Offshore fish farming
technology in Baltic Sea
production conditions
Jouni Vielma and Markus Kankainen
Finnish Game and Fisheries Research Institute, Helsinki
2013
ISBN 978-952-303-064-0
Reports of Aquabest project 10 / 2013
Offshore fish farming
technology in Baltic Sea
production conditions
Jouni Vielma and Markus Kankainen
Finnish Game and Fisheries Research Institute
Description
Authors
Kankainen, M. & Vielma, J.
Title
Offshore fish farming technology in Baltic Sea conditions
Year
Pages
ISBN
2013
23
978-952-303-064-0
Abstract
In coastal regions, spatial planning often leads to the conclusion that the best new cage farming sites are located in open or semi-open
areas with harsh production conditions. It is apparent that, under such conditions, conventional cage farming technology faces high risks
of failure due to high wind speeds, high wave heights and strong currents. In addition to tolerating high-energy and harsh conditions,
systems need to be cost-efficient, safe to work in and must suit the fish species in question, in order to avoid fish welfare problems. In
addition to farming sites, harbors for service vessels, transport of fish to processing and over-wintering sites need to taken into account
during the planning. This brief review introduces the technologies that have been used in cage aquaculture farming in open or semi-open
water areas. We also discuss what challenges conditions in the Baltic Sea may pose to offshore fish farming. Fish farmers have identified
the following product development challenges to offshore aquaculture:
1. Vessels must be safe and usable in harsh conditions.
2. Safety on board vessels and in handling the aquaculture structures under harsh conditions.
3. Cage technology. Cages must retain their shape and size and must be durable but lightweight in relation to their volume.
4. Cage handling operations and technological solutions. It should be possible to lift, install and clean cages under difficult conditions.
5. Technological solutions for monitoring, such as information transfer and energy production, must be further developed.
Keywords
Aquaculture, technology, offshore, Baltic Sea, spatial planning
Publications internet address
http://aquabestproject.eu/reports.aspx
Contact
Markus Kankainen, markus.kankainen@rktl.fi
Additional information
Contents
Description
4
1. Introduction
6
1.1. Definition of offshore aquaculture
6
1.2. Production conditions measurement and equipment standards
7
2. Offshore aquaculture technology
2.1. Cages, nets and mooring
2.1.1. Floating flexible cage systems
8
8
8
2.1.2. Floating rigid cage systems
10
2.1.3. Submerged and semisubmergable systems
11
2.1.4. Nets
14
2.1.5. Mooring
14
2.2. Feeding systems
15
2.3. Vessels and equipment
17
2.4. Environmental monitoring equipment, early warning systems and electricity
18
2.5. Project design and turnkey operations
19
3. Special characteristic of production conditions in Baltic Sea
19
3.1. Winter conditions
19
3.2. Waves and depth
20
3.3. Adaptation of production cycle
20
4. Competitiveness and challenges of offshore farming
21
4.1. Competitiviness
21
4.2. Challenges for research and development
21
References
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1.
Introduction
In the worldwide expansion of aquaculture, a key issue lies in locating suitable locations for farming.
Due to the eutrofication of the Baltic Sea, the nutrient load of aquaculture is controlled, in order to
avoid further environmental damage and diminish conflicts with other uses of the sea. Sectoral
interests and their impact on the environment are managed through spatial planning. Within Northern
Europe, maritime spatial planning has been the subject of several research and development projects,
such as
 COEXIST (www.coexistproject.eu)
 PartiSEApate (www.partiseapate.eu)
 BaltSeaPlan (www.baltseaplan.eu)
 SUBMARINER (www.submariner-project.eu)
 AQUAFIMA (www.aquafima.eu)
 Project “Coastal futures” at Alfred-Wegener Institute, Germany.
 AQUABEST (http://www.aquabestproject.eu/)
In the coastal areas of the Baltic Sea region, aquaculture spatial planning processes have already
been conducted in Denmark in 2002-2003 (Anon. 2003), and in Finland during 2010-2013 (Anon
2013). Lack of suitable space within traditional farming areas is also motivating Norway to look
towards more open sea areas (Karlsen 2012). A similar discussion on directing new aquaculture into
federal waters at open sea is currently ongoing in the USA and Australia, among many other
countries. As a final example in Europe, Turkey and Portugal have drawn up a maritime spatial plan
and allocated zones for mariculture, often leading to offshore sites (Deniz 2012).
