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Research & Education
Mussel Farms in Port Phillip Bay Given a Clean Bill of Environmental Health |
FN0590
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Geoff Gooley, Fisheries Victoria, DPI
Updated: August 2007
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The blue mussel farms of Port Phillip Bay have little, if any, adverse effects on the structure and integrity of the habitats on the seafloor below them, according to the results of a 2003 survey undertaken by aquaculture and ecological specialists at the Marine and Freshwater Systems Platform (MFSP), Queenscliff.
The existing marine aquaculture industry in Victoria is based around the production of blue mussels, with most of the production centred on the Grassy Point and Clifton Springs Aquaculture Fisheries Reserves in Port Phillip Bay, and the Flinders Aquaculture Fisheries Reserve in Western Port. This industry was worth $2.8 million in 2004/05, and it is anticipated that into the future blue mussels will continue to be the main farmed bivalve shellfish in Victoria.
The mussel industry in Victoria has a year-round culture season, with maximum product available from November to April. A typical Victorian farm hangs mussel growing lines (droppers) vertically from tethered longlines (approximately 100 m long). In Port Phillip Bay, each 100m longline typically contains about 300 droppers with each dropper producing 15 to 30 kg of mussels over the 12 to 18 month production cycle. A typical Port Phillip Bay farm of 3 ha would have 8 to 10 longlines, resulting in annual production of 15 to 30 tonnes/ha.
As the environmental impact of Victoria mussel farms had not been determined previously, and to advise the management plans for aquaculture fisheries reserves in Victorian coastal waters, Fisheries Victoria commissioned the Department of Primary Industries’ (DPI) research arm Primary Industries Research Victoria (PIRVic) to undertake a survey to determine the impacts of long-term mussel farming on the organisms and habitat under and around the farms in Port Phillip Bay.
The design of the survey was based on a review of the environmental impacts reported from bivalve aquaculture production activities elsewhere in the world. The survey methods and techniques were tailored to suit Port Phillip Bay conditions.
The scientific data reported elsewhere deals with the impact that bivalve shellfish aquaculture operations have on the water column when production levels are very high (ie they occupy 20% of the waterbody) and/or when they occur in shallow and poorly flushed systems. This is not the case in Port Phillip Bay because bivalve shellfish farming is restricted to approximately 1% of the bay which is relatively deep and well flushed with good water exchange between farmed and unfarmed areas. Consequently, the DPI study concentrated on assessing the impact these operations had on the bay’s benthic habitat and communities.
The survey was conducted at a farm in the Grassy Point Aquaculture Fisheries Reserve. The farm had a high stocking density (relative to the other farms in Port Phillip Bay) and had been in operation for at least 10 years. This farm was located on the corner of the reserve, which allowed the scientists to determine if any impacts extended beyond the farm boundaries and into water not impacted by a neighbouring farm.
A team of ecologists, chemists and benthic biologists, led by Geoff Gooley and Lachlan McKinnnon, surveyed sites located 5, 25 and 50 m from the farm in the direction of the current flow, as well as sites located under the farm.
Little, if any, environmental impacts were detected. The changes observed in this study included:
- a small increase in fine sediments;
- a small increase in the number and variety of organisms living in the sediments; and
- an increase in the abundance of the native eleven-arm seastar beneath the farm.
The changes measured beneath the farm are much smaller than those reported from overseas studies but similar to those reported from Tasmanian bivalve shellfish farms. This may be due to the relatively low density of production and yield of Victorian farms.
Shellfish production in Victoria is about 15-30 tonnes/ha/year. This is an order of a magnitude below the 200-300 tonnes/ha/year production levels, which have resulted in a marked environmental impact overseas. The relatively low intensity production of Victorian farms is probably a reflection of the low nutrient levels in Australia waters, and characteristic of the relatively shallow waters that are farmed.
Under more intensive farming, the deposition of organic material in sediment increases the risk of anaerobic conditions developing thereby reducing infaunal biodiversity; none of which was seen in the present study.
The results of this study have been used by Fisheries Victoria to advise management plans for each of the existing and new aquaculture reserves. These plans provide for the development of appropriate environmental monitoring strategies for the aquaculture fisheries reserves within Port Phillip Bay and Western Port.
Further Information
For more information about this study, contact Geoff Gooley at PIRVic Queenscliff on (03) 5258 0209 or for a copy of the study visit Victorian Marine Aquaculture Fisheries Reserves and follow the links to Publications and Site Relevant Information.
McKinnon, L.J., Parry, G.D., Leporati, S., Heislers, G.F., Werner, G.F., Gason, A.S.H., Fabris, G., and O’Mahoney, N. (2003) The Environmental Effects of Blue Mussel (Mytilus edulis) Aquaculture in Port Phillip Bay, Fisheries Victoria Research Report Series No. 1.
For more information on the Aquaculture Fisheries Reserves, call the Department of Primary Industries on 136 186.
Fisheries Research and Education Notes are available on the DPI website. Follow the prompts to Fishing and Aquaculture and then to Publications and Fisheries Notes. The notes are listed under the heading Research and Education.
The previous version of this Information Note was published in July 2006.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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