Archives For Ulva Island

We check in with the Oscar, Stanley and their family, who won our Conservation Week competition last year to experience Ulva/Te Wharawhara Island. Oscar and Stanley tell us about their family trip.

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The DOC website has the latest updates on the Ulva Island rat eradication.

The work on Ulva Island continues to progress, with the work focussed on planning for an eradication option and obtaining the resource consent for this work.

Operational planning

Planning work is progressing well, key decisions have been made about bait storage, loading site, re-fuelling site etc and organisation of these and other aspects of the operation is well on track.

Documentation such as contracts (bait supply, aerial bait spread), operational plan etc are either completed or in final draft phase.

The operational plan has been sent to the Islands Eradication Advisory Group for feedback, (including questions raised by the community such as merits of pre-feeding and best practice for sowing the coast).

IEAG is a team of DOC experts who provide worldwide technical support for island eradication operations. New Zealand leads the world in this field and the meeting was attended by people from far flung places such as French Polynesia, California and the UK, all seeking advice on how to go about eradicating rats from islands.
Calibration of the helicopter buckets has been organised for the last week of April (April 27th). Bucket Calibration is an important step in the eradication process and is carried out in a flat mowed paddock where all bait can be seen and counted. Non-toxic bait is sown through the bucket that is to be used in the operation and the machinery is tweaked to ensure that bait is sown to the correct swath width (i.e. width of strip sown with bait on each pass) and that the correct number of pellets per hectare are sown. Once the correct bait application spread and rate has been achieved the bucket settings are noted so that the toxic bait can be spread correctly on the day.

Biosecurity meeting

As mentioned in the last update, a public meeting will be held at 7.30pm on 28th of April in the Stewart Island Community Centre. This meeting will discuss any and all ideas about possible ways to improve the biosecurity on Ulva Island to further reduce the chances of rats establishing in the future. If you have any ideas, or are simply interested to hear what might be proposed, please come along.


The University of Otago’s bird research group (who monitor robins on Ulva Island every summer) have offered to monitor the effects of the baiting operation and the effects that the rats have had on the birds on Ulva Island. It will be great to have this independent monitoring of the operation.

Trapping stopped

Some confusion seems to have arisen around the reasons as to why we have stopped trapping on Ulva Island.

The long term exisiting biosecurity measures on the island are aimed at preventing a rat population becoming established. In this case, they have failed and a rat population has established. Continuing to run these traps and bait stations will not even now slow the rat population expansion and is therefore considered to be a waste of time. Servicing them has stopped so we can focus efforts on a proper eradication attempt. This has been misinterpreted by some as DOC giving up. The fact is that we are well down the planning track for an aerial eradication attempt.



The DOC website has the latest updates on the Ulva Island rat eradication.

A few days ago I promised an update as soon as I had the figures from the last trap check and I indicated that we were close to a decision on which method we would choose to pursue. I’ll cover both of these topics in this update.

Latest trap check

Staff were out checking the traps on Friday and caught another 26 rats. This brings the total caught since Christmas to 96. As discussed in the last update, the rat traps have gone past the point of preventing population growth. The rat population has reached a point where its growth will no longer be influenced by any efforts that we put into trapping – even if we were checking traps daily. Therefore, the rat traps have now been closed so that the three days of effort per check can be used elsewhere. The traps will stay in location and will form part of our biosecurity network on the island when we have removed the rats.

Rat eating Fantail chicks at nest


Biosecurity is the term that we give to all of the actions that we take to keep an island pest free. On Ulva Island it consisted of traps and bait stations on the island, traps on people’s boats, quarantine procedures for gear going to Ulva, signage and regular publicity. While the biosecurity network on the island was effective at preventing a rat population establishing for 15 years, it has failed this time round. This has prompted lots of people to have ideas on how it could be improved to further reduce the chances of this situation occurring again.

We would like to capture all of these ideas, so are planning a public meeting in the next few months to get your input into how to keep rats off Ulva Island. We don’t yet have a set date, but will let you know as soon as we do.

Aerial view of Ulva Island

Method of eradication

After considering the advice of the world experts and the feedback from the local community, the Department has made a decision on which method it will pursue in our attempt to eradicate rats off Ulva Island. It has become apparent in the last few weeks that the only method that gives us any hope of achieving eradication is an aerial spread of bait containing rat poison (brodifacoum). The decision was made as an aerial spread will be the quickest to achieve the result and has the highest chance of succeeding. It is the best tool for the job and we would be complicit if we attempted anything else. This was re-inforced in recent days when we read up about the Fregate Island eradication failure being blamed on the use of bait stations.

Aerial bait spread has been extensively used so we have a lot of information about its effect. It is the method that has resulted in most of New Zealand’s key wildlife sanctuaries (e.g. Codfish Isl/ Whenua Hou, Kapati, Karori, Campbell Island, Taukehepa, Maungatautiri, Orokonui, Little Barrier Isl.).

The Department, in partnership with the Hunter Family, will be lodging a resource consent application with Environment Southland in the next few weeks. Environment Southland will notify this consent allowing anyone to make a submission. Environment Southland run a good process and we think they will be a good independent evaluator of our proposed methods and controls. We encourage you to make a submission (in support or expressing your concerns), so that ES can fully evaluate this application.

Frequently Asked Questions

Q. Why an aerial drop? Surely the ground based approach is the safer option?
R. We have now completed many island eradications using aerial spread of bait that has resulted in some of our most unique and valuable pest free sites, including Codfish Island / Whenua Hou and Campbell Island. Ulva Island is at threat from rats. We only have a limited range of tools to deal with this. We need to use the best tool for the job that will save Ulva from rat-induced devastation. The Department’s preference is for an aerial operation as this has a greater chance of success than a bait station operation and can be completed much more quickly – effectively restoring Ulva Island to a rat free state before too much damage is done by the rats on the wildlife or the businesses that rely on this wildlife. Unfortunately a ground based eradication is far from a “safe option”, with bait available in the environment for a whole year and a much higher chance of failure. It is also a much more expensive option. With an aerial operation, bait will be taken to where the rats are so that they don’t have to move any distance to find some bait to eat. A bait station operation would require rats to travel some distance, through areas of high natural food abundance, to obtain a meal of rat bait – increasing the risk that they simply won’t encounter bait.

Aerial drop on Campbell Island (2001)

Q. Has this been done before?
R. While there have been many eradications worldwide, almost all of these have been with established rat populations that have reached peak numbers and exhausted the food supply. The situation on Ulva is very different where rats are newly invaded and have unlimited food supplies. This situation has only been encountered once before, on Fregate Island in the Seychelles where rats invaded in 1995 and they attempted to eradicate them using bait stations. This failed and the recommendations from this attempt were that the rats weren’t using the bait stations and if the situation was encountered again then bait should be presented to the rats in a way that didn’t use bait stations (e.g via an aerial application). Rats were eventually eradicated from the island 5 years later by an aerial baiting operation after the rat population had peaked.

Q. Will this work? What are the chances of success?
R. This is new ground and, even though we are using the best tool in the box, we may still fail to eradicate these rats. The rats have unlimited food available and may not have any interest in eating the bait. Even though there is a very real risk of failure, there is also a good chance of success and this, coupled with the current value of Ulva Island, make us think that an attempt is worth it. The alternative is to wait until rats have reached peak numbers and exhausted the food supply.

Q. When would an aerial drop occur and how long would it take?
R. An aerial drop would occur sometime between May and September. The exact timing depends on obtaining a resource consent and then having a four day fine weather forecast. Four days of fine weather will keep the bait in good condition for enough time for rats to find and eat it. The best practice for eradications is for two bait drops to occur about a week apart. The bait drops will only take a few hours on each of the two days.

Q. Will the island be closed? When? How long until Ulva could be used as normal again?
R. It is likely that we would close Ulva Island on each of the days of the two bait drops. Bait will be cleared from tracks and beaches early the following morning and the island will again be able to be visited. Signs warning that bait may be present will be present and visible until such time as we are sure there is no further risk of bait being present. As long as people don’t let children go unsupervised and avoid eating or handling any baits they encounter, then the island could be used as normal from the day immediately following each bait drop.

Q. What is the effect in the coastal marine area. Will you poison people who fish in the area?
R. In reality the risk of this is very low. Some bait will indeed enter the marine environment. This will be in the order two pellets per metre of coast, or less than half a kilogram of bait in a 100m stretch. The well monitored Kaikoura bait spill dropped 18 tonne in a 100m stretch and effects were limited to that 100m stretch. While the marine reserve is obviously not the local food basket, we will be discussing concerns about bait entering the marine environment with the Mataitai committee. One option that has been raised has been for a Rahui to be placed around Ulva Island to completely eliminate any possibility of eating fish that may have had contact with bait. Exploring potential solutions such as these may pave a way forward. We are also seeking advice from national marine and fisheries experts.

The DOC website has the latest updates on the Ulva Island rat eradication.

It has now been two weeks since the public meetings and I’m sure that many of you are wondering what is happening. Unfortunately, we have very little news from the island itself. As mentioned previously, the rat traps have gone past the point of preventing population growth, so we have scaled our trapping checks back to once per fortnight so that staff can focus on the planning to eradicate rats. The last check, just prior to the meeting, brought the total number of rats caught to 70. These have been caught all over the island. The next trap check is scheduled for Friday – I’ll update you as soon as I get the results.

This upcoming rat trap check will be our last. We will close the traps after this so that the 3 days of effort per check can be redirected onto more urgent tasks – such as planning for the eradication. It is important to understand that the rat population has reached a point where its growth will no longer be influenced by any efforts that we put into trapping – even if we were checking traps daily.

Project Manager

Effort has continued toward planning for an eradication operation. The Department will finalise its planned approach by the end of this week and we will then focus our effort onto the required preparation and planning. Regardless of the method chosen, we have appointed a project manager, Paul Jacques, who will be able to work full time on making Ulva Island rat free again. Paul has been the project manager for the possum control work on Stewart Island and we are reallocating his essential possum control tasks to other people and deferring or cancelling non-essential work.

Has this been tried before?

