Ecasa Toolbox

Shell-fish farming: Finding a site

'Shellfish' here refers to filter feeding molluscs, especially mussels and oysters. Finding a site for a new shellfish-fish farm involves the following considerations:

Environmental considerations

  • finding a site where the surrounding waters contain a sufficient amount of phytoplankton and particulate organic matter to provide an adequate food supply for your bivalves;
  • finding a site where the mechanical disturbance, or the by-products of shellfish cultivation such as the large quantities of pseudo-faeces produced by mussels, do not adversely impact on sea-bed communities or sediment stability;
  • finding a site that is sufficiently well flushed to prevent a build-up of ammonia or a decrease in dissolved oxygen, which will slow bivalve growth;
  • finding water in which toxin-carrying algae rarely occur in sufficient numbers to require cessation of harvesting;
  • finding water that will not contaminate your shellfish with toxic pollutants from urban or industrial discharges or historically polluted sediments;
  • finding water that is not, and is unlikely to be, contaminated with pathogenic microbes (which will cause you extra expense for depuration).

 

Economic considerations

  • finding a site not far from your existing or scheduled activity base, to reduce the cost of access;
  • finding a site where the access to the sea is already available, and easy to use for your operations.

The best single indicator of a good site for growing filter-feeding bivalves is the presence of succesful farms. In addition to indicating good growing conditions, the existence of shellfish farming - or, indeed, or publically-sanctioned shellfish harvesting - is likely to mean that the area has been designated a Shellfish Growing Water under national transpositions of the Shellfish Waters Directive. This gives public authorities the duty of ensuring good water quality for shellfish in these waters. However, you will need to consider whether the existing farms already use up the carrying capacity of the water body. If they do, you may be able to produce shellfish, but it will be at the expense of bivalve growth at existing farms, and your own farm will not achieve existing rates of growth. The page on Assessing a site's potential lists models that can be used to estimate carrying capacity.

Should you be considering a site that at present has no shellfish aquaculture, you should consult public environment management authorities to get information about water quality. They will also be able to tell you if there are planning guidelines aimed at directing new aquacultural developments to particular regions. After this, the next best indicator of a good site (from an environmental perspective) is high dispersion (the result of persistent strong currents). A site with poor dispersion or poor flushing, is likely to prove bad for farming as well as likely to suffer obvious environmental impact: waste products will build up and the supply of food will be poor.

Sites that have, or are close to, 'conservation features', are also a poor choice: production may need to be highly constrained to prevent damage to these features, which are exemplified by seagrass meadows or reefs of serpulid worms.

See also the page dealing with Environmental impacts on aquaculture.