Choosing the right objective

The ability to identify new invaders and/or emerging species through surveillance is key to ensure proper early detection and rapid response. Surveillance is, indeed, necessary to have a good knowledge of the situation. In addition, it is essential to select the adequate measures which include eradication, containment, maintaining pest free areas or mitigation measures.

obj 197 Eradication, the most effective measure to achieve the recovery of native biodiversity and ecosystems, is most likely achievable and successful in the early stage of invasion, when there is only a limited number of individuals at defined locations (See section “Time is key”). This technique requires, however, careful and sound assessment prior to its implementation.   
obj 198 Nevertheless, when eradication is not feasible, another option is to contain species in core areas to limit their spread and restrict them within known locations. In this case, species are prevented, through the implementation of diverse methods, to spread and colonise other areas.
obj 200 A further measure is the maintenance of pest free areas such as upstream parts of river basins and protected areas. In opposition to the containment measure, this method prevents the arrival of individuals into specific and selected areas.


For the implementation of these two methods, priority sites must, therefore, be identified. The selection of priority areas must take into account various criteria such as:

  • IAS spatial distribution
  • risk of reinvasion and of dispersal towards and from other sites
  • site conservation value and status
  • restoration potential
  • technical feasibility
  • public acceptance
  • management costs
obj 199 When the species is too abundant and widespread to implement any of the measures previously mentioned, mitigation measures and long-term management efforts can be considered to reduce IAS population size and limit their impact. When no management measure is achievable due to technical, economic or political reasons, the IAS is likely to cause even more damage to even more areas and become, therefore, a huge issue. Adaption and ecosystem resilience are therefore critical. 


Choosing the right objective also depends on priority-setting for species. Indeed, multiple criteria must also be considered including:

  • the manageability of the species and related costs
  • current and foreseen impact the species has on biodiversity
  • ecosystem services
  • invasion level
  • pathways of introduction
  • means of dispersal (risk of re-introduction)
  • detectability
  • public acceptance.

Priority-setting is, therefore, key to enhance large-scale effective and sustainable results for the management of IAS.