Assessment of population management options for Styela clava

New Zealand wide vessel movements, MAFBNZ project ZBS2005-13 and an epidemiological
simulation model for yacht movements developed by NIWA.
Executive Summary
Potential vectors associated with the Tutukaka Marina included recreational yachts, diving and fishing
charter vessels and commercial fishing vessels. Fifty-four percent of recreational vessels, 15.4% of
diving vessels and 66.7% of fishing vessels resident at the marina were found to carry fouling
organisms on their hulls. All of these vessel types regularly or frequently travel between Tutukaka
Marina and the Poor Knight Islands HVA, but few movements occur to other HVAs.
Potential vectors associated with the Lyttelton Port included recreational yachts, scenic and fishing
charter vessels, merchant ships, commercial fishing vessels, operations and maintenance vessels,
towed barges and a towed pontoon. Of these, 69%, 34%, 72%, 25%, 100% and 100% were found to
carry fouling organisms on their hulls, respectively. Styela was observed on some of the barges and
the workshop pontoon. However, these vectors never leave the Port. All other vessels types
undertake regular to frequent visits to the Banks Peninsula, Akaroa Harbour and Marlborough Sounds
HVAs. Very occasionally, recreational craft travel from Lyttelton Port to the Poor Knights Islands
HVA.
Potential vectors associated with the Magazine Bay Marina included recreational yachts and a single
inactive commercial fishing vessel. Seventy-four percent of the recreational yachts encountered
carried fouling organisms on their hulls, in one case Styela. Occasional visits to all four HVAs occur
by recreational vessels from Magazine Bay Marina. Overall, this marina has by far the lowest vector
activity of the three surveyed source locations.
Movement patterns of vectors between New Zealand’s coastal ports and marinas are complex. The
four HVAs examined in this study are visited by vectors originating from all three source locations,
but at varying frequencies. In addition, they receive a considerable amount of vector traffic from the
Auckland region, where Styela is widely distributed. The Poor Knight Islands are very rarely visited
by vessels from Lyttelton, but receive frequent visits from marinas around Auckland where Styela is
known to be established. The Akaroa Harbour and Poor Knights Islands HVAs are unlikely to
become inoculated with Styela through aquaculture related vectors. Instead, recreational and
commercial (charter) vessel movements have a higher likelihood of transporting Styela to these HVAs.
Aquaculture operations, commercial and recreational vessel traffic all have the potential to transport
Styela to (and throughout) the Banks Peninsula and Marlborough Sounds HVAs.
Deliverable 3: Identify and determine the risk of Styela clava spreading from delimitation
locations to HVAs.
We calculated the risk of Styela being transported directly from known source populations to HVAs.
The source populations considered included the three delimitation locations and the wider Auckland
region (including Waitemata harbour and the Hauraki Gulf). The Auckland region was added since
we felt a nationwide assessment of the risks of Styela spreading to HVAs would be substantially
incomplete and potentially misleading without it. The HVAs considered were identified as being at
high risk in deliverable two. We considered four possible human-mediated vectors (recreational
boating, commercial shipping, aquaculture activities and the towing of barges and structures), as well
as natural dispersal as key vectors likely to spread Styela. As such there were 80 possible pathways
between source populations and HVAs considered.
MAF Biosecurity New Zealand Assessment of population management options for Styela clava • 3