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.