Farming high-value fish species in shallow coastal waters or in tanks on land is difficult, and nearly fifty years ago producers in Japan began for the first time to produce them in the open sea, i.e. offshore. These waters offered optimum living conditions to many marine species. The water is usually cleaner there, the wind and waves carry a regular supply of oxygen, and ensure largely constant temperatures. Disease and parasites also occur less frequently than in locations directly off the coast. The idea to move aquaculture facilities into offshore regions became popular elsewhere, too, because the traditional farms along the coast were increasingly meeting with rejection. There are several different user groups who are interested in the strip of water directly off the coast with the result that conflicts regularly develop when aquaculture starts to expand. In disputes with fishermen and hobby anglers, harbours, shipping lines, companies from the tourist sector, or with the energy industry with its wind power plants aquaculture mostly stands only a poor chance of asserting itself.
The temptation is thus big to get around these disputes by moving aquaculture into the offshore region. And probably a lot more companies would already have moved their farms away from the coast if there were not also serious problems to be coped with there, too. The sea is considerably rougher further away from the coast; storms, heavy swell and metre-high waves take their toll on the net cages, and there are also logistical problems. A farm needs seaworthy vessels to maintain and control the farms, and to transport feed, fishes and farming materials. During storms the farms can be inaccessible for several days on end. Electronic, automatic devices and techniques are necessary in order to still be able to monitor the fishes and to enable recognition of any problems in good time. The equipment and apparatus required for this often has to be developed first, however. Some issues have already been addressed and solved, others are still open. How difficult is it to handle the fishes in offshore farms? Routine jobs such as feeding, sorting and harvesting or maintenance work such as antifouling measures probably cost more time and perhaps demand other methods. Are the risks of offshore farming manageable and is it possible at all to insure such facilities? These points alone are enough to make clear that the costs of offshore farming will likely be disproportionately higher than coastal aquaculture. That is probably why the European Commission said in 2002 that aquaculture should look more at research from other branches of industry to see how they coped with offshore problems: “Fish cages should be moved further from the coast, and more research and development of offshore cage technology must be promoted to this end. Experience from outside the aquaculture sector, e.g. with oil platforms, may well feed into the aquaculture equipment sector, allowing for savings in the development costs of technologies.” That sounds wise, but taking over individual solutions can do little to change the fact that the aquaculture industry has nowhere near the financial, technical or logistical possibilities that the oil industry or energy producers have.
Offshore region offers optimal preconditions for aquaculture
Difficulties already begin for aquaculture with the simple question of where exactly the offshore zone begins and how far it stretches. There is no unambiguous definition of the term ‘offshore’. It is a relatively vague description of a region that begins beyond the shallow coastal waters and extends a random distance into the sea. Offshore can be understood as both “far from the coast” and “outside of coastal waters”. It is thus decisive that when using the term not only the distance of the farm from the coast be mentioned but also the benefits resulting from the shift in location. It can sometimes be enough to move a farm just a few hundred metres further out to sea to benefit from the advantages of offshore farming. Stronger currents and greater water depths can mean that feed remains and fish excreta are quickly removed from the farm area and distributed over a larger area and thereby “diluted”. This reduces the strain on benthic ecosystems, prevents lack of oxygen on the sea bed, and contributes towards maintaining water quality within the location. And that can increase the likelihood that an offshore farm will be accepted by local communities and the general public. But even offshore aquaculture cannot dispel all its opponents’ reservations. For example, it doesn’t solve the problem of escapes, i.e. of fish getting out of the cages and interacting with the wild stocks.
In the meantime numerous commercial farms have shown that it is technically possible to produce fishes, shellfish, crustaceans and algae in the offshore zone. The precondition for the economic success of such operations is the collaboration of all stakeholders, from engineering technology, through biology, feed and logistics, to product marketing. The USA have been particularly keen to push ahead development of techniques and technologies for offshore farming. Already in 1970 the National Oceanic and Atmospheric Administration (NOAA) brought together a group of oceanographers, marine biologists, plant technicians and engineers to sound out the possibilities and limits of offshore aquaculture. In their opinion offshore farms can be profitable provided attention is paid to some basic rules during the planning phase. One of the biggest challenges is the design and construction of net cages that are able to meet the requirements of the offshore zone. The sheer force of the open sea necessitates the construction of extremely robust and resilient net cages. These are, of course, considerably more expensive than conventional systems. At present the size of such cages is between 400 and 11,000 cubic metres. In the pipeline, however, are projects with up to 64,000 cubic metres. With stock densities of 30 kg of fishes per cubic metre, production could then amount to nearly 2,000 t of fish per farming cycle.
