iguana

Assessment of Iguana iguana Saba subpopulation, Saba Green Iguana
Assessment by: van den Burg, M.P. & Debrot, A.O.
 

Dutch below

Known for its striking appearance and important ecological role, the Lesser Antillean Iguana plays a crucial part in the ecosystem on St. Eustatius. In October, the Dutch government will officially propose to upgrade this speciesfrom Annex III to Annex II of the Protocol Concerning Specially Protected Areas and Wildlife (SPAW) during the next Conference of the parties for the Cartagena Convention (COPS) in October on Aruba. This change will give the authorities within the Caribbean the tools they need to further protect this species. 

(lesser Antillean iguana (Iguana delicatissima) Photo credit: Philippa King-STENAPA- all rights reserved)

The Lesser Antillean Iguana (Iguana delicatissima) is a critically endangered species endemic to the Caribbean Lesser Antilles, a chain of islands stretching from the Virgin Islands in the north to Grenada in the south. Within the Dutch Caribbean, since its extinction on St. Maarten, this iguana can only be found on the island of Statia. These iguanas are typically found in scrub woodlands, dry tropical forests and mangroves but are also known to venture into human-altered landscapes like abandoned quarries and urban areas. 

Distinctive Appearance 

On St. Eustatius, the Lesser Antillean Iguana is distinguishable by the lack of the large scale on the corner of its jaw and the absence of black stripes on its tail for which the non-native ‘green’ iguanas (Iguana iguana) are known for. The confusion with the protected native iguana can be reduced by calling the non-native species ‘striped-tailed iguana’. As both the non-native and native species are green during some parts of their life cycle, the use of colors within the name can be confusing. At the date of this publication, there is only one confirmed sighting of a green/striped-tailed iguana on St Eustatius. Even though it’s currently only one animal, an adult invasive female iguana can lay a nest of hybrid offspring if she mates with native male iguanas. Over the recent years, more than 10 non-native iguanas have been removed from Statia. The native iguanas have evolved several adaptations that help them thrive in their challenging environments. Their long, muscular tails aid in maintaining balance, enabling them to navigate trees and branches with ease. Moreover, their strong, sharp claws allow them to climb trees and rocky surfaces, providing access to safe havens, typically a nearby burrow, and prime basking spots. 

Conservation Status and Threats 

Unfortunately, the Lesser Antillean Iguana faces numerous conservation challenges. The International Union for Conservation of Nature (IUCN) has classified this species as Critically Endangered. In addition to habitat loss and degradation due to urbanization, tourism, and introduction of feral predators (such as cats, dogs and mongooses), the main reason for their decline is competition from introduced green iguanas that continue to threaten the remaining populations. Green iguanas can compete with native iguanas for resources, and interbreeding between the species leads to hybridization; a process through which the native populations is slowly displaced.  Additionally, illegal poaching for the pet trade poses a considerable threat, as these charismatic reptiles are sought after as exotic pets. 

Conservation Efforts 

To safeguard the Lesser Antillean Iguana, conservation efforts have been implemented across the island of St. Eustatius. Protected areas have been established to preserve crucial habitats and prevent further destruction while research and monitoring programs aid in improving overall understanding of the iguanas’ behavior, population dynamics and habitat needs. Furthermore, on St. Eustatius this species is protected under the National Nature Conservation Framework Act BES. Although these steps are important for their protection, it is important that residents and visitors stay vigilant in protecting these local iguanas from the continuous threat of non-native iguanas arriving from for example St. Maarten. 

Another important step is to further strengthen its protection and legal status. The Kingdom of the Netherlands will propose to upgrade the Lesser Antillean Iguana from Annex III to Annex II of the Protocol Concerning Specially Protected Areas and Wildlife (SPAW).  This upgrade would mean that these iguanas would now be under the highest level of protection, meaning the possession, trade or even disturbance of these species is forbidden.  

The Lesser Antillean Iguana is a captivating and ecologically significant species that enriches St. Eustatius’s biodiversity.  Given this species’ ecological role and importance as a key stone species in the Caribbean dry forest ecosystem, these iguanas deserve our admiration and improved conservation efforts. By promoting awareness, implementing protective measures, and respecting their natural habitats, we can ensure that future generations can appreciate the beauty and importance of these remarkable reptiles in the Dutch Caribbean. 

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 the press. 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.     

