A new study by Wageningen Marine Research, St. Eustatius National Parks Foundation and Caribbean Netherlands Science Institute highlights the need for a continuation of the rapid response removal campaign to control the invasive green iguana population. Through displacement and hybridization, the green iguana threatens to wipe out the endemic Lesser Antillean Iguanas of St. Eustatius.
The Lesser Antillean Iguana, , is an IUCN Red List Critically Endangered species, which has disappeared from most of its habitat, including St. Maarten. This species is endemic to St. Eustatius and is the largest native vertebrate on the island. Its main threat comes from displacement by and hybridization with the invasive species green iguana, Iguana iguana. In fact, St. Eustatius is one of the last three major islands where this species was (until recently) still free from hybridization. Biological invasions can create several issues which threaten biodiversity, the environment, agriculture, livelihoods, health, and local culture.
Photo credit: Philippa King
In February of 2016, an adult female green iguana was caught in Princess Estates on St. Eustatius. Green iguanas and their hybrid offspring can be most easily distinguished from the native iguana based on their banded tail and the large scale on their cheek (see figure). It was unknown how long this individual had been on the island and if she had already laid eggs, potentially introducing additional iguanas to the area. In response, the Ministry of Economic Affairs agreed to fund a limited Rapid Response Removal Campaign (RC) on the island.
During the RC, three visual surveys were conducted throughout key risk areas. In total, 409.5 hours were spent over 40 days, resulting in a single detection. This low detection rate suggested that the RC occurred early in the invasion process and highlighted the need to stay vigilant. Luckily, local publicity via newspaper and radio programs led to a number of publicly reported sightings. Among these reports and opportunistic encounters by park management staff, an additional five green iguanas and their hybrids were captured before the campaign ended in January 2017, and an addition eight have been captures since.
As part of the RC, a study was conducted by Wageningen Marine Research, St. Eustatius National Parks Foundation and Caribbean Netherlands Science Institute (CNSI) to learn more about this invasion. In addition to tracking population data during the surveys, they also worked to identify introduction events, points of entry and likely points of origin. The harbor of St. Maarten was identified as the source of the most recent 2020 introductions, as this harbor serves as a major inter-island transshipment hub within the Lesser Antilles. This recent study highlights four apparently distinct green iguana introduction events between 2013 and 2020, one of which was likely intentional and three of which were from incidental stowaways arriving on container ships.
Photo credit: Dolfi Debrot
Luckily even four years after the RC the numbers of green iguanas and their hybrids appears to be limited. This gives researchers hope that it is not too late to stop the invasion before it heavily interbreeds with and thus effectively wipes out the island’s critically endangered Lesser Antillean iguana. Research alone will not be enough to control this issue. Investment both in finances and in capacity necessary to prevent introduction and spread of these iguanas will be required. RCs are significantly lower in cost than full invasive species removal projects, so the early detection and active management provides a unique opportunity for the island to eradicate this threat while still possible and affordable.
Report your sightings
If you happen to spot a green iguana while on St. Eustatius, you can report it to the local park authority STENAPA (+599 318 2884) or CNSI (+599 318 2040) as well as on https://dutchcaribbean.observation.org. This is a free website and app which allows local citizens to report sightings of important plants and animals. These tools are available in over 40 languages and can be used by biologists and citizens and tourists alike. Species reports by local communities are invaluable for nature conservation efforts to help increase public awareness and overall species protection.
Read the full report on the Case Study of a Rapid Response Removal Campaign for St. Eustatius on the Dutch Caribbean Biodiversity Database.
Article published in BioNews 47