Aquaculture is a global industry that relies upon the culture of alien species – either referring to non-native species that were introduced through human activities or species resulting from selective breeding, hybridization or domestication that are now genetically or phenotypically distinguishable from their ancestors.
The (possible) biodiversity consequences of these species escaping into the natural environment are rarely studied, nor quantified in a consistent or standardised way. This is largely due to variability in how ecosystems respond, the delayed emergence of ecological effects, and the complexity of interacting factors that influence biodiversity. Despite this, clear cases of severe biodiversity impacts are known, e.g. crayfish introductions in Europe or (big head) carp introductions in the USA.
Policy makers, including aquaculture third-party certification schemes, are challenged with regulating the culture of alien species as considerable resources and efforts are needed to intervene in controlling these species. This has resulted in the clear need for scientific risk assessments to evaluate, compare, and predict the magnitudes of the impacts of alien taxa and to determine and prioritise appropriate measures where necessary.
The Environmental Impact Classification of Alien Taxa (EICAT) is a unified assessment method based on the mechanisms of impact used in the International Union for Conservation of Nature (IUCN) Global Invasive Species Database. EICAT evaluates alien species against thirteen potential Impact Mechanisms (e.g. competition, hybridisation) based on evidence of observed harm and classified according to five Impact Categories (Minimal, Minor, Moderate, Major, Massive). Taxa categorised in the latter three categories are considered “harmful”. In addition, the Methodology also has a category for taxa that are data deficient, when no alien populations are found, or not (yet) evaluated. Based on the outcome of the Impact Mechanism and Impact Category, policymakers are better informed regarding which interventions are relevant – and justifiable towards the industry.
Here we outline the use of the EICAT methodology as part of the Aquaculture Stewardship Council (ASC) Certification Programme. We draw upon several examples of assessed species to demonstrate how scientific risk assessments can inform policy setting.