Why fanworm are escaping the net

Despite vessel owners trying their best Mediterranean fan worm are still hitching a ride out of the north and turning up in the south. Fanworm were found on two vessels but no structures or seabed during the Top of the South summer survey this year. No invasive species new to the region were found in the survey although there were over 1,100 data points logged.

“We are still processing the data which will be up online at https://marinebiosecurity.gitlab.io/report in March” said Dr Barrie Forrest who leads the survey.  “We had a great response from the boating community with good cooperation from most vessel owners.   My overall impression is that vessels were cleaner this year and it will be interesting to see if the data bear this out.  Early in the season we saw mostly local vessels and visitors from Wellington and Porirua.  Later in January vessels started arriving from the north where Mediterranean fan worm is more prevalent.  We found fanworm on two vessels that had spent time in Auckland.  In both cases the vessel owners reported efforts to ensure their boats were clean before they came down to our region.  That we still found fan worm highlighted issues with the lack of national standards for inspection and cleaning.  One reported engaging commercial divers to check and clean the hull.  However, when we inspected five months later worms that would have been too small for divers to detect had grown to a size where we could find them.  The other had hauled the vessel and high pressure water blasted before rounding Cape Reinga.  Unfortunately the bottom of the keel was not treated and fanworm were found amongst hard fouling there.  In both cases visible worms were removed during the inspection and the relevant council directed the owner on next steps” he said.

Marine Biosecurity Coordinator for the Top of the South Peter Lawless said “There are a few things vessel owners and boat maintenance professionals need to be aware of to get this right.  First, in water inspections cannot find small fan worm.  Fan worm can grow from too small to see to 30mm in a month.  This means that in water inspection and removal of fan worm is only useful where vessels will be slipped and cleaned properly within a couple of months at their destination.  Second, out of water cleaning is effective only when all parts of the hull and niche areas are properly treated.  That means cleaning the bottom of the keel and inside bow thrusters and pipework.  Most often we find the fan worms hiding amongst encrusting organisms that have not been properly treated.”