In coastal regions, spatial planning often leads to the conclusion that the best new sites are
located in open or semi-open areas with harsh production conditions. It is apparent that, under such
conditions, conventional cage farming technology faces high risks of failure due to high wind speeds,
high wave heights and strong currents. In addition to tolerating high-energy and harsh conditions,
systems need to be cost-efficient, safe to work in and must suit the fish species in question, in order to
avoid fish welfare problems.
This brief review introduces the technologies that have been used in cage aquaculture farming in
open or semi-open water areas. We also discuss what challenges conditions in the Baltic Sea may
pose to offshore fish farming. Our two other, related reports present production conditions (wind, wave
and ice) in the Finnish coastal areas (Kankainen et al. 2013) and a case study of the cost-structure of
the investment and operational costs of fish farms located in semi-open conditions (Kankainen and
Mikaelsen, in prep.)
1.1. Definition of offshore aquaculture
Various definitions are applied to offshore aquaculture. Sometimes, conventional but robust cage
farming technology withstanding harsh wave conditions is termed offshore technology, such as in the
case of Ryan (2004). This definition is most often used in connection with activities such as salmon
farming in semi-open coastal areas. On the other hand, the term “offshore aquaculture” sometimes
refers to unconventional or even futuristic marine aquaculture or open ocean aquaculture techniques,
where such systems are quite different to mainstream commercial cage aquaculture. On these
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occasions, offshore aquaculture has mainly been piloted for farming valuable marine fish species such
as cobia and tuna.
In many cases, even distance forms part of the definition of offshore farming. Offshore technology
is used both far from the coast, such as around 40 km off the coast in the Bay of Mexico in the United
States, or in exposed and deep sites very close to the shoreline. In both cases, similar cage
technologies can be used, whereas high distances from the shoreline pose a variety of challenges to
logistical systems and have varied effects on operating costs.
1.2. Production conditions measurement and equipment standards
Because the risks and investments involved in offshore aquaculture are substantial, the conditions at
potential locations, such as currents, wave climate and seabed profile, are often assessed in advance
in the planning of investments and production methods.
Various regional studies are used in the selection of locations and tools for offshore fish farming
facilities. A Norwegian standard, NS 9415, is used in the classification of sea areas according to their
wave height and currents (Standards Norway 2008). This standard also includes recommended
technological solutions for conditions of various kinds. It is expected that the classification of sea areas
presented under this standard will be adopted beyond Norway. The highest classification, Ee, is for
areas where the momentary significant wave height exceeds 3 m and the water flow exceeds 1.5 m/s.
Significant wave height is the average height of the values among the top third results, based on a
series of measurements. The highest individual wave is usually around twice the significant wave
height.
Many manufacturers and quality systems classify fish farming equipment and mooring systems
similarly, according to the conditions for which they are designed. The technology selected for a
particular application must be able to withstand strong waves and/or water flows, but must also have a
safety margin for momentary extreme conditions. For instance, facilities farming Atlantic salmon in the
Faroe Islands are sited at locations where the significant wave height (over a measuring period of 3
hours) has varied from 3.4 m to 7.4 m in a 10-year period. The highest ever recorded significant wave
height in the Baltic Sea was almost 8 m, with the highest individual wave being 14 m high (northern
Baltic Sea, December 2004). There are unprotected areas in the Finnish outer archipelago, where
individual waves can attain a height of 10 m, with an average height of more than 3 m. Wind and wave
conditions on the Finnish coastal areas are presented in detail in Kankainen et al. (2013).
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2.
Offshore aquaculture technology
Adopting offshore aquaculture may require structural changes and new technology in all phases of
production prior to fish gutting. In this report, we discuss offshore aquaculture technology under the
following headings:
 Cages, nets and mooring
 Feeding systems
 Vessels and equipment
 Environmental monitoring equipment, early warning systems and electricity
2.1. Cages, nets and mooring
Equipment used for offshore aquaculture includes traditional floating cages and various semisubmerged or wholly submerged units. Cages may have flexible or rigid frames. The following is a
discussion of various offshore aquaculture solutions based on commercially available products. Some
have never progressed past the experimental stage, while others are used in thousands of facilities
around the world.
2.1.1. Floating flexible cage systems
The most familiar type of floating cage in offshore aquaculture is based on a circular frame made of
polyethylene tubing. This tubing is generally 200 to 300 mm in diameter, but 500 mm tubing is also
used (Figure 1). There may be one to three such tubes making up a frame. A narrow working platform
can be built on top of the load-bearing circular frame and the tubes can be filled with a floating filler.
