Aquaculture In Focus

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 to reduce 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.

Some, carnivorous finfish farming (including Atlantic salmon, Yellowtail Kingfish 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 1.2-1.8 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. In recent years, improvements have been made to trace the sustainability of fish for fish meal.

The dependence on wild fish in the diets of farmed omnivorous species (including barramundi and prawns) is generally decreasing, so that fish farms now produce more fish protein than is caught in the wild. For example, less than 1kg of wild-caught fish can now used in feed to produce 1kg of farmed prawns.

The growth of prawn farming in South-east Asia in particular has led to the destruction of vast areas of mangroves and irreversibly altered coastal ecosystems. 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.

Many aquaculture operations in Australia are located in ex-agricultural land, meaning no dedicated land-clearing has taken place.

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. Sea-cage farming for Atlantic salmon in Tasmania has gained significant and justified interest in recent years due to the negative impact of salmon farming on surrounding marine habitats, particularly in the ecologically sensitive habitat of Macquarie Harbour. For more information see Atlantic Salmon rating.

Farming of the endangered southern bluefin tuna involves the capture of juvenile wild tuna from the ocean. The overwhelming majority (98%) of southern bluefin tuna caught in Australian waters is destined for fattening pens in South Australia, placing further pressure on this species.

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 the sea floor beneath the cages and 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. Global environmental concerns include loss and degradation of coastal habitats to construct new prawn farms and release of wastewater into surrounding habitats. Domestically, Australia’s 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.

5. Recirculating systems
Description: Recirculating Aquaculture Systems (RAS) are a highly intensive farming approach where indoor tanks are used that recycle water and effluent waste through filtration systems and sometimes plant crops (‘aquaponics’). RAS systems tend to have high power demands and require careful monitoring of water quality and disease issues; but fish grow rapidly and efficiently and there is little or no discharge of farm effluent to the natural environment.