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Release of Recreational Vessel Fouling & Marine Pest Survey 20187 August at 09:23 from atlas
This report describes a summer survey of biofouling and marine pests on recreational vessels and structures across the Top of the South (TOS) region. The survey focused on locations outside the main vessel hubs, and included areas commonly visited by boaters from other regions. The scale of the survey was considerably greater (17 days) than in the two previous summers (5-6 days), reflecting increased surveillance effort for the Mediterranean fanworm Sabella spallanzanii. The regional programme described here supports fanworm surveillance and control activities being undertaken in and around the main hubs where this organism has been found to date (Picton marina, Nelson marina, Port Tarakohe).
The survey was conducted from December 2017 to April 2018, with an intensive period of effort during peak boating activity over Xmas and January. Biofouling on boats was assessed by snorkel diving, using a level of fouling (LOF) scale that describes categories of fouling ranging from no macrofouling (LOF ≤ 1) to very heavy macrofouling (LOF 5). As well as LOF assessment, boats and associated structures were simultaneously checked for the presence of six target marine pest species. When boaters were present, they were asked questions about their home port and their vessel maintenance habits.
Key findings and implications
In total 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. Although no Mediterranean fanworm was detected during the surveys, other marine pests were recorded. The key findings described below reinforce the role of recreational vessels in the spread of marine pests, and highlight the importance of managing this pathway effectively.
The 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. The long-established marine pests, Undaria pinnatifida and 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 is consistent with human-mediated spread rather than natural dispersal. The current prevalence and wide distribution of Undaria and Didemnum likely reflects the future distribution (e.g. over the next 10-20 years) of Styela, and also of the fanworm in the absence of comprehensive management.
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 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.
The above results reinforce the importance of direct management of vessel fouling as an integral part of effective biosecurity. Achieving effective vector management is not straightforward, as it requires means to address the risk from vessels coming into the TOS from other regions. For this purpose, the TOS Coordination Team is already working with Wellington marina managers, and is considering the best ways to address potential risks from Northland and Auckland.
A significant challenge for effective vessel management 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 fouling. The Coordination Team is continuing to explore the potential for development of effective antifouling practices for keels. A related challenge, and critical issue to address, is the lack of capacity at haul-out facilities in Nelson, to enable boaters to be lifted from the water for cleaning or maintenance. The risk profile of recreational vessels plying the region's waters is probably going to worsen unless this issue is addressed. Exacerbating this situation is the likelihood that some boaters will scrape these pests to the seabed while they are moored or anchored in high-value areas. Arguably, it is futile to be advocating or regulating improved hull hygiene without systems in place to support best practice.
Considerations for future surveillance
Future surveillance needs are discussed, including the need for further investigation of options for ensuring that visiting vessels: (i) arrive in the TOS with a clean hull, (ii) get cleaned upon arrival if they weren't cleaned before departure, or (iii) are subsequently detected if the first two measures fail. Gaps in regional surveillance are also discussed, and recommendations made for the allocation of effort among snorkel-based and SCUBA-based surveys. It is important that these two separate activities are well-aligned. SCUBA-based surveys within the key hubs need to be systematic and comprehensive, with snorkel-based surveys filling in the regional gaps and maintaining a broader data collection and boater interaction focus. Simultaneously, efforts to integrate other stakeholders (e.g. marine farmers, mooring service providers) into the surveillance programme should be continued. With all of these elements in place, the programme has the best chance of managing the ongoing threat from fanworm to the TOS region's values.
Download a copy of the report: Regional Recreational Vessel Fouling and Marine Pest Survey 2017/18 (PDF, 1M)