Preparing Lord Howe Island for the Phasmid
by Carmen Welss

One of many facets of the "jewel in the pacific" - World Heritage Listed Lord Howe Island Photo: Ian Hutton

A report on rat eradication on Lord Howe Island, funded by the Foundation for National Parks & Wildlife, raises hope for the reintroduction of the Phasmid on the island.

The ship rat (Rattus rattus) caused the extinction of the Phasmid, Lord Howe’s endemic giant stick insect, on the island. It now only survives on nearby Ball’s Pyramid. (See our previous PAWS edition for more information. Close the new window to return to this article.) While current captive breeding programs aim to increase the number of Phasmids, only total eradication of the predators will allow a reintroduction on the island.

The Foundation funded report is a cost-benefit analysis of three options to manage the rats, based on the impact of rats on both the island’s biodiversity and kentia palm industry. The Kentia Palm and eco-tourism are the backbone of the island’s economy.

If uncontrolled, rats destroy about 30% of palm seeds. Current control measures reduce this loss to 5-15%. The considerable effects of rodents eating palm seedlings and shoots have not been taken into consideration.

Palm seeds destroyed by rats Photo: Ian Hutton

Total Eradication – does it pay?

The report explores three options to face the problem; total eradication of rats or both rats and mice, sustained control or to do nothing at all.

Based on income loss through seed predation alone, the total eradication of rats at a cost of $635K gives the best cost benefit ratio. Not only would eradication pay for itself within four years; over the next 30 years, the palm industry on a rat free island would generate over 5.7 million dollars more than it could under current pest control regimes.

Biodiversity values may be difficult to quantify in dollar terms, but there is no question that there would be an increase in abundance of both fauna and flora that has survived the initial rodent invasion but are still directly eaten by rodents or compete for food with rodents.

A former resident of Lord Howe Island awaiting a possible return - the phasmid Photo: Ian Hutton

Rat eradication would allow for threatened species like the Lord Howe Phasmid, Skink, Gecko and Land Snail to be either reintroduced or to recover. Similar programs on offshore islands of New Zealand yielded a five-fold increase in plants and animals.

Risks and opportunities

While total rat eradication stands up favourably in dollar terms, there are environmental concerns about the method of eradication. The endemic Woodhen and Currawong along with another five island species would be at risk from aerial baits from primary or secondary poisoning.

The near future, however, may hold alternative rodent control options. The Pest Animal Control CRC is investigating the use of genetically engineered mouse cytomogalovirus that would sterilise mice that contracted the virus. The CRC is about to apply for permission to conduct contained field trails in 2005.

Landcare Research Pty Ltd, New Zealand, is currently developing two new toxins that are aimed to be specific for rodents only. The first, RST, is specific to rats only and may be ready to trial within a year.

“It’s curtains for the rats”

“Feral pests are causing mass extinctions across Australia,” says Leonie Gale, Foundation Executive Officer. “We have more hope of reversing the tide of extinction on an island than on the mainland. Pigs were eradicated from Lord Howe as part of our successful campaign to save the Woodhen. Goats and feral cats no longer prey on the island’s unique birds. Rats are next on the hit list but it is a big ask. We have to be sure that eradication is a viable option. Such a large outlay of cash needs to be backed with a sound business case.

“That is why the Foundation has used funds raised from Lord Howe lovers to have this report commissioned. The results are favourable for the island natives, but it’s curtains for the rats of Lord Howe.”

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