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					           ROPE-GROWN MUSSEL CULTIVATION                                                                                                  ROPE-GROWN MUSSEL CULTIVATION

             General advice                                                                                                                Further advice
                                                                                                                                                                                            ROPE-GROWN MUSSEL CULTIVATION
                                                                             Generally, avoid areas close to boatyards, marinas,            For further advice on any aspect of
              Draw up a business plan and consult independent
                                                                                                                                          rope-grown mussel cultivation please
           financial advisors.                                             industrial developments or large urban areas.                  contact the aquaculture advisor for
                                                                           This minimises the risks from pollutants or other              your area.

              Identify your market(s) at the outset.                       anthropogenic inputs. Potential inputs from within the         They are:

                                                                           wider water catchment area (eg land-based farming              England and Wales

              How likely are you to receive planning permission            activity, both arable and livestock, forestry, horticulture,   Martin Syvret
                                                                                                                                          Tel: 07876 035746
           from the competent agency (eg Local Council, Crown              chemical industry etc) should be investigated.                 E-mail:           This leaflet is intended to offer a summary of the methods used to
           Estate)? Consult local aquaculture development plans,                                                                                                                   cultivate rope-grown mussels in the UK. More detailed information
                                                                                                                                          Scotland and Northern Ireland
           where they exist, and speak to the staff involved in              Evaluate the potential risk (disease, nutrient input,
                                                                                                                                                                                   about specific aspects of the business may be found in Seafish
                                                                                                                                          Craig Burton
                                                                                                                                                                                   publications, technical publications from other agencies and
           granting licenses.                                              therapeutant use, predator displacement, controls on           Tel: 07876 035771
                                                                                                                                                                                   books. Prospective cultivators are advised to
                                                                           stock movement/sales following from disease events on                                                   consult these in addition to this sheet.
              Is the local infrastructure (roads, piers etc) adequate to   other sites etc) from other marine aquaculture activity in     Alternatively, please visit our          Preliminary business planning assistance can be
                                                                                                                                          website at           found in the associated Seafish economic model
           support your proposal, or will you have to construct them?      the vicinity.                                                  for more information. The website        and ‘Hyperbook’ publications.
                                                                                                                                          also contains details of the CD-
                                                                                                                                          ROM based resources produced
              Can a Crown Estate lease be secured? Consult them.             How secure is the site? What is the risk from                by Seafish. There is a specific
                                                                           interference or other unwanted human activity? Can the         Hyperbook, which combines in-depth
              What conservation value/interest does the site                                                                              information regarding the culture
                                                                           site be secured if required?
                                                                                                                                          of this species together with an
           have? What about the surrounding area? Consult                                                                                 economic modelling tool for business
           the nature conservation agencies, statutory (English                                                                           planning purposes. In addition,
                                                                             Try and establish whether the area has a shellfish
                                                                                                                                          there is a more general Guide to
           Nature, Countryside Council for Wales, Scottish Natural         cultivation or harvesting waters classification from the       commercial bivalve molluscs with
           Heritage, Environment and Heritage (Northern Ireland)           local Environmental Health office or equivalent.               information on aspects of cultivation,
                                                                                                                                          harvesting, the fishery, depuration
           and voluntary, for the area.                                                                                                                                                                                                                 Rope-grown mussels
                                                                                                                                          and distribution for all species.
                                                                             Try and establish whether the site has a history of
              Is there likely to be any hazard to navigation or            algal biotoxin (PSP, DSP, ASP etc) accumulation or
           transport? Consult the Maritime & Coastguard Agency             harmful algal blooms (‘red tides’), although past track
           and the Department of Transport.                                record is a poor predictor of future performance.

              Are local inhabitants or other user groups of the                                                                           Sea Fish Industry Authority
                                                                             What potential predators, competitors or fouling
                                                                                                                                          Seafish House
           marine environment likely to object? Can objections             organisms are likely to be encountered?                        St Andrew’s Dock
           be overcome through dialogue or design modifications?                                                                          Hull
                                                                                                                                          HU3 4QE
           Consult them early on.                                            Once the business is operational, the site must              Tel: 01482 327837
                                                                           be registered. Consult the Centre for Environment,             Fax: 01482 223310
              Does the proposition require grant aid or other              Fisheries and Aquaculture Sciences (CEFAS), Scottish
           assistance and how likely is it to be awarded? Consult          Executive Environment and Rural Affairs Department
           the agencies administering grant and other business             (SEERAD) or Department for Agriculture and Rural
           assistance in the area from the start.                          Development (DARD) in Northern Ireland as appropriate.

