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escapes' are plants or animals that are either not native to an area or have been selectively
bred or genetically modified and have escaped from mariculture enclosures.
Escapes pose a threat to ecological and socioeconomic stability if they compete with or prey upon native species.
Even if native species are cultivated, they are often bred to emphasize traits that could reduce the fitness of wild populations if escapees interbreed with wild specimens.
Escape of non-native species could also introduce foreign parasites into the local ecosystem.
Improving standards for containment methods, limiting the cultivation of exotic species, and restricting mariculture to sterile populations may effectively minimize the risk of genetic escapes.
How Was It Measured?
Measurement of the potential for harmful genetic escape was based on whether the species being cultured is native or introduced. Data came from the
Mariculture Sustainability Index (MSI), which reported data for 359
country-species combinations (53 countries represented). In the MSI analysis each species grown received a score from 1 to 10. Low scores indicate lower potential for ecological harm. Native species received the highest score (10), while foreign and introduced
species received the lowest (1), based upon the premise of potential impacts to
local biodiversity if these species were to escape. Native but
non-local species received intermediate scores, based on the assumption that they could negatively affect local genetic biodiversity but to a lesser extent than foreign or introduced species. In regions where multiple species are grown, each species was scored and the yield- weighted average of all scores was used. Scores for all regions were then rescaled from 0 to 1, using the maximum raw score of 10 and minimum of 1.
All pressures are ranked for their differing affects on different goals. For each goal, the effect of each pressure is weighted 'low' (1), 'medium' (2) or 'high' (3). The actual data-derived value of the pressure is then multiplied by the weight assigned to it for that goal. That process is repeated for each pressure-goal combination. The sum of those values divided by 3 (the (the maximum pressure-goal value) expresses the total affect of pressures on the goal.
Genetic escape affects three goals, Food Provision (Fisheries), Livelihoods & Economies (Commercial Fishing) and Biodiversity (Species). Its impacts on all of them are low (weight = 1).
What Has Been Done?
In 2004, the Norwegian government introduced a new technical standard, NS 9415, which strengthened the standards for aquaculture equipment to help prevent escapes. While the population of farmed salmon has increased since 1994, the number of escapes from salmon farms has dramatically decreased since the implementation of the new standard (Jensen et al. 2010).
NOAA is developing a model to evaluate the genetic risks associated with mariculture. The OMEGA (Offshore Mariculture Escapes Genetics Assessment) model shows that the magnitude and duration of the impact of genetic escapes depends on the number of fish that escape versus the wild population size; and the degree of genetic difference between the cultivated and wild fish. A slide show and webinar are downloadable at NOAA's site.
Beardmore, J. A. and J.S. Porter. 2003. Genetically Modified Organisms and Aquaculture. Food and Agriculture Organization of the United Nations: Wales, United Kingdom.
Bekkevold, D., M.M. Hansen and E.E. Nielsen. 2006. Genetic impact of gadoid culture on wild fish populations: predictions, lessons from salmonids, and possibilities for minimizing adverse effects. ICES J. Mar. Sci. 63, 198–208.
Hindar, K., I.A. Fleming, P. McGinnity and O. Diserud. 2006. Genetic and ecological effects of salmon farming on wild salmon: modelling from experimental results. ICES J. Mar. Sci. 63, 1234–1247.
Jensen, Ø., T. Dempster, E.B. Thorstad et al. 2010. Escapes of fishes from Norwegian sea-cage aquaculture: causes, consequences and prevention. Aquaculture Environment Interactions 1, 71–83.
Skaala, Ø., V. Wennevik and K.A. Glover. 2006. Evidence of temporal genetic change in wild Atlantic salmon, Salmo salar L., populations affected by farm escapee. Journal of Marine Science 63, 1224–1233.
Trujillo, P.A. 2007. A Global Analysis of the Sustainability of Marine Aquaculture. (Resource Management and Environmental Studies: University of British Columbia.