A framework for species translocation: Prospects of returning the black-veined white butterfly to England

Abstract

Insect translocations following historic extirpations and assisted colonisation into regions without historical records require assessment prior to species being released. We present a nine-step framework to assess translocations and use this to evaluate the opportunity to reestablish the black-veined white butterfly, Aporia crataegi, in Britain, a century after its extinction. The framework first establishes the rationale for translocation (step 1) and assesses whether a species will colonise naturally (step 2). It then assesses why a (reintroduced) species became extinct historically (step 3), whether the climate at proposed release sites is suitable (step 4) and if its habitat requirements are met (step 5). A risk assessment (step 6) is also required. For implementation, source populations are identified (step 7), followed by releases and monitoring (step 8) and ongoing reporting of outcomes and lessons learned (step 9). Aporia crataegi seemingly meets all of the criteria. Unsuitable climate is likely to have led to extirpation but, despite 21st century climate and habitats now appearing to be suitable, natural and human-created barriers have prevented colonisation. The target area in England contains potential A. crataegi host plants and habitat that would accommodate dispersal across >100 km2 of connected landscape. The risks are assessed as low, and potential source populations in western Europe have been identified using climate-matching analyses. Steps 6–9 are under continuing development. The nine-step approach provides a convenient framework to assess translocations and has potential to become a model to guide future translocation projects and inform future ‘best practice’ releases.