As part of the planning, we have also been reviewing other island eradication operations and discovered that we aren’t the first group to be in this situation after all. Back in 1995, Fregate Island in the Seychelles group (located in the Indian Ocean) was invaded by rats and they attempted to eradicate them while numbers were still low using bait stations. This is a similar situation to Ulva in that rat numbers were building rapidly and had unlimited food supplies. The bait station operation failed and they had to wait until rats reached peak population density and exhausted the food supply before they were able to eradicate them using an aerial bait drop.


Recently we received a real boost to fundraising for the eradication from Birdlife International Community Conservation Fund. This fund donated $5000 to kick-start fund raising. If you wish to help Ulva Island become rat free again, then the Ulva Island Trust will be co-ordinating any donations. Keep an eye on their website ( for details about how to donate.

Do you have a Question?

In the last few weeks there have been lots of good questions asked about what is going on and why. We will try to capture these questions and answers in a Frequently Asked Questions section loaded on the Ulva page of the DOC website. We should have this in place within the next two weeks.

If you have a question, feel free to give me a call or send me an e-mail.


Hi Everyone,

I wanted to keep you informed of the events unfolding on Ulva Island at the moment.

Twelve rats have been caught on Ulva Island in the last two weeks.

After four rats were caught on Ulva Island in June/July 2010, DOC staff were hopeful that the incursion to this rat free island had been contained. However, in October a keen eyed member of the public passed on a photo of animal prints he took in a muddy creek on the island. DOC experts confirmed that these were made by a rat.

Ulva Island has a network of traps and poison bait stations that are run year round to kill any rats that may get to the island and extra traps were added to this and the frequency of checks increased. Tracking tunnels were also used to try and detect any rats on other parts of the island.

Between August and December, no further rats were caught or detected. This all changed after Christmas day – a total of 12 rats have since been trapped. Of greatest concern is that one of the rats was a juvenile which indicates there is now a breeding population on the island.

DOC staff have been diverted from other work to check the traps and tunnels on a weekly basis. A DOC team of experts will meet shortly to plan a course of action to remove rats from Ulva Island as rapidly as possible.

Since rats were first removed from Ulva Island, on average one rat a year manages to get to Ulva Island either by swimming or hitch-hiking with boats. To date, we have managed to catch these rats as they arrive, preventing them from breeding. This is the first time a rat has evaded all of our traps, established and bred.

Removing and then keeping rats off the island is a difficult task and there is always a chance that we may not succeed. DOC has an excellent record in this field but as always we will need the help and support of the public to achieve this.

I’ll aim to send regular updates out over the next few weeks.


26 January update

Unfortunately, the picture isn’t getting any better on Ulva Island. Further trap checks have now brought the total number of rats caught to twenty. On top of this, we have been running ten lines of tracking tunnels (baited with peanut butter and have an ink card in them that records footprints). Five of these lines have recorded rat footprints (34% of tunnels). This confirms that the rats are widespread over Ulva Island.

We are meeting tomorrow to plan the best way to eradicate these rats. Luckily, within New Zealand, we are able to draw on some of the best rat eradication expertise in the world. I will let you know what the recommendation is as soon as I practically can.

The rats that we have caught aren’t going to waste. Tissue samples are being sent away for DNA analysis to confirm that they are all related (and hence only one invasion event) and to work out where they came from. This will be achieved by comparing the DNA of rats on Ulva with sample rats from different locations around Paterson Inlet and Bluff. The rest of the rat will be sent to the vet school at Massey University who will be able to provide information on sex, age and if they have bred or not.

We will continue trapping and running the monitoring tunnels to keep track of the dispersal and population growth of these rats. Hopefully, this will also keep numbers suppressed. The set-up that we have on Ulva will not achieve eradication of the rat population that has established. Something further will be required.

We have had many offers of help and support. These are really appreciated and are being built into the planning of how we might achieve eradication.


8 February update

The last few weeks that we have been doing intensive trapping have revealed quite a depressing picture. Over 40 rats have now been caught and most of the tracking lines across the island are tracking rats. In short, the population of rats is widespread and rapidly growing.  The trap set up that is presently on Ulva Island was designed to catch and dispatch individual rats as they invaded the island. The trap set up is no longer going to prevent this rat population from growing rapidly on Ulva Island. They are expected to reach maximum population density (regardless of trapping effort) within the next 12 months, possibly as soon as five months. The impacts on the island at this point will be severe. We plan on continuing to check the traps and tracking tunnels to keep track of rat population growth, but apart from this, the traps are past the point of achieving anything useful.

The best focus of activity now is on actions around eradication options. Last weeks expert meeting (involving members of the Islands Eradication Advisory Group) came out with only two options that had any hope of achieving eradication. Both of these involve getting widespread rat bait onto Ulva Island either by an intensive bait station network or by helicopter spreading. We are currently working through the financial costs and the pros, cons and risks of both options and this is what we will be discussing at the series of meetings on Stewart Island during the week of the 14th Feb. Once we, as a community, agree to the best path forward then we can get stuck into achieving it as rapidly as possible.

So, thanks heaps for your support and I am very sorry to have to send this message. It is really hard to believe that it was only one month ago that the first of these rats started turning up in traps.