Opérations d’éradication de prédateurs mammaliens introduits sur des îles françaises de la façade atlantique européenne : une méthode, deux protocoles et trois décennies d’expérience

Faced with one or more introduced mammalian predators, managers of island territories are led to define a control strategy, involving scientists and competent external operators. The final objective of that strategy is to achieve biodiversity and ecosystem functioning close to those prior to the arrival of the introduced species, by eliminating harmful effects they pose on populations or communities of fragile and rare species. Eradication, i.e. the elimination of all individuals from the island population in question, is generally the operational objective of that strategy. Here, we detail the history of eradication operations carried out against rodents (mainly), the Brown Rat Rattus norvegicus (Berkenhout, 1769) and the Roof Rat (often called Black Rat) Rattus rattus (Linnaeus, 1758), and (to a much lesser extent) carnivores, the Ferret Mustela furo Linnaeus, 1758 and the American Mink Neogale vison (Schreber, 1777), on islands of the Atlantic coast in six French departments (Loire-Atlantique, Morbihan, Finistère, Côtes-d’Armor, Ille-et-Vilaine, and Manche). These operations began in 1994. An old operation, carried out in the early 1950s with a violent poison on île Rouzic (les Sept Îles), was also recalled. Following a description of the methodology advocated for eradication, we detail the two protocols used successively for rats. The first, applied from 1994 to 2010, was based on the use of mechanical control (using live-traps) followed by chemical control (anticoagulant rodenticides). The second, put in practice since 2016, utilizes chemical control only. We review technical aspects (ecological expertise ; choice of station density, type of trap and toxic molecule ; necropsies and sampling of biological material ; calculation of abundance indices), as well as regulation standards. While 95 % of the rats trapped at the end of the operation (first protocol) are trapped on average after eleven days, 95 % of the baits consumed (second protocol) are consumed on average after 17 days. The results of rat eradication operations on the French islands of the Atlantic coast, applying one or other of the two protocols, are 13 successes out of 18 operations with known results (with only one operation for the Roof Rat). An in-depth analysis of failures shows that Brown Rat eradication operations using either of the two protocols have always been successful, except in two cases. Firstly, when the possibility of recolonization by the foreshore had not been sufficiently considered, i.e. if biosecurity measures following trapping and/or baiting were insufficient. On the other hand, when the conditions of application of the protocols could not have been fully respected, due to logistical problems and/or of unavoidable human-caused disturbances. Although we consider both protocols to have achieved very satisfactory results, we recommend for the future to apply the second one, using chemical control only, for purely logistical reasons.