Why doesn’t everyone want to get rid of rats, rabbits and feral cats on Great Barrier Island? What are the perceived downsides to an eradication campaign?

1. Cost. It is a huge task – where will the money come from? Is it worth that much?

2. More ‘trouble’ for residents (e.g. more biosecurity at wharves, more controls imposed over activities on private land).

3. A strongly held belief that toxins are bad for the environment.

All of these important concerns are being addressed by other island communities throughout the world (see item on Recent Progress on Eradications on Inhabited Islands) and currently on Stewart Island, where a Technical Feasibilty Study was completed by Brent Beavan in 2007 with support from the Stewart Island Rakiura Community Environment Trust (GBICT can provide this as a PDF, see also item from Brent Beavan in this Issue).

In different ways all these questions have come to the fore in 2010. Our State of the Environment Report for Great Barrier demonstrates the ‘worth’ of the island. It outlines the history of environmental changes on the island, emphasising the National significance of the remaining biota and the potential of the natural environment to form the focus of the island’s economy in future. The Report calls for the production of a Technical Feasibility Study to explore methods, issues, costs and benefits of island-wide eradication of rats and feral cats. This call has had a positive response from potential funders. Given stronger support from the Great Barrier Island Community a feasibility study could almost certainly get started next year.

Biosecurity is clearly an issue for some residents, who imagine it will be very difficult to keep rats off the island in future. But, there are plenty of examples throughout the world where residents have opted for biosecurity measures to keep rats out – for example rats have been eliminated from, and subsequently kept out of, the landlocked state of Alberta in Canada since 1950, despite their presence in surrounding states (Google: rat control Alberta Canada for articles). The Pribilof Islands, Alaska (U.S.A., c.700 inhabitants), have implemented a strict rat prevention program, which includes laws barring infested ships from entering the harbor and requiring onshore industries to establish rat prevention measures (Ebbert & Byrd 2002; Fritts 2007). On Great Barrier a possum was recently thought to have jumped off a freight boat in Tryphena – demonstrating both the risks to our environment, and the need for more effective controls. The rapid response by Auckland Biosecurity staff to this event was re-assuring, but the possum should never have got to Great Barrier in the first place. The re-invasion of Motu Kaikoura (since 2008) by rats from ‘mainland’ Great Barrier also provides a salutary lesson: we need to do the research and listen to all points of view before we write the cheque. Good intentions are not enough. From the biosecurity perspective this local example, and the continued efforts needed to keep rats out of Glenfern Sanctuary, are all part of the learning process. But isolated islands, such as Tiritiri Matangi, are more relevant to Great Barrier as a whole. Rats were eliminated from Tiritiri using an aerial brodifacoum drop in 1993. Thousands of visitors go to Tiritiri every year to witness the indigenous biodiversity. However, despite this influx of people, plus many others coming ashore and picnicking at Hobb’s beach from private boats anchored in the bay, there has not yet been a re-invasion by rats. Preventing colonisation by rodents is not impossible.

Mammalian toxins also came to the fore on Great Barrier in 2009 and 2010. The film on 1080 by the Graf brothers made compelling viewing, but was in my view barely relevant to an island with neither possums nor deer, and with no conceivable use of that toxin. However, the boundaries between different toxins were blurred, and many people clearly felt strongly that the risk of ‘contaminating the environment’ with any sort of poison outweighed the advantages that might come from rat elimination. We pointed out the misleading way in which some of the New Zealand research on the effects of toxins on bird populations was presented in the film (see Environmental News Issue 20, Spring 2009), but of course science cannot answer all the questions with certainty.

The debate over mining on Te Ahumata also included toxins in the environment, but centred mainly on the nature of the island’s economy in the future. The vehemence of the island’s rejection of the inappropriate mining proposals was reassuring – mining of Schedule 4 land on Great Barrier was stopped primarily by opposition from residents. The island residents and the ‘off-islanders’ spoke with one voice on this issue. Moreover, with a few individual exceptions, all segments of the Great Barrier Community were united.