Mauritius reptile restoration programme

For their size the islands of the Mascarenes once held more unique reptile species than anywhere else in the world and most of these reptiles were found on Mauritius. However, the arrival of humans and the resulting habitat destruction and introduction of non-native animals and plants have accounted for 45% of all known reptile extinction events on the planet in the last 400 years. Prior to people arriving, there were no cats, dogs, deer, rats or any other mammal except for bats. It was an island of unique reptiles and birds. In the absence of mammals the reptiles occupied many of the roles that mammals occupy elsewhere. There were giant tortoises that were the grazers, browsers and seed dispersers and predatory snakes and lizards that ate smaller reptiles and birds.

The lizards were the main prey for some of the unique birds and also helped to disperse the seeds of Mauritian trees and pollinate their flowers. As the reptile communities were torn apart, many relationships between the reptiles and other Mauritian animals and plants were destroyed, which led to further degradation of the ecosystem affecting many more species.

Five Mauritian reptile species became extinct and more than 60% of the remaining reptile fauna became restricted to just a few small surrounding islands. Round Island is a famous example of this and became the last location where the Telfair’s skink, Guenther’s day gecko, Durrell’s night gecko, the Burrowing boa and the Keel-scaled boa survived (although the Burrowing boa has not been seen since 1975). These reptiles survived on Round Island because it is one of the few locations in the Indian Ocean to have never been colonised by rats, one of the principle causes of reptile extinction. Other islands around Mauritius also became the last place to find certain reptile species, such as the orange-tailed skink on Flat Island. Having an entire species restricted to one small location means that it can be more susceptible to disturbances, which can lead to extinction, especially if that location is invaded by an introduced predator. It is therefore beneficial to have two or more populations of a species in different locations to lessen the risk.

It would be advantageous to re-establish reptiles where they once occurred on mainland Mauritius, but the level of destruction has been too severe and there are too many invasive predators to remove or control. However, it has been possible to remove the causes of reptile extinction and restore habitats on some of the other small islands where the reptiles once occurred. Island restoration work started in the 1970s and most of the problematic introduced animals, such as rats, cats, mice, hares, rabbits and goats were removed from the northern and southeastern islands. Introduced plants have been weeded from some islands and native species have been replanted, such as on Ile aux Aigrettes and Round Island. These actions have made it possible to start moving unique reptiles back to islands where they used to occur.

Through a three year Darwin Initiative project, the Mauritian Wildlife Foundation, with the Durrell Wildlife Conservation Trust, UK and the National Parks and Conservation Service initiated the first lizard re-introductions in 2006. The project’s initial intent was to restore endangered reptile communities on the offshore islands and great progress has and is still being made.

 The reptiles that have been the focus of the reintroduction programme on the islands are highlighted here. For each island we work on we closely monitor the progress of the reptiles we have moved, including the populations we have moved them from. We also monitor the impacts upon the resident terrestrial vertebrate and invertebrate communities to determine the benefits of our actions in restoring island ecosystems. Our activities on the islands also allow us to detect new threats, such as the introduction of non-native animals and plants, littering and open fires. Where possible we work to reduce or remove the threats to the reptiles, but also the other species that inhabit the islands.

The Telfair’s skink Leiolopisma telfairii

Once widespread throughout Mauritius, this large lizard became restricted to Round Island sometime in the mid 1800s due the invasion of rats elsewhere. Restoration work on Round Island allows it to support an estimated 26,000 skinks. In 2006 and 2007 we released 260 individuals onto Ile aux Aigrettes in the southeast and 250 individuals onto Gunner’s Quoin in the north. The population on Gunner’s Quoin was estimated at over 1,000 individuals in 2009, but the population on Ile aux Aigrettes has not grown as rapidly. Nevertheless, the skinks are helping with the restoration process of the islands by dispersing the seeds of endemic plants and on Ile aux Aigrettes they have contributed to the decline of problematic introduced animals that we cannot remove, such as the musk shrew, wolf snake (couleuvre) and African land snail. To help get the population of skinks growing on Ile aux Aigrettes we released a further 500 individuals in 2010. The growth of the population on Gunner’s Quoin is predicted to increase to approximately 2,500 individuals by 2011, and should be large enough to support the release of the keel-scaled boa, the main predator of the skink, which is also currently restricted to Round Island.

