Stewart Island rat eradication - technically feasible?

Speech by Brent Beavan, edited by David Speir.

Environmental News Issue 26 Winter 2011

Brent Beavan (at left) recently spoke to a public meeting co-ordinated by the GBICT at Whangaparapara Lodge. The subject was the developments on Rakiura (Stewart Island) subsequent to a Technical Feasibility Study on the eradication of introduced predators. In this article David Speir quotes extensively from Brent’s dialogue and fills in some of the background.

Stewart Island is New Zealand’s largest offshore island and at 169,000 Ha is six times larger than Great Barrier. It has a resident population of some 400 persons, albeit more tightly clustered in one area than GBI, but similarly it has a host of introduced predators relentlessly impacting on native species.

In 2009 the Stewart Island/Rakiura Community and Environment Trust (SIRCET) initiated a feasibility study to see if (technically) rats could be eradicated from the island. Since that study the questions that the study has raised are continuing to be debated within the Community. Brent Beavan co-ordinated the Technical Feasibility Study and has played a pivotal role in the ongoing community consultation.

The Stewart Island/Rakiura Community and Environmental Trust had set up the Halfmoon Bay Habitat Restoration Project in 2003 (See Issue 11). Mostly driven by volunteer labour, the project aimed to protect sooty shearwater (titi) and Little Blue Penguin nesting habitat on Ackers Peninsular from predators by trapping and improve the habitat through revegetation. This project has been dramatically successful in improving nesting outcomes for both species and increasing the overall populations and then holding these numbers. On a community level this has galvanised a community environmental ethos which has led onto bigger things.

In recent history the local economy has transitioned from fishing to tourism as a primary earner, with significant permanent population loss and all the attendant seasonality and transient issues around catering for visitors.

“The genesis of (our) thinking was to sustain and grow the community, creating wealth through protecting our key assets – our environment. By enhancing the environment we enrich the community. Our vision was about keeping our community strong and making it a great place to raise kids.

“The Tindall foundation provided funding to look at the feasibility (of island-wide pest eradication) and after one year of work it was apparent that after putting the social barriers and everyone's’ reservations aside, technically the eradication of rats, cats and possums was possible. There were very few barriers to stop that occurring.

“So what were the other issues? What therefore is stopping the community from doing it? Since that point the community has become engaged.

“The feasibility study was there to raise the difficult questions – not to answer them. The community need to find their own answers. So we started to look at the principles around involving the community:

“The primary principle was ownership. This was a community-led development and the community needs to keep ownership of the decisions rather than have a government department taking ownership and thrusting the process upon us. For example, deer and deer hunting were obviously a key issue – the local community value the opportunity around deer. So (within the debate) give the ownership of the problem to the deer hunters – they don’t want rats either. We can agree to get rid of the rats but at what costs. And are those costs acceptable to them? They should have the ownership of finding a solution acceptable to them. That is the general process of the moment.

“We are setting up an independent driving committee – independent of any organisation or government department or Iwi. This group needs to capture a bit of all the diverse elements, making sure that any people who will be affected have a voice in plotting a course forward.

“The vision needs to be articulated in a form that everyone recognises a common interest and benefit – if not maybe the model of how we operate needs to change so that the benefit is more widespread. The answers will lie within the community rather than outside of it. Even with off-island landowners the aim is to have these conversations when they are there – everyone needs to have an opportunity to have their say.”

A recent local initiative in wildlife tourism has graphically demonstrated what looking after environmental assets is worth to a community. The Ulva Island Trust was able to get Sirocco the kakapo (who was hand-reared and very comfortable with humans) from Codfish Island (Fiordland) onto Ulva Island (in Patterson Inlet) for a couple of weeks visit.

“The public response for six weeks was huge – the New Zealand community as a whole has hardly any chance to actually see kakapo.

“A costing study estimated that the added value to the community was between $400 and $700 thousand dollars. This was in additional tourist activity, accommodation, flights and other tourist spin-offs. The Ulva Island Trust made a small profit but the community benefit was much greater. It was clear from that exercise that in our community – Conservation can pay. As far as we are concerned the environment is well worth looking after.”

The shift in community opinion was also clearly demonstrated when recently the small predator-free Ulva Island was re-invaded and populated with ship rats.

“Ulva has been rat-free for 16 years. Stewart Island gets about 40,000 visitors per year – not huge but enough to make the industry viable, but of that number 30,000 go to Ulva Island. It’s the significant tourism drawcard. That has been going really well until this year when we found a rat population on Ulva.

“We have just finished the appeal period on the resource consent and in the next fine weather window we will do another aerial bait drop to get rid of them.. Twelve years ago the community was very uncomfortable about any aerial toxin drop but this time round at our resource consent application to Environment Southland we had almost full community support for the aerial bait drop.— people even travelled to Invercargill to speak in support of this operation. The three people who objected and took us to a consent hearing, didn’t even live on Stewart Island.”

Ulva’s reinvasion is a testament to rat fecundity and their instincts for survival.

“Ulva has had on average over the last 16 years one rat invading per year; one rat which was caught. The genetics showed that the entire population recently found came from one female –the rate of invasion hadn’t increased, we just missed trapping this one pregnant female invader.

“We had done quite a bit of work releasing radio-collared rats on Ulva to try and understand their behaviour and movement as they invade new sites. We found that generally when they arrive they stay for two or three days in the arrival locale and then about 50% will disperse – one rat travelled up to a kilometre in one night and back again before being caught in his arrival area. So a two kilometre movement in one night is not uncommon for these invaders. Ulva Island has a ring of traps at 200m spacing round the coast but somehow this one got through. What was amazing was how long we took to detect them. We think we caught half of her first clutch (in traps) whereupon we scaled up monitoring tunnels and trapping but got no more indication of rat presence for 6 months and then we started to catch them again as the population increased.
“The original eradication was an 18 month long ground baiting operation – this time round the key difference is the availability of food – now after 16 years pest-free there is so much food we can’t guarantee the rats will travel 50m to a bait station. We need to get the bait to the animals so the aerial application was the appropriate technique, and had wholehearted community support.

“We know rats come off boats and there is one spot within swimming range. Looking overall at biosecurity we are learning constantly – Ulva Island has many visitors and many boats but they all access the same wharfs, same points of departure and entry etc, it’s manageable if we have the buyin from the individual users.

“Worldwide there are some 600 eradicated islands and Ulva is only the second to be reinvaded – it’s not such a major issue.”

The debate goes on but as Brent says: “It would be a great outcome if we find that the benefits (of eradication) outweigh the costs; but working through it we may find that this is not the right time. Nor might we achieve the intended outcomes. After all it’s only a debate (so far), a yak over a beer.”