Ecasa Toolbox

Fin-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 farming. However, a site that is suitable for X tonnes of fish may not support the growing of 2X tonnes because of insufficient capacity to flush away wastes or supply oxygen. Impact on the sea-bed may become too great. In addition, the capacity of the water body to assimilate waste may become an issue. You will need to investigate at least some of these matters to protect your farm against deterioration and also because (in some jurisdictions) application for a revised licence may need to be accompanied by estimates of additional environmental impact.

The indicators listed below can be used to assess a site's potential for assimilating the extra wastes that will result from farm expansion. Begin by considering farm-scale indicators. Compare present values (at X tonnes) 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 site.

Next, consider water-body scale indicators. Compare present values (at X tonnes) with values in the water body before the farm was in place. How much have they changed? 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 site. It may be that the changes are due to other uses of the water body; if you suspect this, it will be desirable to discuss the matter with a public environment manager.

Environment/farm type/speciesIndicator categoryScaleIndicators
more to be added? links to be made
Comments
All pelagic environments; all speciesPressureA: farmAmmonia and ammonium
Dissolved oxygen
amongst cages, compared with reference conditions
These water column indicators are relatively cheap to measure continuously, using electronic probes.
All benthic environments; all speciesPressure and state/impactA: farmITI, AMBI, Redox ...
beneath cages, compared with reference conditions
These sea-bed indicators are relatively expensive to measure, requiring sampling by divers and, in some cases, specialized analyses
All pelagic environments; all speciesStateB: water bodychl, transparency ...
measured outside zone A, and compared with conditions before farm in place
Transparency, measured by Secchi depth, requires a human observer, but is otherwise cheap

 

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. See also: Management for Sustainability.

 

Model (alphabetical order) Model category: scale and relevanceEnvironment categoryFish type for which applicableTested at ECASA sites:
(Auto)DEPOMOD needs measurements of currentsA (farm-scale); sea-bed impactenclosed, and open coastal, mesotidal waterssalmon, codno report available
FjordEnv includes 3-layer hydrodynamic modelB:water body; effects on water columnNarrow Regions of Restricted Exchangesalmon, sea-bream, sea-bassCreran, Vidlin, Cephalonia
KK3D needs measurements of currentsA (farm-scale); sea-bed effectsMediterranean open waterssea-bream, sea-bass ?no report available

LESV includes 3-layer hydrodynamic model
B:water body; effects on water columnNarrow Regions of Restricted ExchangesalmonCreran
MERAMOD needs measurements of currentsA (farm-scale); sea-bed effectsMediterranean open waterssea-bream, sea-bass, tunano report available
MOM needs measurements of currentsA (farm-scale); sea-bed and water-column effectsenclosed, and open coastal, waterssalmon, sea-bass, sea-breamDalmar, Sounio, Cephalonia, Piran, Porto Ecolo, Bisceglie
TRIMODENA includes LPT - particle tracking, and HYDRO - gridded 3D hydrodynamic modelA: farm-scale, and B: water-body; effects on sea-bedMediterranean open coastal watertuna ?no report available