Black striped mussel outbreak in Darwin – 1999
A case study of the response to the 1999 outbreak of black striped mussel in Darwin Harbour
CSIRO divers discovered massive infestations of suspect mussels in Cullen Bay Marina during a survey for introduced marine species on 27 March 1999.
- Samples were identified as black striped mussel by the Museum and Art Gallery of the Northern Territory on 29 March 1999.
- Further infestations of black striped mussel were found in Tipperary Estate Marina and also on the hull of a yacht in Frances Bay Marina on 31 March 1999.
- At the time of the detection 147 vessels were in Cullen Bay, 70 in Frances Bay and six in Tipperary Waters. Another 197 vessels, including 57 from the Northern Prawn Fleet were at sea but identified as having left the contaminated sites between October 1998 and March 1999.
Immediately following identification of the mussels, the Minister and Chief Executive Officer of the Department of Primary Industry and Fisheries were briefed on the outbreak, its implications and initial response options. A Northern Territory incident management taskforce was established with units responsible for media, vessel tracking, emergency services, public health, diving/survey, eradication biology and treatment.
A special meeting of the Northern Territory Cabinet agreed to amendments to the Northern Territory Fisheries Act 1988 and Regulations to allow for the implementation of emergency arrangements. These changes:
- listed the black striped mussel as an aquatic pest
- designated ‘aquatic pests’ alongside ‘disease and contaminated fish’
- decreed that restricted areas could be imposed around areas with aquatic pest outbreaks
- declared the affected marinas to be restricted areas and prohibited the movement of aquatic life from these areas.
Cabinet also approved the expenditure of funds necessary to effectively address the response actions, without stipulating a specified funding limit.
The aims of the response were to:
- survey the extent of the black striped mussel outbreaks
- quarantine all confirmed infected areas in Darwin
- treat the marinas and all infected vessels to eradicate the black striped mussel
- track and treat potentially infected vessels that had left the infected Darwin sites.
Northern Territory taskforce control
The taskforce established a control centre at the Department of Primary Industry and Fisheries with a 1800 hotline to answer enquiries from the public.
The taskforce met twice daily to coordinate on-ground containment and treatment activities. Primary decisions were recorded and formally signed as evidence of authority to take actions. The Minister for Primary Industry and Fisheries attended almost every meeting.
The three infected sites were quarantined, using the Northern Territory Fisheries Act 1988 (amended for the purpose) and the Commonwealth Quarantine Act 1908. The combination of these actions enabled vessel movements to be controlled and, where appropriate, vessels ordered out of the water through the issue of quarantine notices. No vessels inside the marina were permitted to leave until the marinas were declared free from the mussel.
Media and communications
The media team was established at the outset of response activities. Its primary role was to establish public information and awareness mechanisms to meet the needs of local, national and international stakeholders.
The team focused on delivering coordinated and up-to-date messages on the importance of the response actions through the following activities:
- public meetings at Cullen Bay Marina, addressed by relevant NT Government ministers and senior taskforce members to reinforce the authority for the response
- development and distribution of information fliers to residents, businesses and vessel operators
- daily media advertisements
- coordinating responses to enquiries through the 1800 hotline
- development of a website to provide immediate access to the latest technical information, management decisions, directions to vessel owners, public awareness material and to track decisions and actions taken over the course of the outbreak.
The media campaign has been widely acknowledged as a successful model approach for managing the information requirements of an emergency situation.
A national taskforce was established on 6 April 1999 due to the national significance of the outbreak and the need to coordinate national action to prevent spread of the mussel to other states.
The role of the national taskforce was to provide a communication network between the Australian Government, the states and the Northern Territory and to provide support for strategies being developed by the NT taskforce.
The main issues addressed by the taskforce included:
• effective communications between all stakeholders nationally
• support for checking movements of commercial and recreational vessels interstate
• development of effective scientific treatment protocols
• legislative requirements to take appropriate containment and treatment actions.
Identification of ‘at risk’ vessels and subsequent tracking and treatment of vessels that had left the infected marinas prior to 27 March 1999 was a taskforce priority.
Initially 420 vessels were deemed at risk as they had been in the infected marinas since the likely start of the contamination period.
With the cooperation of key agencies, local ship repair and maintenance facilities and word of mouth, a large amount of information on the whereabouts and movements of vessels was obtained and a database established. Alerts were sent to vessel owners and authorities to check and treat vessels.
The 57 vessels of the Northern Prawn Fisheries Fleet that had already left for the start of the prawn season were of particular concern due to the risk they posed of spreading the pest through contact with other vessels and visit to other ports, marinas and anchorages. Fortunately these vessels carried GPS systems and could be contacted and inspected. No mussels were found on these vessels.
Tracking interstate and international ‘at risk’ vessels was more difficult. However the vessels that were able to be tracked and inspected were not found to be contaminated.
An initial survey conducted between 29 March and 3 April 1999 indicated that mussels were contained within the three marinas.
This was confirmed by subsequent systematic surveys of all potential sites of pest contamination in the marinas and around Darwin Harbour, including vessel hulls, the naval base, careening poles, surrounding buoys, wharves, oil rigs, barge landings and nearby Darwin Harbour shorelines. Sewage and storm water drains were also inspected.
