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Aquaculture and the environment
Australian aquaculture production
The Australian aquaculture industry (see tables 17.12 and 17.13) occurs in diverse environmental areas including tropical, subtropical and temperate sectors. The production of juveniles of several species of finfish, molluscs and crustaceans has been undertaken for some years, initially for restocking wild populations and more recently as stock for grow-out operations providing mature fish to restaurants and export markets. The location of aquaculture is dependent on seasonal factors, the type of species being cultivated, the stage of aquatic organisms in their life-cycle and proximity to marine parks. Point-source pollution from aquaculture is increasingly subject to regulation. For example, in the Great Barrier Reef region new regulations were established in 1999 to control the quality of aquaculture discharges (SoE 2001). It is likely that aquaculture in regional areas will experience strong growth due to the lack of suitable sites and high competition for coastal zones near metropolitan cities.
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 tuna, pearl oysters, salmon, edible oysters and prawns (FRDC 2000) (graphs 17.18 and 17.19).
Australian aquaculture production rose by 146% in the decade to 2000-01, compared to a rise of 46% for the total gross value of fisheries production (graph 17.20; see also tables 17.12 and 17.13). In 2000-01, aquaculture accounted for 30% of the total gross value of fisheries production, to the value of $746m, for 43,602 tonnes produced, compared with $237m in 1990-91 (ABARE 2002). Prawn farming production rose from 15 tonnes in 1984 to 2,800 tonnes in 2000-01. Australian aquaculture is expected to continue to show strong growth for the next 10 years and, on current estimates, the value of production will be in excess of $1b by the end of this period. The industry directly employs about 5,000 people (ABS 2002), provides regional development opportunities in rural Australia and contributes to export growth. Nevertheless, total production is low compared to that in other countries.
There are many types of aquaculture systems using a variety of management techniques. The main emphasis of the industry is on producing high value species in near-shore or land-based sites within the coastal zone; only about 10% of total production value is from freshwater species (Preston et al. 1997). Systems can be open or closed depending on the water flow. Open systems allow water to move through the cages such as in open seas or flowing rivers. In closed systems, the water flow is contained as in a lake or an aquarium. In some cases, more than one aquaculture system is used for the farming of a single species; for example, in the south-east of Tasmania, in the Huon Estuary, juvenile Atlantic salmon are hatched in freshwater facilities and, after several months of growth, they are transferred to acclimatisation ponds where the salinity of the water is gradually increased. After about eight months the salmon are transferred to open sea cages, where they are grown to a marketable size (Brown, Van Landeghem & Schuele 1997). Trout are usually farmed in conjunction with Atlantic salmon, in ocean water cages and marketed as ocean trout. Freshwater trout are also produced on small farms, often for the tourist trade through the provision of 'catch your own trout' ponds and dams.
Fish farming is one type of aquaculture that involves intensive cage culture of fish in multiple use water bodies. This method represents a more demanding challenge to achieving environmentally sustainable production than any other form of aquaculture. This is a result of the high level of input of nutrients to the water body in the form of fish faecal waste and uneaten food (Gowan & Bradbury 1987). Tuna and salmon are the two main species farmed in open sea cages in Australia. For example, wild juvenile Southern bluefin tuna are caught, then towed in special purpose-built towing cages to offshore farms where they are placed in floating sea pontoons in the coastal waters off Port Lincoln, South Australia. Tuna are fed on wild pilchards, jack mackerel and squid (Holland & Brown 1999). Initial tuna aquaculture production in 1991 of 26 tonnes increased to 2,089 tonnes in 1997 (Allan 1999). By July 2001, 9,051 tonnes of tuna were produced by aquaculture in South Australia, to the value of $263.8m (ABARE 2002).
