Limfjord blue shell mussel (rope grown)
MSC status
Certified as sustainable in April 2012.
Summary
Species: Mussels, (Mytilus edulis)
Location: Limfjorden, Denmark
Fishing methods: Rope grown
Number of fisheries: 1
More about mussels
The blue mussel, Mytilus edulis (Bivalvia: Mytilidae) is a sessile bivalve attached to the substratum by a byssus. Mussels can withstand wide variation in salinity, desiccation, temperature and oxygen concentration, resulting in the ability to occupy a large variety of microhabitats. Mussels can be found on any substratum providing a secure anchorage such as rocks, stones, gravel, shingle, dead shells, and even mud and sand. In soft bottom areas as the Limfjord, the mussels form stabilised mussel beds of interconnected mussels and dead shells. The blue mussel Mytilus edulis is a filter-feeding bivalve filtering primary on micro-algae and organic detritus but at lower rates also on zooplankton. Mussels follow a reproductive strategy of producing a very large number of gametes and hence planktonic larvae, of which a small proportion survive to settle and establish on the seabed. Mussels can adapt their reproductive strategy depending on environmental conditions; hence the reproductive cycle depends on the population’s geographical situation. The planktonic life of Mytilus edulis varies from 2-4 weeks depending on temperature, food supplyand availability of suitable settlement substratum; hence it can take 10 and more weeks between thefertilisation and the settlement of the mussel. The maximum settlement period is in June – Julyalthough a cohort of larvae and settlement are often observed in September. The growth rate of mussels varies greatly and is dependent largely on the availability of food.
More about the fishing methods
The 12 unit of certification cultivation areas under certification are licensed to five operators, and cover a total area of 2.1367km² (213.67ha). The smallest area covers 12ha, and the largest 22.6ha. Most of the licensed areas can be used for cultivation of both blue mussels (Mytilus edulis) and oysters (Ostrea edulis). No oyster cultivation activity is reported to be taking place in these areas at present. There are two aspects to stock status for an enhanced fishery. One aspect concerns the state of the stock within the cultivated system; and the other is the state of the wild stock outside that system.
Cultivated stock
The status of the cultivated stock is monitored by each mussel farmer within their farm area. Effective mussel farm management requires careful recording of stocking densities and harvest output from the farm to ensure that it is managed optimally. The husbandry of mussels within mussel farms results in the production of around 2,500 tonnes of cultivated mussels per year. Each one of the cultivated mussels has the potential to produce around 3 million gametes per year, so the reproductive output of the mussel stock in cultivation is enormous.
Wild stock status
The MSC Scheme is principally concerned with the effect of the enhanced fishery on the wild stock. The ongoing success of the mussel farming industry in the Limfjord is dependent on the existence ofthe wild stock, which, initially at least, provides the mussel larvae that settle on spat collectors and aresubsequently cultivated. However, once a farm is established it could become a net exporter of larvae.This section briefly considers the status of the wild mussel stock in the Limfjord.
Fishery tonnage
2, 541 tonnes in 2010
Commercial market
The main commercial market for the Limfjord rope grown mussels have been identified as Europe and the Middle East.
Actual eligibility date
2 August 2011
