New Zealand’s marine biosecurity system is designed to prevent marine pests arriving – and managing the impact of those already here. A bit like Covid’s vaccination/mask regime, much of the battle’s about stopping the spread. How can boaties help? By using their boats and keeping hulls clean.

As a ‘containment strategy’ using your boat might sound counter-intuitive: visiting different anchorages would surely increase the risk? Well, not if you have a clean hull, and clean hulls are largely a function of a well-used boat.

“The most widely-used antifouls are ablative and rely on the boat moving through the water to wash away any slime layer and release the biocides in the paint,” says Peter Lawless. “Wiping off the slime every month or so – coupled with regular use of your boat – will extend the paint’s life. That way pests have less chance to adhere.”

Pests have an extraordinary ability to adapt to our conditions.

When marine pests attach to a hull the biocides can’t be released – they are essentially blocked by the fouling. A boat lying in a marina for months – even with the best antifoul – he says, is a sitting duck.

Lawless coordinates the Top of the South Marine Biosecurity partnership – an initiative launched in 2009. It includes Tasman District Council, Nelson City Council, Marlborough District Council, the Ministry for Primary Industries (MPI), Department of Conservation (DOC), the aquaculture industry, port companies, tangata whenua and other stakeholders.


It’s geared to monitoring vessels, harbours, marinas and anchorages in the upper South Island (and Wellington). The team not only surveys around 450 vessels annually for fouled hulls but also runs a series of comprehensive workshops five times a year. Aimed at boaties, marina operators and Council staff, these help with identifying marine pests and offer bestpractice antifouling guidelines.

Fanworm growing on a poorly-antifouled keel.

Manufacturers suggest a good application of antifoul paint might last up to two years. But in addition to regular slime layer removal and boat use, says Lawless, the paint’s performance also depends on how it’s applied. “Owners should follow the manufacturer’s guidelines about application and surface preparation. Using the right paint is also crucial – a copperbased antifoul on aluminium hulls/appendages is not a good idea. Galvanic corrosion is unforgiving.

“But our inspections reveal a fundamental problem – we typically detect growth in difficult-to-reach areas which have little or no antifoul paint. And the number one culprit is under the vessel’s keel, followed by a bow thruster tunnel.

“On the hardstand a vessel’s keel rests on wooden blocks. Because those areas are inaccessible most boat owners quickly slap on a thick coat of paint while the boat’s hanging in the travel lift. That’s useless – the paint simply washes off a few minutes after relaunch – leaving prime spots for organisms to set up home.”

Some of the worst invaders: fanworm

One way of fixing this is to vary the position of the blocks between antifoul applications – a tactic used at commercial slipways. He also points out that owners of commercial vessels usually exceed the paint manufacturer’s recommendations (in terms of application) – because antifouling is much cheaper than a haul-out.


“Recreational boaties tend to go the other way – the paint’s expensive so they’re inclined to skimp. And when there is any excess paint, they use it in the wrong areas. It should be applied to the hull’s high-current areas – the bow, keel and rudder – which take the brunt of the water’s velocity. Most antifoul paints are ablative – these areas lose paint more quickly.”

styela clava


Most marine pests arrive in our waters on ships – either in water ballast discharged near our coastline – or on the hulls (around 70%).

MPI has managed ballast water discharge from overseas vessels since 1998 and in 2018 implemented a world-first tool – the Craft Risk Management Standard – Biofoul – to govern the biosecurity requirements for all arriving vessels. Though an excellent first-line-of-defence, the regulations are preventative and aren’t designed to manage the marine pests already here.

On behalf of MPI Abraham Growcott manages a national marine surveillance programme to aid the early detection of marine pests in our 12 busiest ports. He says the pests’ ability to survive – and indeed thrive – in our waters is extraordinary.

sea squirt

“The earlier we find new arrivals the higher chance we have of being able to manage them, either through eradication or population suppression to prevent their spread. We’ve got a pretty good handle on the species already here as NIWA staff have been completing these surveys every summer and winter since 2002 to look for marine pests. We’ve definitely noticed a ‘plasticity’ in their tolerance – they’re very good at adapting. The Mediterranean fanworm, for example, is from warmer waters but in New Zealand grows faster than what has been observed overseas.”


Japanese Kelp (Undaria) is another pest that’s spread around the country, says Don McKenzie, the Biosecurity Manager at Northland Regional Council (NRC). “Ten years ago we believed Undaria would only survive in the South Island’s waters – but today we find it growing up north in Houhora harbour.

“Fanworm is also thriving – around 10 years ago the literature suggested it grew to about 50cm in cold water. Well, in Northland growth rates are exceeding that. And it’s also exhibiting other, odd biological phenomena, like doublespawning. So there’s large-scale adaptability.”


Climatic factors also affect the pests’ activity. “About two years ago,” says Lawless, “we received a flurry of calls from marine farmers in the Pelorus Sound, concerned about a sudden proliferation of a slimy green algae (Cladophora).

“It had been around for at least six years but rarely bloomed – until a high temperature excursion arrived (3o) in the Marlborough Sounds and triggered the outbreak. Some organisms lie dormant for years and suddenly emerge with climate variations. Predicting the behaviour is very hard – which is why constant vigilance is so important.”

