Since a $17 million eradication effort on the world heritage-listed island, only about 100 rats have been detected, but experts insist all is not lost.
Since April, nearly 100 rats have been spotted on Lord Howe Island, despite the deployment of 22,000 lockable traps and more than 40 tonnes of poison sprayed by helicopters - but scientists remain optimistic that the $17 million eradication campaign was a success.
The last rat detected on the island was meant to be flushed off by a detection dog in 2019, but the recent mop-up attempt represents a crucial test for the program on the isolated, world-heritage listed island 700 kilometers north-east of Sydney.
Lord Howe Island had an estimated rodent population of 300,000 rats and mice before eradication operations began in 2019 - nearly 1,000 rodents for each island's 350 people.
Finding Invasive Rats
A rat was discovered on the road near Ned's Beach Cemetery by a local woman in mid-April, fueling suspicions that the program had failed. Two rats were killed within days, and an autopsy indicated that they were a juvenile male and a pregnant female.
Since the eradication attempts began, the duo was the first verified rats to be discovered.
Following the finding, officials installed 250 motion-activated cameras in bushland and dispatched teams of specialists and specially trained canines from mainland New South Wales and New Zealand to track any surviving rodents. As a consequence, 96 black rats have been seized and killed since the beginning of the year.
The last rat sighting was 85 days ago, and DNA testing was conducted to determine whether the rats were survivors or had come from the mainland. However, the results will not be available until December.
An extra $3 million in grant cash was provided for the newest phase, of which $1.8 million has already been spent. The surveillance program will be cut back if no more rats are found by the end of December.
According to Atticus Fleming, chair of the Lord Howe Island Board and head of NSW National Parks, the focus would then shift to "biosecurity measures" to prevent additional rats from entering by boat from the mainland. However, some monitoring would continue as a precaution.
"It's not an option to do nothing," Fleming added. "Success is demonstrated by the fact that one of the world's most endangered species has quadrupled its number.
"We're talking about a UNESCO World Heritage Site." We're talking about a region of the world that is widely recognized as having exceptional worth - one of the planet's crown jewels. As a result, we must take this very seriously."
Rats were alleged to have jumped ship and arrived on the island. Mice initially arrived on the island in 1850, followed by rats in 1918, who had escaped from a ship that had sunk off the shore.
Rodents posed a threat to endangered species like the flightless Lord Howe woodhen, and other species, including five land birds, 13 invertebrates, and two plant species, became extinct due to their invasion.
Woodhen populations have risen fast after returning to the island's environment, from 250 birds in February to over 600 in March.
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