Aquaculture

Aquaculture has been around for thousands of years (Clarke 1996), but it was still a relatively new and growing industry in Australia in the early 1990s (Commonwealth of Australia 1991, Paterson 1994). Aquaculture has been defined as the 'farming of aquatic organisms, including fish, molluscs, crustaceans, and aquatic plants. It includes the breeding, hatching, rearing and cultivation for sale of all aquatic organisms' (SARDI 1996, p. 1). It can be conducted in both fresh or marine water, and marine-based aquaculture is often referred to as 'mariculture' (DNRE 1998).

Some 25% of the world's fisheries production is derived from aquaculture, with approximately 26 million metric tonnes produced per year in the 1990s (DAFFA 2000). However, like commercial fishing in Australia, the productivity of Australia's aquaculture industry is low in terms of global standards, and contributes only 0.6% to world production (Carvalho & Clarke 1998). Nonetheless, the industry is rapidly expanding, with a productivity increase of approximately 15% each year (Cordover et al. 2000). In South Australia, aquaculture has been described as a 'new gold mine' for primary industry (Marchant 1997, p. 29).

In 1997-98, 6000 people were employed in Australia's aquaculture industry, 27 000 tonnes of aquaculture products were produced, and the value of aquaculture was placed at approximately $490 million dollars (Gordon 1999, Caton & McLoughlin 2000, DAFFA 2000). At a national level, the aim was to reach a value of $2.5 billion by the year 2010. Like commercial fishing, only a small number of species has particularly high economic value, including Pearl Oysters, Atlantic Salmon, Southern Bluefin Tuna, prawns and edible oysters (Gordon 1999, Cordover et al. 2000). The fishery that has undergone the most rapid expansion is the Southern Bluefin tuna fishery, which is significant in that wild stocks are becoming severely depleted (BRS 1999).

While there is still a relatively low productivity, Australia has an advantage over many other countries because of the length of the coastline, limited pollution, the variety of climates, and lack of major diseases (Commonwealth of Australia 1991). the location and types of aquaculture farms around Australia vary, depending on the local environmental conditions and the availability of food supplies and land and water resources. unlike most overseas operations, which are primarily based in fresh water, most aquaculture in Australia (95%) is based in coastal or estuarine waters (Cordover et al. 2000). table 3.11 summarises the tonnage, economic value, and key species within

Table 3.11 Aquaculture by state or territory, showing approximate catch and value in 1997-98

n.a. = not available

Source: Cordover et al. 2000

Australia's states and territories. The greatest economic value is generated in South Australia, and the greatest tonnage is produced in Tasmania.

Marine species in aquaculture can be either suspended in the water or placed on the seabed, and either contained within ponds (e.g. prawns), cages (e.g. tuna), trays (e.g. oysters in intertidal areas), raceways or recirculating systems (Cordover et al. 2000). Five types of farming techniques exist (Mather 1993, quoted in Clarke 1996):

• intensive aquaculture (fully controlled environment, artificial supplies of food and energy, concentrated in small area)

• semi-intensive aquaculture (most conditions controlled, supplementary feeding, high stocking density)

• extensive aquaculture (no food or energy supplied, low stocking density)

• polyculture (stocking variety of species)

• integrated aquaculture-agriculture (aquaculture integrated with agricultural activities).

Some species are collected from the wild and then fanned (e.g. eel larvae, mussels, Sydney Rock Oysters, Southern Bluefin Tuna), while others are fully domesticated (e.g. Pearl Oysters, salmon, Pacific Oysters; Cordover et al. 2000).

In addition to the economic benefits of aquaculture, a number of other advantages have been cited, including reduction in fishing pressures, the re-establishment of exploited species, improvements in scientific knowledge about wild stocks, and the establishment of programs to selectively breed resistance to diseases or to increase productivity (Zann 1995, DNRE 1998a, Cordover et al. 2000). There are also several adverse impacts on the coastal/marine environment associated with aquaculture, yet like the issue of ballast and fishing, these effects are still not fully understood because of the limited knowledge about coastal/marine ecosystems in Australia and the interactions with aquaculture operations (Clarke 1996, DNRE 1998, EPA1998, CSIRO 2000).

It is also not possible to generalise research findings to all situations given that the impacts of aquaculture on the coastal/marine environment will vary depending on the farm's location (e.g. water depth, type of seabed such as sea- grass, local currents, existing nutrients), the type of farming techniques (e.g. density of stock, species farmed, size of operation, feeding patterns, water flow), and the adequacy of management measures (Clarke 1996, Lewis et al. 1998, Cordover et al. 2000, CSIRO 2000). In South Australia, for instance, an inadequate knowledge and the planning/management framework was believed to be contributing to inappropriate aquaculture siting, and an unsustainable industry (Marchant 1997; Carvalho and Clarke 1998).

The main impacts associated with aquaculture relate, among others to:

• conflicts with other coastal uses, such as recreation

• loss of public access and visual amenity

• increased traffic associated with land-based operations

• changes to existing coastal habitats, waste generation

• changes to sediments and local water quality with increased nutrient levels from fish food and excretions, e.g. resulting in algal blooms, possible declines in seagrass populations due to smothering by epiphytes

• reduced water oxygen content, culling of natural predators such as seals and sharks

• pressures on particular marine species used as food sources, such as pilchards and anchovies

• loss of other marine mammals when caught in cages or nets, use of chemicals and disease control agents

• spread of exotic species, e.g. introduced species escaping from an enclosed area, as occurred with the Pacific Oyster in South Australia

• navigation hazards from infrastructure such as buoys and jetties

• erosion resulting from pipes which transport seawater to land-based operations (Zann 1995, Clarke 1996, SARDI 1996, DNRE 1998, EPA SA 1998, Lewis et al. 1998, Cordover et al. 2000, CSIRO 2000).

While there has been relatively little research on the extent and significance of aquaculture impact in Australia, the Huon Estuary in Tasmania has been the subject of a three-year research project, resulting in a comprehensive report (CSIRO 2000). Aquaculture in this estuary is rapidly expanding (finfish, shellfish, seaweed), and most of Tasmania's salmon is produced there. In addition to some areas with reduced oxygen near the farms, elevated levels of nutrients and phytoplankton blooms were discovered, but the sources of these occurrences were unable to be determined. Modelling did, however, suggest that if aquaculture in the area doubled, nitrogen would increase by 50%, thus enhancing the risk of algal blooms; and if operations were expanded 10 times, it was believed that the ecosystem would become eutrophic. Despite the extensive and detailed nature of this research on the estuary environment, few conclusions were reached about the long-term effects of aquaculture, and several more questions were raised. This highlights the need for ongoing research and monitoring in this area to reduce the impacts of aquaculture on the coastal/marine environment.