Research

Sarasins' Giant Gecko Rhacodactylus sarasinorum

Conservation status: Vulnerable

Description: A large species of gecko growing to a body length of 135 mm with a tail approximately as long as the body, and moderately broad toes. The colour is pale to dark brown above, variably with obscure to bold, pale, V-shaped nape neck markings and scattered pale spots or blotches either side of the middle of the back. So far it is only recorded from closed forest habitat.

Natural distribution: Known only from southern New Caledonia.

Distribution within Province Sud: Recorded from six locations in the very far south of the island, ranging from Baie du Prony in the south, to Mt Koghis in the north.

Threats:

• potentially high level of threat to populations in low elevation closed forest from high infestation levels of introduced fire ants (Wasmannia auropunctata), leading to a possible decline in abundance
• high level of threat to populations inhabiting low elevation closed forest on the east coast through loss of closed forest to subsistence agriculture, resulting in a decline in area of occupancy, and degradation and fragmentation of once continuous lowland forest habitat
• high level of threat to isolated closed forest on ultramafic soils through activities associated with mining (particularly gully forests affected by mining spoil), resulting in a decline in area, extent and quality habitat
• moderate to high level of threat to closed forest edge through repeated firing of adjacent maquis shrubland habitat, resulting in a decline in area, extent and quality of habitat
• potentially moderate to high level of threat from exotic pests such as rats, cats and pigs (predation of adults, young and eggs), particularly in closed forest habitat adjacent to intensive settlement or urban development or small remnant forest patches
• localised but moderate level of threat to populations inhabiting closed forest adjacent to urban development from general degradation of the forest, increased likelihood of fire in adjacent habitats, and increased pressure from pests and predators, resulting in an overall decline in area, extent and quality of habitat
• localised but potentially intensive decline resulting from collection for illegal trade at readily accessible sites

Ultramafic - soils that are dominated by minerals high in magnesium and iron, and which tend to be dark-coloured rather than pale
Maquis shrubland - low and heath-like vegetation

Conservation status: Rhacodactylus sarasinorum is a large gecko with a very restricted distribution, it is known from only six locations in the south of the island, each representing an isolated sub-population. It is highly likely that other isolated sub-populations of R. sarasinorum will be found, particularly in some of the closed forest patches in gullies of the Plaine des Lacs. However, these forest patches are usually small isolates with little connectivity between them. Although the number of sub-populations is likely to increase with further survey work the species overall real area of occupancy will remain low, and the individual sub-populations at risk by virtue of their very small size. Its distribution lies within one of the most highly developed parts of the island that has been modified through subsistence agriculture on coastal lowlands of the east coast, by its proximity to urban development near Noumea, and more recently by activities associated with the Goro nickel mining project on the Plaine des Lacs. As such the species is considered to have undergone a decline in area of occupancy and/or quality of closed forest habitat. These factors in combination with the range of threats identified above indicate the species can conservatively be categorised as Vulnerable, and could be moved to a higher level of conservation concern given the intensity of those threats.

Future research required:

• determine basic life history parameters and habitat requirements
• undertake targeted survey work to more comprehensively document the species overall distribution
• identify distinct geographic units
• determine the levels of infestation of introduced fire ants at low elevation sites, and monitor population trends for the species at these locations

Copyright © Australian Museum, 2002