Aquaculture sectors and production systems

The range of aquaculture sectors and production systems employed are shown in table 2.1. Most jurisdictions have a mix of marine and land-based production with finfish, crustacean and mollusc production. The potential environmental impacts associated with different production systems are discussed in section 2.3.

Table 2.1 Selected aquaculture production 2001-02, by jurisdiction and species

Jurisdiction Species Production method Licences Value ($’000)

Oysters Rack, raft and longline 406 31 538

New South Wales

Prawns Pond culturing 12 5 440

Silver perch Pond 148 2 450

Trout Ponds and raceway 66 2 020

Yabbies Ponds and farm dams 152 364

Victoria Trout Ponds and raceways 38 10 666

Mussels Longline 25 3 734

Yabbies Ponds and farm dams 56 338

Warmwater finfish Recirculation units 63

-Abalone Flow through systems 15

-Queensland^a Prawns Pond culturing 78 59 000

Barramundi Cages and ponds 188 7 500

Redclaw Ponds and farm dams 251 990

Oysters Rack, longline, stick 111 520

Jade and silver perch Pond 168 330

-Southern bluefin tuna Cage culture 40 260 500 South Australia

Oysters Rack, longline 290 13 303

Barramundi Recirculating tanks 34 2 653

Marron Ponds and farm dams 141 282

Yabbies Ponds and farm dams 202 95

Murray cod Ponds, recirculating tanks 54

-Abalone Raceway and ocean rafts 64

-Gold and silver perch Pond culturing 121

Scallops Longline 78

-Yellowtail kingfish Cage culture 26

-Tasmania Atlantic salmon Cage culture 43 111 476

Pacific oysters Rack, longline 113 11 566

Mussels Longline 36 758

Sea trout Sea cages 17

Scallops Longline 23

-Northern Territory Pearls - 26

Barramundi Cage culture -

-- Information is not available. a Licences can contain more than one species so the number of licences may be overstated. b Microalgae (betacarotene) is understood to be the second highest value sector in Western Australia. However, information is not available due to confidentiality restrictions (Lendich 2003).

Sources: ABARE (2003); Lendich (2003); state departments of primary industries or fisheries.

Aquaculture enterprises, across jurisdictions, vary from small enterprises using ponds and farm dams for freshwater crustaceans, to very large enterprises with more developed production systems, such as sea cage farming of tuna and salmon. One factor affecting the returns of larger producers is their capacity to vertically integrate functions, such as processing, marketing and transport, and thereby benefit from supply efficiencies and opportunities to value add (NADC 2002).

Most production systems (such as cages, longlines, raceways, and rack, tray and stick) are open (or flow-through) systems. These systems rely on interaction with natural water bodies to provide inputs, such as dissolved oxygen and nutrients, and to assist in removal of waste products, such as fish and food waste (see box 2.1).

Closed (or recirculating) systems (such as those using ponds and tanks) can control the supply and condition of water both entering and being discharged from a production system (USEPA 2002).

Box 2.1 Selected aquaculture production systems

Cages — can be used within ponds, lakes, rivers, estuaries, and in the sea. The use of cages within a large body of water can allow for the removal of wastes. Cages are usually constructed of nylon or plastic, although steel mesh pens are now also in use.

In Australia, cages are used for farming finfish, such as salmon and tuna.

Raceways — are enclosures where the water moves through, carrying wastes out at the lower end. Trout are most commonly produced in raceways.

Rope longlines — are used for growing mussels and pearl oysters. Mussels are grown using a longline system consisting of one or two headlines (horizontal ropes anchored at both ends and connected to large floats). The headlines support culture ropes or droppers at 0.5 to 1 metre intervals on which the mussels are attached.

Rack, stick and tray — rack culture is the most common method of rock oyster farming.

Oyster spat settle on sticks placed on intertidal racks. When the young oysters are established, sticks are moved up river to allow the oysters to grow without further settlement of spat. The oysters remain there for two to four years prior to harvesting.

Pacific oyster spat, however, are produced in hatcheries and then ongrown in baskets on racks in the intertidal zone or suspended below longlines.

Ponds — are artificial impoundments and are usually constructed of earth. Prawns are grown in ponds that must be near an adequate water supply. The amount of water used and the quality of the discharged water depends on the management regime.

Tanks — can be used as flow through systems (as in raceways) or in static systems (as for ponds). Tanks are typically used in closed systems that involve water being recirculated through filters and pumped back into the tank. Tanks make efficient use of water but are expensive to set up and operate. Species produced in tanks include barramundi and abalone.

Sources: Love and Langenkamp (2003); Natfish (1998).

The farming of most species is undertaken using hatchery broodstock (juveniles produced in a closed system). The ‘grow out’ farming of southern bluefin tuna is a significant exception — juvenile and young adult tuna are caught in the Southern Ocean under a quota system administered by the Australian Fisheries Management Authority. The two to four year old fish are then towed from the Great Australian Bight to Port Lincoln, where they are fattened and conditioned in sea cages for between three and five months (PIRSA 2000a).

Other aquaculture sectors that rely on wild fisheries include Sydney rock oysters, which are generally ongrown from naturally spawned spat collected in the wild, and the farming of gold and silver lipped pearl oysters, which are harvested from the sea floor following the seeding of wild caught shell (Lendich 2003).