Key findings

Toggle between tabs to see summaries for each year of monitoring. Links to previous reports are available on the resources page.

2023/24

Summary of Survey Effort

In the 2023/24 season, 270 recreational vessels were inspected (167 in Marlborough, 52 in Nelson and 51 in Tasman). This brings the total of vessels surveyed over the last nine years to 3,695. Two rounds of hull surveys were carried out during the Christmas break (3 - 9 January 2024) and the second between 25 – 30 January 2024 to coincide with the Nelson Tasman Anniversary weekend. Divers targeted areas popular with boaties, including Abel Tasman National Park and Queen Charlotte Sound and utilised Automatic Identification System (AIS) tracking to identify active vessels.

During the survey, divers inspected vessels for marine pests and biofouling. Vessels are assigned a Level of Fouling (LoF) by the divers, with 0 being the cleanest, and 5 being the highest level of fouling. A score of 0-2 is considered clean, and a score of 3-5 is deemed considerably fouled.

Marlborough District Council, Nelson City Council and Tasman District Council also carried out additional surveys and/or removal programmes for Mediterranean fanworm (Sabella spallanzanii) in the main Top of the South ports and marinas, as part of other council-funded marine biosecurity work.


Level of Fouling (LoF) and Marine Pests

This season, there was a significant increase in the percentage of active vessels that had no macrofouling (17% compared with 9% from the previous eight survey seasons). 79.6% of all vessels surveyed had a LoF between 0-2 (>5% cover). Over a quarter of all vessels had conspicuous fouling (>5% cover).

50% of vessels inspected in Nelson had conspicuous fouling (LoF between 3-5, with more than >5% cover) compared with Marlborough (12.6%) and Tasman (16.7%). This could be due to many vessels being moored long-term at Nelson Marina.

Two vessels were found to be carrying Mediterranean fanworm (Sabella spallanzanii) during the summer surveillance programme. These were the only marine pest species identified during the surveys, with no new pests observed by divers.

The first incidence of Mediterranean fanworm occurred on 3 January 2024 in Bark Bay, Abel Tasman. Divers discovered fanworm on the bottom of the keel of an active vessel. Approximately 4-6 mature worms were removed and bagged on site. The vessel had a LoF score of 4 (extensive macrofouling, between 16 – 40% cover). A Notice of Direction was issued for the vessel to be cleaned at Nelson Marina the following day. The vessel’s home port is Lyttelton.

The second discovery of fanworm occurred on 26 January 2024, also in Bark Bay, Abel Tasman. Approximately 10-15 juvenile worms were found on the hull and rudder by survey divers. The vessel had a Level of Fouling score of 2 (limited macrofouling, between 1 – 5% cover). A Notice of Direction was issued for the vessel to be cleaned at Nelson Marina. During cleaning, up to forty juvenile fanworms were discovered on the vessel. The vessel’s home port is Sandspit Marina, Warkworth.


Recreational boater maintenance habits

Vessel owners had a good awareness of the risks associated with a high level of fouling. However, there was a lack of thorough cleaning, cleaning within the prescribed timeframes or using the correct methods and facilities. Therefore, a disconnect exists between boaties’ understanding and taking the appropriate action.

The first vessel discovered with Mediterranean fanworm was last cleaned approximately two years ago. The owner of the vessel has attempted to clean the vessel in Lyttelton but was unable to dive deep enough to reach the bottom of the vessel. This is where the Mediterranean fanworm was found. The second vessel discovered with Mediterranean fanworm was last cleaned in December 2023 and had an antifoul paint applied seven years ago.


Implications and further considerations

Level of Fouling and Marine Pests

Generally, vessels had a low level of fouling. However, this does not guarantee that a vessel is free from marine pests. Marine pests can hide in niche areas such as the keel, rudder, intakes, outlets, propellers, shafts, rudders, and casings. Mediterranean fanworm was found on vessels that had a LoF of 2 and 4.

