Open systems
 Open
system farming is the term used to describe the process of farming fish (including
shellfish and seaweeds) in cages or pens that are open to the sea. These comprise
nets suspended from either a floating metal framework or from round plastic
floating structures, both of which are anchored to the seabed. It is important
that the nets are kept free from debris and accumulation of marine life to
allow seawater to flow through to maintain water quality within the cage.
All waste generated by fish in the cage falls through the bottom of the net
to be deposited on the seabed underneath or around the cage. This waste can
build up in areas with poor or low water flushing. Being open to the surrounding
water means that the fish can potentially be infected with and/or transmit
water bourne disease and sea lice infestations to/from wild stocks.
Open sea cage farming happens almost exclusively in the west coast of Scotland
and the Scottish Islands due to their good water quality and coastline topography,
which provides numerous sheltered sea-lochs and voes.
Closed systems
Closed system farming is the term used to describe farming finfish, shellfish
or seaweed in enclosed systems not open to any water body. There are a number
of methods that can be used: enclosed ponds, tanks or raceways. Within these
closed systems water can be obtained and treated in either of two ways: 1.
Pumped from a nearby water source such as a river or the sea, filtered, used
in the system, filtered and treated to remove any waste or contaminants and
then pumped back or 2. As above but where the water is not pumped back to
the source but remains in the system using re-circulation technology. The
latter (2) relies on the water within the system being constantly passed through
filters to remove waste matter and the water being continually reoxygenated.
Fully enclosed or recirculating system farming has the advantage of being
land based and not having to be in close proximity to the sea. The waste from
the farm is totally contained and there is no risk of predation or fish and
parasites escaping into the wild.
Sea ranching
Sea ranching is the process of releasing artificially raised juvenile fish
or shellfish into the sea, allowing them to mature to market size and then
recapturing them. This is not a common practice in the UK because other EU
countries have historical fishing rights in our waters from 6nm out, however
lobster restocking programmes have taken place within 6nm. Further information
on a manmade lobster hatchery programme at Loch Linnhe in Scotland can be
seen at http://www.sams.ac.uk/schools/artreef.pdf
Tuna ranching
Tuna ranching involves catching juvenile tuna from the wild and growing them
on in cages. This is particularly aimed at the commercially valuable but severely
depleted bluefin tuna, which is highly prized for the sushi market. Predominantly
juvenile fish, that have not had a chance to reproduce, are caught in nets
and towed slowly through the sea to nearshore waters where they are transferred
to netpens or cages for on-growing. Here they are fed on large amounts of
small pelagic fish such as sardines and anchovies, taking as much as 20 kg
of wild fish to produce 1kg of tuna. After several months, when the tuna have
reached optimal market size, they are harvested and sold primarily for the
sushi and sashimi markets. Tuna ranching is based primarily in Australia,
Spain and Croatia.
Salmon
Commercial salmon farming began in the 1970s although the ability to raise
juvenile salmon in hatcheries was achieved in the 1800s. The salmon farming
industry rapidly expanded during the 1980s and 1990s and today Atlantic salmon
is the most commonly farmed species in the UK, with approximately 70 companies
producing over 140,000 tonnes of farmed salmon each year, 90% of which is
in Scotland.
Juvenile salmon are grown in hatcheries from eggs produced by broodstock,
when the eggs hatch the young fish are called alevins until they discard their
yolk sac when they are termed fry. Fry are grown in freshwater tanks, where
they undergo a series of size sortings called gradings, a process to ensure
that fish of a similar size are kept together. They remain in these tanks
until they undergo a process called smoltification, a physiological process
that enables the fish to live in seawater, which normally occurs when they
are 12-18 months old. After smoltification the fish are termed smolts. Once
transferred to sea cages the salmon take between 18 months and 2 years to
reach harvestable size of 3-4kg.
Other farmed species
Other finfish species currently farmed in the UK are rainbow trout, sea trout,
Atlantic halibut, Atlantic cod and turbot. The trout species are farmed in
closed systems such as raceways, whilst the halibut and turbot are raised
in enclosed tanks containing seawater. Cod is a new species for cultivation,
currently farmed in Scotland and Norway in a manner similar to salmon using
open sea cages. Unlike salmon, cod do not go through a smoltification process.
