Progress report on Didemnum vexillum control measures completed to 21 Sept 2006

Tarakohe Harbour

Treatment
• All affected wharves, jetties and moorings treated in July

Follow up
• Dived again in August and September some re-treatment completed.

Results
• Very good kill on 99% of structures. Considering the large and complex area that was affected the small amount of re-treatment needed is pleasing.

Outer Queen Charlotte Sound

Fence Bay

Treatment
• Jetties, seabed, moorings and one vessel treated July

Follow up
• Plastic removed and seabed checked August, vessel slipped September

Result
• Good kill on all structures and 95% successful on seabed. At follow up check it was noted that very little remained on the seabed, seemed to have reduced from what was noted at treatment, even though some areas were not treated at the time due to poor visibility. Any remaining on seabed was removed at follow up check.

Whatamango Bay

Treatment
• Jetties and mooring treated in July. Seabed not treated as considered too much to remove by hand. Will treat with plastic at follow up.

Follow up
• Plastic removed in August.

Result
• Appeared to be a total kill on structures. It was noted that the Dv on seabed had entirely disappeared in the month since the structures above were treated. The theory for this is that once recruitment from above was halted, the combination of soft sediment and predation by cushion starfish had eradicated the Dv.

Hitau Bay

Treatment
• Jetties, moorings, vessels, abandoned mooring blocks, an area of seaweed and large sunken pine tree were all treated or remove in July.

Follow up
• Several follow up checks were made during August.

Still to be completed
• Treatment of Lic 309 (late September)
• Follow up checks on jetties (as above)
• More follow up checks on seaweeds and old tree site(as above)

Result
• At this stage it appears that the treatment to date on this bay has been successful. Due to the nature of the affected seaweed and the tree site, there will have to be multiple follow up checks to ensure that we have got it all.

Other outlying bays (Onapua, Ahitarikihi, Waikaramea Bays)

Treatment
• All small scale. Various moorings and jetties treated in July

Follow up
• Still to be done in most areas, should be completed by end of September.

Results
• Not known for sure at this stage but expected to be positive.

Picton Harbour

Treatment
• 2 piles on west shore jetty and one mooring wrapped in July

Follow up
• Plastic removed in September, surrounding area checked and a further 6 piles wrapped

Result
• This will be checked again in a few weeks

Shakespeare Bay

Treatment
• Commercial barges, moorings, vessels, seabed and QCC mussel line were treated in August.
• The Waimahara wharf pile wrapping was completed in August and the seabed under the wharf is being treated now.
• This has been interrupted from time to time by log vessel operations.

Still to be completed
• Seabed under wharf, some seabed under the large barges and a full survey of the seabed of Shakespeare Bay to be completed by end of October.

Follow up
• Plastic was removed off recreational vessels and some of the barges in August.
• Plastic will be removed off the moorings and remaining barges during October.
• One barge has been removed since treatment and antifouled and another is to be removed for scrapping in the next month.

Lic 464 Ngaruru Bay, Tory Channel and Port Underwood

Background
• In July Dv was discovered on this farm amongst seed which has been harvested some months before and reseeded into Port Underwood. A survey completed in August in Port Underwood on these farms and others nearby concluded that Dv was not present.

Treatment
• All lines on Lic 464 were swum and checked and where Dv was found it was treated except for one part line of seed which was used for a Cawthron trial on eradication of Dv in seed.

Follow up
• Follow up still to be completed although this farm is being closely watched by staff working on it.

Results
• It appears to date that for some unknown reason the Dv did not survive the transfer and seeding process into Port Underwood, this result has not been demonstrated in other cases in the Pelorus.

Pelorus Sounds

Old Homewood Bay

Treatment
• The affected line on this farm was stripped off and all lines and the seabed were dived in June.

Follow up
• Further follow up dives were competed in July and August and another affected line was discovered on one of these follow up dives. This line was treated in August, in the same way as the initial affected line.

Results
• Although we are confident that the initial treatment of the affected line and seabed was successful; another line was found to contain Dv. This however had been transferred from Te Puraka since the initial treatment and therefore was treated as a new discovery rather than a re-infection from a previous treatment.

Te Puraka spat farm

Treatments
• The warps on 18 lines were changed in August after Dv was discovered on these warps earlier that month. Dv was not detected on the seed on this farm; however it has been detected on a number of lines seeded with seed off this farm. The timing of these seedings suggested it has been on this farm for 2 years prior to its discovery.
• Lines which have been seeded with seed from this farm have or are being checked at present and in some cases where Dv was detected they have been treated by removing the crop if large enough to harvest, or stripping off the seed and reseeding.

Follow up
• Not completed at this stage however many companies with affected lines are doing their own monitoring and control.

Result
• This is the most concerning find to date as it is in the heart of our growing area and has possibly been spread widely from the Te Puraka site. We will continue to monitor any lines seeded from this farm which were suspected to be affected. It will require extreme vigilance from all farmers in the Pelorus over the coming summer to prevent this from getting out of control.
• There is some feeling that because Dv has been present on this farm for 2 seasons it may suggest that it will not be a problem in the Pelorus. Previous experience with this species suggests that due to its larval biology it can have a slow establishment phase but once established its further spread is exponential.

Page last updated: 30 April 2008