Bekend om zijn opvallende verschijning en belangrijke ecologische rol, speelt de antillenleguaan een cruciale rol in het ecosysteem op Sint Eustatius. In oktober zal de Nederlandse regering officieel voorstellen om deze soort op te waarderen van bijlage III naar bijlage II van het Protocol Concerning Specially Protected Areas and Wildlife (SPAW) tijdens de volgende Conference of the parties for the Cartagena Convention (COPS) in oktober op Aruba. Deze verandering zal de autoriteiten in het Caribisch gebied de instrumenten geven die ze nodig hebben om deze soort verder te beschermen. 

De antillenleguaan (Iguana delicatissima) Foto: Philippa King-STENAPA- all rights reserved

De antillenleguaan (Iguana delicatissima) is een ernstig bedreigde diersoort die endemisch is voor de Bovenwindse Eilanden, een eilandenketen die zich uitstrekt van de Maagdeneilanden in het noorden tot Grenada in het zuiden. Binnen het Nederlandse Caribisch gebied komt deze leguaan sinds het uitsterven op Sint Maarten alleen nog voor op het eiland Sint Eustatius. Deze leguanen worden doorgaans aangetroffen in struikgewas, droge tropische bossen en mangroven, maar het is ook bekend dat ze zich wagen in door de mens veranderde landschappen, zoals verlaten steengroeven en stedelijke gebieden. 

Onderscheiden

Op Sint Eustatius is de antillenleguaan te onderscheiden door het ontbreken van de grote schub op de hoek van de kaak en het ontbreken van zwarte strepen op de staart waar de niet-inheemse ‘groene’ leguanen (Iguana iguana) om bekend staan. De verwarring met de beschermde inheemse leguaan kan worden verminderd door de uitheemse soort ‘gestreepte staartleguaan’ te noemen. Omdat zowel de niet-inheemse als de inheemse soort tijdens sommige delen van hun levenscyclus groen zijn, kan het gebruik van kleuren in de naam verwarrend zijn. Op de datum van deze publicatie is er slechts één bevestigde waarneming van een groen/gestreepte staartleguaan op Sint Eustatius. Ook al is het momenteel maar één dier, een volwassen invasieve vrouwelijke leguaan kan een nest van hybride nakomelingen leggen als ze paart met inheemse mannelijke leguanen. De afgelopen jaren zijn ruim tien niet-inheemse leguanen van Sint Eustatius verwijderd. De inheemse leguanen hebben verschillende aanpassingen ontwikkeld die hen helpen te gedijen in hun uitdagende omgevingen. Hun lange, gespierde staarten helpen bij het bewaren van het evenwicht, waardoor ze gemakkelijk door bomen en takken kunnen navigeren. Bovendien zorgen hun sterke, scherpe klauwen ervoor dat ze in bomen en rotsachtige oppervlakken kunnen klimmen, waardoor ze toegang kunnen krijgen tot een veilige plek, meestal een nabijgelegen hol, en uitstekende locaties om te zonnebaden. 

Staat van instandhouding en bedreigingen 

Helaas wordt de antillenleguaan geconfronteerd met tal van uitdagingen op het gebied van natuurbehoud. De International Union for Conservation of Nature (IUCN) heeft deze soort geclassificeerd als ernstig bedreigd. Naast het verlies en de achteruitgang van het leefgebied als gevolg van verstedelijking, toerisme en de introductie van wilde roofdieren (zoals katten, honden en mangoesten), is de belangrijkste reden voor hun achteruitgang de concurrentie van geïntroduceerde groene leguanen die de resterende populaties blijven bedreigen. Groene leguanen kunnen concurreren met inheemse leguanen om hulpbronnen, en kruising tussen de soorten leidt tot hybridisatie; een proces waardoor de inheemse bevolking langzaam wordt verdreven. Bovendien vormt de illegale stroperij voor de handel in huisdieren een aanzienlijke bedreiging, omdat deze charismatische reptielen gewild zijn als exotische huisdieren. 

Beschermen 

Om de antillenleguaan te beschermen, zijn er op heel Sint Eustatius natuurbehoudsinspanningen uitgevoerd. Er zijn beschermde gebieden ingesteld om cruciale leefgebieden te behouden en verdere vernietiging te voorkomen, terwijl onderzoeks- en monitoringprogramma’s helpen bij het verbeteren van het algemene inzicht in het gedrag van de leguanen, de populatiedynamiek en de benodigde leefgebieden. Bovendien wordt deze soort op Sint Eustatius beschermd op grond van the National Nature Conservation Framework Act BES. Hoewel deze stappen belangrijk zijn voor hun bescherming, is het ook belangrijk dat bewoners en bezoekers waakzaam blijven bij het beschermen van deze lokale leguanen tegen de voortdurende dreiging van niet-inheemse leguanen die bijvoorbeeld uit Sint Maarten komen. 

