Mussel Farming in the Marlborough Sounds

Last Modified: 21-2-2019 8:59

Mussel harvesting in the Marlborough Sounds
Mussel harvesting in the Marlborough Sounds
© Christopher Cookson  License this image

The mussel farming industry in the Marlborough Sounds started in the 1960s. The early days of the industry were dominated by research and development, local sales, and an extract promoted as a remedy to help alleviate arthritis.

New Zealand today has over 550 mussel farms totalling 4500 hectares, most of them in the Marlborough Sounds. Large farms proposed for open coastal regions could result in a 10-fold expansion in area in the near future, and increased awareness of mussel farming?s impact on the marine environment. 

We know that the Marlborough Sounds is a place of outstanding beauty, where wedge-shaped hills shelter a network of shining waterways. With few roads connecting the Pelorus, Queen Charlotte, Anakiwa and outer Sounds, many bays and coves are seldom visited. This is the environment where several hundred mussel farmers cultivate New Zealand Greenshell mussels, inconspicuous beneath barrel-like floats. This paradise is the workplace where marine farming staff, utilising world leading technologies, cultivate Marlborough's world famous products.  

The deep, clean and cool waters of the Marlborough Sounds provide an ideal environment for raising mussels from spat through to harvest, with sound cultivation methods ensuring they grow quickly and are sand and grit-free. Shellfish health and seawater purity are rigorously monitored, and the various companies and farmers have adopted an environmental code of practice which ensures our the safety of the area's unspoilt beauty. 

One firm, Marlborough Seafoods Ltd., sources around 35% of its throughput from its own farms and the balance from contract growers and long-term suppliers.  


Stage One: In the New Zealand greenshell mussel-farming cycle are seeding nursery lines of tiny baby mussels or spat, held in place with a continuous tubular cotton stocking which biodegrades when no longer needed. Greenshell mussels are farmed using a series of buoys and ropes. A line of buoys is anchored to the sea floor at both ends, using a rope (referred to as a longline) on either side. These longlines can not exceed 110m in length. Attached to the longline at regular intervals is the growing line, which is a single rope that can be up to several kilometres long. The length of this rope is determined by the depth of water that the farm occupies, and the maximum depth desired.  

The use of a single rope was pioneered in New Zealand. Prior to its development, single weighted ropes were dropped at regular intervals from the longlines. Mussel spat is attached to the rope, and encased in a mesh stocking that dissolves in seawater over a few weeks, by which time the spat is normally attached to the line. The bulk, though, is sourced from the beaches of Kaitaia, in New Zealand's north and nearby Golden Bay. After three to six months, the nursery lines are lifted and the young mussels removed then seeded at a sparser rate onto a thicker and much longer rope, where they remain until harvest.                     

Depending on site and the number of mussels growing per metre of rope, the cycle from seed to harvest takes 12 to 18 months for 90-120 mm mussels. 

Stage Two is harvesting which takes place throughout the year, timed to coincide with mussels reaching peak condition. The early-bird crew of Aotearoa Seafoods' specialist harvesting vessel, the Te Au Miro, leave the port of Havelock in darkness, pulling up the first lines as the sun melts early morning mist off the sea.              and Atmospheric Research (NIWA), is employed to monitor rainfall using automatic gauges   situated throughout the Marlborough Sounds. All of New Zealand's shellfish-producing waters are regularly monitored for the presence of naturally occurring but potentially toxic algal blooms, with harvesting temporarily ceased if their presence is confirmed. Such blooms are extremely rare in our Marlborough Sounds and never widespread, possibly due to geographical isolation and relatively cool waters.  

The Marlborough Regional Development Trust has the following to say about aquaculture in Marlborough. 

Marlborough is New Zealand's aquaculture capital. Over 80% of the country's aquaculture exports are grown in Marlborough. Greenshell mussels (Perna caniculus), King salmon (Oncorhynchus tschawytscha), Pacific oysters, paua (abalone), Kingfish, and Koura (fresh water crayfish) and seaweed, all find a place. As one of the largest industries in Marlborough, almost every facet of the social and economic base of the region is touched by aquaculture. Export earnings from Marlborough produce exceed $200,000,000 pa.  