Future farmed species
There are a number of alternative species that can possibly be farmed in
the UK, some of which are being trialed at present. These include: Arctic
Charr; haddock; Senegal, Dover and lemon sole; turbot; spotted wolfish (prized
not only for their flesh but also for their skin which is made into leather);
sea bass and gilthead sea bream both of which are currently farmed extensively
in the Mediterranean) and three freshwater species: barramundi; pangasius
and Tilapia.
Fish feed
Different species of farmed finfish require different diets. Some species
such as Tilapia can be fed on an entirely vegetarian diet, whilst the majority
of UK farmed species are fed a carnivorous diet. The feed for carnivorous
fish comprises fishmeal and fish oil derived from wild caught species of small
pelagic fish predominantly anchovy, jack mackerel, blue whiting, capelin,
sandeel and Medhaden. These pelagic fish are processed into fishmeal and fish
oil, with the final product being a pelleted (for larger fish) or flaked (for
juveniles) feed. The other components of the feed pellet are vegetable protein,
vitamins, minerals and pigment as required.
It takes on average 3kg of wild caught feed grade fish to produce 1kg of
salmon, and 12kg of fish to produce 1kg of fish oil. Although these figures
represent a significant improvement in feeding technology over recent years,
the fact remains that farming carnivorous fish relies on wild capture fisheries,
and removing a large number of smaller species of fish from the food chain
can have adverse ecosystem affects.
Organic requirements for feed composition differs in that it currently uses
offal and trimmings from the fish filleting industry as the main ingredient.
Ultimately, organic feed will be sourced from offal and trimmings from certified
sustainable fisheries, but as yet no such feed-grade fisheries have been certified
as sustainable. Using offal addresses one of the key sustainability issues
of farming carnivorous fish by using the waste product of another fishery,
which would otherwise be discarded, rather than relying on large quantities
of wild caught fish.
Environmental impacts
In addition to the dependence on wild capture fisheries to supply fish feed
there are a number of other environmental impacts associated with fish farming
such as:
Benthic impacts affecting the seabed beneath the cages
in open systems. As the cages are open to the sea all faeces and uneaten
food falls through the cage bottom to be deposited on the sea floor. In
some areas, such as those with poor water flushing, low water exchange or
shallow depth this organic build-up can prevent oxygen from reaching the
underlying sediments and eventually lead to the formation of bacterial mats.
Benthic impacts can be minimised by siting the farm in highly flushed areas
and limiting the biomass and stocking density of the fish to avoid excessive
waste.
Diseases can occur amongst farmed fish which are kept
in much higher stocking densities than would naturally occur in the wild.
Disease and parasites can be easily transferred between individuals due
to their close proximity. Many diseases are now largely (but not entirely)
prevented by the use of effective vaccines and strict regulations. Controls
and Codes of Practice are in place to prevent spread of any disease outbreaks.
Sea lice is a term used to describe many species of ectoparasitic
copepods. These are small parasites, naturally occurring in the sea, that
attach themselves to salmon and trout and feed on their host’s mucus,
skin and blood. If excessive infestation occurs then death can result. Choosing
the best site for fish farms can play a significant part in determining
the sea lice burden and spread of these parasites. When infested, however,
the fish need to be treated either by direct (bath) or indirect (in-feed)
application of sea lice treatments. Unfortunately, a number of sea lice
treatments are either toxic for some marine life such as crustaceans or
their effect on many other marine organisms is unknown. The use of sea lice
treatments is regulated by the Scottish Environment Protection Agency.
Escapes from open sea cages cause problems for wild fish
populations, in particular salmon. Farmed fish can escape for a number of
reasons: pens can be torn open or damaged by storms; accidents and poor
management can lead to escapes and predators can also damage nets allowing
fish to escape. The main concern regarding escaped farmed fish is their
interaction with the threatened wild populations of Atlantic salmon.
Farmed species of Atlantic salmon are genetically different from their wild
counterparts: they are genetically selected to have farm-adapted suitability
and as a consequence only come from a limited genetic stock. Wild salmon
by comparison have a much larger gene pool. Each wild population is genetically
adapted to its specific environment and has an inherent homing instinct,
which allows them to return to their natal river to spawn.
