Rat Biosecurity Surveillance and Response Following Eradication on a Tropical Atoll

Biosecurity is a key element following any eradication operation, employing tools that allow both the identification and elimination of survivors or the early detection of new invaders. Eradication managers must ensure the surveillance strategy is correctly adapted to the spatial context and that the potential causes of a pest's presence are understood to optimise their operational plans. We used the case of the eradication of black (Rattus rattus) and Pacific rats (Rattus exulans) from Honuea and Onetahi islets (Tetiaroa Atoll, French Polynesia) in 2020 to test an approach that combines rapid eradication assessment modelling and genetic profiling to evaluate the effectiveness of biosecurity and the success of eradication. Although the initial monitoring strategy (that principally relied on the use of trail cameras) was found sub-optimal, genotyping of a rat detected post eradication and third-party information confirmed the eradication had been successful but that recolonisation occurred from a nearby islet. The addition of other detection tools (traps, chew cards, wax tags, and tracking tunnels), while partially increasing spatial coverage for surveillance, did not change overall estimates of surveillance effectiveness. Only the use of a detection dog (Canis lupus familiaris), given that it could search a much larger area of the island, increased the estimates of surveillance effectiveness to an acceptable level. We provide practical information to enhance surveillance and incursion response efforts following rat eradication.