Within the load-bearing frame and above the water, a floating structure supports the net, preventing
birds from accessing the cage and fish from leaping out. There may be a further circular frame
underwater, to prevent cage deformation. Underwater frames can also be used to hang sealproof
nets. Flexible cages are produced by manufacturers such as AKVA Group (PolarCirkel), Aqualine,
Fusion Marine, Corelsa, Refamed, AquaSURE and Ocea. Frame manufacture may also be
subcontracted out to local entrepreneurs.
In the Baltic Sea, the largest cages are 100 metres in circumference. In Atlantic salmon farming,
the new frames currently being installed have a circumference of at least 100 m in general. In the
Mediterranean, the most common cage frames have a circumference of 40 to 50 m, but cages with a
circumference of around 200 m are used for tuna farming. As cage depth in open sea areas is at least
20 m, such frames have a growth volume of more than 50,000 cu.m and yield a harvest of about 1,000
tonnes.
In open sea areas in the northern Baltic Sea, floating cages must be removed for the winter,
because their structures cannot be built to withstand the movement of thick ice floes. This restricts the
circumference of the frames, because the largest frames and cages are difficult to tow with the
available equipment. The sea does not freeze over in Norway, Chile or Scotland, so floating cages are
not necessarily removed for the winter in these areas.
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Figure 1. Circular PE-tube frame is the most widely used technology for cage farming at exposed sites. Companies such as
AKVA group, Aqualine, Corelsa, AquaSURE, Ocea, Refamed and Farmocean are producing or have been producing circular
cage frames. On the right hand side picture, the model from 90’s (Gigant) on the right, and next to that one modern tubing
for exposed sites made of 500 mm tubes. Pictures by AKVA group.
The Japanese manufacturer Bridgestone has produced frames suitable for offshore aquaculture from
the mid-1970s onwards. These are made of the rubber hoses used for transferring oil from tankers to
terminals (Figure 2). Rather than being circular, the frames usually have 4 to 8 corners. The largestknown frame of this kind had a circumference of 160 m and was shipped to Ireland. In some cases,
conventional PE frames have been installed within such frames, which then function as breakwaters
as well as aquaculture cages. There are at least 300 units in use worldwide, but their manufacture was
discontinued in the early 2000s. A similar technology is used in Dunlop Tempest frames (by Bonnar
Engineering Ltd from Ireland), introduced on the market around the year 1990.
Figure 2. Dunlop frames are based on rubber tubing used for oil pumping in oil terminals (Picture on left by Bonnar
Engineering Ltd.). Bridgestone has used similar technology (Picture on the right by Bridgestone).
Floating flexible cages can be built to withstand sea conditions with the highest rating, Ee, i.e. a
significant wave height of more than 3 m. There are plenty of size options available, and frames can
be installed in close proximity to one another, to form clusters that can be fed from a single feeder
platform, for instance. Under harsh conditions, the movement of the frames and the mooring system
cause wear and tear on the joints of the structure and the cage, and they thus need to be replaced
more frequently than in sheltered locations. Frames have been known to break in harsh conditions if
feeders are attached to the cages, because this prevents the strain of heavy seas from being
distributed evenly across the frame. Because the structures are rather lightweight, in heavy seas
maintenance must be carried out using a vessel that can be held steady, so that it does not damage
the frames.
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2.1.2. Floating rigid cage systems
Metal frames are used in some applications, particularly in sheltered locations. In such systems,
access bridges, which in some cases are large enough to support a forklift truck, are built between the
cages. Perhaps the best-known brand name in this area is Wavemaster (AKVA group), which has sold
more than 4,000 frames worldwide (Figure 3). The largest, 20 x 20 m frames have been used in rather
exposed locations; if rigid frames are used in offshore aquaculture, they must be remarkably robust
(Figures 4–5). For instance, the Scottish-made Cruive was developed jointly by shipping companies
and salmon farmers, but this facility is apparently prone to storm damage and ice accumulation.
Structures above the surface accumulate ice, which can considerably increase the weight of the unit.
Figure 3. Wavemaster is probably the most sold rigid cage system. Picture by AKVA group.
Figure 4. Farming systems by Spanish company Marina System Iberica. At least four systems like the one shown in the
picture have been built in the Mediterranean Sea. At the deck there are a feed storage, electricity generator and small cabin
for workers. The pillars reach appr. 10 m below the water surface. Picture by Marina Systems Iberica.