Mediterranean fanworm was the only marine pest identified during the surveys. No species new to the TOS or new to New Zealand pests were found. The identification of Mediterranean fanworm highlights the importance of the surveillance programme. It shows that there continue to be pathways for the introduction and spread of marine species into the region, particularly from high-risk areas such as Auckland and Canterbury.

The identification of only one pest species may indicate that other marine pests could be present but remain undetected. The diving team were experienced in marine pest ID, but continuing to upskill staff will be critical in identifying species, particularly those that have not been found in New Zealand before. The timing of the surveys will be reviewed ahead of next season, with a pre-Christmas survey proposed to ensure a large number of vessels are inspected at the start of the summer holidays.

Availability of cleaning facilities

There continues to be concern about the availability of haul-out facilities, both within the TOS and other regions. Using an approved haul-out facility means that biofouling and antifouling chemicals are captured and disposed of without harm to the environment. It reduces in-water cleaning and ensures vessels receive thorough treatment, including in hard-to-reach areas. Lyttelton Port currently has no haul-out facilities for recreational vessels.

The Tasman region does not have a haul-out facility due to infrastructure challenges. This requires the vessel to travel with known pests, such as the case for the second Mediterranean fanworm incident where the vessel travelled from Tasman to Nelson with up to 40 juvenile worms. Although this risk was assessed as low due to the worms not being reproductive, it is still not best practice to move infested vessels between regions. Capacity at Nelson Marina can also be limited and can be difficult to book in a haul-out.


2022/23

Summary of survey effort and vessel origins

Over the last eight years, annual summer checks have been made of 3425 boats, 2970 structures (90% of which were swing moorings) and 441 seabed locations. Most of the effort has focused on the Marlborough Sounds and Abel Tasman National Park coastline, where active boaters are most prevalent. Additional surveys and/or removal programmes for Mediterranean fanworm are undertaken in the main TOS ports and marinas, as part of other council-funded work.

In the 2022/23 survey we checked 502 vessels (mainly recreational), 606 structures and 90 seabed locations. Of the vessels surveyed, 316 (63%) were classified as ‘active’ in the region (e.g. the boat was at anchor), of which 100 (34%) were visiting from outside the TOS. Of the latter, 67 vessels were from marinas in Wellington and 23 from locations considered high-risk for fanworm introduction.


Marine pests and vessel ‘Level of Fouling’

No pests that are new to the TOS region have been found over the six surveys. In terms of established pests, points of interest are as follows:

  • In 2022/23 low numbers of Mediterranean fanworm (Sabella spallanzanii) were recorded on two vessels: one from Auckland that had a clean hull but small fanworks in its stern thruster, and another from Lyttelton that was heavily fouled.
  • Other long-established pests (Asian kelp Undaria pinnatifida, sea squirt Didemnum vexillum) are widespread regionally on vessels and structures. The more recently established sea squirt Styela clava is becoming increasingly common on structures and/or vessels in a few locations (Tarakohe, Nelson, parts of Pelorus Sound), and for the first time we found a seabed population at Anchorage on the Abel Tasman National Park coast. For these established species, the disjointed distribution is consistent with human-mediated spread rather than natural dispersal, highlighting the importance of managing hull biofouling.

The Level of Fouling (LOF) status of boats in 2022/23 was similar to previous surveys, with general trends over the last eight years being as follows:

  • Around 21% of active boats had conspicuous fouling that exceeded a ‘light fouling’ (LOF 2, >5% cover) threshold. Only 9% of active boats had no macrofouling.
  • Hull fouling tends to be the greatest on vessels originating from Nelson, less on vessels from Marlborough, and least on vessels visiting from outside the region.
  • There is a clear trend for marine pests to become more prevalent with increasing LOF. However, even LOF 2 vessels (i.e. with a light fouling of 5% or less) can have pests present, often in niche areas like the bottom of the keel, as this area is difficult to antifoul.

