Our aim is to understand rat movement & invasion, to protect sanctuary islands Our research at the University of Auckland: 1. Put a rat invader on an uninhabited island and study its behaviour 2. Use genetics to study current and historic movement between islands
1. Put a rat on an island and see what happens... Study led by Mick Clout (UoA) and Dave Towns (DoC) …with unsuspecting PhD student James Russell… Controlled releases of lone rats on small islands
Rangitoto Noises Islands 1. Put a rat on an island and see what happens... Motutapu
1. Put a rat on an island and see what happens... Noises Islands Rat ‘Razza’ released on Motuhoropapa After a month, tried to catch him again...
1. Put a rat on an island and see what happens... Noises Islands Razza dropped his tag and swam 400m to Otata... James caught up with him two months later, but by boat...
Bad news for us, but 100 newspapers worldwide loved the story... New York Times Oct 2005
Broken Islands Results Lots of overlap between Rangiahua and Mahuki Motutaiko separate
Broken Islands Results Lots of overlap between Rangiahua and Mahuki Motutaiko separate Real separation between islands and mainland One rat caught on the mainland appears to have come from the islands
We see this pattern all over New Zealand: No gap in genetics over 10s of km of mainland
We see this pattern all over New Zealand: Then a short water crossing…
We see this pattern all over New Zealand: … and a clear gap.
We see this pattern all over New Zealand: Ship Rats!
Reinvasion or failed eradication? All three species of rats were eradicated from Pearl Island in July 2005: Pearl Island, off Stewart Island By May 2006, there were 4 Norway rats and 1 ship rat back on the island… HOW DID THEY GET THERE?
Reinvasion or failed eradication? Survive the eradication? Reinvade from Stewart Island? HOW DID THEY GET THERE? Worst possible news! Better security needed
Norways are strong swimmers, but this far south…? 10 rats caught on Pearl Island after eradication, May-July 2006 12 rats caught on Pearl Island before the eradication (July 2005) 9 rats caught on adjacent Stewart Island Norway Rats Eradication planning Reinvasion response
Ship rats are weaker swimmers, so did some survive the eradication? 1 rat caught on Pearl Island after eradication (May 2006) 11 rats caught on Pearl Island before the eradication (July 2005) 8 rats caught on adjacent Stewart Island Ship rats
Once again, the ship rat is grouped with the Stewart Island rats: NOT a survivor! HOW DID THEY GET THERE? THEY SWAM! The genetic work showed DoC that their eradication procedures had not failed: all rats found on Pearl Island were reinvaders.
Conclusions Ship rats are weaker swimmers than Norways We see genetic separation even over small water crossings But we don’t know whether this is because they don’t swim, or don’t breed Norway rats are strong swimmers, luckily absent from Aotea