the catchment, availability of land, rainfall and access to tidal waters.
PROTECTING MARINE PLANTS
Under state laws, marine plants are totally protected. This includes all species of mangrove, seagrass and seaweed. If any plants are approved to be removed, they can only be removed after investigation by authorities who generally only allow removal conditional on appropriate mitigation. In the process of making that decision, authorities are required by law to consult with all interested members of the community – this includes conservation groups, scientists, recreational and commercial fishing interests.
HEALTH MANAGEMENT
Australian prawn farmers produce native species. Exotic pests are the most critical disease threat to Australia’s prawn producers. The Australian Quarantine and Inspection Service (AQIS) enforce regulations that prevent the importation of live prawns and certain kinds of prawn products. These regulations are designed to prevent the introduction of exotic diseases which could effect wild and aquaculture prawn populations. Australia’s prawn farming industry does not support the importation of uncooked prawn from countries which cannot demonstrate freedom from OIE-listed diseases.
To date, diseases found in Australian aquaculture prawns, including viruses (Owens, 1997), are already present in local wild populations. While not harmful to humans such diseases can effect prawns when they are in a weakened or stressed state. Under conditions of poor water quality (eg low temperatures or salinity) prawns may develop symptoms and suffer mortalities.
Disease management in Australia is therefore based on preventing exotic diseases from entering the country and, at the farm level, providing the prawns with a low stress healthy environment.
On farm disease preventative measures include the dry out of ponds after harvest. This helps break down organic materials to reduce bacterial and viral numbers in the pond substrate. Many farmers carry out health checks on postlarvae before stocking ponds. This is to ensure no new diseases are being introduced to the farm and also enhances survival. Such checks involve diagnostic services provided free of charge by government, although private laboratories also undertake such work.
State laws require all disease outbreaks be reported to the authorities. If a serious exotic disease outbreak was to occur, state and federal agencies can enforce measures to control and prevent the spread of the disease. Measures include stock destruction and pond and water sterilisation.
In partnership with the Fisehries Research & Development Corporation, Australian industry has invested $5 million in a major research project to close the lifecycle of the Black Tiger prawn. Pond-reared animals help to minimise the risk of introducing pathogens from wild stocks. Future research will examine options for a breeding program.
ANTIBIOTIC, CHEMICAL & HORMONE FREE ENVIRONMENT
Antibiotics are not used in Australian prawn farms. Why not? First, treatments become excessively diluted in a pond situation rendering antibiotics and chemicals ineffective. Second, because consumers are concerned about the use of chemicals and antibiotics in food production. To ensure consumer-confidence, residue testing is done on an ongoing basis for both domestic and export markets.
Occasionally they may be used in an enclosed situation such as a tank in a hatchery. However in these cases, their use is limited and strictly controlled. Permission must be sought from a qualified veterinarian and access to antibiotics is only granted by prescription. Use of antibiotics in Australia is then only allowed under quarantine conditions and only where it can be shown to be within acceptable standards for human health.
Similarly, very few chemicals are used in prawn farming. Common household garden chemicals like lime and gypsum may be used to condition and sweeten pond soils between crops. When the pond is filled, they break down into harmless chemicals. Chlorine is often used as a cleaning agent in processing plants to meet state food health standards.
There is no use of hormones in prawn ponds in Australia. Only a qualified veterinarian can prescribe access to hormones, and any approval must be recorded on a national register. No hormones are registered for use in prawns destined for food in Australia.
FISHMEAL FACTS
There is increasing global demand for fishmeal as an important high protein ingredient in animal feeds. The high omega 3 content in fishmeal makes it an attractive ingredient in prawn feeds.
However, there is concern about the long-term sustainability of fishmeal as a feed resource due to increasing demand and concerns about the sustainability of fish stocks (such as the Peruvian anchovetta).
An alternative view, backed by analysis of fishery and economic data for fishmeal, is that aquaculture has improved the sustainable use of fish stocks relied on for fishmeal. This argument is further examined by the Global Aquaculture Alliance in the attached download “Fishmeal Fact Sheet” (see below).
The Australian Prawn Farmers Association Research & Development Committee considers low-protein feeds and nutrition research as an important priority for further research.