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             Site selection                              Cultivation techniques                                                                                                                                                                          Harvest                                                               Markets

             Seawater temperatures above                  Rope-grown mussels are usually grown on ropes                                                                                                                                                    Depending upon the location          Mussel declumping, washing       Rope-grown mussels may be retailed
           8 – 9ºC for much of the year are             suspended from either surface longlines or rafts.                                                                                                                                               and size at harvest, the first ‘crop’   and grading line              direct from the grower or via a wholesaler.
           preferable for fastest growth.                                                                                                                                                                                                               of rope-grown mussels can be
                                                           A typical longline in the UK would consist of either a                                                                                                                                                                                                                The markets, both home and export,
                                                                                                                                                                                                                                                        obtained in between 2 – 3 years.                                      for rope-grown mussels are strong and
              Salinity generally above 20 ‰.            single or double headrope supported by grey plastic floats
                                                        at regular intervals. The line is anchored to the seabed or                                                                                                                                                                                                           premium prices are commanded in the
                                                                                                                                                                                                                                                          Depending on the size of the                                        market place.
              Shelter from extreme wave action          shore at either end. The specification of the anchor system                                                                                                                                     business, harvesting may be by
           or strong tidal flows is preferable.         is tailored to the local conditions. The length of the line can                                                                                                                                 hand or fully automated.                                                 Individual
                                                        be varied to suit the location, but it is generally between 200                                                                                                                                                                                                       growers or
             Tidal flow of 1 – 2 knots (50 - 100        – 400 m. The spacing of the plastic floats (buoys) depends                                                                                                                                         Each dropper is raised from the                                    wholesale
           cm sec -1) is acceptable, although           upon their buoyancy and the expected load upon the line.                                                                                                                                        water and the mussels removed                                         co-operatives
                                                                                                                           Mussel seed on dropper ropes                                    Mussel dropper lines underwater
           less is also acceptable.                     Generally, they are spaced at up to 3 m apart. Rope of                                                                                                                                          either by hand or by machine.                                         are developing
                                                        between 20 – 32 mm diameter is commonly used for the                                                                                                                                                                                                                  processed or
              Water depths in excess of 12 m            headlines. The separation between longlines is largely                                                                                                                                            They may then be transferred to                                     value-added
                                                                                                                            The spat settle from the water column on to the ropes         these organisms is expected, although this is hard to
           at extreme low water on spring tides         dependent upon the size of the servicing vessel; sufficient                                                                                                                                     a shore-based facility or the next                                    product lines to
                                                                                                                          and attach using their bysuss threads.                          predict accurately since it varies from year to year and
           are preferable, although shallower           clearance should be allowed to enable the vessel to work and                                                                                                                                    stages may take place on-board                                        further enhance
                                                                                                                                                                                          between locations. An alternative is to move stock to
           sites can also be utilised.                  manoeuvre safely. In some locations, the longlines may be                                                                                                                                       the harvesting vessel.                                                the value of
                                                                                                                            Once the spat are firmly attached, the ropes can be           an area where settlement is usually light or absent.
                                                        kept slightly submerged in order to avoid disturbance from                                                                                                                                                                                                            their crop.
                                                                                                                          carefully uncoiled and lowered to their full length.            Experimentation is often required to find such locations
                                                        wave action.                                                                                                                      and even so the pattern may vary from year to year.             The mussels are separated or ‘declumped’, washed and                                     Rope-grown mussels
                                                                                                                             For growers in areas of poor spat settlement, it may be                                                                    graded, again by hand or automated line.                                                   bagged ready for sale
                                                           A typical UK raft would be approximately 10 m square           possible to purchase spatted ropes from growers in areas           Avian predators, such as eider and golden-eye
                                                        and consist of two floatation pontoons or float arrays, one       of denser settlement.                                                                                                          Each dropper may yield between 5 – 7 kg of
                                                                                                                                                                                          ducks, can present the grower with problems in some
                                                        either side, overlaid with a wooden framework, with supports                                                                                                                                    marketable mussels.
                                                                                                                                                                                          areas. Both are protected species and it is illegal to
                                                        approximately 0.5 m apart. Each raft may be anchored                 The stock should be assessed regularly in order
                                                        separately or it may form part of a larger array.                                                                                 kill them without a licence. One of the most effective
                                                                                                                          to check growth and to remove any predators which                                                                                Small mussels may be retubed and returned to the sea
                                                                                                                                                                                          methods of deterring their presence around the mussel         for further growth, although not every grower will do this.
                                                                                                                          may also settle from the plankton on to the droppers
                                                          The rope ‘droppers’, on which the mussels are grown, are                                                                        lines is to harass them by boat whenever they are