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Figure 5. First ever semi-submerged Farm Ocean was built in Sweden in 1986. Thereafter, at least 40 such units have been
used worldwide. Picture by Farmocean.
2.1.3. Submerged and semisubmergable systems
Submerged systems have become common in open sea areas. Submerging cages would enable the
avoidance of storm effects close to the water‟s surface. In addition, in certain marine areas toxic algae
blooms could be avoided by submerged systems. Various shapes and structures of submerged cages
types have been designed (Figures 6-11). Submerged cages require a system for raising and lowering
the structures into the water column during maintenance.
Submerged farms have not been installed as frequently as, say, surface flexible plastic rings, for
reasons such as high investment cost per volume, the relative impracticality of feeding and handling
the fish, and potential problems with fish welfare (Karlsen 2012). For example, Atlantic salmon do not
thrive throughout their ocean growth phase in systems where they are unable to reach the surface to
fill their air bladders. Fish also may suffer from pressure differencies or stress while lifting the
submerged system to the surface.
Submerged systems do have some benefits; for instance, the water temperature is steadier
deeper down, and the cages do not need to be cleaned as often as those on the surface. Moreover,
heavy seas do not stress the fish, which may improve their growth, mortality and feed efficiency. There
is the additional benefit of submerged systems not being visible within the seascape, which may make
them less controversial from the perspective of recreational activities.
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Figure 6. SeaStation farms by company Ocean Spar have no floating collar structures, but are based on wires attached to
mooring systems. Over 25 such systems are being used in e.g. Puerto Rico and Hawaiji. Pictures by Ocean Spar.
Figure 7. AquaSpar units by Ocean Spar are used e.g. in Canada and Spain. Pictures by Ocean Spar.
Figure 8. Refamed TLC (Tension Leg Cage) farms change shape and depth with currents. Picture Refamed TLC.
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Figure 9. Ocean Farm Technology is the manufacturer of Aquapod systems. It is composed of a rigid frame and a globe
shape net cage within the frame. The technology is being used at extreme offshore sites for e.g., cobia farming in Puerto
Rico and Panama, and for yellow tail farming in Hawaii. Pictures by Ocean Farm Technology.
Figure 10. A Russian SADCO system can be partly or completely submerged. They are currently used e.g. at Mediterranan
Sea, Caspian Sea and Black Sea. System includes technology for fish feeding and monitoring (pictures on the right). Pictures
by GosNIORH Leonid Bugrov.
Figure 11. PolarCirkel has in addition to regular frames a cage system that can be submerged. Picture by AKVA group.
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2.1.4. Nets
Nylon is the most common net material used in cage aquaculture. New materials include PET
(Polyethylene terephthalate) marketed as EcoNet by AKVA group (Johnson 2012), or Dyneema
marketed by DSM. Copper and stainless steel mesh solutions are also available. These have several
benefits; they offer more protection against storm damage and predators. They also enable the net to
maintain its shape better in heavy currents. This affects the maximum capacity of fish per cage, as
well as fish welfare. However, such materials are also more expensive, even if they have a longer
shelf-life. They also weigh more, which may further complicate the handling of large nets.
Net cage shape is maintained by separate weights, or by a heavy bottom ring/sinker tube.
Maintaining this shape is important, not only due to its effect on the net‟s capacity but also to
protection against seals, which push against the net wall in order to attack the fish inside. Chains
maintaining the sinker tube may abrade the net in heavy waves and should therefore be replaced by
other, strong material such as Dyneema ropes. In sum, small engineering and material selection
details become important in harsh conditions.
Fouling of the net increases its weight and decreases the water flow in and out of the cage. For this
reason, antifouling and/or frequent cleaning are important. Cleaning can be carried out using divers, or
by using specific remote controlled cleaners. If the entire cage system is towed close to the shoreline
in order to harvest fish, nets can eventually be removed and washed in special net washing drums.
When the fish are delivered for harvesting with wellboats, the nets can be removed for washing and
antifouling.
