Deformation of a large fish cage in high currents.

The shift towards salmon farming at more exposed locations has been an industry-wide trend in Norway for the past decade. Moving fish farms to areas where high currents and waves exist can improve production, through providing more stable temperatures and water quality, and reduce the environmental impacts of modern fish farming. However, exposed environments create challenges for salmon farming. If high currents and waves result in flows that exceed the typical swimming speeds of salmon, they may reduce the effectiveness of production. In addition, net deformation is often significant at exposed locations, which greatly reduces the space available for fish. Fish welfare is highly dependent on both the internal volume of the net structure and the hydrodynamic conditions. Thus, the synergistic effects of fast swimming in elevated flows generated by high waves and strong currents and reduced net volumes may prove particularly challenging for fish.

This paper presents the full scale measurements of the deformation of a large scale fish cages submitted to high currents. Pressure tags have been used to measurement the cage deformation and the vertical displacement of the bottom ring while Acoustic Doppler Current Profiler (ADCP) and Acoustic Doppler Velocimeter (ADV) have been used to measure the current reduction. The results show a reduction of 40% of the cage volume for current velocity above 0,5 m/s. Also a simulation model based on super-elements describing carefully the cage shape is applied and the results show good agreement with the cage deformations.