Open Water Net-Pens
Appropriate siting, design and construction of Atlantic salmon cage farms is essential to limit adverse impacts on the environment and natural ecosystems. In addition, if floating net-pens are located within navigable water bodies, consideration should be given to ensure that they 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.
As Atlantic salmon net-pens are often located in areas with relatively rich wildlife, species that prey on fish can be attracted to them (e.g. seals, cormorants). This can potentially become a significant problem for a farmer due to the stress caused to the stocked fish and injuries caused to them. In the worst case scenario there could be significant losses to stock and/or escapes if predators breach net-pens.
National and local laws should be adhered to and all farms should have the required licences, permits and registrations in regards to their site and its operations, with documentation being kept to evidence compliance. Where aquaculture development plans exist, then new farms should be located within the appropriately identified areas. Salmon producing 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)1, 2. Marine cage culture has ‘minimal’ impacts to the environment where farms are appropriately sited and properly managed3.
Atlantic salmon net-pens should be located, constructed, and have management measures in place to mitigate entry and damage by predators. Non-lethal control methods are available to the industry and considered good practice4. 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.
Land-based aquaculture facilities involve a greater level of complexity and utilise more technical equipment than open-water systems (e.g. net-pens), especially intensive salmon smolt production with numerous growing units5, 6. Major components include:
- Water abstraction and transfer
- Water treatment and wastewater discharge
- Production units
- 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 land-based 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.)7. Land-based RAS are currently only economical for the freshwater stages of Atlantic salmon production, but there is increasing interest in farming salmon in these systems to market size8.
The physical and locational requirements for a large RAS facility include access to supporting infrastructure such as power, road and sea links, whilst being sited on an adequate land area that is easily developed and low enough and close enough to water levels in order to reduce pumping costs7. Energy is one of a number of critical operating costs that influence the location RAS farm developments9. On-shore aquaculture systems often require large buildings, may increase road traffic (e.g. goods and service flows) and generate noise (e.g. generators, pumps, compressors). These impacts may be of concern if located in sensitive areas.
Designing, building and operating on-shore aquaculture facilities must be undertaken with due regard to the sensitivities of the local area (e.g. not disturbing the skyline, screening by trees or other structures, respect for other local amenities/users), and work as best it can with local infrastructure (e.g. road capacity). Working through the necessary planning policies is vital. Capital costs for land purchase (or land rental charges) needs to be appropriate in order to make an on-shore aquaculture facility viable5. As RAS are isolated from the external environment they can be extremely biosecure and as such predator risks can be eliminated.
- Scotland’s National Marine Plan
- FAO/World Bank
- Code of Good Practice for Scottish Finfish Aquaculture
- Lekang, O-I., 2007. Aquaculture Engineering. Blackwell Publishing
- Cawthron Institute
- Seafood Source