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/species | Indicator category | Scale | Indicators more to be added? links to be made | Comments |
| All pelagic environments; all species | Pressure | A: farm | Ammonia 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 species | Pressure and state/impact | A: farm | ITI, 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 species | State | B: water body | chl, 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 relevance | Environment category | Fish type for which applicable | Tested at ECASA sites: |
| (Auto)DEPOMOD needs measurements of currents | A (farm-scale); sea-bed impact | enclosed, and open coastal, mesotidal waters | salmon, cod | no report available |
| FjordEnv includes 3-layer hydrodynamic model | B:water body; effects on water column | Narrow Regions of Restricted Exchange | salmon, sea-bream, sea-bass | Creran, Vidlin, Cephalonia |
| KK3D needs measurements of currents | A (farm-scale); sea-bed effects | Mediterranean open waters | sea-bream, sea-bass ? | no report available |
LESV includes 3-layer hydrodynamic model | B:water body; effects on water column | Narrow Regions of Restricted Exchange | salmon | Creran |
| MERAMOD needs measurements of currents | A (farm-scale); sea-bed effects | Mediterranean open waters | sea-bream, sea-bass, tuna | no report available |
| MOM needs measurements of currents | A (farm-scale); sea-bed and water-column effects | enclosed, and open coastal, waters | salmon, sea-bass, sea-bream | Dalmar, Sounio, Cephalonia, Piran, Porto Ecolo, Bisceglie |
| TRIMODENA includes LPT - particle tracking, and HYDRO - gridded 3D hydrodynamic model | A: farm-scale, and B: water-body; effects on sea-bed | Mediterranean open coastal water | tuna ? | no report available |