The majority of farms are located in the Pelorus Sound with smaller production bases in the Croiselles Harbour, East Bay (Queen Charlotte Sound) and Port Underwood. The area occupied by marine farms in the Marlborough Sounds is approximately 2,600ha and occupies less than 3% of the total area of the Sounds.  

Support and infrastructure facilities for the industry are centred on local ports such as Picton, Havelock and Elaine Bay. Boat building and equipment supply services are located in Blenheim, Renwick, Havelock, Picton and Rai Valley. The industry has spawned a significant boat construction industry with the largest aluminium vessel ever produced in the South Island completed in 2002.  

Marine farming contributes significantly to employment in Marlborough with an estimated 1500 full time equivalent jobs. The industry has a global reputation as the leader in farming innovations and the management of food safety programmes, especially in the field of biotoxin management of the growing waters. The industry and the Nelson Marlborough Institute of Technology are developing significant training programmes from pre-employment through to post graduate with the central focus in Marlborough. The Marlborough District Council (Unitary Authority) is the most experienced Council in New Zealand processing marine farming applications under the Resource Management Act. Marine farming has revitalised the small rural towns such as Havelock and Rai Valley and coastal communities of the Marlborough Sounds such as Waitaria Bay.   World demand for seafood is growing. The wild fishery cannot increase to equal this demand while the aquaculture industry can and will. Already nearly one third of the world?s fish and shellfish is produced by aquaculture. Aquaculture is the fastest growing sector of the international food industry with production growing at 15% per annum.  

The aquaculture industry is forecasting growth to achieve $1 billion export revenues by the year 2020. As the capital of the New Zealand aquaculture industry, a significant proportion of the industry?s intellectual property resides in Marlborough, presenting an array of opportunities, especially in the supply of infra-structural products and services and the commercialisation of intellectual property.   Greenshell mussels is the largest segment of the aquaculture industry, nationally growing around 55,000 tonnes annually (2002). The product is processed locally at factories located in Picton, Havelock, and Blenheim or sent to Nelson and Christchurch. Processed mussels are exported to over 50 countries world-wide. Production from mussel farms in Marlborough account for 80% of the country?s export production. Almost all the mussels grown in Marlborough are exported. 

Stage Two: The mussels are harvested when ready by lifting the lines and removing the mussels from it. Harvesting is synchronised with factory production so as to ensure mussels spend a minimum time out of the water, and is suspended if significant rain falls (to eliminate the risk of bacteria being washed off the land and ingested) and during spawning (when shellfish become undernourished). The National Institute of Water and Atmospheric Research (NIWA), is employed to monitor rainfall using automatic gauges situated throughout the Marlborough Sounds.

All of New Zealand's shellfish-producing waters are regularly monitored for the presence of naturally occurring but potentially toxic algal blooms, with harvesting temporarily ceased if their presence is confirmed. Such blooms are extremely rare in our Marlborough Sounds and never widespread, possibly due to geographical isolation and relatively cool waters.
Mussel farms tend to act as man made reefs and as such attract a large number of small fish.

But the Guardians of the Sounds are most unhappy with the burgeoning mussel industry and make the following two points:

1.    A gold rush mentality by developers has overridden environmental considerations despite concerns being voiced by many members of the Sounds community, including experienced mussel farmers. Many people believe the Sounds are already operating at full capacity for mussel production.

2.    The Marlborough Sounds is an ecologically rich area and home to many unusual and, unfortunately, endangered species. The biodiversity of the Sounds is integral to its character and value. Many bays in the Sounds have the majority of their sensitive inshore communities smothered by mussel farm debris (shell drop and wastes) and in turn colonized by predatory starfish. There is an additional risk to these communities from introduced bivalve diseases and exotic species.

Gross tonnage of mussels harvested from the three main production areas:
Nelson/Marlborough 75,500
Firth of Thames 17,500
Stewart Island 2,000

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Mussel Farming in the Marlborough Sounds. (2019) Retrieved December, 5, 2023, from