Inspection protocols were developed to check vessels that had been in the marinas during the likely contamination period. Particular attention was given to hull surfaces, ropes, chains, anchors, sea water inlets and internal water systems. Around 250 vessels were inspected in this way, including barges and oil rigs.
The dive teams had a critical role in the clearance of vessels and other potentially contaminated sites and also in verifying the success of subsequent treatment actions.
Chlorine was considered the most likely available chemical to kill black striped mussel, based on its past use to counter infestations of the closely related zebra mussel in the USA. Chlorine is biodegradable and considered unlikely to persist in the marine environment and cause significant harm to the surrounding Darwin Harbour.
Immediately following the declaration of the quarantine areas, the locks of the three marinas were treated with granular calcium hypochlorite to kill any mussel larvae and to act as a sterile plug between the marina and the harbour.
Treatment of Cullen Bay Marina began on 4 April 1999 with the first addition of liquid sodium hypochlorite. The chemical was mixed into the 12 hectares of water by running the propellers of a cruising sports fishing yacht moored to the pontoon within the marina. In addition large pumps were used to help the mixing particularly in the 'dead end’ parts of the marina. Chlorine concentrations were measured daily and additional hypochlorite added to try to keep concentrations of chloride at about 10 parts per million of free chlorine.
However, monitoring of caged mussels showed that some mussels were surviving the chlorine treatment. Also obtaining sufficient chlorine to maintain an effective concentration in the marina became logistically very difficult. Following a trial of copper sulphate in Tipperary Waters Marina Estate that resulted in 100% mortality, copper sulphate was used in conjunction with chlorine at Cullen Bay and Frances Bay marinas. Copper sulphate was added to the marinas by initially dissolving the powder in the tank of a road construction watering truck and then hosing this over the water surface of the marinas.
In total 187 tonnes of liquid sodium hypochlorite and 7.5 tonnes of copper sulphate were added to the three marinas over two weeks.
Fish removal teams were deployed shortly after chemical treatments to remove dead organisms, ensuring there were no health issues. Four tonnes of dead fish were removed from the Cullen Bay Marina.
Vessels inside the marina were treated through the addition of chemicals to the surrounding water. Internal pipes on all vessels were treated by running the relevant pumps or engines and adding copper sulphate solution or detergent to pipes with standing water. In cases where the owner was unavailable to treat their vessel this was conducted by Fisheries officers.
All vessels outside of the marinas that had been potentially exposed to these infected marinas were inspected and any infected vessel hauled out and cleaned.
Vessel operators were provided with instructions on precautionary actions to treat and prevent further spread of the mussel. These included:
- avoidance of shallow water in case mussels were accidently scraped off the boat
- no scraping of vessel hulls at sea
- cleaning of internal water systems (with boiling water, or water hotter than 50 degrees Celsius for an hour, or 5% detergent solution for 14 hours, or copper sulphate at 4mg/l for 48 hours)
- protective linings around vessels when hauled out to prevent mussel escape into surrounding areas
- steam cleaning on haul out or drying on hard stands for 7 days
- disposal of debris and water after cleaning.
Stand down phase
Following no further detections of live mussels, quarantine arrangements were lifted and all three marinas re-opened for normal use on 23 April 1999. The end of the emergency was clearly communicated by the media team.
The Northern Territory Government maintained a precautionary approach immediately following the outbreak to mitigate against a recurrence of the incursion. Actions included:
- continuation of diving and sampling around the infected marinas until a formal ‘all clear’ was given on 7 May 1999
- maintenance of inspection and treatment protocols for vessels returning to the Darwin marinas, such as those from the Northern Prawn Fishery
- consultations with key stakeholders to develop future inspection and treatment measures
- monitoring of marinas and hot spots for a further 12 months.
Costs and resources
The cost of the response was estimated to be over $2.2 million. In the absence of a prior cost sharing agreement, the Australian Government agreed to reimburse the NT Government $998,000 towards response costs.
It was also estimated that the closure of the marinas and other control actions cost the private sector hundreds of thousands of dollars in lost revenue. The NT Government faced 15 litigation actions arising from the response, however most were dismissed.
Other key resources utilised
- over 280 personnel directly involved
- 187 tonnes of liquid sodium hypochlorite and 7.5 tonnes of copper sulphate applied
- 28 divers involved, many with specialist qualifications for hazardous work
- over 760 vessel entries in the vessel monitoring database
- over 250 vessels, including barges, oil rigs and wharf piles inspected.
A national workshop was held in Darwin in August 1999 to evaluate the response and how it was handled. Recommendations were made for future emergency response situations. The workshop also made recommendations for improved longer term management arrangements for marine pest incursions at the national level.
Download the full workshop report
This case study has been developed from the following documents:
Bax, N., Hayes, K., Marshall, A., Parry, D. and Thresher, R. (2002). Man-made marinas as sheltered islands for alien marine organisms: Establishment and eradication of an alien invasive marine species. In: Veitch, C. R. and Clout, M. N. (Eds.) Turning the tide: the eradication of invasive species. IUCN SSC Invasive Species Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK, pp. 26-39.
Ferguson, R. 2000. The effectiveness of Australia’s response to the black striped mussel incursion in Darwin, Australia. A report of the Marine Pest Incursion Management Workshop, 27-28 August 1999. Department of Environment and Heritage, Commonwealth of Australia, Canberra, Australia, Research Report, 13.