Current flow and dissolved oxygen in a full-scale stocked fish-cage with and without lice shielding skirts

Abstract Shielding skirts are widely used on Atlantic Salmon sea-cages as a non-invasive preventive measure against salmon lice infestations. The skirts are however known to impact the current flow and thereby the environment within the cage. As the current is influenced by local factors such as topography, farm layout and stocking density of the cage, it is difficult to compare results from sites that apply skirts with those without. The same high-stocked cage was therefore studied with and without the skirt deployed, including the transition from shielded to unshielded, to investigate the influence the skirt had on the current flow within the cage and dissolved oxygen. When the skirt was deployed the velocity vector in the centre of the cage had a vertical component towards the surface and the reduction in current speed was higher. The dissolved oxygen level inside the cage improved within 30 minutes when the skirt was removed and there was no indication of the skirt influencing the vertical swimming behaviour of the salmon.