‘Mariculture' is the farming of marine animals and plants such as fish, shellfish and seaweeds. The more commonly used phrase ‘aquaculture' refers to farming in both fresh and seawater.
A third of the seafood destined for dinner tables worldwide is currently produced by fish-farms - 40 million tonnes per year. Increasing global demand for fish and the limited quantity of wild fish stocks means that aquaculture production is expected to double to 80 million tonnes per year by 2030.
The UK is the third largest producer of farmed fish in the European Union (EU), 90% of which is farmed in Scotland, with Atlantic salmon being the predominant farmed species. The dramatic growth in fish-farming during the 1980s & 1990s led to conflicts with nature conservation and other fisheries interests.
Sustainable Practices for Farmed Fisheries
It is vital that fish-farming practices continue to become more environmentally sustainable. The MCS Mariculture programme aims to:
- develop, promote and encourage adoption of environmentally sustainable practices within the mariculture industry that:
- minimise damage to local wildlife, habitats and landscapes from pollution and poor siting;
- utilise the best sustainable feed options available;
- provide better protection of wild stocks from disease and escapes associated with fish-farms;
- ensure the health and welfare of farmed species; and
- utilise the least damaging shellfish harvesting methods.
- increase consumer understanding of the environmental costs of farmed fish and the availability of sustainably farmed fish.
MCS works with organisations to promote more sustainable, environmentally sensitive fish-farming and shellfish harvesting practices. For more information download the MCS Fish-farming Policy. Further information on mariculture methods, impacts and the most sustainable choices for buying farmed fish are available on the MCS Fishonline website.
Fish-farming
Farming of marine species in open sea cages and farming of carnivorous species in general can have various environmental/sustainability concerns:
- Organic waste and antifoulants can pass from sea cages into surrounding waters;
- Sea-lice parasite treatments if used, can either accumulate on the sea bed or be released into adjacent waters, which may affect local non-target species;
- Fishmeal and fishoil (except where organic certified feeds are used) is largely comprised of wild fish caught specifically to make fish feed (some of which come from overfished/depleted stocks) which may affect other wildlife such as seabirds;
- Escape of farmed salmon threatens wild salmonid species through genetic dilution, disease transfer and competition;
- Disease can be transferred to and from wild salmon to farmed salmon; and
- Predator control of species such as seals and cormorants can bring fish-farming and wildlife conservation into conflict.
Gyrodactylus salaris – don’t bring it home
Gyrodactylus salaris (GS) is one of about 400 species of small, leech-like parasites, which occupy both marine and freshwater. This barely visible parasite infects the fins and skin of salmon, trout and some other species in freshwater causing serious damage which can lead to secondary infection and death.
Since its introduction into Norway in the 1970s, 44 rivers have been infected with GS and salmon populations within 20 of them have been lost completely. Treatment used to eradicate this parasite - a chemical called "rotenone" - kills all the fish in the river and is not always successful.
Research has shown that GS does not occur in UK rivers, and we have to ensure that it remains that way. The parasite is very hardy and is capable of being inadvertently introduced by fishermen via equipment used in infected areas. For more information, particularly on prevention measures against accidental introduction, refer to the leaflet “Keep Fish Disease Out” available from this link.
The Scottish Executive have recently published an article "Keeping Scotland's rivers bug free" - Click here to read it.
There are a number of studies and initiatives being undertaken to address these issues and MCS is working with representatives in the mariculture industry to help develop and promote the most environmentally responsible practices.
Shellfish farming
Various shellfish species are farmed in the UK. The main species (in terms of volume and value) is the common mussel Mytilus edulis. Mussels are cultivated either by collecting "seed" (young) mussels and relaying them into more favourable growing areas, or by growing up mussels that have settled naturally onto ropes suspended from floating buoys.
Other shellfish species farmed in the UK include oysters (Pacific and native), scallops, clams and cockles. In general, farming of these species involves on-growing of spat (young animals) that have been either collected in the wild or reared in hatcheries.
Overall, shellfish farming tends to have a lower environmental impact than salmon farming, although the use of dredges to collect shellfish can cause significant disturbance to sensitive habitats.
