green iguana

Island Iguanas: Tales of Survival and Conservation in the Caribbean

Dutch Below

The status of a single species in the Dutch Caribbean can vary significantly among the islands. For example, the green iguana, which is native to some islands, is regarded as invasive in others. The presence of non-native iguanas on the northern Dutch Caribbean islands has resulted in considerable ecological consequences and poses a risk of extinction to the local iguana species. Continued surveillance is essential to avert further dissemination and hybridization of the non-native green iguana with the indigenous iguana species. 

Native Iguanas 

Saba green iguana. Photo credit: (Christian König)

Saba and St. Eustatius each have their own unique native iguana populations.  On Saba, the Saba Green iguana, despite its name, becomes darker in color compared to non-native iguanas, with black or dark brown skin and occasional lighter markings on its throat and belly. On St. Eustatius, the critically endangered Lesser Antillean iguana is distinguishable by the lack of the large scale on the corner of their jaw and the absence of black stripes on its tail that the non-native green iguanas are known for. 

Native iguanas are critical to local ecosystems as they serve as important seed dispersers. However, like many species from the islands, these iguanas are vulnerable to habitat loss and competition from introduced species like the green iguana. Green iguanas can compete with native iguanas for resources, and interbreeding between the species can lead to hybridization through which the native populations is slowly displaced. 

The green iguana 

Green iguana. Photo credit: Hans Smulders

The introduction  of the green iguana’s to St. Eustatius is believed to have occurred through the pet trade, where they are popular pets due to their striking appearance and docile nature. Unfortunately, many pet owners are not prepared for the long-term commitment, leading to releasing them into the wild. Additionally, green iguanas find their way to the SSS-islands  as hitchhikers on container ships that are transported between the islands. 

Once introduced, green iguanas can quickly establish themselves in new environments. With females laying up to 70 eggs per year, they can breed prolifically, outnumbering the native iguanas who lay fewer eggs. As a consequence, the green iguana population can grow rapidly, leading to hybridization, and competition with native species for resource and habitat. 

Management Strategies  

Lesser Antillean iguana. Photo credit: Philippa King-Stenapa

On Saba and St. Eustatius, local conservation organizations and government agencies have implemented control measures to reduce the numbers of non-native green iguana populations. These include trapping and euthanasia programs, and public education campaigns to discourage pet ownership and release.  

While these efforts have been successful in reducing the green iguana population on Saba and St. Eustatius, ongoing vigilance is needed to identify remaining non-native animals and to prevent more iguanas arrive from St. Maarten. Strict biosecurity measures between the islands are essential, especially at the harbors on St. Maarten to prevent non-native iguanas from being transferred to Saba and St. Eustatius. Invasive species pose a significant threat to the unique biodiversity of island ecosystems, and their management requires sustained cooperation and commitment from all stakeholders. 

DCNA  

The Dutch Caribbean Nature Alliance (DCNA) supports science communication and outreach in the Dutch Caribbean region by making nature related scientific information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and through the press. This article is part of a series of articles on ‘Invasive Alien Species in the Dutch Caribbean”. This article contains the results from several scientific studies but the studies themselves are not DCNA studies. No rights can be derived from the content. DCNA is not liable for the content and the in(direct) impacts resulting from publishing this article. 


 

 

De status van een enkele soort in Caribisch Nederland kan aanzienlijk verschillen tussen de eilanden. Bijvoorbeeld de groene leguaan, die op sommige eilanden voorkomt, wordt op andere eilanden als invasief beschouwd. De aanwezigheid van niet-inheemse leguanen op de Noord-Nederlands Caribische eilanden heeft aanzienlijke ecologische gevolgen gehad en vormt een risico van uitsterven voor de lokale leguanensoorten. Voortdurend toezicht is essentieel om verdere verspreiding en hybridisatie van de niet-inheemse groene leguaan met de inheemse leguaansoort te voorkomen.

Inheemse leguanen

Saba groene leguaan. Fotocredit Christian König

Saba en St. Eustatius hebben elk hun eigen unieke inheemse leguanenpopulaties. Op Saba wordt de Saba-groene leguaan, ondanks zijn naam, donkerder van kleur in vergelijking met niet-inheemse leguanen, met een zwarte of donkerbruine huid en af en toe lichtere markeringen op zijn keel en buik. Op Sint Eustatius is de ernstig bedreigde Antilliaanse leguaan te onderscheiden door het ontbreken van de grote schaal op de hoek van hun kaak en de afwezigheid van zwarte strepen op de staart waar de niet-inheemse groene leguanen bekend om staan.

