Flora and Fauna

Grand and Otago Skinks

Skink biology

Grand and Otago skinks (Oligosoma grande and O. otagense) are two of New Zealand’s largest and most striking skinks but are also among the most threatened. Both are classified as ‘Nationally Critically Endangered’. Grand skinks and Otago skinks are rock dwelling skinks that are endemic to Otago. Surveys conducted in the 1980s and 1990s identified that both species had retreated to <10% of their former distribution, were rare across their range and that decline seemed to be continuing. The most significant stronghold for both species is now Macraes Flat, eastern north Otago where there is a 2500ha reserve surrounded by an extensive trapping network managed specifically for their conservation.

The skinks are naïve to mammalian predators, take four years to reach sexual maturity and breed relatively slowly (producing two to three offspring per year). These traits are typical of many native New Zealand animals, which makes them vulnerable to population decline. The skinks also exist in a radically altered ecosystem, converted from forest-shrubland to grassland by early Polynesian burning, further degraded by European agricultural development and introduced weeds. This and other threats mean that grand and Otago skinks are extremely vulnerable to extinction.

Mammalian impacts

A three year experimental management programme (2003-2005) was designed by DOC to investigate the impact of predators on grand and Otago skinks at Macraes Flat. The experiment focused on eradicating pests from two predator proof fenced sites and targeting invasive mammals in a variety of traps over a wider area. The control of a range of predator species via trapping and via exclusion fences have both resulted in a direct increase in the number of skinks across the managed area. Predators including cats, ferrets, stoats, weasels, hedgehogs and rats have all been implicated in declining skink numbers. Mice are also under suspicion of predation causing a direct impact on skinks, as well as indirectly via food competition for invertebrates and fruit.

Habitat degradation

Whilst habitat degradation and modification is not the major cause of the decline in skink numbers it is likely that it has an effect.  Research has shown that grand skinks move around less in developed pasture than in tussock which may lead to a decline in dispersal. Modified or degraded habitat may result in diminished fruit and invertebrate resources for skinks. A reduction in habitat cover also leads to increased exposure and vulnerability to predators.

Inbreeding depression

The effects of inbreeding depression have not been quantified in grand and Otago skinks and are not known to exist in wild populations. Inbreeding and the loss of genetic variability is however a concern for re-establishing skink populations via translocations. For a translocated population to be viable in the wild we need to ensure that sufficient skinks with genetic variation are introduced as founder animals for a population.

Parasitology and disease

Ectoparasites (e.g. red and scale mites) and hemoparasites are both present in grand and Otago skinks. Whilst Otago skinks in particular have high numbers of ectoparasites in the wild there is no evidence for them impacting upon the host’s body condition. Captive skinks however have to be carefully screened for ectoparasites which are eradicated where possible to avoid any potential problems.

Other species for reintroduction

Many other native fauna are under threat because of the predation and habitat degradation issues faced by Otago and grand skinks. If translocations of skinks and vegetation restoration are successful, it may be possible to reintroduce other endangered native species that once roamed this area. These species could include green geckos, Duvaucel's gecko, takahe, kiwi and tuatara.This would provide a wonderful showcase of what this ecosystem may have looked like 200 years ago.

Click on the images below to enlarge.

Kiwi
(© James Reardon)

Takahe
(© James Reardon)

Jewelled Gecko
(© James Reardon)

Tuatara
(© Sue Keall)

Threatened plant reintroduction

A critical part of this project involves restoring the vegetation for lizards, including the reintroduction of threatened native plants. Threatened plant species could be translocated into the wild by propagating locally sourced seed. Although many of these species are not currently known from Aldinga, the area is within the known historical range of all the species listed.

The species list below is broad enough to enable wider future conservation aims and not just those relevant to skink translocations. They match the conservation opportunities identified on the nearby Flat Top Hill Conservation Area. Recovery plans exist for the following native flora; Inland Lepidium, threatened grassy plants, Hebe cupressoides, native broom (Carmichaelia) and tree daisy (Olearia spp.). Recovery of these species will be achieved by the collection, propagation and establishment of captive insurance populations, supplementation of existing wild populations and the creation of new populations.

Below is a selection of the species mentioned above, courtesy of John Barkla.  Click images to enlarge. 

Carex inopinata

Pachycladon cheesemanii

Olearia fimbriata

Deschampsia cespitosa

Olearia hectorii

Carmichaelia crassicaulis subsp. crassicaulis