Een andere belangrijke stap is het verder versterken van de bescherming en juridische status ervan. Het Koninkrijk der Nederlanden zal voorstellen om de antillenleguaan op te waarderen van Bijlage III naar Bijlage II van het Protocol Concerning Specially Protected Areas and Wildlife (SPAW). Deze upgrade zou betekenen dat deze leguanen nu onder het hoogste beschermingsniveau zouden vallen, wat betekent dat het bezit, de handel of zelfs verstoring van deze soorten verboden is. 

De antillenleguaan is een ecologisch belangrijke soort die de biodiversiteit van Sint Eustatius verrijkt. Gezien de ecologische rol en het belang van deze soort als sleutelsoort in het Caribische droge bosecosysteem, verdienen deze leguanen onze bewondering en verbeterde inspanningen voor natuurbehoud. Door het bewustzijn te bevorderen, beschermende maatregelen te nemen en hun natuurlijke leefgebied te respecteren, kunnen we ervoor zorgen dat toekomstige generaties de schoonheid en het belang van deze opmerkelijke reptielen in het Nederlandse Caribisch gebied kunnen waarderen. 

DCNA 

De Dutch Caribbean Nature Alliance (DCNA) ondersteunt wetenschapscommunicatie en outreach in de Nederlands-Caribische regio door natuurgerelateerde wetenschappelijke informatie breder beschikbaar te maken via onder meer de Dutch Caribbean Biodiversity Database, DCNA’s nieuwsplatform BioNews en de pers. 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 68

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

The Caribbean Netherlands island of Saba is home to a unique but relatively unknown iguana population. Given the many threats faced by islands worldwide, including the Lesser Antilles and Saba, fieldwork was conducted in 2021 in order to bring attention to this unique species and the threats it faces. As on St. Eustatius, the most urgent threats appear to be low survival of hatchlings, limited nesting sites, and the presence of non-native iguanas.

Precise taxonomic status in discussion

Saba black iguana. Photo source: Thijs van den Burg

The iguana population on Saba forms part of a recently described species, Iguana melanoderma. Although there is no doubt about the unique appearance of the iguanas, experts are still deliberating over its exact taxonomic status. Despite this, it is clear that the population requires urgent protection given the number of threats it faces. The biggest concern is the presence of and possible further influx of non-native iguanas from nearby St. Maarten.

Thankfully more iguanas than originally thought

A recent study estimated the iguana population at just 200-300 individuals. This number is worrying and would be extremely concerning for the long-term survival of the population. However, because the data in the aforementioned study were preliminary, additional fieldwork was conducted on Saba in 2021. During this time, 38 transects were surveyed multiple times using distance sampling methodology, which allowed the population to be estimated more accurately. An unexpected positive result of this analysis is that the population is at least ten times larger than originally estimated, in the thousands rather than hundreds.

Saba black iguana. Photo source: Thijs van den Burg

More melanism at higher altitudes?

It is widely believed that black reptile species have evolved this color in order to be able to get warmer faster in colder climates, given that they are cold-blooded. This may also apply to the iguanas on Saba, which boasts the highest mountain in the Kingdom of the Netherlands: Mount Scenery (887m). This high volcano ensures that Saba is often cloudy, which could make it difficult for reptiles to get warm. However, we did not find any relationship between the extent of melanism and the elevation at which iguanas were found. In other words, iguanas that live higher up the volcano are not darker than iguanas at lower elevations.

Is there another explanation for why the iguanas on Saba are black? One hypothesis is that the original iguanas that established on Saba were already black. This is in line with the existence of partially black iguanas in Venezuela, which appear to be closely genetically related to the iguanas on Saba.

Few nest sites or juvenile iguanas

In order for successful reproduction and conservation of an iguana population, good quality nest sites are essential. It is well known that goats can destroy iguana nest sites through overgrazing, which leads to habitat destruction. Furthermore, goats can trample iguana nests and destroy the embryos inside eggs.

On Saba there is an enormous goat population (several thousands) which negatively impacts the island’s vegetation and causes erosion. During fieldwork we searched for iguana nest sites to evaluate their availability, distribution and quality. While this was not the main goal of the research, we were disappointed to find only four nest sites.

Juvenile iguana. Photo source: Thijs van den Burg

Another area of concern was the low number of juvenile iguanas found during fieldwork. Despite finding over 600 individuals, just 2.4% of these were juveniles or hatchlings. While the exact reason for this is unknown, one possible cause could be the feral cat population. Previous research on Saba demonstrated that feral cats exist in the lower altitudes of the island where they hunt for prey, which are exactly the same areas where iguanas prefer to nest. In fact, iguana remains were found in 9% of the cat scats examined.