2.1.5. Mooring
The number of mooring points, the material chosen for anchors and lines and how they are attached
to the frame are important factors in structural durability. Large units are often moored using several
orthogonal moorings. In many cases, double anchors and more durable lines are installed in the
direction of the highest prevailing winds and water flows. Mooring lines and solutions require sufficient
flexibility to ensure that even large movements of the net structures do not fully stretch the lines and
thereby generate a full load (Karlsen 2012). A dense network of mooring lines and buoys makes it
difficult for the maintenance vessel to manoeuvre around the facility. Manufacturers of large
aquaculture cages offer expert services for mooring planning. Anchorage design depends on the
quality of the seabed: in fine sediment, fluke anchors are usually used, since traction embeds them in
the seabed. If the seabed is rocky, screw anchors may be drilled into the rock. In particularly deep
water, a single-anchor anchorage is sometimes used, with several aquaculture units attached to a
single main mooring line.
In Finland, water depth is not as much of an issue as in many other offshore aquaculture
locations, where the depth may be more than 100 m. Partly for this reason, there is a tendency to
locate units in the immediate vicinity of islands, so that in some cases they can even be anchored to
the shore.
One option for assisting in mooring and protecting from waves would involve integrating fage
farming with wind farms or oil platforms. In such cases, specific consideration would need to be given
to structures, including mooring, together with the other functions and structures (Buck 2013).
In addition to stable stations with mooring, drifting or even self-propelled farms have been
suggested and developed for open ocean conditions.
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2.2. Feeding systems
Fish may be fed using automated feeders, either unsupervised or with someone supervising the
process at the cages. During the growing season, it is preferable to feed the fish on a daily basis, or
even several times a day, in order to maximise growth. Exceptions to this are periods in which the
weather is particularly warm or cold and the fasting periods before the fish are transferred, gutted or
subjected to other stressful handling. In offshore aquaculture, circumstances may limit the use of
various automation systems and feeders. On the other hand, circumstances may also hamper or make
it impossible to visit the cages every day.
The feeder types currently in use in Finland would not necessarily withstand the heavy seas
involved in offshore aquaculture. For example, traditional pendulum feeders are unsuitable for offshore
conditions due to instability and possible overfeeding in strong waves. Another type of traditional
feeder, which is attached to the cage collar, is questionable due to the strong forces placed on the
cage collar structures.
Feed barges have become common in feeder systems in offshore fish farming facilities. Their
capacity may be anything up to hundreds of tonnes (Figure 12). Feed barges are generally placed
beside the cages, or in the middle of a cage cluster. The feed is propelled through pipes by
pressurised air fed from the barge to the cages. The largest barges have a control room and staff
facilities for employees. Feed barges are generally unpowered; they need to be towed to the location
and anchored. They can be refilled directly from feed producers‟ cargo ships. The largest feed barges,
which can be found in Norway, are designed to withstand waves up to 7 m high. Thus, these systems
do not appear to tolerate as harsh conditions as the most robust regular cages.
Feeder platforms, particularly cage-specific feed transfer pipes, may be damaged or compromised
by harsh conditions. In open-sea areas, it is common for fish to be fed from a boat. In such cases,
personnel visit the cages whenever circumstances allow. Although boat feeding reduces the risk of
storm damage and avoids major investments in feeder platforms, it is not necessarily the most efficient
approach. Every unit has to be fed separately, and the feeding does not occur automatically. Since the
distance from feed storage to the aquaculture facility may be long, the feeding process takes a great
deal of time and fuel (Kankainen & Mikaelsen 2013). Feed efficiency may also be lower than with
automated, continuous feeding, because the fish are fed less often, and in many cases to the point of
satiety. Fish growth may be compromised if the fish are not fed every day.
A submerged aquaculture facility must be raised to the surface for feeding from a boat, unless
there is a system in place for underwater feeding. Using underwater feeding pipes from a feeder
platform is a possible solution for avoiding feed pipe damage on the surface. The challenge in
underwater feeding lies in distributing the feed evenly, so that all fish are fed sufficiently. It is also
more difficult to monitor the fish.
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Figure 12. Feed barges have become more common in cage farming. Barges by AKVA group may have capacity between
100 to 700 tons of feed. (Top left). On the bottom left, feed barge in Turkey, snd on the right in Norway. Alhaalla,
vasemmalla ruokintalauttoja Turkkista, oikealla Norjasta, Pictures on top by AKVA group, on bottom by M. Kankainen
FGFRI.
