Australia State of the Environment Report 2001 (Theme Report)
Australian State of the Environment Committee, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06751 5
Aquaculture [CO Indicator 4.2]
Over the past 30 years there has been a significant increase and diversification of aquaculture species farmed in Australia. Of the approximately 60 different species farmed, the major contributors are: pearl and edible oysters, Atlantic salmon, prawns, and Southern Bluefin Tuna (FRDC 2000).
Australia's ability to produce such diverse products is due mainly to its wide-ranging climatic conditions, from the tropical north to the temperate south. Australia is also fortunate to be free of many of the major diseases that affect aquaculture production in other parts of the world.
Figure 26: Value of aquaculture sectors.
Source: O'Sullivan and Dobson, (2000)
Over the last decade, aquaculture production has grown substantially, from 11 900 tonnes and a value of $136 million in 1988-89 to some 32 360 tonnes worth around $614 million in 1998/99 (O'Sullivan and Dobson 2000). Until the last decade, most commercial aquaculture was for oysters (edible oysters and pearl oysters) and a limited amount of fish and prawn culture. In recent years, the caged culture of fish has grown rapidly. Atlantic Salmon in Tasmania and the fattening of caged Southern Bluefin Tuna in South Australia account for one-third of Australia's production.
Wild-caught Southern Bluefin Tuna have been fattened in sea cages off Port Lincoln since 1994. There are now 110 cages operated by about 12 companies in an area of approximately 200 km2. Predator exclusion nets surround the main nets of many cages. Although the wild catch has been maintained at 5265 tonnes, most is now farmed, leading to significant value-adding of the product. The tuna are fed on pilchards and other bait fish for four to eight months, when they reach a size of about 30 to 40 kg.
However, tuna farming in feedlots can generate a significant amount of pollution (Parliament of SA 2000). Recent research suggests that pollution is causing the sudden appearance of strange micro-organisms capable of poisoning fish. It has been suggested that a toxic algae was the cause of death of the tuna in Boston Bay, Port Lincoln, in 1996.
The Parliamentary Committee (Parliament of SA 2000) noted that the Tuna Farming Code of Practice was still not finalised, and although some of the issues of concern are addressed in the Draft Code of Practice, in reality the Code is not being adhered to.
Dolphins, whales and seals can become entangled in the predator nets. The South Australian Museum has been collecting records of dead and stranded dolphins around the South Australia coast for many years. In an initial study of the problem (Kemper and Gibbs 1997), at least 13% of all dolphin carcasses studied were believed to have died as a result of entanglement, including many in the tuna feedlots near Port Lincoln.
There are several challenges for the Southern Bluefin Tuna Fishery in the future, a major one being to breed tuna in captivity and cease the total reliance on capturing wild stock, the availability of which is limited.
There are also many experimental and pilot schemes in place within the aquaculture industry, and some are becoming commercially viable. For example, a pilot-scale culture of the Fat-bellied Seahorse (Hippocampus abdominalis) in Tasmania has recently grown to a commercial scale.
Successful aquaculture depends on a combination of factors, including appropriate site selection, design and construction of facilities, good water quality, and suitable markets. Site selection and the associated impacts involved in initial developments can be a contentious issue where there are competing uses of the coastal or marine environment, such as urbanisation, recreation or community interests (Preston and Rothlisberg 2000).
Local government and State planning agencies are the responsible land planners, and increasingly aquaculture operations will have to meet strict environmental controls in order to coexist with other land and coastal water uses. The major environmental issues for aquaculture are:
- water quality impacts from aquaculture operations,
- introduction of pest species through translocation and possible escape,
- introduction of disease through translocation,
- genetic impacts from possible escapes,
- sourcing of brood stock or juveniles, particularly if it is from wild populations,
- compromising habitat and amenity values, and
- sourcing of feedstock from wild-harvest fisheries.
Where aquaculture operations depend on wild-caught juvenile fish, there can be an effect on the wild stock populations. As yet there is little evaluation of this aspect of aquaculture.
Aquaculture requires access to high-quality water but has the potential to increase nutrient enrichment of surrounding coastal or estuarine waters. Land-based practices such as urbanisation and industrial or agricultural practices may also have adverse water quality effects on aquaculture operations, leading, for example, to algal blooms that can affect shellfish quality.
There is the potential for fish feed and wastes to affect water quality through the accumulation of wastes in the vicinity of the farms or the movement of nutrients into the water column. The main source of nutrients in discharge water from prawn farms, for example, is undigested food. The contribution of prawn farming effluent into waters already experiencing impacts can be significant. For example, around 110 hectares of prawn farms are situated in the Logan River catchment in southern Queensland, producing around 45 tonnes of nitrogen effluent.
Unintentional escapes of aquaculture species, either native or exotic, into the wild could affect the genetic diversity of native species. In recognition of the possible risks associated with unintentional escapes, the Commonwealth, State and Territory governments have strict policies regarding the transfer and translocation of exotic species, including larvae.
The responsibility for the development and regulation of aquaculture in Australia rests with local, State and Territory governments. Several States have aquaculture and coastal development plans in place.
Many industry associations have developed codes of practice for their particular aquaculture operations, e.g. the Australian Prawn Farmers Association and the Australian Tuna Boat Owner's Association (Caton and McLoughlin 2000).
There are a number of promising developments for the aquaculture industry. The use of saline groundwater is being trialed for aquaculture in pilot studies, and may become commercially feasible. The integration of aquaculture with conventional farming systems to allow multiple and sequential usage of water resources and related infrastructure is also attracting significant interest. Another developing trend is the use of genetic engineering in aquaculture.
The management of diseases that affect aquaculture is a challenge for the future. For example, the marine protozoan pathogen Neoparamoeba pemaquidensis that occurs seasonally in Atlantic Salmon in Tasmania is now regarded as a major disease which costs the industry $10 to $15 million annually.
The Australian Prawn Farmers Association recently (2001) decided at a workshop to implement national environmental practices that will ensure prawn farming has no detrimental effect on water quality. The workshop documented potential problems resulting from the discharge of nutrient and sediment-laden pond water and decided to develop a plan with targets, deadlines and assigned responsibilities to achieve world's best practice within 10 years. This initiative was taken in the knowledge that the total pond area of prawn farms may double during that time to about 800 hectares.
Management of other land-based activities becomes crucial to the maintenance of coastal water quality for aquaculture, as these are generally conducted on a much larger scale. Increasingly, there is a need for planning authorities to engage in integrated catchment management considering all activities that may affect a waterway, rather than attempting to regulate aquaculture in isolation.
Considerable research is under way to develop more efficient and environmentally friendly food for aquaculture species, as the world supply of fishmeal - a major component of aquaculture food - is not increasing and its production is vulnerable to climatic variability. Improvement in feeds and feeding practices also has significant potential to boost the profitability of aquaculture through reduced wastage and costs, as some aquaculture operations are net consumers of fish products rather than net contributors (FRDC 2000). This would reduce the amount of bait fish, currently 50 000 tonnes per annum, used as aquaculture feed.