Threatened Biodiversity Potential of Hon Khoai Island, Southern Vietnam

Habitat of the endangered, endemic Psychedelic rock gecko

Posted: 4 June 2021
By: Truong Quang Nguyen1, Hai Ngoc Ngo2,4, Khoi Vu Nguyen3, Manh Huu Bui3, Phuong Huy Dang1, Cuong The Nguyen1, Tru Vu Hoang1 & Thomas Ziegler4

1 Assoc. Prof. Dr. Truong Q. Nguyen: Institute of Ecology and Biological Resources (IEBR), Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Hanoi, Vietnam. E-mail:
2 Hai Ngoc Ngo: Vietnam National Museum of Nature (VNMN), Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Hanoi, Vietnam.
3 Khoi Vu Nguyen: Wildlife At Risk (WAR), 45/68 Nguyen Van Dau Street, Binh Thanh District, Ho Chi Minh City, Vietnam
4 Prof. Dr. Thomas Ziegler: AG Zoologischer Garten Köln, Riehler Str. 173, D-50735 Köln, Deutschland. E-Mail:

Hon Khoai Island is located in the Rach Gia Archipelago, about 20 km distant from the southernmost tip of mainland Vietnam. The small offshore island of Ca Mau Province has a surface area of only four km2. The terrestrial ecosystem mainly consists of granite basements and thick evergreen forest scattered by small grassland patches (Ngo et al. 2016, 2018). One decade ago, the island became world-renowned for the discovery of one of the most colorful gecko species (Grismer et al. 2010) – The psychedelic rock gecko (Cnemaspsis psychedelica).

The endemic psychedelic rock gecko (Cnemaspis psychedelica) at WAR’s conservation breeding facility in Vietnam. Photographed by T. Ziegler

Since then this endangered, endemic diurnal gecko species is one of the focal species in our international German-Vietnamese working group. We already have reported about the setup of first conservation intitiatives at this point (Ziegler & Nguyen 2016b). We have built up a conservation breeding facility in southern Vietnam (Ziegler et al. 2015, 2016). Ecological research revealed the preferred habitat, large granite boulders in the shade of dense forest canopy, is scarce on the island (Ngo et al. 2018). In addition, our first population analyses revealed a relatively small population size, approximately only 500 mature individuals (Ngo et al. 2016). Subsequently, another subpopulation was discovered on the neighboring Hon Tuong Isle (Ngo et al. 2018), however, the species was only found in the densely forested centre of the isle, in addition representated by only very few scattered individuals. This data in concert with our trade analyses (Nguyen et al. 2015, Auliya et al. 2016) finally led to the inclusion of the species as endangered on the IUCN Red List of Threatened Species (Nguyen et al. 2016) and in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

However, despite all this conservation based research and engagement, to preserve this species, we had to realize, that habitat destruction continues on Hon Khoai, which in view of the small size of the island and the only limited availability of suitable forested granite boulders is a serious threat for the in any case tiny natural population of the psychedelic rock gecko (Ngo et al. 2018).

Forest destruction on Hon Khoai Island, here for road construction. Photographed by H. N. Ngo

As important as the discovery of the psychedelic rock gecko was, as well as subsequent research and conservation measures – there is definitely more that must be done. In particular, as knowledge about the remaining biodiversity of Hon Khoai Island remains poor. Because you can only protect what is well known, we decided to study the island’s terrestrial biodiversity in large scale to provide further baseline data for improved conservation.

With the financial support of the DGHT/ZGAP species conservation fund and Cologne Zoo, a biodiversity exploration was conducted in 2017 by scientists from the Institute of Ecology and Biological Resources (Hanoi) and Wildlife at Risk (Ho Chi Minh City), further supported by the provincial authorities of Ca Mau Province and the Ca Mau FPD (Forest Protection Department). Species identification was generally done by photographic records and, if required, in some cases by means of preserved specimens / molecular samples for subsequent taxonomical analyses.

To come to the point – the top sensation of the excursion was the discovery of a new mammal species at the same time representing the second endemic terrestrial vertebrate species for Hon Khoai: Callosciurus honkhoaiensis – the Hon Khoai squirrel (Nguyen et al. 2018). This discovery alone has fully justified the efforts of an excursion because it has also high political relevance for the conservation of the rain forest of Hon Khoai. Its next relative is the Grey-bellied squirrel (C. caniceps), an abundant species in mainland Southeast Asia, but from which it differs both in morphology and by molecular divergence. Similar to the situation of the psychedelic rock gecko, the population size of the Hon Khoai squirrel and the magnitude of its resources were predicted to be very small. As arboreal species, forest protection will be essential for the survival of the endemic Hon Khoai squirrel (Nguyen et al. 2018).

The endemic Hon Khoai squirrel (Callosciurus honkhoaiensis). Photographed by M. H. Bui.

The excursion was quite successful, 487 terrestrial species could be identified (275 plant and 212 animal species) within two weeks during the dry season.

Plants contained 242 native and 33 invasive species. Among animals there were 18 mammal species, most diverse bats with nine species. The insular long-tailed macaques (Macaca fascicularis) were presumed to be introduced, as well as Sambar deer (Rusa unicolor) (see Ngo et al. 2016) and wild boar. Furthermore we could prove 21 bird species and for the first time amphibians (a caecilian and a tree frog species). With 17 recorded species (Ngo et al. submitted), we further could extend the preliminary list of reptiles given in Grismer et al. (2010). Insect records contained 154 species, with butterflies with in total 48 species (31 %) representing the most diverse group (for further details see Nguyen et al. submitted).