Recreational boater maintenance habits

Despite efforts to educate skippers about the importance of regular high-quality antifouling, and vessel cleaning before departure from their home port, the vessel maintenance habits of recreational boaters have not changed appreciably over the last seven years. Of 27% of boaters reporting that they had cleaned their hull since last being antifouled, almost half had cleaned in-water. In-water cleaning is less effective as a management tool than a haul-out and water blast, and can also lead to antifouling coating damage and rapid regrowth of biofouling. In addition, many boaters in-water clean while anchored up in remote and pristine locations; a practice that could exacerbate the spread of pests.


Implications and further considerations

Although most out-of-region boat have only ‘light fouling’, these vessels still represent a particular risk of introducing new pests to the TOS due to fouling of niche areas (e.g. bottom of the keel). Wellington marinas are not currently thought to have pests of significance to the TOS, but if such pests established, those locations could become significant sources for spread into the region. In this respect, the TOS Partnership continues to work to help ensure that visiting vessels:

  • Are detected before arrival through an effective intelligence system; we use vessel AIS tracking to identify vessels inbound from high-risk regions.

  • Arrive in the TOS with a ‘clean’ hull where this can be achieved, or are subjected to risk-profiling and an appropriate management response upon arrival.

Changing the maintenance behaviour of within-TOS boaters is critical for reducing the regional spread of established pests. Recognised barriers include a lack of capacity at haul-out facilities in Nelson to enable boaters to be lifted from the water for cleaning or maintenance (currently being rectified), relatively high costs associated with cleaning, and recommendations to avoid in-water cleaning within marina areas. The risk profile of recreational vessels plying the region’s waters will not improve until these issues are addressed. The current practice of in-water cleaning in remote locations provides a potentially significant mechanism for the spread of pests to high-value areas across the TOS. It is important that advocacy or regulation to improve hull hygiene is accompanied by systems and infrastructure to support best practice.


2021/22

Summary of survey effort and vessel origins

Over the last seven years, checks have been made of 2923 boats, 2019 structures (89% of which were swing moorings) and 248 seabed locations. Most of the effort has focused on the Marlborough Sounds and Abel Tasman National Park coastline, where active boaters are most prevalent. Additional surveys and/or removal programmes for target pests are undertaken in the main TOS ports and marinas, as part of other council-funded work that is not reported here.

In the 2021/22 survey we checked 474 vessels (mainly recreational), 512 structures and 148 seabed locations. Of the vessels surveyed, 329 (69%) were classified as ‘active’ in the region (e.g. the boat was at anchor), of which 75 (27%) were visiting from outside the TOS. Of the latter, 53 vessels were from marinas in Wellington.


Marine pests and vessel ‘Level of Fouling’

No pests that are new to the TOS region have been found over the six surveys. With respect to established pests, points of interest are as follows:

  • In 2021/22 low numbers of Mediterranean fanworm (Sabella spallanzanii) were recorded on two vessels: one from Auckland that was anchored along the Abel Tasman coastline, and another from Picton that had spent time in Auckland since last being antifouled. The worms were located mainly along the bottom of the keel on each boat. Previously, fanworms have been found on vessels outside the main TOS marinas on only five occasions.
  • Other long-established pests (Asian kelp Undaria pinnatifida, sea squirt Didemnum vexillum) are widespread regionally on vessels and structures. The more recently established sea squirt Styela clava is becoming increasingly common on structures and/or vessels in a few locations (Tarakohe, Nelson, parts of Pelorus Sound). For these established species, the disjointed distribution is consistent with human-mediated spread rather than natural dispersal, highlighting the importance of managing hull biofouling.

The Level of Fouling (LOF) status of boats in 2021/22 was largely similar to previous surveys, with general trends over the seven surveys being as follows:

  • Around 21% of active boats had conspicuous fouling that exceeded a ‘light fouling’ (LOF 2, >5% cover) threshold. Only 9% of active boats had no macrofouling.
  • Hull fouling tends to be the greatest on vessels originating from Nelson, less on vessels from Marlborough, and least on vessels visiting from outside the region.
  • There is a clear trend for marine pests to become more prevalent with increasing LOF. However, even LOF 2 vessels (i.e. with a light fouling of 5% or less) can have pests present, often in niche areas like the bottom of the keel, as this area is difficult to effectively antifoul.