Unfortunately, the situation for the melanistic iguana on Saba appears to be similar to that of the Lesser Antillean iguana on St. Eustatius, where the presence of cats and goats and an absence of suitable nest sites are well-known issues.

Remaining areas of concern

Despite the larger than expected iguana population on Saba, there are still many causes for concern. Clearly the species needs better protection as well as continued knowledge-building. Pressing concerns for the long-term existence of this species are the presence of free-roaming goats and feral cats, as well as the low number of juveniles and absence of suitable nest sites. However, by far the biggest threat is the presence of non-native iguanas which, though competitive hybridization, can mate with and thereby suppress the native population. During fieldwork, some individuals were found that looked different to the native iguana, and preliminary genetic research has confirmed that these animals were indeed invasive. This situation therefore requires the authorities to take immediate action in order to halt the invasion of non-native iguanas.

More info

For more info, e.g. considering student projects please contact dolfi.debrot@wur.nl and thijs.burg@gmail.com

More info in the Dutch Caribbean Biodiversity Database

Published in BioNews 56.

Abstract

The Lesser Antilles, in the Eastern Caribbean, is inhabited by three Iguana species: the Lesser Antillean iguana Iguana delicatissima, which is endemic to the northernmost islands of the Lesser Antilles, the introduced common iguana from South America, Iguana iguana iguana, represented also by the two newly described endemic subspecies Iguana iguana sanctaluciae from Saint Lucia and Iguana iguana insularis from Saint Vincent and the Grenadines, and Grenada, and the introduced Iguana rhinolopha from Central America. Drawing on both morphological and genetic data, this paper describes the Iguana populations from Saba and Montserrat as a new species, Iguana melanoderma. This species is recognized on the basis of the following combination of characteristics: private microsatellite alleles, unique mitochondrial ND4 haplotypes, a distinctive black spot between the eye and tympanum, a dorsal carpet pattern on juveniles and young adults, a darkening of body coloration with aging (except for the anterior part of the snout), a black dewlap, pink on the jowl, the high number of large tubercular nape scales, fewer than ten medium sized–triangular dewlap spikes, high dorsal spikes, and lack of horns on the snout. This new melanistic taxon is threatened by unsustainable harvesting (including for the pet trade) and both competition and hybridization from escaped or released invasive alien iguanas (I. iguana iguana and I. rhinolopha) from South and Central America, respectively. The authors call for action to conserve Iguana melanoderma in Saba and Montserrat and for further research to investigate its relationship to other melanistic iguanas from the Virgin Islands and coastal islands of Venezuela.

Keywords: Conservation Biology, Iguana, Lesser Antilles, microsatellites, mtDNA, new endemic species, phylogeny

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

Abstract.– Intraspecific diversity is among the most important biological variables, although still poorly understood for most species. Iguana iguana is a Neotropical lizard known from Central and South America, including from numerous Caribbean islands. Despite the presence of native melanistic I. iguana populations in the Lesser Antilles, these have received surprisingly little research attention. Here we assessed population size, distribution, degree of melanism, and additional morphological and natural history characteristics for the melanistic iguanas of Saba, Caribbean Netherlands based on a one-month fieldwork visit. Using Distance sampling from a 38- transect dataset we estimate the population size at 8233 ±2205 iguanas. Iguanas mainly occurred on the southern and eastern sides of the island, between 180-390 m (max altitude 530 m), with highest densities both in residential and certain natural areas. Historically, iguanas were relatively more common at higher altitudes, probably due to more extensive forest clearing for agricultural reasons. No relationship was found between the degree of melanism and elevation, and few animals were completely melanistic. Furthermore, we found that body-ratio data collection through photographs is biased and requires physical measuring instead. Although the population size appears larger than previously surmised, the limited nesting sites and extremely low presence of juvenile and hatchling iguanas (2.4%), is similarly worrying as the situation for I. delicatissima on neighboring St. Eustatius. The island’s feral cat and large goat population are suspected to impact nest site quality, nest success, and hatchling survival. These aspects require urgent future research to guide necessary conservation management.

Locations (lat/lon) of sightings of Iguana recorded in:

• 2015, 191 sightings
• 2016, 89 sightings
• 2017, 114 sightings
• 2018, 70 sightings

No dates or effort (survey time) is recorded.

