Shielding skirt for prevention of salmon lice (Lepeophtheirus salmonis) infestation on Atlantic salmon (Salmo salar L.) in cages – A scaled model experimental study on net and skirt deformation, total mooring load, and currents

•Experiments were conducted on a 1:17 scale model of a fish cage with mounted skirt.•In currents up to 10 cm s−1 model scale, the skirt is not lifted more than 10%.•In currents above 10 cm s−1 water passes more easily underneath the skirt.•The total mooring load on the cage increased approximately 40% with skirt mounted.•Cages downstream in a fish farm system will experience lower loads.

Salmon lice are a serious threat to the Norwegian salmon aquaculture industry. Salmon have been found to develop higher infestation of salmon lice at the upper parts of the water column. The use of tarpaulin skirts for shielding the upper part of a salmon cage has therefore been used as a measure for reducing the salmon lice infestation. A tarpaulin skirt will however increase the effective solidity of the net, and it is necessary to study the cage mooring loads, the net deformation and the water flow through and around the cage to prevent damage to the structures and the fish. Experiments were conducted at the North Sea Centre Flume Tank in Hirtshals, Denmark, with a model salmon cage and skirt in scale 1:17. The experiments showed that the skirt sheet on the upstream side gets increasingly pulled back and up toward the surface as currents increase, and lice are likely to pass underneath and into the cage. The mooring load on the cage was also increasing with the current speed, and approximately 40% higher than that of a cage without skirt. Due to the increase in mooring loads applied by a shielding skirt it is important to include the effects of a skirt when calculating mooring loads on a farm system.