Inheemse leguanen zijn cruciaal voor lokale ecosystemen omdat ze belangrijke zaadverspreiders zijn. Zoals veel soorten van de eilanden zijn deze leguanen echter kwetsbaar voor verlies van leefgebied en concurrentie van geïntroduceerde soorten zoals de groene leguaan. Groene leguanen kunnen concurreren met inheemse leguanen om voedsel, en kruising tussen de soorten kan leiden tot hybridisatie waardoor de inheemse populaties langzaam worden verdreven.

De groene leguaan

Groene leguaan. Fotocredit: Hans Smulders

De introductie van de groene leguanen op Sint Eustatius zou hebben plaatsgevonden via de dierenhandel, waar ze vanwege hun opvallende uiterlijk en handelbare karakter populaire huisdieren zijn. Helaas zijn veel eigenaren van gezelschapsdieren niet voorbereid op de langetermijnverplichting, wat ertoe leidt dat ze in het wild worden vrijgelaten. Daarnaast vinden groene leguanen hun weg naar de SSS-eilanden als lifters op containerschepen die tussen de eilanden worden vervoerd.

Eenmaal geïntroduceerd, kunnen groene leguanen zich snel vestigen in nieuwe omgevingen. Met vrouwtjes die tot 70 eieren per jaar leggen, kunnen ze overvloedig broeden, meer dan de inheemse leguanen die minder eieren leggen. Als gevolg hiervan kan de populatie groene leguanen snel groeien, wat leidt tot hybridisatie en concurrentie met inheemse soorten om voedsel en leefgebied.

Management Strategieën

Antilliaanse leguaan  Fotocredit: Philippa King-Stenapa

Op Saba en Sint Eustatius hebben lokale natuurbeschermingsorganisaties en overheidsinstanties controlemaatregelen genomen om het aantal niet-inheemse groene leguanenpopulaties te verminderen. Deze omvatten programma’s voor vallen en euthanasie en openbare voorlichtingscampagnes om het bezit en het vrijlaten van huisdieren te ontmoedigen.

Hoewel deze inspanningen succesvol zijn geweest in het terugdringen van de groene leguanenpopulatie op Saba en Sint Eustatius, is voortdurende waakzaamheid geboden om resterende niet-inheemse dieren te identificeren en om te voorkomen dat er meer leguanen uit Sint Maarten komen. Strenge bioveiligheidsmaatregelen tussen de eilanden zijn essentieel, vooral bij de havens op Sint Maarten om te voorkomen dat uitheemse leguanen naar Saba en Sint Eustatius worden overgebracht. Invasieve soorten vormen een aanzienlijke bedreiging voor de unieke biodiversiteit van de ecosystemen van eilanden, en het beheer ervan vereist duurzame samenwerking en inzet van alle belanghebbenden.

DCNA

De Dutch Caribbean Nature Alliance (DCNA) ondersteunt wetenschapscommunicatie en outreach in de Nederlandse Caribische regio door natuurgerelateerde wetenschappelijke informatie breder beschikbaar te maken via onder meer de Dutch Caribbean Biodiversity Database, DCNA’s nieuwsplatform BioNews en via de pers. Dit artikel maakt deel uit van een serie artikelen over ‘Invasive Alien Species in the Dutch Caribbean’. Dit artikel bevat de resultaten van verschillende wetenschappelijke onderzoeken, maar de onderzoeken zelf zijn geen DCNA-onderzoeken. Aan de inhoud kunnen geen rechten worden ontleend. DCNA is niet aansprakelijk voor de inhoud en de indirecte gevolgen die voortvloeien uit het publiceren van dit artikel.

 

 

Published in BioNews 65

Date
2023
Data type
Media
Theme
Research and monitoring
Geographic location
Aruba
Bonaire
Curacao
Saba
Saba bank
St. Eustatius
St. Maarten
Author

Action required to curb Statia’s invasive green iguana threat

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

Rapid Response 

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. 

Research 

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

Moving Forward 

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. 

https://www.dcbd.nl/document/st-eustatius-invasive-alien-green-iguana-ca...

 

Article published in BioNews 47

Date
2021
Data type
Media
Theme
Education and outreach
Research and monitoring
Geographic location
St. Eustatius
Author