Recreational boater maintenance habits

Despite efforts to educate skippers about the importance of regular high-quality antifouling, and vessel cleaning before departure from their home port, the vessel maintenance habits of recreational boaters have not changed appreciably over the last seven years. Of 25% of boaters reporting that they had cleaned their hull since last being antifouled, almost half had cleaned in-water. In-water cleaning is less effective as a management tool than a haul-out and water blast, and can also lead to antifouling coating damage and rapid regrowth of biofouling. In addition, many boaters in-water clean while anchored up in remote and pristine locations; a practice that could exacerbate the spread of pests.


Implications and further considerations

Although most out-of-region boat have only ‘light fouling’, these vessels still represent a particular risk of introducing new pests to the TOS due to fouling of niche areas (e.g. bottom of the keel). Wellington marinas are not currently thought to have pests of significance to the TOS, but if such pests established, those locations could become significant sources for spread into the region. In this respect, the TOS Partnership continues to work to help ensure that visiting vessels:

  • Are detected before arrival through an effective intelligence system; we are increasingly using vessel AIS tracking to identify vessels inbound from high-risk regions.

  • Arrive in the TOS with a ‘clean’ hull where this can be achieved, or are subjected to risk-profiling and an appropriate management response upon arrival.

Changing the maintenance behaviour of within-TOS boaters is critical for reducing the regional spread of established pests. Recognised barriers include a lack of capacity at some haul-out facilities to enable boaters to be lifted from the water for cleaning or maintenance (currently being rectified), relatively high costs associated with cleaning, and recommendations to avoid in-water cleaning within marina areas. The risk profile of recreational vessels plying the region’s waters won’t improve until these issues are addressed.


2020/21

Summary of survey effort and vessel origins

Over the last six years, checks have been made of 2449 boats, 1852 structures (90% of which were swing moorings) and 203 seabed sites. Most of the effort has focused on the Marlborough Sounds and Abel Tasman National Park coastline, where active boaters are most prevalent. Additional surveys and/or removal programmes for target pests are undertaken in the main TOS ports and marinas, as part of other council-funded work that is not reported here.

In the 2020/21 survey we checked 502 vessels (mainly recreational), 345 structures and 103 seabed sites. Of the vessels surveyed, 284 were classified as ‘active’ in the region (e.g. the boat was at anchor), of which 64 (27%) were visiting from outside the TOS, primarily from marinas in Wellington (n=45 vessels). It is uncommon to encounter vessels from overseas (only eight checked in six years). In general, many of the visiting boats are found in outer parts of Queen Charlotte Sound.


Marine pests and vessel ‘Level of Fouling’

No pests that are new to the TOS region have been found over the six surveys. With respect to established pests, points of interest are as follows:

  • In 2020/21 a low number of Mediterranean fanworms (Sabella spallanzanii, assumed to be juveniles) were recorded on a single vessel from Auckland that was anchored along the Abel Tasman coastline. The worms were located in a niche area near the rudder that had been missed when the vessel was commercially cleaned by divers prior to travelling to the TOS region. As the vessel was too large for regional haul-out facilities the worms were removed in-situ by divers. Previously, fanworms have been found on vessels outside the main marinas on only four occasions.
  • Other long-established pests (Asian kelp Undaria pinnatifida, sea squirt Didemnum vexillum) are widespread regionally on vessels and structures. The more recently established sea squirt Styela clava is becoming increasingly common on structures and/or vessels in a few locations (Tarakohe, Nelson, parts of Pelorus Sound). For these established species, the disjointed distribution is consistent with human-mediated spread rather than natural dispersal, highlighting the importance of managing spread by hull fouling.