Among the terrestrial organisms occurring on Hon Khoai which are officially ranked being threatened, four plant species are included in the IUCN Red List, three of them as endangered, and one as vulnerable. Five plant species recorded from Hon Khoai are listed in the Vietnam Red Data Book, and three species listed in the Governmental Decree Nr. 06/2019/ND-CP. Two of the recorded mammal species are on CITES Appendix II (the Flying foxes Pteropus hypomelanus and P. lylei), with Lyle’s flying fox also being listed as vulnerable on the IUCN Red List. The Sambar deer is listed as vulnerable on the IUCN Red List. Among the reptiles, the psychedelic rock gecko is on CITES Appendix I and as endangered on the IUCN Red List. Three animal species are included in the Vietnam Red Data Book and five animal species in the Governmental Decree (see Table 1).

And the taxonomic analyses still are being continued, and potential further candidate taxa are currently investigated so that further new descriptions from Hon Khoai cannot be excluded. There are also further questions to be answered, for example why some species occur on the mainland but not on the island, how island inhabitants reached Hon Khoai, for example through separation from mainland populations during Pliocene, as it was the case for the Hon Khoai squirrel, or actively or passively through humans. And of course why only in some groups new taxa evolved on Hon Khoai

Map showing location of Hon Khoai Island, Vietnam.

The tiny island of Hon Khoai with its even smaller patch of rain forest harbors a remarkable amount of biodiversity – including two endemic vertebrates and a considerable number of officially protected species. This biodiversity potential deserves protection, in particular as there still is high threat potential (see also Ngo et al. 2016, 2018):

In the first place habitat fragmentation and degradation through infrastructure development. A considerable extent of primary forest on the small island was destroyed for road construction and artificial ponds for water supply (Ngo et al. 2016, 2018). For example the psychedelic rock gecko has been extirpated due to habitat conversion through blasts of granitic blocks in an island region previously demonstrably inhabited by the species. And this clear-cutting further eats through the remaining island forest. Collecting of wildlife for food consumption and pet trade still persists (Ngo et al. 2016, 2018). Local fishermen reside on the island and pitch their camps inmidst the forested areas and live from local resources. Long-tailed macaques (Macaca fascicularis), which were introduced to Hon Khoai island in 2008 for touristic purpose, may have negative impacts on the biodiversity, particularly to the endemic psychedelic rock gecko (Grismer et al. 2010). Furthermore, expanding non-sustainable tourism activities account for disturbances and pollution. Forest fire in particular in between November and April is another problem, because the island’s forest is the major biodiversity priority region. The island also is in the focus of the military, so that different activities/interests have to be coordinated. Thus, the problems are complex and not to be solved at one go.

To proceed notwithstanding, we have provided the so far available survey results to the local authorities. The official protection of the psychedelic rock gecko by inclusion on CITES Appendix I certainly was an important success, in particular as the species subsequently was also protected in Vietnam by inclusion in group IB of the Governmental Decree No. 06/2019/ND-CP as well as the Governmental Decree No. 64/2019/ND-CP. Besides the buildup of an in country conservation breeding facility, additional support for biodiversity conservation was provided by the Nature Conservation Project of Cologne Zoo and IEBR to the Forest Protection Unit on Hon Khoai island, for example providing signboards for awareness, patrolling equipment (GPS and camera devices), and waste baskets. Because sufficient controls in site that guarantee the implementation of legal protection measures are crucial. As suggestions for optimized conservation we also have recommended improved law enforcement in concert with respective public awareness. Finally, the establishment of a Species and Habitat Conservation Areas (SHCA) for the psychedelic rock gecko and Hon Khoai squirrel is highly recommended in order to better protect the existing forest habitat and populations of the endemic flagship species as well as other terrestrial creatures of Hon Khoai Island and surrounding isles.

As the psychedelic rock gecko is a micro-endemic of Vietnam and an internationally protected species (CITES Appendix I), we have recently investigated, documented and published the reliable photographic identification (Gewiss et al. 2021). This now provides species conservation enforcement authorities with a useful tool to ensure the implementation of CITES and the European Wildlife Trade Regulation EC- 338/97 regarding this species. This tool will also assist respective other authorities in wildlife conservation and is highly recommended to be used in field research as a non-invasive method of individual identification which can be applied for long term monitoring activities to safeguard wild populations of Cnemaspis psychedelica in its natural range.

Psychedelic rock gecko

As habitat destruction in Hon Khoai still continues, and the breeding success in the facility for Cnemaspis in South Vietnam is currently not yet sufficient for a potential reintroduction to the wild, it was recently decided, in consultation with the German Federal Agency for Nature Conservation and other colleagues within EAZA, to expand the breeding efforts to Europe. This time, captive-bred specimens from private keepers were also taken over into this project in order to contribute to the conservation of this species by incorporating them into a controlled and structured, institutionally managed breeding programme. This controlled approach ensures that these animals do not simply disappear on the market, but instead contribute to the survival of the meta-population, and to a possible reintroduction in the future, should they or their offspring be needed for this purpose.


We thank the directorates of the Forest Protection Department of Ca Mau Province and Hon Khoai Forest Protection Unit for their support of our field work and issuing relevant permits. We are grateful to H.V. Le and B.T. Nguyen (FPD of Ca Mau Province), and T.V. Nguyen, S.T. Nguyen (IEBR, Hanoi) for their support and assistance in the field. Field work on Hon Khoai was supported by funds from Cologne Zoo and the Deutsche Gesellschaft für Herpetologie und Terrarienkunde (DGHT) / Zoologische Gesellschaft für Arten- und Populationsschutz e.V (ZGAP) species conservation fund. Previous research on population status and trade of the psychedelic Rock Gecko were funded by the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) and Rufford Foundation. Cologne Zoo supports biodiversity research and conservation in Vietnam and Laos with an amount of up to 60,000 Euro per year.


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