Fish Farming in Floating Structures

Abstract – The world will see an increased use of floating structures for various purposes. The world will also see an increased harvesting of food from the sea. Farming of salmon has become a major contributor to food. Norway has excellent conditions for farming salmon; a long coastline (100,000km including islands) with nice and fresh water. Norway produces 1.3 million tons of salmon per year (the weight of all Norwegian people is 0.3 million tons). The export value of salmon is the second largest after oil and gas. Starting in a small scale some 50 years ago, entrepreneurial fishermen have developed salmon farming into a huge business. Traditional salmon farming is performed in open nets. The open net solution is inexpensive, and suitable when placed in pure and clean water with ample current that provides for changing the water, which is important for salmons. However, there are challenges for the open net approach. The nets are vulnerable, and a broken net allows farmed salmons to escape, and possibly mingle with the wild salmons. The open net allows faeces to fall through, and polluting the sea. Sickness may be spread by toxic water, and sea lice may enter and infest the fish. The obvious remedy to these challenges is to farm in closed buckets. One prototype bucket was designed, built and installed on the west coast of Norway, with excellent results. No salmon lice was found in the bucket. The salmon “liked” the closed bucket because one can provide a current that gives the salmon exercise. Salmons farmed in this way are bigger and thereby command a higher selling price. There are many activities around closed farming at the moment that will be described in the paper, and they are linked to the experience of marine concrete structures in general.