Supervision and detection of holes in nets for fish farming
Escape of fish from open facilities at sea has been a major problem for the aquaculture industry for a number of years. Escape leads to economic losses, genetic influence and risk of infection to wild salmon, as well as a reputation problem. The main cause of escape is holes in the net. Figures from the Directorate of Fisheries show that around 284.000 salmon have escaped so in 2019 (as of 20 September 2019). There are many reasons for escapes. One possible reason is that the top of the net comes under water. Another possible reason is that holes are made in the net due to storms, washing of the net, propellers that touch the net, etc. In recent years it has happened that mackerel sturgeon have broken across net and caused large holes.
Today's method of detecting holes in nets consists of visual inspection with divers or ROV, a time-consuming method with a long response time, and an increased risk of a holes in a net being left undetected and entailing greater consequences than would be the case with better technology for monitoring and warning. There is currently no sensor technology available other than visual inspection with divers or ROVs. Such visual inspection is time consuming, exposed to weather and wind and dependent on advanced image processing to be able to detect holes and damage. In a fish farm facility with 6-7 nets, an ROV will need long time to reach over all the nets.
The overall idea of the project is to develop cost-effective and reliable sensor technology for continuous monitoring of the condition of nets. Rapid detection of holes in nets is crucial to gain control of escape. The concept is based on the fact that a groove, like any mechanical or electrical system, must have its signature or transfer function. The transfer function can then be used to describe the condition of the net, especially if there are holes in the net that can cause fish to escape. In addition, a system that "listens to the net" will be able to detect events that could potentially cause holes.