This instrumentation raft in the centre of the farm houses a range of sensors (Photo: Craig Stevens)
This sensor mounted on a mussel line measures the water turbulence in the flow as it approaches the feeding mussels (Photo: Jens Larsen)
Exploring Danish
N
SHELLFISH FARMS
BY CRAIG STEVENS, NIWA MARINE PHYSICS
ew Zealand's involvement in an international project aimed at reviving the Danish mussel industry will help keep us at the forefront of world aquaculture
development, say NIWA scientists Drs Craig Stevens and David Plew. They recently returned from a high-profi le collaborative
fi eld experiment in Limfjorden Jutland, where a three-year international project is underway to enhance mussel farming in Denmark.
While a wild fi shery has existed there since the 1940s, Denmark's mussel aquaculture is a relatively new venture. Its expansion has been rapid in the last decade, when the Danish government began issuing farm licences for Limfjorden Jutland. Total farmed production was nearly 3000 tonnes by 2009 and while that is only about 10 percent of New Zealand's output, Denmark is now the fourth-largest mussel producer in Europe and plays an important role in the local economy.
The Danish industry grows blue mussels (Mytilus edulis), a species widely distributed in European waters from Russia to the Atlantic coast of southern France. Although blue mussels can live for up to 24 years, most cultured mussels are produced in less than two years. Despite its success, Denmark's mussel aquaculture industry
is currently facing signifi cant issues which distinguish it from New Zealand's own aquaculture development. It's historically strong wild shellfi shery is struggling because of economic and environmental pressures. The centre of the industry - both wild and cultivated – is the largely landlocked Limfjorden, a complex series of basins connected to both the North Sea and the Kattegat, the strait between Denmark and Sweden. Because the area is surrounded by agricultural farming and the basins are relatively low-fl ushing, the Limfjorden Jutland is typically quite eutrophic, with low water quality and frequent algal blooms, due to excessive nutrients. To mitigate these effects, mussel farms are being used to soak up excess nutrients in the water. Being able to sell the mussels for feed or human consumption is a bonus. To help boost the industry, an international team of scientists, funded by the Danish government's Strategic Research Fund, is part of the way through a three-year project to make mussel farming more effi cient, while at the same time ensuring ecologically sustainable production that complies with environmental management requirements. As a result of the project, sophisticated aquaculture
Blue mussels ( 14 ■ NZ AQUACULTURE ■ ) feeding (Photo: Jens Larsen) NOVEMBER/DECEMBER 2011
approaches to harvesting mussel crops are evolving to complement and enhance the existing industry. The project team includes biologists, oceanographers, economists and computer modellers from Canada, the United States and Germany, as well as Denmark and New Zealand. They are based at the Danish Shellfi sh Centre, a
My
tilus edulis
