Salmon is one of the most popular edible fish in the world. In the EU alone, the largest market for salmon, over one million tonnes were consumed in 2023. The majority of salmon traded worldwide today comes from aquacultures where the fish are bred under controlled conditions. This involves the use of large net cages anchored to the seabed, which provide space for up to one million fish. Around 70 per cent of global salmon production takes place in this way, mainly in the Norwegian fjords and off the coast of Chile.
However, this form of intensive farming provides ideal conditions for the salmon louse, a parasite that significantly impairs the health of the fish. Combating this pest and the resulting damage costs several hundred million euros each year - up to 10 per cent of total production expenditure.
An electromagnetic "fence"
In order to minimise these financial losses, the Norwegian company Harbor AS has developed a robust and now patented preventive solution against salmon lice under the name Harbor Fence. Verification and pilot tests were carried out in large commercial facilities between 2015 and 2019. Harbor has tested a successful technical and mechanical verification over two generations of salmon in commercial pilot plants, which was completed in spring 2020.
Research has shown that lice larvae lose their ability to attach to salmon when exposed to small electromagnetic fields. Harbor Fence utilises this effect through an enclosing electromagnetic field that is stretched around the cage. The field takes the form of an open fence and neutralises the lice larvae on their way into the cage. Harbor Fence is now in commercial operation and supplies several customers along the entire Norwegian coast. Installation and service are carried out by our own teams.
In addition, a good flow of water helps to neutralise the lice larvae produced in the cage when they emerge from the harbour fence system. This helps to reduce the infection of neighbouring cages, other sites and wild salmon. Harbor Fence has a localised effect and does not harm the fish within the aquaculture.
LAPP supplies cables for use in the sea
Harbor AS enlisted the expertise of LAPP Norway to develop this solution. Together with LAPP Muller and the LAPP Engineering & Advanced Technology department, the Norwegian specialists developed a special electrode cable. This was used to construct a kind of "fence" of thin electrodes that are attached around the outside of the entire net pen. The system poses no risk to the health of the salmon, partly due to the low voltage and the fact that it is attached to the outside of the net pen.
The electrode specially developed by LAPP is a semi-conductive power cable that conducts electricity and forms an electromagnetic field or barrier. By hanging the electrodes in a row one behind the other, they form an electromagnetic open fence and an open-air protection that acts as an external fuse. "The challenge was to design the cables in such a way that they could withstand seawater without significantly losing their effectiveness during their intended service life," says Lars Nilsen, Product Manager at LAPP Norway. LAPP Norway has already supplied more than 130 kilometres of electrodes for such salmon fences.
Real-time monitoring
The electrodes, which hang in the sea at a distance of 12 - 17 centimetres outside the net, are connected to a power / control cabinet. This controls the frequency and length of the pulses that are sent via the electrodes. The control cabinet continuously transmits real-time data on the state of the sea as a basis for optimisation, monitoring and control. Normal net pens today are equipped with two automation and control boxes. A Harbour Fence installation has an annual power consumption of 9,000 kWh. The standard depth for a Harbour Fence system installation is 10 metres.
Harbor Fence is just as suitable for plastic cages as it is for steel cages. The company concludes service contracts with its customers and ensures that the fence functions properly. Harbor also takes care of returns and the repair or replacement of the system if necessary. In addition, a remote monitoring solution can provide real-time hydrographic data such as salinity, temperature and current velocity. This data can be used to optimise the current pulse and current consumption in the fence. The systems are constantly being further developed, as are the electrode materials used.
High demand around the world
Christian Fritzland is project manager at Harbor. He is experiencing high demand for Harbor Fence: "We have also received international enquiries from Canada, Chile and Scotland. We are continuously working on product development and are pursuing several interesting avenues. Some of these involve easier assembly and disassembly as well as remote monitoring and control of the power cabinets." Such a system could also provide early warning of other undesirable events, such as sudden fouling or increasing algae growth. Fritzland adds: "If the lice still get into the cages, complementary solutions such as cleaner fish and lasers can work well with the electric fence. Together with cleaner fish or lasers, the system is a very important measure against lice that is not only environmentally friendly, but also cost-effective."