Gunner’s Quoin and Round Island are closed nature reserves and access is prohibited. Ile aux Aigrettes is also a nature reserve, but is open to the public and can be visited with Rangers from the Mauritian Wildlife Foundation.

The Ilot Vacoas skink Gongylomorphus bojerii sp.

Once widespread through the southeastern area of Mauritius, this small skink has been restricted to a population of 350 to 400 individuals on the tiny island, Ilot Vacoas for some time. This lizard was lost from the neighbouring islands Ile aux Fouquets (also known as Ile aux Phare) and Ile de la Passe, because of the introduction of shrews, although other introduced predators, such as the wolf snake have also contributed in their demise elsewhere. Shrews were eradicated from Ile de la Passe in 2000 and died out sometime in the 1990s on Ile aux Fouquets. In 2007, we re-introduced 20 individual skinks back to Ile aux Fouquets. We allowed the Ilot Vacoas population to recover and then moved another 20 in 2008. To ensure the healthy growth of the population we released a further 20 in 2010. To date we have over 650 skinks on Ile aux Fouquets and are now working to further enhance the population and support the re-establishment of a population on the neighbouring island Ile de la Passe.

Access to Ilot Vacoas is prohibited because of the risks of disturbance to the unique fauna and flora. Ile de la Passe and Ile aux Fouquets are open to public access, but illegal camping, littering and open fires are a threat to the existence of wildlife on the islands.

The orange-tailed skink Gongylomorphus spp.

Very little is known about the past distribution of this skink, but is thought to have once been found throughout the lowlands of Mauritius. As with the other small skink species, predation from the introduced shrew and the wolf snake are likely to have been the cause of its restriction to Flat Island. Rats, mice and cats were removed from Flat Island in the mid 1990s, which led to the skink being discovered and the recovery of its population. When the mammals were eradicated the skink could hardly be detected, but by 2000 the population was estimated between 810 to 6,000, by 2009 we estimated the population at approximately 23,500. Sadly, developments on Flat Island have led to the introduction of shrews, which were detected in 2010. Shrews cannot be removed from large islands like Flat Island using current techniques and its introduction will lead to the loss of the island’s terrestrial reptiles and ultimately the extinction of the orange-tailed skink. The fear that this may happen to Flat Island was recognised in 2007 so we translocated 79 skinks onto the neighbouring island, Gunner’s Quoin in 2008. By 2009, we found that the skinks on Gunner’s Quoin were reproducing, but because of their secretive nature they are very hard to monitor without disturbing their preferred habitat. With shrews on Flat Island, we needed to improve the chances of the skink’s establishment on Gunner’s Quoin. Soon after shrews were discovered we translocated an additional 300 individuals to Gunner’s Quoin and 90 individuals to Gabriel Island. Time will tell how successful our actions have been to save the skink from extinction, but we are planning more actions to save the population on Flat Island and to support a captive population from 2011.

The lesser night gecko Nactus coindemirensis and Durrell’s night gecko Nactus durrelli

The tiny lesser night gecko was thought to have gone extinct by the early 1990s, only a decade after its discovery on Gunner’s Quoin. Fortunately, the removal of rats from Gunner’s Quoin in the mid 1990s permitted the growth of the previously undetectable population, which was subsequently rediscovered. Since then, small populations have been found on three other islands. Sadly the population of approximately 60 geckos on Flat Island is likely to disappear following the introduction of shrews that were detected in 2010. The risks of predator invasion to other small island populations are high, particularly for the most southern and isolated population of approximately 400 individuals on Ilot Vacoas.

