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Code of Practice for Reducing Spread of Sea Squirt

New Zealand Aquaculture Council Code of Practice for Reducing the Risk of Spreading Styela Clava

6th December 2005

The New Zealand Aquaculture Council today released the marine farming industry’s Code of Practice aimed at reducing the risk of spreading the clubbed tunicate, Styela clava.

The Code of Practice, which is voluntary, seeks industry participants to use best practice to avoid the risk of spreading the unwanted sea squirt. The Code of Practice is the first such measure to have been adopted since the organism was detected in the Viaduct Basin in August of this year.

Styela clava has a history of smothering marine farming structures in Canada and its appearance in New Zealand is of extreme concern to marine farmers. Styela has been declared an unwanted organism by Biosecurity New Zealand and the marine farming industry wishes to add its support to any control or eradication programmes by way of the Code of Practice.

Chairman of the New Zealand Aquaculture Council, Callum McCallum, an oyster farmer in the Hauraki Gulf, one of the affected areas, comments that the Code of Practice accepts that some areas of the New Zealand coastline are affected by Styela clava, and that the marine farming industry wishes to do its part in controlling the risk it spreading further. The industry expects all its members to adhere to the Code, the first of its kind in relation to this unwanted incursion.

“We are working hard to assist Biosecurity New Zealand to respond to the ongoing serious threat from Styela” says Mr McCallum. “The Code of Practice is about the treatment of farming equipment in affected areas and movements of vessels between affected and clear areas. Farmers are asked to remove for disposal any specimens found on equipment and to ensure that vessel moving between affected and clear areas are clean of the sea squirt. We believe the Code is a positive and helpful step by our industry to minimise the risk of spreading Styela”

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The Code of Practice has been adopted by industry stakeholder groups including the New Zealand Mussel Industry Council, the Oyster Industry Association and the New Zealand Salmon Farmers Association. Regional marine farming organisations in the Marlborough Sounds, Golden Bay and Coromandel also support the Code.


Additional Notes:


The purpose of this voluntary Code of Practice is to reduce the risk of spreading Styela clava within the Coastal Marine Area of New Zealand through the introduction of good industry practices.

Styela clava (commonly called the clubbed tunicate, a sea squirt) has been identified as a marine invader in parts of New Zealand. The incursion is thought to have occurred via marine fouling on the hull of a transcontinental vessel moored in either Lyttleton Harbour or the Viaduct Basin in the Waitemata Harbour. The organism appears to have got to NZ before 2003 and has now been declared an unwanted organism by Biosecurity New Zealand. This new status means that management controls can be introduced to eradicate or control the movement of Styela clava.

In parts of the world, and especially Prince Edward Island, Canada, Styela clava has become a major fouling organism on marine farms. In order to minimise the potential impact of Styela clava in the coastal marine area, the Aquaculture Council has prepared the following industry Code of Practice.


3.1 Affected area means a regional body of water (e.g. Hauraki Gulf, Firth of Thames) in which living Styela clava has been found and positively identified

3.2 Approved refuse facility means a refuse site where living waste material will not percolate back into the coastal marine area

3.3 Clear area means a regional body of water in which living Styela clava has not been found or positively identified


4.1 A laminated copy of the NZMIC Styela clava Information and Identification Guide will be displayed in a prominent position on all marine farm vessels, marine farms service vessels (including crop assessors) and shellfish processing factories.

4.2 Specimens and suspected specimens of Styela clava identified on marine farming equipment (trays, growing lines, floats, warps and anchor blocks) will be removed by cutting the stalk as close as possible to the holdfast without squeezing the bulbous end portion. The dismembered portion is to be stored in a secure container, sealed plastic bag or frozen prior to future identification and or disposal.

4.3 Disposal of the specimens collected will be on land in approved refuse facilities. Other alternative means of destruction such as drying, sterilising, burning or drowning in freshwater may be considered in consultation with the relevant Regional Council Pest Control Manager.

4.4 Marine farming equipment removed from an affected area must be inspected, cleaned of all tunicates, washed and dried prior to re-use.

4.5 Marine farming equipment that is not carrying crop and has been used in an affected area should not be transferred to a clear area. If such a management process is not possible then the processes outlined in 4.4 must be adopted before the equipment is transferred to the clear area.

4.6 All endeavours must be made to ensure that marine farm crop (spat, seedlings and adult shellfish) is not transferred from an affected area to a clear area.

4.7 The risk of spreading Styela clava is reduced if vessels are in regular use and have hulls that are cleaned and/or are painted with antifouling material on an annual basis.

4.8 Vessels that have been stationary for periods of 30 days or more and have not been cleaned or anti-fouled within the previous six months must be inspected for sea squirts prior to relocating from an affected area to a clear area. All sea squirts found during the inspection must be removed from the hull before departure and disposed of as outlined in 4.2 above.


5.1 Any positive identification or suspected samples of Styela clava found in a clear area must be declared to Biosecurity New Zealand as soon as possible after the find or identification (Contact 0800 809 966).


6.1 To give effect to the industry Code of Practice the following processes and equipment must be part of the operating manual of all marine farming vessels working in affected areas
 NZMIC Styela clava ID charts
 sealable plastic bags or other sample containers to hold suspect specimens
 instructions on how and where to send samples
 large containers to hold Styela clava removed from equipment, crop or vessels

6.2 Styela clava may be intercepted at various points in the harvest and farming process. Vessel skippers must ensure that during the harvest of crop and the removal of equipment that crews are made aware of the possible presence of Styela clava and be instructed in the approved removal and storage processes.

6.3 During harvests lifting crews must watch for Styela clava on lines or racks as they are taken from the sea. Any specimens located are to be removed and stored in the appropriate containers for later disposal.

6.4 During sorting and grading at sea staff must inspect product and waste material for Styela clava and remove specimens for later disposal.

6.5 Whenever possible waste water will be inspected and any Styela clava specimens found must be removed from the waste water and stored for later disposal.


7.1 This Code of Practice will be reviewed by the industry Styela clava Advisory Group no later than 90 days after its adoption by the Aquaculture Council.

New Zealand Aquaculture Council
30th November 2005

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