High cost pressure makes production of expensive fish species necessary
In offshore farming it is basically possible to use net cages like those that are normally used in coastal facilities. Prior to use, however, they have to be made “seaworthy” by undertaking certain constructional alterations that will render them resilient enough to cope with the often metre-high waves. In spite of their robust design the cages are still open to huge risks at the water surface which is why a lot of aquaculture companies in offshore zones prefer to use net cages that are closed on all sides and can thus be completely submerged below the water surface. Although this is a way of getting around the problems that confront net cages on the water surface, e.g. the impact of stormy seas or dangers resulting from shipping traffic in the region, the complexity of production, anchorage and operation of submersible facilities is disproportionately higher which makes these systems a costly alternative to conventional shallow water cages.
The fact that offshore aquaculture facilities cannot be compared with traditional systems becomes clear upon perusal of a cost account that Hauke Kite-Powell (Woods Hole, USA) presented. Nearly everything is more complicated and more expensive in offshore farming: the cages have to be more stable, the boats have to be bigger, and the distance from the ports to the farms is greater. In his calculations Kite-Powell names the costs for an offshore cage at 30 to 50 dollars per cubic metre plus nearly 100 dollars/ m³ for anchorage. Even a relatively small cage measuring 400 cubic metres thus costs about 60,000 dollars. And then the necessary vessel costs have to be added, too, which on average add up to 200 to 300 dollars per hour. The huge investment and operational costs make aquaculture in the offshore zone much more expensive than in conventional inshore facilities. And the further out to sea the offshore farms are the higher the costs rise. Because this is a clear competitive disadvantage compared to inshore aquaculture offshore faming can at the moment really only be profitable for very high-priced fishes, or species whose production in coastal regions presents problems. A further possibility is the production of bivalves and algae. Farming facilities for these two species groups become profitable much more quickly because they do not have to be fed. This leads to a major reduction in supervision and handling on the farms. On top of that, bivalve and algae farms have a cleaning effect because they take nutrients out of the water. This effect might even contribute towards improving the acceptance of offshore aquaculture among the public.
Aquaculture in the offshore zone demands new technologies
Whilst conventional aqua farms that float on the water surface are mostly shaped like a cube or a cylinder the variety of shapes and forms of submersible net cages is much greater. These cages are often spherical, but cages are also designed in the shape of cylinders, discuses, hexahedrons or octahedrons. The frequently futuristic looking shapes are thought to reduce water resistance when the facility is submerged beneath the water surface. For stocking and harvesting the fishes the cages are hauled to the water surface but otherwise they are kept at the desired water depth which can be changed as required or necessary. When submerged, the cages do not pose any obstacle to shipping and they are optimally protected against storms that rage at the water’s surface. Apart from that, they can be specifically positioned at water depths whose temperatures offer optimal conditions for the fishes. These advantages have their price, however, since the technical effort required to move the cages upwards or downwards is extremely high. A complicated system of ropes and anchors, floats, ballast tanks and special steering devices is necessary to move an installation and keep it at exactly the required depth.
In other aspects, too, offshore facilities require much more technical effort than inshore systems. It is not rare, for example, that offshore cages have double netting around them. Whilst the inner net holds the fish stock together the external net (which is made of metal or highly resilient polyethylene fibres) offers protection against predators. In the case of underwater cages, in particular, this double protection is important because if damages to the net mesh are not noticed immediately this can quickly lead to the loss of the whole fish stock due to escapes or predators.
A lot of tasks that require hardly any effort to perform close to the coast are considerably more exerting in the offshore zone. This applies for example to the storage of feed, and to feeding itself, which demand a high degree of technology in the case of submersible facilities. Because the farms are often not accessible during unfavourable weather conditions appropriate feed supplies have to be available on site. The feed can clump together, however, if humidity is high, and it spoils relatively quickly and so can only be stored for a short time. The size of the feed silos is thus a compromise between the frequency of visits by the service vessels, the necessary feed reserves, and the shelf-life of the feed. Apart from that, pipe systems and dispensing facilities are needed to transport the feed from the silos to the submerged cages. In addition to these devices sensors and underwater cameras are needed to monitor the fishes’ appetites and avoid unnecessary feed loss.
