Fact Sheet - Ecological Interactions Between Wild and Farmed Fish

---

Farmers place great importance on maintaining healthy fish stocks. Advances in aquaculture research, additional federal and provincial regulations and programs, improved farming techniques, and health management have significantly reduced risks to wild fish and marine and freshwater ecosystems from aquaculture operations.

Aquaculture operations can have complex effects on the environment. To clearly understand these effects, scientists must examine them in the context of the ecosystem in which they occur. Interactions between wild and cultured fish or shellfish are inevitable - they can occur with small invertebrates or large predators both in the ocean and in freshwater. Science for a sustainable aquaculture industry is a priority for DFO. Research to date provides us with a level of assurance that environmental interaction from aquaculture operations can be controlled to ensure an acceptable level of environmental performance.

On-going monitoring and research help to provide the foundation upon which Canada's federal and provincial governments make informed decisions relating to public policy on aquaculture practices, regulations and environmental performance measures.

Competition for food and habitat

Despite suggestions that escaped farmed salmon contribute to the decline of wild salmon stocks, research indicates that the level of ecological risk is low.

• Competition between farmed and wild salmon for food or habitat is limited. Atlantic salmon, in particular, are more docile and adapt better to a farm setting. Farmed fish are poorly suited to compete for food or survive in the wild.
• Stomach content analysis of recovered farmed salmon indicates low intake of wild food and only trace amounts of herring or invertebrates that live in farm nets. Most escaped salmon succumb to starvation or predators.
• Farmed salmon interact with many species of invertebrates and fish that swim through their net cages. These species are part of the normal diet of wild salmon but farmed salmon eat little wild feed, existing instead on food pellets provided by operators.

Disease

Cultured aquatic animals, like all other living organisms, are at risk of sickness and disease for a variety of reasons.

• There is little evidence to support the suggestion that the presence of fish or shellfish farms increases the risk of disease in wild stocks. Farmed aquatic animals can acquire infections from the surrounding marine or fresh water. Wild fish can carry the infection, but do not necessarily become sick from them. Conversely, the risk of farmed fish or shellfish infecting wild stocks is relatively rare.
• Concerns have been raised that fish farm conditions can increase opportunities for an infectious agent to spread and multiply. Although this is possible, farmers prefer early intervention to letting infections build up in an uncontrolled manner. Farmers can take a number of measures to manage and maintain healthy stocks.
• Advances in research, strong federal and provincial regulations, programs such as the National Aquatic Animal Health Program, improved farming techniques and vaccination programs have all contributed to the reduction in disease.

Genetic interaction

Farm fish escaping from net cages can affect wild stocks, yet with good quality management, this is also preventable.

• Research has shown that Atlantic salmon (wild or farmed) cannot mate successfully with Pacific salmon.
• Some escaped Atlantic salmon have survived for a time in freshwater streams, but there is no evidence of any established populations. This lack of evidence supports scientific opinion that the risk to wild stocks from escaped farmed Atlantic salmon is low.
• Farmed Atlantic salmon can successfully mate with wild Atlantic salmon. Little research on the genetic interactions between escaped farmed Atlantic salmon and wild Atlantic salmon has been conducted in North America. It is too early to speculate or draw conclusions on the overall effect of escaped farmed Atlantic salmon on wild Atlantic salmon in Eastern Canada. DFO is conducting research, which will help put more pieces of the puzzle in place.

Other interactions

Interaction with predators at net cages can pose a threat to farmed fish and result in economic losses to farmers. Extra netting over the tops of pens deters birds that prey on young salmon.

Seals and sea lions preying on farm salmon can damage and tear nets, consume fish and contribute to escapes. One successful method used to deter predators is to place a heavier second net around the primary one. Other methods, such as lights or acoustic devices, have been tried with little long-term success. As a last resort, farm operators may cull marine mammals that become persistent predators. A DFO permit is required for this and the operator must report the number of predators it culls to the department each year.

The primary interaction with the marine environment is limited to the floor under fish farms. Wastes such as feces and uneaten feed can fall to the bottom and decompose faster than can they can be consumed causing temporary oxygen reduction and other chemical changes in bottom sediments. The effects are temporary and can be reduced when nets and other structures are moved or the farm is left fallow for several months after harvesting.

Farms properly sited in deep water with good currants and tidal flow also reduces the risk to the marine environment.

Land-based farming

DFO has studied closed containment systems and supports research into the development of innovative technologies that enhance the efficiency of production systems while reducing risk to the environment.

Site selection and system design are critical to the success of aquaculture operations. Land-based farms require a year-round supply of high quality water. Accessibility, waste management and site-servicing costs must also be considered. As well, access to markets, availability of supplies and technical expertise are important to an operation's success.

It should be noted that freshwater hatcheries for marine finfish (egg to juvenile stage), "U-Fish" operations and freshwater finfish (Arctic char, Tilapia) operations use land-based systems.

A land-based system for salmon farming - from the juvenile to the adult stage - would reduce the level of interaction with the marine or freshwater environment. However, such a system is currently not a practical alternative to the existing, wide-scale, commercial net-cage design.

Land-based salmon farming would require large amounts of seawater to be pumped inland. Farming in remote locations would be difficult without hydroelectric power and the need for fossil fuels to power generators.

For sources and further information visit these websites:

Fisheries and Oceans Canada - www.dfo-mpo.gc.ca

University of Guelph, Aquaculture Centre - http://www.aps.uoguelph.ca/

Note: This page contains links to Web sites not under the control of the Government of Canada.  For further information on our hyperlinking practices, please refer to the Hyperlinking Notice.