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2.3. Vessels and equipment
Work vessels are needed for day-to-day management of fish farming units: transporting feed and fish,
and handling the cages, nets, buoys and anchors. It is becoming common to use vessels 10 to 20 m
long, fitted with cranes for lifting nets and feed bags (Figure 13). These have a carrying capacity of a
few dozen tonnes. Depending on their size, speed and fittings, seaworthy vessels of this kind cost an
estimated EUR 0.5 to 2 million. However, it has been questioned whether the work vessels currently in
use would be useful or safe in open-sea areas. A maintenance vessel for a major salmon farming
facility near the open sea may be 40 m long and have a carrying capacity of up to 100 tonnes (Figure
14). Investments in vessels may easily be many times higher than investments in all other production
equipment (Project „Service Vessel 2010‟, Heide et al. 2012). Smaller seaworthy service boats are
usually used for briefer inspections.
Sometimes, it is cost-effective to feed the fish directly from a vessel. In such cases, feed tanks
and a feeding system are usually installed in the vessels themselves, and the feed is blown out to the
fish. Boat feeding is used at locations where feeders cannot be attached to the cages, because they
cannot withstand the conditions in question. Boat feeding may also be sensible if the units are small
and investing in a feeding system in situ would not be cost-effective. The drawback of boat feeding is
that only one or two visits can be made per day, and bad weather may prevent visits altogether. Boat
feeding also takes up a great deal of working time.
Various specialised vessels can be used in addition to work vessels. For instance, if large feeder
platforms are used, it may make sense to have the feed delivered in large quantities, by feed vessels,
directly from the feed plant. This would make the related logistics more efficient, as it would not be
necessary to transport the feed in small batches on work vessels. Also, on-shore feed storage would
not necessarily be needed if the feed were delivered directly from the plant. Such a delivery service
would probably best be outsourced, unless the aquaculture enterprise were very large.
Fish can be transported for processing in vessels that are fitted out with tanks and pumps for fish
transport, or in well boats. Another option is to use work vessels to tow the cages and frames to the
shore as they are and extract the fish for gutting there. There are specialised vessels for using various
devices, such as cage-cleaning robots.
The vessels and equipment required by any particular enterprise depends on what action needs
to be taken regarding the fish and the aquaculture facility during growing. It is basically unnecessary to
obtain new equipment for tasks such as the removal of dead fish or the transfer or sorting of fish in
offshore conditions, but heavy seas, the size of the cages, the structure of the frames and the feeding
methods chosen do have an impact on the choice of equipment and tools.
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Figure 13. 20 ton catamaran boats are often used for various daily routines at Norwegian salmon cage farms. Cranes are
used to lift feed bags and nets. Feeding systems can also be installed on such working boats. Figures by AKVA group.
Figure 14. Remote farms at exposed sites may be maintained by up to 40 m long vessels. Picture by Aceaquaculture.
2.4. Environmental monitoring equipment, early warning systems
and electricity
In offshore aquaculture, because it is not always possible or feasible to visit the cages daily,
monitoring and measurements are carried out automatically and remotely, for instance at an on-shore
control unit. Feed control requires real-time information on fish behaviour, the water temperature and
water oxygen levels. Systems for monitoring these comprise well-established technology at modern
aquaculture facilities. Feeder control systems are available that monitor the appetites of fish. These
systems observe whether any feed is being left uneaten: if so, they discontinue feeding. Cage
monitoring or observing fish activity using cameras reduces risks and may even improve the feed
efficiency of fish. Information can be wirelessly transferred to the control room, if the distance is not too
great. In the case of cages that are distant from the control room, relay stations may be needed for
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information transfer. Solar panels or wind turbines are sufficient for minor power needs, but generators
are needed to provide electricity for feeder platforms.
2.5. Project design and turnkey operations
Major manufacturers provide a range of products that covers all needs associated with cage
aquaculture, including frames, cages, anchors, mooring lines, feeder systems, metering, monitoring
and even the work vessels required. Most manufacturers also provide services such as location
assessment, to assist in the selection of technology. In challenging conditions, all technological
components must integrate seamlessly and be suitable for the routines of the aquaculture operation.
In addition, consultant enterprises in the sector conduct wave and cage movement modelling based
on data from the facility location (e.g. the Riflex modelling used by Det Norske Veritas).
3.
