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ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.
Dumb barge teaches important lessons: the translocation and management of a cryptogenic sea squirt
Cawthron Institute, Nelson, New Zealand
Email: ashley@cawthron.org.nz
This paper presents a case study about a slow moving barge, the ‘Steel Mariner’ and a cryptogenic compound ascidian. The barge was responsible for the translocation of Didemnum vexillum from Tauranga Harbour, North Island to the heart of the New Zealand Greenshell™ mussel industry: the Marlborough Sounds in the South Island. Some scientists considered the species to be a serious biosecurity threat to the mussel industry, given its fouling and smothering capabilities, particularly of artificial structures such as mussel lines.
Despite the Ministry of Fisheries (MFish) contracting two world authorities on ascidian taxonomy to identify the species, controversy still exists over the origin (native or introduced) of the ascidian. Consequently, the delegation of responsibility (MFish and Regional Councils) for managing the biosecurity threat has been significantly delayed. Since its arrival on the ‘Steel Mariner’ in Picton on 23 April 2001, the species has spread to the seabed below the ‘Steel Mariner’, another barge the ‘Waimarie 1’ and the Waimahara wharf (500 m away in Shakespeare Bay). D. vexillum look-a-likes have also been witnessed on salmon cages in Shakespeare Bay.
Despite an attempt to reduce the biomass of D. vexillum on the ‘Steel Mariner’ in early August 2002, colonies reached an estimated 1,945 kg of wet biomass weight in March 2003. This exceeded an initial biomass estimate of 1,396 kg in February 2002. In addition to the presence of the undesirable D. vexillum on the ‘Steel Mariner the Marlborough District Council (MDC) was also concerned about the seaworthiness of the barge. Hence MDC applied to the Environmental Court for enforcement orders under Section 316 of the Resource Management Act 1991 to scuttle the ‘Steel Mariner’. On 16 April 2003, the Environmental Court ordered that by 31 August 2003 the bulk of the D. vexillum be removed from the barge and that it then be scuttled in Cook Strait.
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