Appropriate siting, design and construction of rainbow trout farms is essential to limit adverse impacts on the environment and natural ecosystems.
Freshwater trout farms have traditionally been sited close to rivers or springs where large quantities of clean freshwater are available. Some production in floating net-pens in freshwater lakes/lochs also exists, but generally such farms are of a much smaller scale than net-pens in marine waters. Major components of a traditional, land-based freshwater trout farm include:
- Water abstraction and transfer
- Water treatment and wastewater discharge
- Production units e.g. ponds, raceways
- Equipment and space for: feeding / feed storage; internal fish transport and size grading; transport of goods and services in and out (e.g. feed, staff, harvested fish); monitoring of the culture environment (e.g. water quality parameters)
There are many factors to be considered in locating a freshwater aquaculture facility. Many will be project-specific depending on the type and scale of the operation and the environmental requirements needed by the cultured species (e.g. temperature, salinity, etc.)1.
When locating a rainbow trout farm, adequate care needs to be taken to ensure that:
- The abstraction of water does not adversely impact on the source supply and associated ecosystem
- Discharge of solids (including earth/pond sludge) and dissolved wastes can be assimilated by the receiving ecosystem without causing significant changes in its trophic state and biodiversity2
- There are measures in place to minimise the potential for fish escaping the facilities
- If located in a sensitive area, structures and activities do not alter significantly the landscape, respect other local amenities/users, do not generate excessive noise and work as best they can with local infrastructure (e.g. road capacity)
Trout farms are often located in areas with relatively rich wildlife. Species that prey on fish can be attracted to farms (e.g. herons, otters), and this can potentially become a significant problem for farmers due to predatory losses, stress and injury to the stock, and escapes if predators breach the rearing facilities. Trout farmers should ensure all possible management measures are taken to protect stocks and facilities from predators. This might be via location, netting of the smaller juvenile fish ponds or fencing of site perimeters. Non-lethal control measures are available to the industry and considered good practice3. Deterrents, scarers and increased on-site activity may be effective. Lethal methods of predator control should only be resorted to when appropriate licences are in place and the predatory species are not threatened in any way.
National and local laws should be adhered to and all farms should have the required permits and registrations in regards to their site and its operations, with documentation being kept to evidence compliance. Working through the necessary planning policies is vital.
In addition to the considerations outlined above, when rainbow trout is farmed in floating net-pens within navigable water bodies, it must be ensured that facilities do not impinge and restrict movement of boats, aquatic animals and the water itself. There may also be concerns over the visual impact of siting net-pens in the areas of natural beauty; in such areas it is important that the design, construction and colour of farm facilities are sympathetic with the landscape in which they sit.
Where aquaculture development plans exist, new farms should be located within the appropriately identified areas.
Major producer countries are increasingly creating policies and using marine spatial planning to regulate where aquaculture can take place in relation to other farms and other marine users (e.g. appropriate areas where production is allowed, including allowable production densities, the use of appropriate infrastructure, and so on)4, 5. Marine cage culture has ‘minimal’ impacts to the environment where farms are appropriately sited and properly managed6.
Trout farms can apply for certification against schemes7, 8 which ensure they address issues such as: location in positions that allow connectivity of wildlife and human traffic; compliance with water abstraction limits with potential for part or complete recirculation systems; discharge of solid and dissolved wastes into water bodies; negative impacts on endangered species.