Moving Mussels Offshore

24 September 2007

Trish DalyBIM

Killary Harbour

Rope mussel Production and value 1990-2006

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2 000

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12 000

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Year

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0

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2,000

3,000

4,000

5,000

6,000

7,000

8,000

Val

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Volume(tonnes)

Value('000)

Licensed Areas in Kilmacillogue

Licensed Areas in Ardgroom

Licensed Areas V Hectarage in use

0

50

100

150

200

250

300

350

Loug

h S

willy

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Mul

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Bay

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Production areas

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Licensed

In use

Production V FloatationProduction versus floatation

0

500

1000

1500

2000

2500

3000

Loug

h S

will

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Mul

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Bay

McS

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Production areas

To

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0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

Lit

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Production

Floatation

Why Move Offshore

• Many established Bays are overcrowded• Growth rates have dropped off in some Bays• Risk of bacterial and viral pollution is reduced• Conflict with other Bay users is reduced• The nature of our coastline offers many

opportunities• There is possible reduction in incidence of

biotoxins

Offshore Mussel Trials in Ireland

• Semi submerged mussel longlines, single headrope lines

• Submerged mussel longline, Seaflex mussel float

• Longtube longlines, Smart Farm system

Semi-submerged longlines

• First trial 1990, Seal Harbour

• Adopted and modified a system from IFREMER, France

• Single headrope longline, 1-3m below surface

• Purpose built Irish mussel floats

• Floatation kept to a minimum

Seal Harbour

Outer Bantry Bay

Galway Bay

• Started in 2005, 7 longlines and 2 Smart lines• Maximum site depth is approx. 30m• Hard sandy bottom• Fully exposed to southwesterlies• Difficulties with droppers tangling• Collected on a new heavier Spanish rope,

400g/m• Preference for single anchor at either end • Site access limited

Submerged Mussel Longline

• “Seaflex mussel float• 2 x 20m x 300mm sandor hose• Moored at both ends and in the centre• Buoyancy in the water controlled through a

hose connected at one end• Situated 5m below surface• Trial abandoned• No dedicated workboat

Longtube System Smart Farm

• Individual HDPE pipes, 126m x 250mm, wall thickness 7.7mm

• 2 – 2.8m deep collector made from square mesh, 8mm p/p, 250mm x 250mm square

• 32mm headrope lashed to pipe• Stainless steel clamp• Pipes generally moored as grid system with

prefabricated fan.• Two machines available for husbandry &

harvesting

Collector mesh & fan system

Thinning machine, Kenmare

Harvesting machine, Kenmare

Smart Farm in Ireland

• Three Bays selected: Lough Swilly, Bantry Bay, Kenmare River

• Different focus for each trial site

• Lough Swilly: strong currents, seed collection

• Bantry Bay & Kenmare River: Varying degrees of exposure

Lough Swilly

Lough Swilly

• Max depth 20m• Strong current, up to 4 knots• Traditional system tried and failed, as did semi-

submerged lines• The lines yielded about 10 tonnes of seed each

but a dive survey had estimated 14 – 16 tonnes.• Brushes were not strong enough for removing

the crop • Collector mesh offered great potential for seed

collection and relaying

Smart Farm in Bantry Bay

• Three potential sites

• Permission for two, licensed to Southward Ltd at Horse Island and Whiddy

• Lines moored individually

• Two lines damaged, clamp failed.

• Clamp design has since changed

• Slippage at more exposed site

Kenmare Bay

Kenmare Trial Site

Kenmare Bay Site characteristics

• Maximum depth 40m

• Seabed varies from hard sand to rocky

• Fully exposed to prevailing southwesterlies

• Over 12m swells recorded, current speed of about 2 knots

• Highly productive site

Mooring point specification

Trial Results

• Disappointing• Pipes failed on all sites.• Harvesting machine never operated to its full

potential• Availability of workboat and machinery major

limiting factor• Load cells attached to 2 westerly anchors, 2

anchor ropes and fan ring unreadable.• Currently 32 lines on commercial site in Kenmare

Summary results

• Semi-submerged lines have been the most successful to date

• A dedicated, purpose built workboat is essential.

• Limited opportunities to manage and harvest lines

• In all these systems the tidal range of 4m is always a major factor

Strengths

• Growth rates, shell quality and meat yield all improve

• With advancements in reusable drop ropes and the natural flushing out associated with exposed sites the environmental impact of these farms is greatly reduced

• Significant advances in husbandry technology in recent years make it more achievable on a practical level

Weaknesses

• Limited technical data available on sites• Workboat must be capable of operating in

exposed conditions• Cost of setting up V market price of

mussels• Weather windows limited from Autumn

through to Spring• Results to date did not show an improved

biotoxin profile for sites tested.

Opportunities for the Future

• Shellfish farming has a place offshore and Irish coastal waters offer huge potential for mussel production in exposed and semi-exposed sites.

• A detailed understanding of environmental parameters, including wave climate, topography, water exchange, current speed, temperature, salinity, oxygen and assessment of risk of harmful algal blooms is needed

• Collaboration between the Agencies and between the sectors is essential