Land-based aquaculture production systems in Australia include shallow ponds, freshwater dams and controlled environment indoor tanks in inland or coastal regions (Allan 1999); such systems tend to have lower operational costs than off-shore sites. For example, prawns are farmed in ponded areas along coastal waters and account for the highest proportion of pond aquaculture production in Australia. The majority of aquaculture prawn production in Australia is of black tiger prawns and kuruma prawns. Crustaceans such as yabby, redclaw and marron are farmed in dams and natural water bodies. Abalone are farmed in high technology on-shore tank facilities in which they spend their entire lives in a fully controlled environment (Brown, Van Landeghem & Schuele 1997).
The environmental impacts of aquaculture vary according to the species cultivated, the management practices used and location of the production system (Preston et al. 1997). Aquaculture has the potential to alter coastal foreshores, estuaries, mangroves, salt marshes, and marine and other aquatic environments. The main environmental impacts of aquaculture are water pollution, pest species, the strain placed on wild fish populations for brood and feed purposes, and the culling of natural predators.
Water pollution from aquaculture is usually caused by faecal and urinary products, uneaten fish food, chemicals and antibiotics or vaccines used to control diseases. These may result in the significant organic pollution and increased turbidity of the water and the sea floor sediments in the vicinity of the cages, resulting in the temporary disappearance of animals and plants that live on or in the seabed. The contribution of effluent into waters already experiencing impacts can be significant (SoE 2001). Less than 30% of the protein in aquaculture feed is retained by the species farmed; the rest is either excreted or not eaten (CSIRO 1998). As an example of water pollution from aquaculture, the 110 hectares of prawn farms situated in the Logan River catchment in southern Queensland produce around 45 tonnes of nitrogen effluent. As a response, the Australian Prawn Farmers Association decided to implement national environmental practices which will ensure that prawn farming has no detrimental effect on water quality (SoE 2001). The regions of greatest concern are those adjacent to unique and environmentally sensitive areas such as the Great Barrier Reef Marine Park (see the article The Great Barrier Reef Marine Park in Tourism), and other marine parks (Preston et al. 1997). Tuna farming in feedlots can generate a significant amount of pollution (Parliament of South Australia 2000) and recent research suggests that pollution is causing the sudden appearance of strange micro-organisms capable of poisoning fish (SoE 2001).
Aquatic pest species (native or exotic) have the potential to adversely affect wild fish stocks and their environment when they escape from aquaculture production systems. Escaped fish can, for instance, cross breed with wild fish, and this may have effects on the genetic integrity and survival of fish stocks (Holland & Brown 1999). Escaped fish may also contribute to the transfer of disease or may be in direct competition for habitat with wild stocks. Farm fish escape into the wild because of human error, storm and predator damage to net cages and inadvertent release during transport. While much is still unknown about diseases and their impacts, they have the potential to cause significant damage to wild fish and other aquatic plants and animals. 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 $10m to $15m annually (SoE 2001).
Where aquaculture operations depend on wild-caught juvenile fish for brood stocks, there can be an effect on the wild populations (SoE 2001). Threats to wild fish stocks may also arise due to a high demand for wild captured fisheries (e.g. pilchards and anchovies) for the sourcing of feedstock and fishmeal. Aquaculture often uses fishmeal to feed farmed species; an estimated 2 kg of fishmeal are required to produce 1 kg of farmed fish or prawns, which places pressure on the fish species used for fishmeal (WRI et al. 2000). The harvesting of larger fish, to meet the need for cost-effective food regimes, may also add further pressure to wild fish stocks due to the lack of alternative fish food (Preston et al. 1997).
Natural predators such as sea birds and sea mammals in the vicinity of aquaculture farms are susceptible to unnatural dangers like entanglement and illegal killing of protected species. For example, dolphins, whales and seals can become entangled in the predator exclusion nets, such as those that surround the main nets of many tuna farm cages (SoE 2001). The South Australian Museum has been collecting records of dead and stranded dolphins around the South Australian coast for many years. In an initial study of the problem (Kemper & 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.
