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The inevitability of escapes from aquaculture facilities has led the U.N. Food and Agriculture Organization (FAO) to recommend that introductions of species in aquaculture should be considered an introduction to the wild, even if the facility is considered a closed system (FAO 1995). Negative impacts on community structure, biodiversity, genetic resources, and ecosystem function are well documented regardless of whether escapees are exotic species (Costa-Pierce 2002, ICES 2005) or native species (Naylor et al. 2005) farmed in the same waters as their wild counterparts. How to predict and quantify the full impact of escapees on community structure and ecosystem services is still a matter of some debate; however, there is consensus that any introduction or translocation of organisms or novel genetic profiles carries risk (ICES 2005).
The impact of escapes of non-native species is particularly challenging to assess. Exotic species establish new interaction patterns in the ecosystem and disrupt established patterns. As such, the pathways of impact are not often predictable and may not be reversible or easily quantifiable in terms of damage (Costa-Pierce 2002; Pullin and Sumaila 2005). Damage can be sustained or even increase with time if escape events are chronic or if escapees produce offspring that are able to survive and adapt to their new environment (ICES 2005).
Farming of native species is not free from risk either. The culture of native species may introduce additional concerns beyond those relevant for non-native species, particularly with regard to introduction of maladapted genes and/or alleles from farmed to wild fish populations. For instance, escapes of farmed Atlantic salmon in the North Atlantic manifest within populations of wild Atlantic salmon. Escapes of farmed Atlantic salmon in regions where the species is non-native, such as British Columbia and Chile, manifest at the higher community and ecosystem levels. In all cases, ecological impacts are density dependent; therefore, the magnitude of impact is tied to escape numbers. In those cases where genetic introgression of wild populations is possible, the per capita impact of an escape increases with each generation in culture as deviation from the wild gene pool increases (Araki et al. 2007).
ESC = GAPI Invasive Score x # Escaped FishInvasiveness Score = summation of 26-question survey
Units: Synthetic unit composed of the product of the number of escapees and per capita risk
Sample Normalised Calculation: Atlantic Cod from Norway, 2007
Impacts associated with inanimate wastes are relatively predictable. However, because escapees (and pathogens) are living organisms, the magnitude of their impact is greatly influenced by local biotic and abiotic conditions. An escape event may be devastating when it occurs in one region, yet produce only a modest disturbance in another. Therefore, assessing performance by the number of escapees alone is inadequate. Some species-country combinations carry a higher per capita escapee risk than others. For this reason, the escapes indicator is the product of the number of escapees and the GAPI Invasiveness Score, which provides an estimate of the per capita risk associated with an escape.
Inspired by the Marine Fish Invasiveness Screening Kit (MFISK) tool developed by Copp et al. (2007), the GAPI Invasiveness Score assesses the risks of impact of escape events within several broad categories. (For more detailed information on the GAPI Invasiveness Score, visit the FAQ page)
GAPI employed the following decision rules to treat gaps in Escapes data: