Skink biology

Grand and Otago skinks (Oligosoma grande and O. otagense) are two of New Zealands most striking and best known skinks but are also among the most imminently threatened with extinction. Both are classified as ‘Nationally Critically Endangered’. Grand skinks and Otago skinks are large rock dwelling (saxicolous) skinks endemic to Otago. Surveys conducted in the 1980s and 1990s identified that both species had retreated to <10% of their former distribution, that both species were rare across their extant range and decline seemed to be continuing. The most significant stronghold for both species is now Macraes Flat, eastern north Otago (approximately Lat S 45° 25’ Long E 170° 25’) where there is a 2400ha reserve currently managed specifically for their conservation.

The skinks are naïve to mammalian predators, are omnivorous, take four years to reach sexual maturity and produce less than three viviparous offspring per year in the wild – all traits typical of New Zealand endemic megafauna, rendering them vulnerable to mammalian depredation. There are no suitable habitats on off-shore islands. The skinks now exist in a radically altered ecosystem, converted from forest-shrubland to seral grassland by early Polynesian burning, further degraded by European agricultural development and introduced weeds.

Mammalian impacts

A predator control operation (1999-2002) focused on cats and ferrets over the range of several grand and Otago skink populations was not associated with any positive responses in the skinks. Stoats, weasels, ship and Norway rats, mice and hedgehogs all exist in the system and are either known or suspected predators of skinks. Rabbit, hare and possum are also abundant and constitute significant browsers of native vegetation likely to be inhibiting recovery of the system towards a more native woody dominated state.

Habitat degradation

On-going conversion of native grasslands to more productive developed pasture or forestry appears to impact negatively on skink population genetic structure and dispersal but apparent declines in some monitored skink populations through the 1990s did not seem to be accompanied by concurrent habitat degradation or change. It is unlikely that carrying capacity and other density dependent effects are the sole agents of decline; but there remains the possibility that there maybe a synergistic effect with predation.

Inbreeding depression and allele effects

The effects of heterosis loss and inbreeding depression have not been quantified in grand and Otago skinks. Whilst all extant populations of grand and Otago skinks appear to be small (<200 individuals) with many populations consisting of less than 100 individuals, so far, rates of decline have not been inversely related to population size which does not indicate that allee effect is yet operating significantly on these populations. Loss of genetic variability is a key concern of the recovery programme especially considering that recovery of the species may involve translocations or habitat alteration which may require adaptation by grand and Otago skinks for long-term survival.

Parasitology and disease

Ectoparasites and hemoparasites are both present in grand and Otago skinks, implicated in inhibiting breeding in captivity and showing a trend towards increased infection rates in wild Otago skinks from 1996 to 2003. However, no pathology has been associated with these infections in the wild. Occasionally, seemingly uninjured corpses of skinks are discovered in the field, but to date post mortem examinations have yielded no causes of death.

Other Species for Reintroduction

Many other native fauna are under threat because of the same issues that the Otago and grand skinks face.  If the translocations of wild 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 invloves restoring the native vegetation for lizards, including reintroducing threatened native plants.  Threatened plant species would be translocated into the wild from propagation using locally sourced seed.  Many of these species are not currently known from Alginga.  Aldinga is within the known historical range of all detailed species.

The species list below is broad enough to enable wider conservation aims into the future and not just those relevant to skink translocations. They match the opportunities identified on the nearby Flat Top Hill Conservation Area. Recovery plans that are relevant to this proposal are Inland Lepidium, threatened grassy plants of dry fertile sites, Hebe cupressoides, native broom (Carmichaelia) and tree daisy (Olearia spp.).  These plans advocate for the collection, propagation and establishment of captive insurance populations, supplementation of existing wild populations and the creation of new populations.  Recovery groups are supportive of this proposal for the Mokomoko Sanctuary. Technical advice is that this proposal is also both suitable and appropriate for the threatened species encompassed that are not subject to a recovery plan.

Scientific name	Threat status	Currently at Aldinga?	Recovery Group?
Grasses
Deschampsia caespitosa	5 Gradual decline
Puccinellia raroflorens	1 Nationally critical
Simplicia laxa	2 Nationally endangered		X
Sedges/Rushes
Carex inopinata	2 Nationally endangered		X
Uncinia strictissima	2 Nationally endangered
Carex tenuicalmis	6 Sparse
Herbs
Atriplex buchananii	6 Sparse
Ceratocephala pungens	1 Nationally critical
Lepidium kirkii	2 Nationally endangered		X
Lepidium sisymbrioides subsp. matau*	1 Nationally critical*		X
Myosotis pygmaea var. minutiflora	3 Nationally vulnerable	X
Myosurus minimus	2 Nationally endangered
Pachycladon cheesemanii	5 Gradual decline
Triglochin palustris	2 Nationally endangered
Shrubs
Carmichaelia compacta	7 Range restricted		X
Carmichaelia crassicaule	5 Gradual decline		X
Carmichaelia kirkii	2 Nationally endangered		X
Coprosma intertexta	6 Sparse
Hebe cupressoides	3 Nationally vulnerable		X
Olearia lineata	6 Sparse	X	X
Olearia fimbriata	4 Serious decline		X
Olearia hectorii	3 Nationally vulnerable		X
Pseudopanax ferox	6 Sparse
Teucridium parvifolium	5 Gradual decline

Below are 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