Special characteristic of production conditions
in Baltic Sea
3.1. Winter conditions
In the Baltic Sea, winter conditions pose challenges to offshore aquaculture technology (Kankainen et
al. 2013). Ice cover, the thawing season and pack ice must be taken into account in equipment and
production cycle design. At cage aquaculture facilities in the northern Baltic Sea, the cages must be
brought in, from open-sea locations to sheltered locations, for the winter so that the structures are not
damaged by moving ice masses. If there are fish in the cages, the wintering locations should be
chosen in such way that the cages can be monitored. During the thaw season, maintenance of the
cages and fish is difficult if the units are not directly adjacent to the shore. Vessels that can cope with
thin ice in early winter and ice floes in late winter are needed to cope with the thaw season. If the ice
cover is strong enough in the winter, monitoring can be performed using motor vehicles such as
snowmobiles, hydrocopters or quad bikes.
In the autumn, pack ice can break or tear loose even robust structures, down to a depth of several
metres. The durability of feeder platforms used in offshore aquaculture has probably not been tested
in conditions where pack ice is formed or large ice masses move around, even if they are known to
withstand some degree of freezing. One option proposed for protecting cages or structures against ice
in open-sea areas involves submerging the structures beneath the reach of the ice cover. However, it
is risky to leave structures unattended for the winter or the thaw season, and leaving fish without daily
monitoring is against animal welfare regulations.
Empty aquaculture structures can be left in situ if the water is deep enough for this purpose.
However, pack ice can build up to a depth of several metres. The benefit of submerging empty cages
is dubious, particularly if the cages are also used for transferring the fish. So far, aquaculture
entrepreneurs have found sheltered locations for unit storage next to islands, where pack ice does not
form and ice masses do not move around. In the winter, these units do not conflict with other uses of
water areas in the inner archipelago to the same extent as in the summer, because there is no nutrient
load and fewer people spend their leisure time in the archipelago.
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In the spring, the ice melts faster in open-sea areas in the Baltic Sea than near the shoreline.
However, because deeper and larger waters warm more slowly than the waters of the inner
archipelago, the best growing season offshore begins later than closer to shore. Similarly, in the
autumn offshore aquaculture facilities must be removed earlier than those closer to shore, in order to
avoid the risks posed by the thaw season and storms. However, the growth season is not necessarily
any shorter, because the rise in water temperature in midsummer is rarely too great.
3.2. Waves and depth
When selecting the appropriate technology, other wave climate characteristics may be just as
important as wave height. In the Baltic Sea, wave lengths are shorter and the waves are sharper than
in the oceans (Kankainen et al. 2013). Because the wave length is short, aquaculture cages do not
ride the waves; the waves thus stress the structures in a different way. For instance, a cage with a
circumference of 100 m has a diameter of 32 m and a typical depth of 10 to 20 m. In heavy seas, the
waves wash over the cages, and the frames can „hang‟ on the waves.
The principal advantage of submerged facilities is protection against heavy seas. However, such
facilities require a water depth of at least 20 to 30 m, so that the structures can be submerged deeply
enough. Areas with water of such depth are rare in Finnish archipelagos. On the other hand, the
relative shallowness of the Baltic Sea makes it easier to moor aquaculture facilities.
3.3. Adaptation of production cycle
Not all production phases can be located in the open sea (Kankainen et al. 2013). Nursery facilities
are not located in the open sea, because juveniles and the required production technology are more
vulnerable to harsh conditions. For instance, cages made of nets with a denser mesh tend to deform
in areas where the water flow is strong. Because juveniles are more susceptible to stress, they should
be grown where they can be monitored continuously. There must therefore be sufficient brooding
facilities on shore or inland, from which the fish are then moved to offshore facilities. Similarly, winter
storage locations and storage facilities for fish ready for gutting must be close to shore, so that fresh
fish can be continuously brought to market, especially during the thaw season.
A production cycle has been proposed for offshore rainbow trout farming, where the juveniles
would be grown at existing facilities in the inner or intermediate archipelago, or on shore to such a size
that they can attain the market size for a traditional large rainbow trout within one growing season,
when transferred to an offshore facility. If the production cycle for processing-ready fish were to be
delayed by one growing season, more winter storage locations would be needed and the risks and
production costs would considerably increase. In addition, lengthening of the production cycle would
increase risks such as mortality. In Baltic Sea conditions, the ability to leverage the entire growing
season would therefore be important. Installations of offshore aquaculture facilities and the transfer to
them of fish should be performed quickly in the spring as the growing season begins, and it should be
possible to remove and store the units quickly before winter, so that none of the relatively short
growing season is lost.
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Offshore fish farming technology in Baltic Sea conditions
4.
Competitiveness and challenges of offshore
farming
4.1. Competitiviness
When adopting offshore farming, many factors affecting production competitiveness change.