The Lesser Antillean Iguana (Iguana delicatissima) is endemic to Sint Eustatius as well as other islands of the Lesser Antilles. Since 2010 I. delicatissima is classified as endangered on the IUCN Red List. Iguana delicatissima has various threats for a longer period, but since last year a new threat has presented itself. The Common Green Iguana (Iguana iguana) was found on the island. The presence of the I. iguana is a serious threat for the I. delicatissima due to hybridization and habitat competition. In this study there is researched what the habitat preference is of I. delicatissima and the hybrid. Besides the habitat preference the distribution of the iguanas is mapped. With this information it hopefully will be easier to find the iguanas and STENAPA will be able to save the I. delicatissima from hybridization. Twelve transects were walked all over the island. Also is information obtained from citizens and opportunistic data is used. The exact location, plant species and whether the iguana was found in the sun were documented. To see if iguanas have a significant preference for sunlight a binomial test has been used. A total of 72 I. delicatissima were caught and the data of 7 hybrids was used. Of the 72 I. delicatissima 13 were found on the ground and of the 7 hybrids 5 were found on the ground. Most of the I. delicatissima were found in trees of which is known to be used as food. One of the hybrids was found in a same plant species which also I. delicatissima was found in. There was too little data to compare the hybrids with I. delicatissima. In the sun were significantly (p=0,013) more iguanas found than in the shade. There was a high density of individuals at the Welfare street, Mansionweg and Lodiweg. Most hybrids were found in one square kilometer. Concluding there was no significant difference found in habitat preference between the I. delicatissima and the hybrids. There were significantly more iguanas found in the sun compared to the shade. Iguana delicatissima was found widely spread over the island while the hybrids were found within one square kilometer. It is advised to keep documenting the plants the hybrids are found in to be able to say something about the habitat preference. Also it is recommended to place camera traps at nests in the area were hybrids have been found. This way you know if the juveniles are I. delicatissima or hybrids and if the problem is increasing or decreasing.

[Student report]

Het aantal genetisch zuivere Antilliaanse leguanen is aan het verminderen. Het belang om de Antilliaanse leguaan op St. Eustatius zuiver te houden, wordt zeer groot geacht. Daarom dienen oplossingen te worden geformuleerd om beperkende bedreigingen te reduceren. Om deze oplossingen te formuleren diende het individuele leefgebied van de Antilliaanse leguaan onderzocht te worden. Tevens moest er meer bekend worden over de bereidheid en het verantwoordelijkheidsgevoel van de bevolking om een bijdrage te leveren aan dergelijke oplossingen. Door dit onderzoek zijn oplossingen om de genetisch zuivere populatiedichtheid van de Antilliaanse leguaan op St. Eustatius te vergroten opgesteld.

Ten eerste is onderzocht wat het individuele leefgebied van de leguaan is, ook wel de home range genoemd. Hier komt een gemiddelde van 167,5m² uit voor één locatie en enkel vrouwelijke dieren. Hierbij bestaat een spreiding van 48,5m² en is slechts 1% van het eiland onderzocht.

Vervolgens is het verantwoordelijkheidsgevoel van de bevolking op St. Eustatius jegens Antilliaanse leguanen in hun tuinen onderzocht middels een enquête. Hieruit komt een gemiddeld verantwoordelijkheidsgevoel van 8,11/10,00. De spreiding van deze uitkomst is 2,18 en antwoorden liggen tussen 3 en 10. Tevens is de bevolking met een gemiddelde van 7,20/10,00 bereid mee te helpen aan oplossingen die de populatie Antilliaanse leguanen op het eiland moeten vergroten. Antwoorden hierbij lagen niet lager dan een 5 en de spreiding van de antwoorden kwam uit op 1,53.

De uitkomsten van de enquête zijn gekoppeld aan oplossingen om bedreigingen te reduceren. Hieruit is geconcludeerd dat de meeste middelen en materialen die beschikbaar zijn voor oplossingen die betrekking hebben op de bevolking moeten worden ingezet om het bewustzijn van familie en vrienden van de bevolking op St. Eustatius te vergroten.

De resultaten van het gehele onderzoek kunnen niet als betrouwbaar worden beschouwd. Voor een betrouwbare home range dient op 90 andere locaties onderzoek uitgevoerd te worden. Voor een betrouwbaar resultaat van het verantwoordelijkheidsgevoel en de bereidbaarheid van de bevolking dienen in totaal 344 inwoners bevraagd te worden.

Er wordt aanbevolen om vervolgonderzoek te doen naar de home range van de Antilliaanse leguaan op andere locaties op het eiland. Tevens is het goed om een planning te maken waarin bedachte oplossingen kunnen worden gesorteerd op mate van belang en toepasbaarheid. Ten slotte zal STENAPA op een efficiënte manier moeten samenwerken met de bevolking en andere eilanden en organisaties om met elkaar het grootst mogelijke resultaat te behalen.

[Student report]