RATS!RATS!Rachel Fewster

Steven MillerJames Russell

Hamish MacInnes

Department of StatisticsUniversity of Auckland

Hauraki Gulf islands in the last year

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 New York Times Oct 20052005

… and Razza still lives on!

Closely related rats mean lots of swimmers.

Unrelated rats mean

isolation.

Our research at the University of Auckland:

2. Use genetics to see how much

movement there is between different

islands

What do genetics look like?

FitzroyMotu

KaikouraFitzroy region, Aotea / Great Barrier Island

-30 -20 -10 0 10 20 30 40

-30

-20

-10

010

2030

Kai

Kai

KaiKai

Kai

Kai

Kai

Kai

KaiKai

KaiKai

Kai

KaiKai

Kai

KaiKaiKai

KaiKai

Kai

Kai

KaiKai

KaiKai

Kai

Kai

KaiKai

KaiKaiKai

Kai

Kai

Kai

Kai Kai

Fit

FitFit

Fit

Fit

Fit

Fit

Fit

Fit

FitFitFit

HakuHaku

Haku

Haku

Haku

HakuHaku

Haku

Haku

Haku

Haku

Haku

Haku

HakuHakuHakuHakuHakuHakuHaku

Haku

Nel

Nel

NelNelNel

Nel

NelNelNel

NelNel

%var: PC1=0.68; PC2=0.15; Tot=0.83

Fitzroy region, Aotea / Great Barrier Island

FitzroyMotu

Kaikoura

-30 -20 -10 0 10 20 30 40

-30

-20

-10

010

2030

Kai

Kai

KaiKai

Kai

Kai

Kai

Kai

KaiKai

KaiKai

Kai

KaiKai

Kai

KaiKaiKai

KaiKai

Kai

Kai

KaiKai

KaiKai

Kai

Kai

KaiKai

KaiKaiKai

Kai

Kai

Kai

Kai Kai

Fit

FitFit

Fit

Fit

Fit

Fit

Fit

Fit

FitFitFit

HakuHaku

Haku

Haku

Haku

HakuHaku

Haku

Haku

Haku

Haku

Haku

Haku

HakuHakuHakuHakuHakuHakuHaku

Haku

Nel

Nel

NelNelNel

Nel

NelNelNel

NelNel

%var: PC1=0.68; PC2=0.15; Tot=0.83

Genetic results

Look for:Overlap: closely related populationsSeparation: isolated populations

Each point is one rat;

Each colour is a different

island

-30 -20 -10 0 10 20 30 40

-30

-20

-10

010

2030

Kai

Kai

KaiKai

Kai

Kai

Kai

Kai

KaiKai

KaiKai

Kai

KaiKai

Kai

KaiKaiKai

KaiKai

Kai

Kai

KaiKai

KaiKai

Kai

Kai

KaiKai

KaiKaiKai

Kai

Kai

Kai

Kai Kai

Fit

FitFit

Fit

Fit

Fit

Fit

Fit

Fit

FitFitFit

HakuHaku

Haku

Haku

Haku

HakuHaku

Haku

Haku

Haku

Haku

Haku

Haku

HakuHakuHakuHakuHakuHakuHaku

Haku

Nel

Nel

NelNelNel

Nel

NelNelNel

NelNel

%var: PC1=0.68; PC2=0.15; Tot=0.83

FitKai

Nel

Haku

FitKai

Nel

Haku

Look for:Overlap: closely related populationsSeparation: isolated populations

Clear left-right divide: is

something stopping the rats from swimming this small gap?

Cliffs at the

landing points?

Or rat sociology

?

Mainland

Kaikoura region

Broken Islands

Broken Islands Results

Lots of overlap between Rangiahua

and MahukiMotutaiko separate

Broken Islands Results

Lots of overlap between Rangiahua

and MahukiMotutaiko 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

250m

Reinvasion or failed eradication?

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

Post-eradication Norways all grouped with Stewart Island rats: phew!

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

Ship rats

Ship rats

Ship ratsOnce 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

Thanks to our funders!