St. Eustatius invasive alien Green Iguana : Case study of a Rapid Response Extermination Campaign (RREC)

The Lesser Antillean Iguana, Iguana delicatissima is the largest extant native land vertebrate of St. Eustatius and was recently lost (~1990s) from the only other Dutch Caribbean island where it was native (St. Maarten). It is an IUCN Red List Critically Endangered (CR) species that has disappeared from most islands in the Lesser Antilles. A recognized principal cause for its endangerment throughout the islands is displacement by and hybridization with invasive alien Green Iguanas, Iguana iguana (IAGI) (Knapp et al. 2014). On 22nd February 2016 an adult female IAGI was caught in Princess Estates, St. Eustatius. The possibility that the animal had been present on the island for a longer period, that it may have laid one or more nests, or the possibility that there may have been other IAGIs on the island, represented an imminent danger to the continued existence of the Lesser Antillean Iguana. We conducted a Rapid Response Extermination Campaign (RREC) with the goal of wiping out the IAGI at an early stage. Three thorough visual surveys were conducted during 2016-2017 in key risk areas in an attempt to detect and eliminate all IAGIs and their hybrids. In total 409.5 observer hours were spent during three dedicated surveys in and around areas where IAGIs or hybrids had been captured, seen or reported. Searches were conducted over a total of 40 days and covered a total of trajectory of 114.2 km. Only a single detection was realized during these directed surveys. This suggests that the RREC took place at an early stage of the invasion. Nevertheless, due to local publicity via newspapers and radio programs, several records were reported by the public. Thanks to these reports, and opportunistic encounters by park management staff, five captures of IAGIs or their hybrids were realized between February 2016 and January 2017. Since then eight additional captures have been realized, demonstrating that the RREC, even when augmented by public support and extra vigilance by park management staff, was insufficient to purge the island of the IAGI. Our study documents three distinct IAGI introductions between 2013 and 2020, one of which was likely intentional and two of which were incidental stowaways on container ships. Our results show that, even though it is a relatively large animal, due to its relatively secretive nature, camouflage, and high fecundity, eliminating the IAGI from an island will require a more intensive and sustained effort than we provided, even by means of an RREC in the early stages of the invasion. Informing stakeholders and the public in an early stage of the campaign can clearly make a critical contribution towards an RREC. Even four years after the campaign, the numbers of the IAGI and its hybrids still appear to be limited and concentrated in and around inhabited areas, their likely main point of entry being the island’s harbour. We conclude that it may not be too late to quell the invasion before the critically endangered, largest surviving island-endemic vertebrate is permanently lost from St. Eustatius. Additional IAGI extermination campaigns need to be launched as soon as possible. The harbour of St. Maarten was identified as the source on the most recent 2020 introduction. As St. Maarten serves as a major inter-island trans-shipment hub in the Lesser Antilles, and the Lesser Antilles are rich in endemic iguanas vulnerable to the IAGI, it is essential that St. Maarten ports cull all Green Iguanas in and around their grounds to prevent the spread of this major pest to the islands with which they trade.