Positive environmental outcomes
Aquaculture provides the basis for improved biological understanding of Australia's native marine and freshwater species and can be used to re-establish populations of endangered and threatened aquatic species (ABS 1997). Aquaculture restocking programs are used to improve the catch in both commercial and recreational fisheries. Some species have intensive research and development programs in place, such as abalone, prawns, oysters and lobster. For example, some abalone that are produced in hatcheries are placed in specific coastal areas where depleted reefs are reseeded for future harvesting (Brown, Van Landeghem & Schuele 1997). The detailed research gathered on some marine species will help maintain healthy stocks in the wild and help preserve their genetic integrity. Scientific investigation and monitoring have an essential role in understanding and evaluating the boundaries of risk to help minimise negative environmental impacts.
In Australia, state and territory governments are responsible for the development of Australian aquaculture. A number of states have aquaculture and local development plans in place. In 1994, a National Strategy for Aquaculture was established and in 1997 a review of this was completed. It highlighted the need for improved management of natural resources such as land and water (Holland & Brown 1999). By May 2000, an Aquaculture Action Agenda program was designed to assist government and industry to develop strategies. The program aimed to maximise industry growth opportunities; increase export opportunities; improve innovation, research and development; and expand the skills base of people working in the area as many skills in aquaculture are still a limited expertise.
Regulatory or prescriptive instruments used to manage resource use are approaches where controls are implemented, compliance is monitored and non-compliance is penalised (ABARE 1993). Some of the mechanisms used to help manage aquaculture whereby operators access stocks by trading with other operators for harvest rights include:
Many industry associations have developed codes of practice for their particular aquaculture operations, for example the Australian Prawn Farmers Association and the Australian Tuna Boat Owners' Association (Caton & McLoughlin 2000).
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 (SoE 2001). The viability of all aquaculture operations is directly dependent on the maintenance of a healthy and productive aquatic environment. It is in the interest of aquaculture operators to ensure minimal pollution and to prevent negative environmental impacts (Holland & Brown 1999). In some countries, the uncontrolled expansion of aquaculture has resulted in environmental degradation and pollution, raising doubts about the long-term sustainability of some aquaculture systems. A conservative approach to aquaculture management has prevented uncontrolled development in Australia (Preston et al. 1997).
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ABARE 2002, Australian Fisheries Statistics 2001, Canberra.
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Caton A & McLoughlin K (eds) 2000, Fisheries Status Reports 1999: Resource Assessments of Australian Commonwealth Fisheries, Bureau of Rural Sciences, Canberra.
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FRDC (Fisheries Research and Development Corporation) 2000, Investing for Tomorrow's Fish: The FRDC's Research and Development Plan, 2000 to 2005, Canberra.
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Kemper CM & Gibbs SE 1997, A Study of Life History Parameters of Dolphins and Seals Entangled in Tuna Farms Near Port Lincoln: Comparisons with Information from Other South Australian Dolphin Carcasses, Report to the Department of Environment and Heritage (ANCA), Canberra.
New MB 1999, 'Global Aquaculture: current trends and challenges for the 21st century', World Aquaculture, vol. 30, pp. 8-14.
Parliament of South Australia 2000, Inquiry into Tuna Feedlots at Louth Bay, Parliament of South Australia Environment Resources and Development Committee: Thirty-Eighth Report of the Committee, Third Session, Forty-Ninth Parliament.
Preston NP, Macleod I, Rothlisberg PC & Long B 1997, 'Environmentally sustainable aquaculture production: an Australian perspective', in DA Hancock, DC Smith, A Grant & JP Beumer (eds), Developing and Sustaining World Fisheries Resources: The State of Science and Management, Second World Fisheries Congress, Brisbane, 1996, volume 2: Proceedings, CSIRO, Melbourne, pp. 471-7.
SoE (Australian State of the Environment Committee) 2001, Coasts and Oceans, Australia State of the Environment Report 2001 (theme Report), CSIRO Publishing on behalf of the Department of the Environment and Heritage, Canberra.
WRI (World Resources Institute, United Nations and World Bank) 2000, World Resources 1998-99 - A guide to the Global Environment, Oxford University Press, Oxford, New York.
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