Ecasa Toolbox

Shell-fish farming: Expanding a farm

If you are considering expansion of your farm at a site, it is likely that the site has, so far, provided favourable conditions for growing bivalve shellfish. However, a site that is produces X tonnes of shellfish may not produce 2X tonnes if doubled in area and stock. This may be because of insufficient capacity to flush away wastes or supply oxygen, or because the supply of planktonic food is insufficent to feed more bivalves.

Both indicators and models can help assess a site's potential for assimilating the extra wastes that will result from farm expansion. We recommend that you start by considering the indicators listed below. In the case of farm-scale indicators, compare present values (at X tonnes of production) with values at the site before the farm was in place, or values within the same water-body but at a distance from the farm site. How much have they changed? Are they approaching environment thresholds set when you given permission to start the farm? If there is already a large change in indicator values, or if they are close to thresholds, then it is likely to be unwise to expand the local site. If the indicators show little change, and remain well within safe limits, then it could be worth investing in one of the models listed below, in order to ascertain if it is safe to expand to 2X tonnes, 3X tonnes, etc. As in the case of assessing a site, you should examine both farm and water body scales

Environment/farm type/speciesIndicator CategoryScaleUseful Indicators
All pelagic environments; all speciesPressureA: farmAmmonia and ammonium
Dissolved oxygen
Amongst longlines, tables, over beds, etc, compared with outside farm
All pelagic environments; all speciesSensitivityA: farmmean current at farm
(faster is better)
All pelagic environments; all speciesStateB: water bodychlorophyll (look for evidence of decrease)
All pelagic environments; all speciesSensitivityB: water bodyresidence time of water in water body
(shorter times are better)

 

In addition, the models listed on the page dealing with assessing a site's potential can be used to assess the potential for expansion at the site or in the water body.