Research

Rough-snouted Giant Gecko Rhacodactylus trachyrhynchus

Conservation status: Vulnerable

Description: A large species of gecko growing to a body length of 190 mm, with a prehensile tail approximately as long as its body, and moderately broad toes. The species gets its name from the enlarged rugose scales that cover the snout. The colour pattern is variable, being a mosaic of patches of grey-green, whites, and browns of varying hues. It has a live-bearing mode of reproduction, a feature which is otherwise not found outside of the New Zealand gecko fauna.

Natural distribution: Known from a few scattered locations in the central and southern regions of the main island, and the Ile des Pins.

Distribution within Province Sud: Recorded from Mt Gouemba and Goro on the southeast coast, Ile des Pins, and Ile Moro off Ile des Pines.

Distribution within Province Nord: Recorded from Mt Aoupinie and Coula-Boreare in the central ranges, Cui near Canala on the central east coast, and Pindai Peninsula on the west coast.

Threats:

• extremely high level of threat to insular populations (Isle of Pines and surrounding islets) posed by collection for illegal trade
• high level of threat to populations inhabiting low elevation closed forest on the east coast populations 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
• 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 from exotic pests such as rats, cats and pigs (predation of adults, young & eggs), particularly in closed forest habitat adjacent to intensive settlement or on islets off the Isle of Pines
• high level of threat to populations inhabiting sclerophyll forest from repeated firing of adjacent savannah habitat, leading to a decline in area, extent and quality of sclerophyll forest
• moderate level of threat to the area, extent and quality of closed forest habitat and its edge through repeated firing of adjacent savannah habitat
• localised but moderate to high level of threat to populations inhabiting closed forest habitat exploited for timber plantations and logging, resulting in a decline in area, extent and quality of mid elevation forest
• localised but potentially intensive decline resulting from collection for illegal trade at readily accessible sites

Conservation status: The species distribution is small and represents a number of isolates. It is recorded from 6 locations across the south of the main island, representing five disjunct sub-populations, and another two sub-populations on the Ile des Pins and offshore islands, the status of which is uncertain. On the main island the species has been recorded from closed forest habitat and sclerophyll forest, over a broad altitudinal range (50-500 m above sea level). The species is also likely to have a complex biology. These factors in combination with the range of threats identified above indicate Rhacodactylus trachyrhynchus 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
• undertake targeted survey work on the sub-populations on the Isle of Pines and Ile Moro to determine its preferred habitat on the islands, and the threats to that habitat
• determine the levels of infestation of introduced fire ants at low elevation sites, particularly the island sub-populations, and monitor population trends for the species at these locations

Copyright © Australian Museum, 2002