Design considerations and loads on open ocean fish cages South of Iceland

The work presented in this thesis handles design considerations and loads on open ocean fish cages outside the southern shore of Iceland, in aquaculture of the Atlantic cod (Gadus morhua). The focus on the southern shore results from the fact that there growth conditions for the Atlantic cod are considered favorable all year round for all stages of the cods growth and maturity. However, environmental conditions are harsh. A general overview of design considerations is provided, followed with special chapters devoted to most of the crucial aspects for a design and load-study of cages south of Iceland, and a few considerations for the Atlantic cod in relation to aquaculture in the open ocean. Waves and currents are studied from some of the available data. It is concluded that the wave climate south of Iceland is extremely harsh, but noted that the distribution of waves is in such a way that only a small ratio of them reach significant heights above 12 m—a height which has been used for designs regarding some available open ocean cages. Site evaluation follows and it is found that only a few places are available for operation of aquaculture south of Iceland where the ocean has favorable growth conditions for the Atlantic cod. Cage discussion is then carried out with a study of many presently available cages, and a few suggested designs. It is stated that none of those cages are designed to withstand a wave climate like the one south of Iceland, but noted that some arrangements could be made to reduce the loads on them. Forces and loads are estimated, and it is found that by submersing cages deep enough, load conditions may reach similar characteristics to those that surface cages meet in sheltered sites. The Atlantic cod is discussed in relation to aquaculture in harsh conditions. It is concluded that the cod will face great difficulties in thriving in cages in the wave and current climate south of Iceland, and besides that, various problems exist regarding the cods sexual maturity and resistance to long-term loads. The assumption is finally made that offshore aquaculture of the Atlantic cod is probably not a viable option for the open ocean south of Iceland, in respect to environmental loads. Factors of uncertainty are many, and the information available indicates by most part that situations will be harder than what modern technology and designs are recommended for