Durrell’s night gecko is restricted to Round Island, which is considerably larger than the combined range of the lesser night geckos on the four islands. The population of Durrell’s night gecko is relatively safer than the populations of lesser night geckos, because it is not subjected to the same level of human related disturbance. Both species are thought to have once co-existed throughout much of Mauritius, but were outcompeted and predated upon by the introduced house gecko in conjunction with predation from other invasive species. In 2006 we conducted a trial translocation of both night gecko species to the tiny island, Ilot Chat, to determine whether they could co-exist and learn more about how to translocate these small reptiles. The trials were successful and by the end of 2007 there were approximately 75 geckos of each species from the original 30 that were released the year before. However, disaster hit when a rat was introduced to the island. By the start of 2008, we removed the rat, but the geckos could no longer be found. This was a severe blow to the project and emphasised the risks to island reptile populations from just a single invasive predator. We believe that the rat was on the island for up to three months, the duration between our trips. Had the gecko populations been larger, it is probable that it would have given us more time to detect and remove the rat, allowing the re-growth of the gecko populations.

We are currently working towards the release of lesser night geckos onto another southeast island, Ile Marianne. We need to ensure that we retain any regional variation within the species so ideally need to work with the southeast population on Ilot Vacoas rather than move geckos from Gunner’s Quoin. Ile Marianne is the furthest from the southeast coast of Mauritius and is closed to public access. We plan to release over 100 geckos to enhance initial population growth and success. However, we cannot remove large numbers of geckos from Ilot Vacoas without impacting upon the population. From the work on Ilot Chat we know that we could safely remove 30 individuals from the small population on Ilot Vacoas. We therefore harvested 30 geckos at the end of 2008 and took them to the Herpetological Department at the Durrell Wildlife Conservation Trust, in Jersey where they are now being bred in captivity. By 2011 we should have approximately 100 captive bred geckos for release onto Ile Marianne.

The Guenther’s gecko Phelsuma guentheri

The Guenther’s gecko is the largest gecko in Mauritius and one of the largest geckos in the world. The remains of Guenther’s gecko’s egg shell in caves and historical records show that the gecko was once found throughout the lowland forests of Mauritius, but since the mid 1800s it has been restricted to Round Island. As with other large reptiles it is thought that introduced mammalian predators, such as rats and cats have caused the decline of this species. The removal of goats and rabbits from Round Island allowed the regeneration of palms, the favoured habitat of the gecko on Round Island, such that the current population has been estimated at between 4,000 and 6,000 individuals. With ongoing restoration of the vegetation on Round Island and the planting of other coastal tree species the gecko population is expected to continue to increase. With a healthy population on Round Island we have been able to translocate 50 geckos onto Ile aux Aigrettes. The geckos were released on the island in March 2010. Soon after the release, one of the geckos deposited eggs and these successfully hatched in June; the first time that Guenther’s gecko eggs have hatched in the wild outside of Round Island in more than 150 years. After initial supplementary feeding the geckos have settled into their new environment and have remained very healthy. As with the Telfair’s skinks that have been released on the island we will be closely monitoring their progress to enhance their chances of success.

Ile aux Aigrettes is open to the public and can be visited with Rangers from the Mauritian Wildlife Foundation where it is possible to see the Telfair’s skinks and Guenther’s geckos.

Reptiles on mainland Mauritius

There are six native lizards on mainland Mauritius; four of these are small day gecko species. The ongoing spread and impact of introduced mammalian and reptilian predators, the encroachment of invasive plants, agriculture and urban development are causing the gradual decline of Mauritian day gecko species.

Two species of particular concern are the upland forest day gecko Phelsuma rosagularis and lowland forest day gecko Phelsuma guimbeaui, both of which are the focus of current research to determine their requirements for conservation.

The reptiles and amphibians of Mauritius

If you would like to know more about the reptiles of Mauritius, the Mauritian Wildlife Foundation have published a colourful guide to the reptiles and amphibians of Mauritius. The guide can be obtained directly from the Mauritian Wildlife Foundation or from most book outlets in Mauritius. All profits from the sale of this guide go towards the conservation of Mauritian reptiles.

The project is carried out in close collaboration with the National Parks and Conservation Service and Durrell Wildlife Conservation Trust.
Read more on: The last of its kind: bringing the boa back from the EDGE

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