The Level of Fouling (LOF) status of boats in 2020/21 was largely similar to previous surveys, with general trends over the six surveys being as follows:

  • Overall, around 22% of active boats have exceeded a ‘light fouling’ (LOF 2) threshold, with many heavily fouled boats (LOF 4 & 5) active throughout the TOS region.
  • Hull fouling tends to be the greatest on vessels originating from Nelson, less on vessels from Marlborough, and least on vessels visiting from outside the region. Fouling is also relatively low on vessels on swing or pile moorings that dry (or part dry) at low tide.
  • There is a clear trend for marine pests to become more prevalent with increasing LOF. However, even LOF 2 vessels (i.e. with light fouling) can have pests present, often in niche areas like the bottom of the keel, as this area is difficult to effectively antifoul.

Recreational boater maintenance habits

Despite efforts to educate skippers about the importance of regular high-quality antifouling, and vessel cleaning before departure from their home port, the vessel maintenance habits of recreational boaters have not changed appreciably over the last six years.

In the latest survey 30% of boaters had cleaned their hull since their last antifoul, of which nearly half cleaned in water. Over all surveys, around 15% of boaters had undertaken in-water cleaning since last being antifouled. In-water cleaning is considerably less effective as a management tool than a haul-out and water blasting (e.g. some vessels were LOF 5 within a month of being in-water cleaned). Reasons for low effectiveness and rapid regrowth include incomplete removal of fouling, and damage to ablative antifouling coatings, both of which can lead to rapid fouling regrowth.


Implications and further considerations

Out-of-region boaters, while generally having only ‘light fouling’, represent a particular risk of introducing new pests to the TOS due to fouling of niche areas (e.g. bottom of the keel). Wellington marinas are not currently thought to have pests of significance to the TOS, but if such pests established, those locations could become significant sources for spread into the region. In this respect, among the key needs are approaches to ensure that visiting vessels:

  • Are detected before or upon arrival through an effective intelligence system.
  • Arrive in the TOS with a ‘clean’ hull where this can be achieved.
  • Are subjected to risk-profiling and an appropriate management response upon arrival, where feasible (e.g. where the point of arrival is a marina).

Changing the maintenance behaviour of within-TOS boaters is critical for reducing the regional spread of established pests, and understanding current attitudes and barriers to change is part of this picture. Recognised barriers include a lack of capacity at haul-out facilities in Nelson to enable boaters to be lifted from the water for cleaning or maintenance (currently being rectified), relatively high costs associated with cleaning, and recommendations to avoid in-water cleaning within marina areas. The risk profile of recreational vessels plying the region’s waters will not improve until these issues are addressed. Related to this issue, the current practice of in-water cleaning in remote locations provides a potentially significant mechanism for the spread of pests to high-value areas across the TOS. It is important that advocacy or regulation to improve hull hygiene is accompanied by systems and infrastructure to support best practice.


2019/20

Summary of survey effort and vessel origins

In the over the last 5-years, checks have been made of 1947 boats, 1507 structures (90% of which are swing moorings) and 100 seabed sites. Most of the effort has focused on the Marlborough Sounds and Abel Tasman National Park coastline, where active boaters are most prevalent. Additional surveys and/or removal programmes for target pests are undertaken in the main TOS ports and marinas, as part of other council-funded work.

In the 2019/20 survey we checked 469 vessels (mainly recreational), 349 structures and 53 seabed sites. With a greater focus on active vessels in the 2019/20 survey than previously, the total vessel tally was slightly less than last year but the number of active vessels was relatively high (291). A total of 52 of these vessels were from outside the TOS, of which 79% were from marinas in Wellington.

Out-of-region visiting boats made up 29% of total ‘active’ vessel records, but their occurrence was disproportionate across the two regions, with visitors (mainly from Wellington) being most prevalent in Marlborough. Around 25% of visitors from New Zealand ports originate from outside Wellington. It is uncommon to encounter vessels from overseas (only 6 checked in 5 years).