                                                                                                                          (eg starfish and crabs).
                                                        usually 12 mm in diameter although there are a wide variety                                                                       seen. Other control or predation prevention measures             It is now common for the marketable mussels to be
                                                                                   of bespoke ‘mussel line’ designs         As the stock grows or fouling increases, it may be            are used and they are outlined in guidelines produced         passed through a shore-based depuration plant before
                                                                                   available on the market. Plastic       necessary to add additional buoyancy to the longline in         jointly by the Association of Scottish Shellfish Growers      they go to market, even when this is not required by law.            Mussels loaded into chilled transport
                                                                                   pegs or discs may be inserted          order to prevent the droppers touching the seabed. If this      (ASSG) and the conservation bodies. Consult them for          The grower may operate the depuration plant themselves
                                                                                   through the twist of the rope to       occurs large starfish often gain access to the droppers and     the latest guidance.                                          or contract the service from a third party.
                                                                                   provide additional support for         decimate the growing stock.
                                                                                   the mussels. ‘Droppers’ are                                                                               As the stock grows, the density of mussels on a
                                                                                   generally between 6 – 10 m in             Other marine organisms that have planktonic larval                                                                                                                                                 At greater production volumes
                                                                                                                                                                                          dropper may be such that growth falls below optimal
                                                                                   length, depending on the depth of      stages, such as barnacles, tubeworms and sea squirts,                                                                                                                                               increasing mechanisation will be needed.
         Mussel longlines                                                                                                                                                                 levels due to overcrowding. Some growers take action
                                 Droppers and floats                               the water.                             may also settle on to the mussel ropes or on to the mussel      to remedy this by raising the droppers, removing the                                                                                  Additional equipment may include
                                 attached to longline                                                                     shells themselves. They can compete with the mussels
                                                                                                                                                                                          mussels, decreasing their density and then re-attaching                                                                             storage and dispatch facilities, a
                                                                                       ‘Droppers’ may be tied to          for feeding and if settlement is particularly dense they can,                                                                                                                                       depuration facility, larger declumping
                                                                                    the headlines or raft cross                                                                           them to a fresh dropper enclosed in a supportive mesh
                                                                                                                          especially in the case of the hard-shelled varieties like                                                                                                                                           and grading machines, retubing
                                                                                    pieces at between 0.45 – 1 m                                                                          stocking. This process is called ‘resocking’ or ‘retubing’.                                                                         equipment, packing system, stock
                                                                                                                          barnacles or tubeworms, cover the stock to the extent that
                                                                                    apart, depending upon local           it becomes unsaleable.                                          Alternatively, other growers think that the time and effort                                                                         handling system.
                                                                                    tidal conditions.                                                                                     expended in ‘resocking’ is not justified by the returns
                                                                                                                                                                                          and they allow ‘natural thinning’ to occur as stock falls                                                         Depurating           A mussel farmer will also need
                                                                                                                             ‘Soft fouling’, such as sea squirts and macro-algae or
                                                           Most rope-grown mussel cultivators collect their own stock                                                                                                                                                                                       mussels           an assortment of smaller pieces
                                                                                                                          predators like starfish, can be controlled by raising the       from the droppers under its own weight.
                                                        from the wild spat-fall. The rope droppers are coiled so that                                                                                                                                                                                                         of equipment and safety clothing
                                                                                                                          droppers from the water and allowing them to dry in shady                                                                                                                                           in addition to the more specialised
                                                        they remain in the top 2 – 3 m of the water column and they       conditions before they are resubmerged.                           Mussels are generally retubed at densities                    After depuration, the mussels may be shipped to a                   items. Examples of the equipment
                                                        are placed on the line or raft in time to collect the natural                                                                                                                                   wholesale packing and dispatch centre in bulk or they may be
                                                                                                                                                                                          between 1.5 – 2 kg per metre of dropper. This can                                                                                   required include First Aid kit, lifejackets/
                                                        spat. The exact timing of settlement varies around the               ‘Hard fouling’, such as barnacles and tubeworm, are                                                                        packed in to bags or other display containers by the grower.          buoyancy aids, signal flares other boat
                                                                                                                                                                                          be accomplished either manually or using automated
                                                        country, but the main spat-fall is generally in early summer,     more difficult to control and the best method seems to be                                                                                                                                           safety equipment – see the workboat
                                                                                                                                                                                          machinery. The choice of method is largely determined
                                                        although later and earlier settlements also take place.           one of settlement avoidance. This may take the form of                                                                           Mussels should be transferred to market or wholesaler              code of practice for guidance, pressure
                                                        Mussels can spawn several times during the year.                                                                                  by the level of production.
                                                                                                                          raising the droppers from the water when settlement of                                                                        in chilled transport conditions in order to preserve quality.         washer, gloves, knives, communication
         Mussel rafts                                                                                                                                                                                                                                                                                                         equipment (mobile phone or VHF radio).

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