One Flew Over the Salmon Cage
Salmon farming is a major industry in Norway. However sea lice on caged and wild Arctic salmon can stunt their growth and reduce reproduction. When electroshocked, lice keep at a distance. A "fence" of cable electrodes up to 10 meters deep gives them a jolt they dread.
Current in currents
The Arctic coast can be a tough environment. The cable has to endure high waves, storms and seawater corrosion. At the same time, it has to act as an electrode conducting a pulse of electricity via the semi-conductive layer creating an electrical "keep out" zone around the cage.
Initial sea trials were done with standard conductors and off-the-shelf semiconductors. They were positive, but heavy corrosion seriously reduced conductivity. We contacted NRC/Lens (Fr) to analyze the corroded parts, and Halden (Nwy), who had experience with salt corrosion and semicons. Improvements were suggested. Bramsche/Neunburg (Germ) made us a Ni-plated Cu wire for further trials. We also tested a NiCu alloy made by former Nexans company Alsafil. We have now improved corrosion-resistance to outlast the expected lifespan of installations, and have significantly improved the semiconductors.
With Norway's second-largest industry under threat from smaller yields and government forced closure to protect wild Atlantic salmon, cable solutions will continue to be developed with industry support. The only alternative is treatment with chemicals, either by removing fish into floating tanks and then returning them to sea, or temporarily sealing the salmon cages. However, lice are developing resistance to chemicals, and there are serious environmental concerns. A typical fish farm would require 100,000 meters of net-fixed electroshock cables, in addition to an increased number of polyurethane energy cables.
"All of you! Quit bugging me!"