To preserve, monitor or eradicate: Covert rewilding as an emerging conservation trilemma for wildlife managers

Global biodiversity is currently facing an unprecedented extinction rate because of increased anthropogenic pressures, which often cause local or regional extirpations of wildlife populations. Once extinct from a given region, wildlife populations might be officially reintroduced upon the cessation of the threats that caused past declines. However, official translocations often undergo a lengthy assessment process and can be refused by environmental authorities due to various uncertainties related to expected benefits, potential impacts or long-term viability, as well as the risk-averse attitude exhibited by some decision makers. In response to these obstacles and the growing social consideration of official translocations, illegal actors are conducting unauthorized releases of threatened wildlife, which is referred to as covert rewilding. Covert rewilding is an emerging conservation issue that often involves several management challenges and complexities. Here, we provide a decision-making framework to guide management actions once covertly translocated populations are discovered. For this, we used three illegally translocated populations of threatened aquatic vertebrates in southeastern Iberia as case studies, aiming to illustrate the three available management options: to preserve, monitor, or eradicate. Moreover, we provide practical recommendations to tackle covert rewilding at its source and prevent further unauthorized translocations. Our study provides an overview of covert rewilding to increase the visibility of this conservation issue, as well as to advocate for the implementation of preventive actions as the most cost-effective management approach.