Marine pests and vessel ‘Level of Fouling’

No pests that are new to the TOS region have been found over the 5 surveys. With respect to established pests, points of interest are as follows:

  • In 2019/20 the Mediterranean fanworm (Sabella spallanzanii, assumed to be juvenile) was recorded in low numbers on 3 vessels (Nelson Harbour, Pelorus Sound, Queen Charlotte Sound) which were linked to origins outside the TOS. These vessels were cleaned at haul-out facilities. Previously, there had been only one wider regional fanworm find on a vessel, in the 2015/16 survey (although there are separate records from known populations in Picton, Nelson and Tarakohe marinas).
  • Other long-established pests (kelp Undaria pinnatifida, sea squirt Didemnum vexillum) are widespread regionally on vessels and structures. The more recently-established sea squirt Styela clava is becoming increasingly common on structures and/or vessels in a few locations (Tarakohe, Nelson, parts of Pelorus Sound). For these established species, the disjointed distribution is consistent with human-mediated spread rather than natural dispersal, highlighting the importance of managing spread by hull fouling.

The Level of Fouling (LOF) status of boats was largely similar to previous surveys, as follows:

  • Around 20-25% of active boats exceeded the ‘light fouling’ (LOF 2) threshold, with many heavily fouled boats (LOF 4 & 5) active throughout the TOS region.
  • Overall, hull fouling tends to be the greatest on vessels originating from Nelson, less on vessels from Marlborough, and least on vessels visiting from outside the region. Fouling is also relatively low on vessels from Tasman, reflecting that many of the boats surveyed are on swing or pile moorings than dry at low tide.
  • Data from the 5 surveys shows a clear trend for marine pests to become more prevalent with increasing LOF. However, even LOF 2 vessels (i.e. with light fouling) can have pests present, typically on the bottom of the keel, as this area is difficult to effectively antifoul.

Recreational boater maintenance habits

The vessel maintenance habits of recreational boaters have not changed appreciably over the 5 years, despite efforts to educate skippers about the importance of regular high-quality antifouling, and vessel cleaning before departure from their home port.

Combined survey data reveal that around 28% of boaters had undertaken a hull clean since their last antifouling. Based on survey data from 2015/16 and 2019/20 (and a 2017 travel-lift study in the TOS), it is apparent that more than half of these vessel were cleaned in-water, often while moored or anchored in high-value areas. In-water cleaning is considerably less effective at a management tool than a haul-out and water blast (e.g. some vessels were LOF 5 within a month of being in-water cleaned).


Implications and further considerations

Out-of-region boaters, while generally having only ‘light fouling’, represent a particular risk of introducing new pests to the TOS due to fouling of niche areas (e.g. bottom of the keel). Wellington marinas are not currently thought to have pests of significance to the TOS, but if such pests established, those locations would become significant sources for spread into the region. In this respect, among the key needs are approaches to ensure that visiting vessels:

  • Are detected before or upon arrival through an improved intelligence system.
  • Arrive in the TOS with a ‘clean’ hull where this can be achieved.
  • Are subjected to risk-profiling and an appropriate management response upon arrival, where feasible (e.g. where the point of arrival is a marina).

Changing the maintenance behaviour of within-TOS boaters is critical for reducing the regional spread of established pests, and understanding current attitudes and barriers to change is part of this picture. One of the recognised barriers is lack of capacity at haul-out facilities in Nelson to enable boaters to be lifted from the water for cleaning or maintenance. Although this issue is now being addressed, the risk profile of recreational vessels plying the region’s waters will not improve until it is fully resolved. Related to this issue, the current alternative practice of in-water cleaning in remote locations provides a potentially significant mechanism for the spread of pests to high-value areas across the TOS. Arguably, it is futile to be advocating or regulating improved hull hygiene without systems in place to support best practice.


2018/19

Summary of survey

In the 2019 survey checks were made of 521 vessels, 401 structures and 47 seabed sites, with a total effort over the four surveys of 2,683 records, comprising 1,478 vessels and 1,158 structures, as well as 47 seabed sites surveyed in 2019. Key results across four surveys were as follows:

