## 4 Discussion
### Waves, Currents, and Equipment  
Offshore aquaculture presents significant technical challenges in the design, testing, and construction of systems, such as cages and longlines, and there are also many biological, regulatory, social, and economic problems to be solved [145]. The net cages have innumerable factors that require deep analysis to ensure the safety of production. These factors range from the cage structure itself and deployment depth; the location and weight of the anchors; the ropes attached to the cage; the drag forces applied on the structure by currents and waves; backup plans if the anchors get dragged on the sea floor; ropes entanglement; uncommon sea conditions that may damage the materials, such as storms [146; 147; 148]. Light intensity, the availability of dissolved oxygen, rearing density and food supply capacity should also be considered for the survival and welfare of the species produced in submerged cages [59; 149; 150]. Nevertheless, aquaculture cages had rapidly developed in the last decades [148] and can cope with these factors to a certain degree. For instance, the authors [146; 147; 148] studied the impact of currents and waves in aquacultures cages. It was observed by [146] that drag forces are dependent on the cage size and system used, where sea currents from 0.2 m s\({}^{-1}\) to 0.5 m s\({}^{-1}\) had a proportional increase on the lift force. Compared to the results of this study, Area E had currents velocities that reached 0.75 m s\({}^{-1}\), indicating that production in cages in this location has to be equipped and prepared to withstand greater lift forces. The results of [147] were inconclusive regarding the waves and currents on the aquaculture cage system used. Although, some results had significant differences, such as the mooring from the cage system not being affected by waves, neither the currents nor the fine numerical mesh from the net suffered any damage when the current velocity reached 0.3 m s\({}^{-1}\). Since every studied area had a current velocity that exceeded 0.3 m s\({}^{-1}\), using a larger mesh in these areas would reduce the drag from the waves and currents. In case of an emergency, [148] set an experiment where the mooring system failed, and the cage was subjected to waves and currents. The conditions of this experiment were quite extreme, where the significant wave height reached 6 m and the current velocity reached 2 m s\({}^{-1}\). The experiment concluded that, for these conditions, when the mooring system failed, the cage system was subjected to far greater tension, but it stabilized after a while. If combined with an anchor failure as well, the whole aquaculture system becomes unfit for the sea. All studied areas had significant wave heights that exceeded 6 m. According to [119], until further technological solutions allow offshore aquaculture to be developed, the coastal modality is a more pragmatic option for the North Region (Area A) in Portugal. Area E comes close to the wave height studied by [148] with a significant height of 6.97 m. In this area, if the anchor system does not fail, the aquaculture production system should endure storm conditions, and if the aquaculture cage can be successfully placed, other variables need to be added for the biological necessities of the selected species. For example, [59] mention that the Atlantic salmon behaves differently in no light conditions, which results in sub-optimal higher densities (in high-density stocks) but the placement of artificial lights in 15 m depth cages resulted in a lower density. The study of [149; 150] identified that Atlantic salmon in submerged cages swam 1.6 times fasterthan nearer the surface (submerged cages at 3 m depth).