There certainly should be more closed systems where local conditions warrant. The closed bag systems for example don't allow the fish to be seen by the predators, and there is no way for the predators to catch the scent of the fish. The benefits of the closed systems are numerous, and would do well to alleviate many concerns that groups have about fish farming. Effluent is treated and captured, can be made into bio-sludge which is a great fertilizer, which is a huge benefit to the ecosystem near the pens. The wild salmon will have no contact with the farmed salmon, escapes are nigh impossible.
The problem with the closed systems is the cost and environmental conditions needed. Last I heard, the bags can only be used in areas where the tidal action is slight. The majority of net pens are in areas with low tidal action anyways. The cost is probably the most prohibitive. These systems as yet can't be made as large as the open water polar circles. And the technology is very new, so the materials are very expensive. Canadian farmers are in direct competition with countries like Chile, where production costs are very low due to low wages (comparitively) and lax environmental controls.