Escaped farmed salmon can inter-breed with their wild counterparts leading
to genetic dilution of the wild stock, leading in turn to the probability
of the hybrid fish not having the genetic adaptations to survive in the
wild, resulting in the decline of future population resilience, numbers
and further loss of genetic variation.
Best environmental practice
Best environmental practice, is what MCS would like to see adopted by all
fish farmers, regardless of species farmed or the size of company. MCS guidelines
for best environmental practice can be summarised as follows:
Siting of fish farms– most of the adverse environmental
impacts of fish farms can be addressed by siting the farms in the most appropriate
areas. Sites should be in areas of high flushing, deep water, away from
any wild salmon runs or predator hot spots such as seal haul out sites,
away from any areas containing vulnerable or protected marine species and
habitats (e.g. maerl), in areas with historically no/low sea lice levels
and sited in such a way as to minimise visual impacts.
Feed – all feed should ideally be manufactured sourced
from offal and trimmings from certified sustainable, effectively managed
fisheries that have full traceability back to source. Until such feed is
available, feed should be manufactured from filleting waste (offal and trimmings)from
sustainable human consumption fisheries, supplemented by certified sustainable
feed fisheries ensuring a supply where impact on the wider marine ecosystem
is minimised; increased substitution of marine proteins with vegetable alternatives;
and best practice in terms of feed wastage minimisation.
Pollution effects – farms should keep chemical use
to a minimum by not using any treatments (such as antifoulants which are
mainly copper based and toxic to marine life) where there is a tested non-chemical
alternative (such as non-chemical net cleaning), recognising that the environmental
effects of many treatments are unknown. Sea lice treatments are also a source
of localised marine pollution and are toxic to some other marine organisms
such as crustacea. However, as sea lice infestation is a welfare issue for
the farmed salmon and can be transmitted to wild salmon stocks the need
to use such treatments exists. MCS position on the use such treatments is
that they should only be used if welfare is compromised or as part of a
strategic management plan in conjunction with other farms. Some farms, due
to their location, never have a sea lice infestation and MCS would like
to see further research into why this is the case as well as supporting
the research and development of an effective sea lice vaccine. Effective
feeding systems that monitor and reduce uneaten feed should be used and
litter should be recycled wherever possible
Escapes – all cages should be suitable for the environment
they are used in (such as in high energy areas), they should be inspected
regularly and repaired as soon as damage is noted. All staff on the farms
should be trained to handle the fish in the most efficient and effective
way to prevent escapes. All escapes should be promptly reported and a contingency
plan implemented as soon as possible after the escape event to recapture
fish and thus minimise the effects on wild populations.
Welfare – high welfare standards should be maintained,
such as those set out by the RSPCA Freedom Food scheme. Fish farms should
have effective, humane predator control measures in place not only to reduce
stress to the fish but to ensure the nets do not become damaged by predators,
leading to fish escapes.
Effective management – fish farms should be effectively
managed including environmental aspects and monitoring as part of the process.
Farms should monitor and work to improve their environmental performance.
Organic farmed fish
Organic farmed fish –where farming practices meet
high environmental standards, including limits and restrictions on the use
of medicines, chemicals and sea lice treatments. Feed is sourced sustainably
and stocking densities are limited.
Freedom Food Certification
Freedom Food Certification- is the RSPCA scheme to ensure
high welfare standards are implemented and maintained for farmed animals.
A set of standards have been developed for farmed salmon that are based around
the scheme’s five principles, namely, freedom to express normal behaviour
and freedom from: fear and distress; hunger and thirst; discomfort and; pain,
injury and disease.
Offshore aquaculture
Offshore aquaculture (open ocean aquaculture)
Offshore aquaculture is the farming of any species in the sea away from the
coast. It has been defined in the US as occurring “ from the three mile
territorial limit of the coast to two hundred miles offshore”, in Europe
it is generally accepted to mean sites that are subject to ocean waves. The
fish farming industry is looking to move further offshore in the future as competition
for coastal space increases. Although moving into deeper water has a number
of environmental benefits such as increased dilution and little or no seabed
effects, it also has a unique set of challenges such as ensuring cages are sufficiently
robust to withstand the high energy environment.
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