Everyone spoken to for this story emphasised the importance of rapid and appropriate action when fighting marine pests. “With any given event we only have a narrow window in which to act,” Lawless stresses. “If you don’t get to it early the horse will bolt – containment and eradication become impossible.”

daunting growth of fanworm

You only have to consider how the voracious Northern Pacific Sea star has decimated shellfish in southern Australia to understand his point. It’s not been seen in our waters – so far.


While MPI’s Craft Risk Management Standard addresses international vessels arriving to New Zealand, shouldn’t we have a similar biosecurity approach for domestic vessels moving around our country?

Well, the legislation does provide for related regulations for domestic vessels, says John Sanson, a biosecurity manager at MPI. “Domestic Pathway Management Plans (PMP) were introduced through changes to the Biosecurity Act in 2012. Prior to that the legislation only allowed for national or regional pest management plans, but it was recognised that a mechanism to proactively manage the pathways of pest spread would be beneficial and complement rules focussed on specific pests.

Divers carry out hull inspections – but be warned: a clean bill of health is not infallible. Juvenile creatures are hard to detect.

“Environment Southland was the first to adopt a PMP for marine biosecurity in 2017. It contains specific requirements for vessels entering Fiordland – they need a Clean Vessel Pass, proving they meet the specified biosecurity standard before entry.

“At the opposite end of the country,” he adds, “Northland Regional Council (NRC) was the first to adopt a region-wide PMP. It requires ‘good boat hygiene’ and gives NRC the power to deal with fouled vessels – owners must either haul and clean their vessels – or leave.”

NRC’s McKenzie says the PMP was implemented because the region carries 90% of the biosecurity risk. “It’s simple arithmetic – the upper North Island is home to most of the country’s recreational fleet.”

Cawthron Institute’s research programme addresses nonindigenous marine species.

He says the strategy’s been successful in limiting the transfer of marine pests within and between regions and he believes the regulations need to be rolled out nationally. “Only 60% of regions have regulations in their marine pest management plans – and those regulations aren’t consistent. We need a national regime for the country’s domestic water space – one that mirrors what MPI does at the country’s borders.”

Happily, things are moving in the right direction.


Northland, Auckland, Waikato and Bay of Plenty regional/ unitary councils, together with MPI and DOC, are collaborating on the development of a PMP (referred to as a ‘Clean Hull Plan’). This is a key step towards a consistent, integrated marine biosecurity plan for the entire country. Also under development is a national antifouling standard, being formulated in conjunction with the marine industry. It aims to give vessel owners confidence about achieving optimum applications.

Top of the South runs marine biosecurity workshops in the region five times a year.

The draft Clean Hull Plan is expected to be completed later this year, allowing consultation with stakeholders to kick off early next year. “We want feedback from the boating public, iwi, industry – anyone with an interest in marine biosecurity,” says Sanson. The PMP will be presented to the Minister for Biosecurity for approval following consultation.

By and large, boaties are helping to keep the invaders suppressed. “I think boaties are the heroes in this issue because 90% of them want to do the right thing and make an effort to keep their hulls clean,” say McKenzie.

Lawless agrees and says the substantial increase in awareness and the change in behaviour among the boating public is very pleasing. “Fundamentally, it’s about looking after your boat and keeping it clean. The industry’s catch-phrase sums it up perfectly – Clean Below? Good to Go. It’s a core social responsibility.”

Just like wearing a mask. BNZ


They’re among us.

Some 351 non-indigenous species were identified in our marine waters in 2015, of which 187 had become established – a 10% increase since 2009 (Stats NZ). They include algae, barnacles, crabs, bryozoans, sea squirts, mussels and other molluscs.

Part of the increased detections between 2001 and 2010 is probably due to the active surveillance programmes and a greater awareness of the negative impacts of marine pests.


MPI has identified 11 marine organisms which
are highly invasive and of particular concern:
Asian paddle crab (Charybdis japonica)
Chinese mitten crab (Eriocheir sinensis)
European shore crab (Carcinus maenus)
Mediterranean fanworm (Sabella spallazanii)
Northern Pacific seastar (Asterias amurensis)
Australian droplet tunicate (Eudistoma elongatum)
Clubbed tunicate (Styela clava)
Pyura (Pyura doppelgangera)
Aquarium caulerpa (Caulerpa taxifolia)
Wakame/undaria (Undaria pinnatifida)
Asian clam (Potamocorbula amurensis)



Obtaining a clean bill of health for a vessel is good practice for boaties, says Lawless, but warns that it isn’t infallible because invasive pests are often hard to detect.

“Among our recent fanworm detections, six vessels presented the identical profile. All had been inspected and given a tick by scuba divers before arriving in the Marlborough Sounds. But the fanworm wasn’t detected. Until it’s quite prominent – about 30mm long – it’s very hard to spot, particularly in poor light and visibility.

“Similarly, the Spirit of New Zealand was full of fanworm when she visited here – but her clean certificate was more than six months old. In its juvenile state the fanworm hadn’t been detected.”

A Cawthron Institute research team examines a menagerie of nasties.


The Toolbox is another component in our expanding marine biosecurity arsenal. Run by the Cawthron Institute, it’s a five-year (2019-24) collaborative research programme aimed at protecting the marine environment from nonindigenous marine species.

It’s funded by the Ministry of Business, Innovation and Employment and supported by a group of regulatory, industry, Māori and international research organisations.

It aims to develop tools to prevent marine pest establishment, early detection of those that do arrive and modelling of new incursions. It will be implemented in partnership with regional councils, central government agencies, and the maritime and aquaculture industries.