  • No pests were found that are new to the TOS region.
  • The Mediterranean fanworm (Sabella spallanzanii) was recorded only once outside the know infected vessel hubs. This was in 2016, when juvenile specimens were found on a vessel (originally from Auckland) that was holidaying in Queen Charlotte Sound.
  • Other than the single vessel record, the absence of fanworm beyond the known infected areas (i.e. in Picton, Waikawa, Nelson, Tarakohe) likely reflects that populations in those areas are being periodically removed by divers as part of a SCUBA-based control programme, thereby reducing the reproductive reservoir for infection of vessels.
  • By contrast with the fanworm, the sea squirt Styela clava has become regionally common in certain areas, although the longest-established pests (Asian kelp Undaria pinnatifida, sea squirt Didemnum vexillum) are by far the most widespread, especially on artificial structures.
  • For all established species, the disjointed distribution is consistent with human-mediated spread rather than natural dispersal, highlighting the importance of managing spread by hull fouling.
  • The level of fouling (LOF) status of boats in 2019 was largely similar to previous surveys, except for those originating from Nelson-Tasman on which the incidence of heavy fouling appears to have increased. Overall, hull fouling was the greatest on vessels from Nelson, less on vessels from Marlborough, and least on vessels visiting from outside the TOS region.

Out-of-region visiting boats made up 23% of total records, but their occurrence was disproportionate across the two TOS regions, with visitors comprising ~30% and 12% of boats active in Marlborough and Nelson-Tasman, respectively. In the case of Marlborough, most of the out-of-region boats were from Wellington, especially Mana marina on the Kapiti coast. Very few boats come from other parts of New Zealand, and it is uncommon to encounter vessels from overseas. Findings were assessed in relation to compliance with hull biofouling rules developed by Marlborough District Council and Port Marlborough marinas, revealing that non-compliance is likely for a relatively high percentage of visiting boaters. The results reinforce the importance of direct management of vessel fouling as an integral part of effective biosecurity. A significant challenge is reducing ‘niche’ area fouling on the bottom of vessel keels, especially in situations where the main hull appears well-maintained and free of visible macrofouling organisms.


2017/18

Summary of survey

In 2017/18 we surveyed 544 vessels (mainly recreational yachts and power boats) and 546 coastal structures (mainly swing moorings and jetties), and engaged with 232 active boaters. Key results were:

  • No Mediterranean fanworm (Sabella spallanzanii) was detected during the surveys.
  • The long-established marine pests, Asian kelp Undaria pinnatifida and sea squirt Didemnum vexillum, were widespread.
  • The most notable change since 2016/17 was the increased prevalence and relatively widespread distribution of the sea squirt Styela clava. This species was present on >5% of vessels and >7% of structures. New populations were recorded in Kenepuru Sound, which added to new populations found in Okiwi Bay during the concurrent SCUBA survey.
  • The disjointed distributional pattern of Styela clava, as well as Undaria pinnatifida and Didemnum vexillum, is consistent with human-mediated spread rather than natural dispersal.
  • The level of fouling (LOF) status of boats was similar to previous surveys. Overall, hull fouling was the greatest on vessels from Nelson, less on vessels from Marlborough, and least on vessels visiting from outside the region.

Survey results illustrate that intensive population control for target pests in vessel hubs is an effective way to reduce vessel colonisation and subsequent vessel-mediated spread. The fanworm has been managed to low densities in Picton/Waikawa, Nelson, and Tarakohe, and was not recorded anywhere outside of these hubs.

By contrast, the more abundant unmanaged pests in these hubs were the ones that were prevalent on vessels. In the absence of Styela clava population control, or continued fanworm control, it can be expected that vessels in TOS hubs will increasingly act as vectors for the within-region spread of multiple marine pests. In addition, the proportion of boats from Wellington was high (17%), illustrating the potential importance of Wellington marinas as source regions for pests to the TOS. Wellington marinas are not currently thought to have fanworm, but if it did establish, those locations would become significant sources for fanworm spread, especially to Marlborough.


