Oligosoma otagense 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Reptilia Squamata Scincidae

Scientific Name: Oligosoma otagense (McCann, 1955)
Common Name(s):
English Otago Skink
Girardiscincus otagense (McCann, 1955)
Leiolopisma grande ssp. otagense McCann, 1955
Taxonomic Notes: The species is named after the Otago province (Gill and Whitaker 2001).

No significant morphometric differences have been detected between populations. The wide geographic separation and presumably long isolation of the eastern and western populations means genetic differentiation between these regions is possible, although this has yet to be investigated (Whitaker et al. 2002).

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(iii,v); C2a(ii) ver 3.1
Year Published: 2010
Date Assessed: 2009-06-30
Assessor(s): Chapple, D.G.
Reviewer(s): Böhm, M., Collen, B. & Ram, M. (Sampled Red List Index Coordinating Team)
Contributor(s): De Silva, R., Milligan, H.T., Wearn, O.R., Wren, S., Zamin, T., Sears, J., Wilson, P., Lewis, S., Lintott, P. & Powney, G.
Oligosoma otagense has been assessed as Endangered under B1ab(iii,v) and C2a(ii), as it has an estimated extent of occurrence of approximately 2,200 km2, which consists of two isolated populations and is undergoing decline in quality of habitat and in the number of mature individuals. This species has been estimated to have 2,000 individuals, which are mostly found at one location. Although this lizard has been threatened by habitat loss due to agriculture and mining in the past, these particular threats have presumably stopped. However, introduced mammals are still present within the species' range, causing habitat degradation and species mortality by predation. Furthermore, despite a large scale recovery plan being undertaken, including predator proof fences and captive breeding, introduced predators are still very common and continue to threaten this species. The top research priority is to conduct a study to determine that the skink populations are recoverable in situ by removing the mammalian predators, as well as the implementation of conservation measures.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This species is endemic to New Zealand (Norbury 2001). It had been previously found throughout central Otago, South Island (Whitaker and Loh 1995), however, its range has declined dramatically over the last 100 years, and now constitutes only 10% of this former extent (Norbury 2001).

The current distribution includes the two widely separated areas of Macraes Flat and the Lindis Pass region, near the far east and west margins of its former distribution (Roughton and Seddon 2006). This species occurs between 200 and 1,000 m above sea level.

The area in which this species is distributed is 2,227 km2.
Countries occurrence:
New Zealand
Additional data:
Number of Locations:2
Lower elevation limit (metres):200
Upper elevation limit (metres):1000
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:This species is described as rare (Norbury 2001). The population has been estimated to be around 2,000 individuals (Whitaker and Loh 1995). The larger subpopulation lives between Macraes Flat and Sutton, with the subpopulation in the Lindis Pass area being much smaller (Patterson 1997).
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:Yes

Habitat and Ecology [top]

Habitat and Ecology:This species is diurnal and inhabits rocky outcrops and stream canyons within the tussock grasslands of Central Otago (Towns and Daugherty 1994).

This species is heliothermic, and requires a long time to reach optimal temperature due to its large body size. Therefore, it only tends to bask during periods of optimal temperature (Roughton and Seddon 2006) and will retreat to the rock crevices when it becomes too hot (Patterson 1997).

There is evidence that this species engages in long-range movements between rock outcrops (Patterson 1997). Females are known to give birth to two to three offspring at a time (Patterson 1997).

Threats [top]

Major Threat(s): The 90% loss in range over the past century has been attributed to heavy predation as well as degradation of the grassland habitat by grazing and agricultural development (Norbury 2001). A change in farming practices from extensive pastoralism of native grasslands to over-sowing with exotic grasses and intensive grazing is thought to be one of the driving forces in this species decline (Towns and Daugherty 1994). This habitat modification resulted in a series of impacts, such as the removal of shrub cover around the outcrops, which had provided a food source of berries for the skinks, a reduction in cover and therefore increased vulnerability to predators, disturbance of habitat by livestock, and the removal of vegetation by rabbits (Towns and Daugherty 1994).

Furthermore, with the arrival of humans in the region around 150 years ago came introduced predators such as cats and ferrets (Roughton and Seddon 2006).

In a study on skink predation, Norbury (2001) found that the introduction of rabbits has contributed to skink population decline due to an increase in predator abundance, a decrease in refuges, and a decrease in food and shelter for the lizards. Avian and mammalian predators that are known to prey on the Macraes population of skinks include magpies, Australasian harriers, New Zealand falcon, feral cats, ferrets, stoats, weasels, ship rats, Norway rats, mice, and European hedgehogs (Tocher 2006).

Other contributions to the decline of this species may be poisoning from pest control efforts and habitat degradation from mining (Roughton and Seddon 2006).

Conservation Actions [top]

Conservation Actions: Population modelling has indicated a severe threat of extinction within ten years from 2003 (Hitchmough et al. 2005).

A recovery plan has been created by the New Zealand Government, which includes a series of measures to be implemented from 2006-2016 (Norbury et al. 2006). The top research priority is to conduct a study to determine that the skink populations are recoverable in situ by removing the mammalian predators. In situ and ex situ conservation priorities include the implementation of a Captive Management Plan, the creation of a large scale fenced habitat and mammalian eradication in the ranges, and the monitoring of populations (Norbury et al. 2006). This management plan is now being implemented and the results of which are being continually assessed; however the species is still considered at risk of extinction (D. Chapple pers. comm. 2010).

Citation: Chapple, D.G. 2010. Oligosoma otagense. The IUCN Red List of Threatened Species 2010: e.T15260A4507278. . Downloaded on 19 September 2018.
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