Julianna Marsters preforming the first official on board biosecurity check on Marumaru Atua, which picked up the Rat Eradication team. TIS/23092213
A rat eradication exercise has just been completed in Palmerston Atoll. This was for two main reasons.
First, rats cause damage to food crops and
also can get into food stores, impacting the livelihood of local people.
Secondly, rats impact the biodiversity of
the islands, including predating on seabird eggs and young seabirds, and eating
young shoots of native vegetation.
It has taken roughly five weeks to
complete this most recent rat eradication project in the Cook Islands, carried
out on Palmerston Atoll.
The collaborative programme involved a
team of eight field workers from outside of Palmerston, including reps from the
New Zealand Department of Conservation, Cook Islands National Environment
Service, Ministry of Agriculture, and Te Ipukarea Society.
This team worked alongside the Palmerston
Island community to implement this project. The eight visitors proved almost a
30 per cent increase in the Palmerston population which was initially 28 people
before the team's arrival.
Prior to the rat team arriving, Palmerston
community had been busy preparing their island for the project.
This involved removing all chickens and
livestock, or moving these animals temporarily to another rat free motu.
Based on a feasibility study conducted
last year on Palmerston, it was found that chickens would eat the bait in large
amounts, reducing bait availability for rats to feed on.
Active pig pens, where the pigs are fed
daily, provide an alternative food source for rats, and were therefore also
temporarily moved to a rat free motu.
Day to day lifestyle changes which were
practiced and then implemented during the project included community members
storing all food scraps in sealed buckets.
The food scraps were then either dropped
at sea or fed to those pigs moved to the rat free motu.
New livestock will be sent to Palmerston,
facilitated by the Ministry of Agriculture, once it has been declared safe to
bring livestock back to home motu.
With the island prepared and alternative
food sources scarce to come by for rats, the eradication team started the
laborious task of track cutting through the bush to create island wide 20 x 20
metre grids on the two motu that harboured rat populations.
Each 20m point marks a baiting station
where brodifacoum toxin was thrown in a circular pattern, with the goal of
entirely covering both Cook’s and Home motu with bait.
Over 2000 baiting stations were created as
There were also 109 structures, both
vacant or occupied, that had their own special baiting stations.
Each room would have its own plate holding
10 individual baits which were checked every three to five days.
If a bait was missing this would be
replaced, until eventually, the rate of disappearance started to decline.
The brodifacoum toxin contained in the
baits works as an anticoagulant in mammals, preventing blood from clotting.
Fortunately, crabs or invertebrates are
not affected by the toxin as they have different physical and chemical wound
As a precaution, a rau’i was placed on
crab harvesting for several months to ensure there is no risk of humans
consuming toxins which could have accumulated into crab muscle.
Baits were spread at three separate times,
with around 10 days spacing in between.
Brodifacoum needs to be present for at
least 20 days to ensure every rat eats one bait, and to also allow time for
nesting rats to come out of holes to consume a bait.
During the first round of baiting rats
were easily noticed both on Home and Cooks motu.
By the second round of baiting the team
had not seen any live rats, though the “smell of victory” was more obvious by
this stage. Not too bad however, as the wind would air out the stench.
A network of biosecurity devices was also
built to allow for ongoing monitoring to prevent the chances of rats
Ongoing biosecurity will remain the
responsibility of the community and biosecurity officer checking incoming cargo
and items that are not fully sealed.
The rat team members have now returned
back to their respective homes after being picked up by Marumaru Atua.
The Palmerston community now remains
vigilant for the next month, as well as maintaining their daily practice of
storing food scraps in sealed bins.
It will take about six months before we
will know if the Palmerston rat eradication project was a success.
If successful, Palmerston will be the
first rat free inhabited island in the Cook Islands and possibly South Pacific.
The only other one of the Cook Islands to
date that has had rats eradicated is the uninhabited Suwarrow Atoll National
The final rats were killed there by Te
Ipukarea Society in 2022, after several previous attempts were only partially
Rat eradication team members were:
Emmanuel Oyston (DOC), James Ware (DOC), Jenny Long (DOC), Michael Mitchell
(DOC), Julianna Marsters (Palmerston Community/ MoA), John Tuakana Marsters
(Palmerston Community), Deon Frisbee (Palmerston Community), Teariki Tearetoa
(NES), Ieremia Samuela (TIS), Henry Koteka (TIS), and Alanna Smith (TIS).
Palmerston Rat Eradication 2023 was funded
by the New Zealand Ministry of Foreign Affairs and Trade through the MISCCAP