2016/17

Summary of survey

Monitoring was conducted over six days during the peak summer season from 27 December 2016 to 30 January 2017. In total we checked 186 boats, 73 associated moorings, and a few other structures (e.g. pontoons, pilings, rock walls). Key findings and implications are as follows:

  • Many conspicuously fouled boats (i.e. LOF ≥ 3, fouling cover exceeding 5%) are active throughout the TOS, although the prevalence of such vessels in 2016/17 was less than in previous surveys.
  • A total of 19% of boats had at least one of the six target pests present. Well-established pests like the kelp (Undaria pinnatifida) and the sea squirt (Didemnum vexillum) are common on boats and moorings across the region. The sea squirt Styela clava was found on two moorings in Duncan Bay, and on six boats visiting the Abel Tasman coast. These boats originated from Nelson, and Styela clava was present only on the bottom of the keel in each case. The fanworm Sabella spallanzanii was not recorded, although this species is present and actively managed at a few vessel hubs across the region.
  • The current prevalence and wide distribution of Undaria pinnatifida and Didemnum vexillum likely reflects the future distribution (e.g. over the next 10-20 years) of more recently-arrived pests like Sabella spallanzanii and Styela clava, unless stringent management measures are put in place to slow spread. In fact, based on the 2016/17 findings, and reported Styela population range extensions in 2016, it appears that the spread of Styela clava beyond vessel hubs into high value areas is already occurring.
  • Niche area fouling is most apparent on the bottom of the keels of vessels (especially sail boats) whose hulls may otherwise be free of visible fouling; as exemplified by the Styela finds. The keel bottom is one of the most extensive and heavily-fouled niche areas on recreational boats, but the risk could be reduced by developing effective management practices.
  • Some 24% of boats surveyed were from Wellington, highlighting that region as an important source area for the TOS. This situation reinforces the importance of developing effective management approaches for Wellington vessels planning to visit the TOS.
  • Despite the clear benefits of effectively managing external boats at source (i.e. before they leave for the TOS), it is inevitable that some high-risk vessels will continue to arrive. As such, improving the intelligence-gathering and early warning communication network for such arrivals is essential.

2015/16

Summary of survey

Vessel monitoring was conducted over six days during the peak summer season, with effort focused on four sub-regions: Port Tarakohe, the Abel Tasman National Park coastline, Pelorus Sound and Queen Charlotte Sound. Biofouling was surveyed on 226 boats in total across these areas, and 135 associated moorings.

Level of Fouling (LOF) scores in the regional survey were as follows:

  • Overall, 16% of vessels were categorised as “heavily fouled” (LOF ≥ 4; fouling cover ≥ 16%), which is comparable to the levels recorded in earlier studies in Nelson and Waikawa. However, only 8% of boats classified as being in active use were heavily-fouled, reflecting that active boats tend to be better maintained than those that may otherwise be sitting idle (e.g. at moorings or marina berths).
  • Sail boats (mainly yachts) were more fouled than power boats, consistent with the expectation that many fouling organisms can survive the low voyage speeds (c. 7-8 knots) at which yachts travel, whereas they become dislodged or damaged at the faster speeds travelled by power boats.

No pests were found that were new to the TOS region. However, a total of 30% of boats had at least one of the six target pest species present, with an increasing prevalence of pest occurrence with increasing LOF. Pest prevalence appeared related to the duration a given species had been established in the TOS, as follows:

  • The fanworm Sabella spallanzanii (first recorded in 2013/14) was found in outer Queen Charlotte Sound on a yacht from Wellington.
  • The sea squirt Styela clava (first recorded in 2006) was found on five yachts, three being in Tarakohe Harbour. Styela clava was also found on three Tarakohe moorings.
  • The sea squirt Didemnum vexillum (first recorded in 2001) was detected on 10% of boats and 36% of moorings surveyed.
  • The Asian kelp Undaria pinnatifida (first recorded in 1991) was found on 24% of boats and 33% of moorings, despite being the “low season” for this species.

It was often the case that boats with light fouling overall (e.g. a slime layer on the main hull) had well-developed fouling in “niche” areas. Vessel keels are of particular interest in this regard, as on some boats keels provide a large surface that can develop advanced macrofouling and harbour marine pests. This situation primarily reflects that keels may be incompletely coated (or not coated) with antifouling paint during maintenance. The 2015/16 report also summarises the findings of a mail-in boater questionnaire, that sought to understand boater maintenance habits and other behaviours.