Threats to grand and Otago skinks

By far the greatest threat to either species is predation by introduced animal species: feral cats, stoats, weasels, ferrets . . . even hedgehogs have been implicated.

Dead common skinks from the vomit
of just one feral cat! They could easily
have been grand or Otago skinks

Several features of the biology of grand and Otago skinks make them more vulnerable to extinction than other lizards.These include:

• Late sexual maturity
• Low productivity
• Large size
• Highly specific habitat requirements
• Small, isolated populations

They are also quite naive, in the sense that they simply aren't aware of the threat cats, stoats and other mustelids pose. As a result they can easily fall prey.

Research projects

Beginning in the late 1990s a six-year project at the Macraes Conservation Area monitored grand and Otago skinks before and during trapping operations for feral cats and ferrets. The results showed that skink numbers were still declining and population modelling suggested that both species could be functionally extinct within 10 years.

Setting a feral cat trap at Macraes
Conservation Area

This was followed by an experimental management trial at Macraes from 2005 to 2008, to both determine and halt the cause of decline. Skink populations were monitored under three different management regimes:

• No management
• Intensive predator trapping of all mammal species
• Two fenced, mammal-proof exclosures

The results showed a major breakthrough in predator control, with a startling recovery in the protected populations of up to 94 per cent in just three years. This is the first time on the New Zealand mainland that there has been such a dramatic recovery in a critically endangered species.

Predator-proof fence at Macraes

This has given DOC's Grand and Otago Skink Recovery Team a major confidence boost. They have now extended their trapline in the Macraes Flat area to a total length of 60 kilometres; their research showing that intensive trapping is the most cost-effective form of management.

Monitoring

An important adjunct to the research work was the recovery team's development of a ground-breaking photo re-sight monitoring programme. This is non-intrusive and non-invasive, and not only does it detect change in small populations, it's a vast improvement on the previous method, toe clipping!

Monitoring team moving into position

Many of the field techniques, technology and population modelling programmes developed for the recent grand and Otago skink research work are of international significance. It is also, within New Zealand, immediately transferrable to the protection of other threatened fauna on the mainland.

Foremost, though, is the prediction that as a result of markedly reducing the threat from predators to grand and Otago skinks, their threat status could be reduced. In less than a decade it could change from 'Nationally Critically Endangered' to 'Nationally Endangered'.

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