Investments and logistics costs increase, as production is moved further out to sea and into more
challenging conditions. Production equipment such as cages, feeders and vessels that can withstand
open-sea conditions are more expensive than equipment suitable for inner-archipelago locations
(Kankainen & Mikaelsen in prep.). When maintenance distances are longer, fuel costs rise and more
working time is spent. Also, the length of the growing season, the water temperature, the weather at
the location and the organisation of feeding may contribute in various ways to the growth rate,
mortality or feed efficiency of fish.
Whether a new technology is productised depends on whether the investments required will yield
a competitive advantage compared to conventional production technology. Because offshore farming
technology requires more investments, a competitive advantage has been sought by increasing the
size of production facilities. In Atlantic salmon production, facilities for farming millions of kg of fish –
which have many of the features of offshore farming technology (dozens of km from the shore, robust
PE frames) – are economically competitive. In the largest salmon-producing countries, Chile and
Norway, no fish farming facilities have so far been located in completely open sea, being instead
located where some protection is afforded from islands or fjords. These more sheltered locations have
enabled the use of traditional aquaculture technologies, albeit in more robust versions, and production
has become more efficient as unit sizes have been increased (Asche et al. 2013). It would appear that
submerged solutions are not competitive, compared to other technologies, in the farming of salmonoid
fish, judging by the fact that no investments in such solutions have been made in the major producer
countries, even though they have been tested there. Submerged systems have so far only been used
in wide open sea areas and in relation to the more valuable fish species.
Because the major production species in the Baltic Sea, the rainbow trout, competes in the same
market as Atlantic salmon farmed in Norway and Chile, the average size of facilities in the Baltic Sea
should be increased substantially to improve competitiveness. Production should thus be principally
relocated to the edges of the open sea, in areas partly protected by islands, so that conventional
technology and the existing enterprise infrastructure can be used in these offshore facilities.
4.2. Challenges for research and development
It has been postulated that offshore aquaculture represents the only way of responding to increased
needs for protein and increased demand for fish (FAO). There is plenty of room in the world‟s seas for
production facilities, since most of the Earth‟s water surface area is not used in any way. In fish
farming as much as in other forms of animal production, in the search for production growth it has
become necessary to take account of sustainable development factors: the wellbeing of fish,
environmental factors, the safety of employees, and economy (Willumsen 2012). In product
development supporting offshore farming, solutions must be found to the challenges posed by these
factors, so that production can grow sustainably.
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Several worldwide challenges have been acknowledged in terms of the proliferation of offshore
aquaculture. The fish cannot be observed in situ full time, in order to ensure their wellbeing. A long
distance from the shore and local weather conditions may mean that a facility cannot be accessed
quickly, or at all if the weather is bad. Long distances would also complicate the information and
energy transfer needed to improve fish monitoring, reduce environmental impacts and render
production more efficient. Distances would also affect maintenance operations and their costs.
Challenging conditions would have an impact on occupational safety and investment costs.
Environmental impacts would have to be assessed and production equipment designed so as not to
jeopardise the ecosystem of the growth environment. All of these challenges would have to be met in
such a way that offshore aquaculture became sufficiently profitable to attract investment by
entrepreneurs (Willumsen 2012).
Fish farmers have identified the following product development challenges to offshore aquaculture
(Willumsen 2012):
1. Vessels must be safe and usable in harsh conditions. Transfers must be swift, and the
vessels must be equipped with technological solutions facilitating aquaculture operations
and have sufficient carrying capacity.
2. Safety on board vessels and in handling the aquaculture structures under harsh
conditions.
3. Cage technology. Cages must retain their shape and size and must be durable but
lightweight in relation to their volume. The cages should also protect the fish against
predators, particularly seals.
4. Cage handling operations and technological solutions. It should be possible to lift, install
and clean cages under difficult conditions.
5. Technological solutions for monitoring, such as information transfer and energy
production, must be further developed.
Offshore facilities in the Baltic Sea should be large enough to be cost-effective, but on the other
hand must not generate excessive local nutrient loads. Such facilities will most probably have to be
removed to the safety of the shore for the winter. Installation of facilities in the spring and their removal
in the autumn should be well planned, rapid and practical. For unprotected offshore locations, an
estimate should be made of the amount of stress placed on the facilities by the shorter wave length in
the Baltic Sea. In deep water where particularly heavy seas are likely, semi-submerged systems may
be feasible.
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