European eel restocking programs based on wild-caught glass eels: Feasibility of quarantine stage compatible with implementation of prophylactic measures prior to scheduled reintroduction to the wild

Abstract

The anthropogenic spread of pathogens contributes to the decline of some species. However, restocking programs implemented to counteract the decline of such populations can also contribute to the spread of pathogens, in particular for endangered species that cannot be bred in captivity, where populations used in restocking must be sourced from the wild with no control over sanitary status. A prime example of this is the endangered species European eel (Anguilla anguilla). As part of eel restocking programs, glass eels are captured in estuaries for later release further inland. In cases where release occurs immediately after capture, pre-release quarantine is important for mitigation of sanitary risks. In this study, we explored the impact of different quarantine conditions on glass eel sanitary status, morphology, behaviour and quarantine/post-quarantine survival in order to evaluate the feasibility and optimization of quarantine stages. Replicate experiments were conducted in 2017 and 2018, using glass eels of different geographical origin. The results suggest that glass eels entering estuaries are free of pathogens and so that their capture at this early stage reduces the risk of the anthropogenic introduction of pathogens through restocking programs. They support the use of a 15-day pre-release quarantine period to allow easier management of release processes and the implementation of prophylactic and therapeutic measures as part of these useful conservation programs.