Although many of the tasks that have to be carried out in inshore and offshore facilities are basically the same, the greater the distance from the coast the more effort it costs and the higher the risk it entails. Like in shallow water, the net meshes of cages that are located further out to sea can become clogged and combating fouling is much more difficult under rough sea conditions in the offshore zone. Emptying the cages also requires special methods and techniques if, for example, the whole stock is to be harvested from a spherical farm cage. Net cages, anchorage, feeding systems and other technical equipment thus have to be checked and maintained regularly, and the health status of the fishes within the cages and important environmental parameters require constant control, too. If the farm staff are not themselves on site at the farm all the necessary data have to be transmitted electronically. A workforce is thus indispensable at an offshore facility, too, even if a lot of the work processes are automatic. What it might be possible to save in manpower at sea is then required on land because it should not be forgotten that an offshore farm also needs onshore property: administration rooms, changing rooms for farm workers, storage space for feed and equipment, workshops for making any necessary repairs, berths for the boats, etc.
The above also contributes towards making offshore farming activities quite a lot more expensive than inshore farms. Added to this is the fact that offshore operations conceal more risks because small faults and errors that can mostly be corrected very quickly in inshore farms are much more difficult to deal with in the open sea. Offshore farming thus demands the best material, sophisticated technologies and vital, absolutely healthy fishes. In spite of a lot of progress that has been made in this area it should not be forgotten that there is still quite a lot to learn – and possibly the hard way – which can sometimes prove to be very expensive.
Offshore farms often serve experimental purposes
Based on cautious estimations there could be offshore aquaculture projects underway in about 30 different countries, most of them experimental but some of them already running on a commercial basis, particularly in Europe, but also on the American continent and in Asia. In the Mediterranean countries Spain, Portugal, Italy, Greece, Cyprus, Croatia and Malta there are, or were, offshore facilities already in operation. China, Puerto Rico, the Philippines and the Bahamas are also among the pioneers of this promising development in the aquaculture sector. It is particularly in the USA and Norway, however, that there has been intensive research and investments, and one of the central focuses of these efforts is the design of offshore net cages. In Ireland the development of offshore-worthy technologies and aquaculture systems is even part of the National Development Plan that covers the period from 2007 to 2013. In the course of this project sensor systems for the feeding and control of biomass and the health status of the fishes are to be made ready for practical use in the aquaculture industry. Apart from that, offshore net cages are to be improved, new materials tested and the telemetric transmission of data made more reliable.
With the exception of a few countries, activities nearly always focus on carnivore species with a high market value. A lot of these offshore facilities are still unprofitable and have to rely on financial support from research funds but at some point in time it is of course envisaged that they will be self-supporting. High-value fish species that can easily be sold are naturally the best guarantee that investments will have been worthwhile in the long run. Occasionally species such as cod or haddock are also produced in offshore farms but this is mostly only for experimental purposes. For routine production, developers of offshore systems sooner choose species such as cobia and yellowtails, moi (threadfin), mutton snapper and red snapper, red drum, pompano species, summer flounders, halibut or bluefin tuna. Popular – and accordingly expensive – mollusc species such as abalones also play a certain role in these considerations.
Despite the fact that these relatively simple aquaculture facilities for offshore zones are still not technically mature some visionaries are already dreaming about the next stage of development: roaming cages – large mobile cages that move freely in the oceans – which are powered by marine currents and thrusters are imagined drifting between the continents. Such facilities could, for example, be stocked with young tuna in Mexico and then drift to Japan where they would arrive months later when the fishes have reached a marketable size. This admittedly fascinating idea was picked up greedily by various media and has since then been repeatedly “sold” to the public as the future of marine aquaculture. It is questionable, however, whether these freely drifting offshore systems can actually be realised. At present the technical effort and the necessary costs of freely drifting net cages by far exceed the limits of what is possible and what makes sense. This vision, as wonderful as it might be, just doesn’t add up; the risks are incalculable. Who would invest in an offshore project that is no longer directly accessible and can hardly be controlled so far away in the open sea? The offshore zone certainly offers optimum possibilities for extending marine aquaculture. And these possibilities have to be grasped, but it would be wrong to get lost in expensive utopia that are not realisable with today’s state of the art and would, on top of that, be completely unprofitable.