Aquaculture in Focus
Since 2003, wild caught Australian sardines have accounted for the highest volume of any species caught or farmed in Australia. But in 2012, Australia passed a seafood milestone when for the first time, more farmed Atlantic salmon was produced than any other species of seafood from Australia. Salmon production accounted for 19% of the total volume of fish and seafood species caught and farmed in Australia.
Over 40 different types of seafood are cultivated in Australian aquaculture farms, including barramundi, silver perch, Murray cod, mussels, prawns and oysters. In addition we import several different farmed seafood products such as prawns and basa.
One of the fundamental concerns with farming many seafood species is that aquaculture doesn't take the pressure off wild fisheries. Many farmed species in Australia are carnivorous (e.g. Atlantic salmon, rainbow trout) or omnivorous (e.g. barramundi) and eat smaller fish to survive in the wild. Therefore many of our popular farmed fish are fed fishmeal and fish oil that is sourced from the ocean's wild fisheries.
In response to both economic considerations and community concerns about added pressure on our oceans, aquaculture operations and feed manufacture companies have invested significant funds into reducing dependence on wild-caught fish in fish feed. Alternatives currently being used to provide essential fats in fish diets include land based products such as soy and lupins, offcuts (heads and tails) of other fish and by-products from terrestrial farming, such as chicken blood and cartilage.
Currently, carnivorous finfish farming (including Atlantic salmon, Murray cod and rainbow trout) is still using more wild-caught fish in feed than they produce. For example, for every kilogram of farmed Atlantic salmon produced in Australia, approximately 1.8 kg of wild fish must be caught for feed. Most of these fish come from the industrial-scale Peruvian Anchovy fishery, which also produces feed for farmed livestock such as chickens and pigs.
The dependence on wild fish in the diets of omnivorous farmed species, including barramundi and prawns, has generally been reduced to the point where fish farms produce more fish protein than goes in to the food. For example, less than 1kg of wild-caught fish is now used in the feed needed to produce 1kg of farmed fish or prawns.
Modification of coastal ecosystems and habitats
The growth of prawn farming in Southeast Asia in particular has led to the destruction of vast areas of mangroves and irreversibly altered coastal ecosystems. For example, in Vietnam alone, 50% of mangrove forests have been converted into farms over the past 40 years. Mangroves act as carbon sinks and critical nurseries for wild fish. In Australia, the scale of aquaculture in ponds is relatively small and regulations are tighter than in our neighbouring countries. However care must be taken with any further industry expansion, which will inevitably increase pressure on our local coastal environments.
Ecosystems polluted or modified
Discharge of waste from aquaculture facilities into surrounding waterways can be an issue. In general in Australia, effluent output from land-based ponds or tanks is strictly controlled to prevent the spread of disease and reduce pollution. Aquaculture waste is also sometimes used as a fertilizer rather than discharged from the farming operation. In the case of sea cages, a build-up of faecal matter and unused food can lead to nutrient overload and pollute the local environment. The impacts of sea-cage farming on a wide geographical scale are generally unknown, but local impacts are likely to be reversible once the cages are removed.
Farmed tuna are harvested from the wild as juveniles
Farming of southern bluefin tuna (SBT) involves the capture of juvenile wild tuna from the ocean. The overwhelming majority (98%) of SBT caught in Australian waters is destined for fattening pens in South Australia, placing further pressure on these critically endangered fish. Furthermore, the feed used in the tuna ranching operations comes largely from the South Australian-managed sardine fishery, which incidentally catches and kills dolphins each year.
Aquaculture production methods
1. Sea-cage aquaculture systems
Description: Sea-cage aquaculture consists of large netted cages floated in estuaries or embayments in which dense schools of fish are penned, fed and reared for market. Environmental concerns include waste and chemical treatments polluting receiving waters; solid wastes accumulating on sea floor beneath cages; broad scale environmental impacts of large-scale production. Siting of sea-cages is a key consideration in ensuring operations are located in areas well-flushed by seawater to remove waste from the local environment.
2. Prawn pond aquaculture
Description: Large, salt-water ponds for farming prawns built in coastal areas. Environmental concerns globally include loss and degradation of coastal habitats to construct new prawn farms and release of wastewater into surrounding habitats. Domestically, regulation of wastewater generally means impacts of effluent on surrounding terrestrial ecosystems are minimal.
3. Land-based tank and pond aquaculture
Description: Land-based systems of tanks or ponds for farming fin and shellfish species, such as barramundi. Some systems are fully closed and others release treated wastewater, although effluent is managed to ensure impact on surrounding ecosystems is minimal.
4. Stick, rack or line aquaculture
Description: Method of farming shellfish using structures/lines suspended in the water column or standing on the seafloor in bays, inlets and estuaries. Farming of shellfish such as oysters, mussels and scallops is a relatively benign form of aquaculture as they do not require the addition of feed, because the farmed species feed on plankton from the surrounding water.