The issue of what biosecurity or quarantine provisions would come into being following a rat and feral cat eradication on Great Barrier have to be carefully considered. What has to be remembered is that this island would become an ‘open sanctuary’ – a place where people come and go all the time. Biosecurity measures must therefore be practical and not unduly inconvenience people or freight movement.

Some examples of how this works in practice elsewhere:

Practical and minimizing inconvenience to visitors is how biosecurity measures work at Tawharanui Regional Park. This 588ha park has 160,000 visitors a year and is bounded by a 2.5 km pest proof fence. Visitors gain access through the fence by way of an electronically operated gate. Tawharanui has a large well-used camping facility (280 person capacity) and people are simply asked when they make their camp booking to ensure their gear is pest free. Over summer months campers are also provided with a mouse trap for their camp site as mice are still present on the park. On arrival in the park (over summer) visitors are given a pamphlet about the pest free status of the park and can attend talks by the rangers. The park holds 1200 sheep and c. 250 cattle and stock trucks move freely in and out of the park. While it has a pest proof fence right across the peninsula, pests can, and do, enter through the beach ends. Much monitoring, baiting, and trapping is done inside and outside the fence to ensure invaders are identified and caught. Although Great Barrier will not have a predator fence the principles of practical biosecurity measures still apply.

A good place to start when looking at what ‘quarantine' GBIs would need is to look at what already exists for keeping us Norway rat, possum, hedgehog, and mustelid free. The Auckland Regional Council, under the Auckland Regional Pest Management Strategy has a mandate for managing Biosecurity risks on the island. All houses coming to the island are inspected for unwanted ‘passengers’ and smaller buildings such a sheds are to be included in the near future. The Hauraki Gulf Controlled Area includes Barrier for restricted access for possums, mustelids (stoats, ferrets, weasels), deer, wallabies and feral goats. Both the carrier and the owner of any of these species stand to cop a hefty fine if they are caught bringing these animals into this restricted area. The ARC reinforced the law about this by prosecuting the boaties who brought pet ferrets to the island some years back.

Biosecurity measures are already underway at Tryphena, Whangaparapara, and Port FitzRoy wharf environs, supported by the Auckland Regional Council, Department of Conservation, and the Auckland City Council. The ARC contracts the WHRBC Trust to carry out monthly monitoring for Norway rats and stoats at Tryphena and Whangaparapara wharves while Department of Conservation maintains stoat traps in the Port FitzRoy wharf environs. As another partner in this Biosecurity programme Auckland City provides bait stations which are deployed and maintained by Twomey and Warrick around the rubbish bins at all three wharves. The objective of this programme is to hopefully identify if a Norway rat or mustelid has arrived – their paw prints may show in the ten monitoring tunnels at each area – and to dispatch any such invader with the baits provided in the area. This programme provides part time work for a local and additional work for the local rubbish contracting business.

Practically speaking, biosecurity has to be realistic and cost effective. Because of the size of the island only the pathways of highest risk can be focused on – currently highest risk areas for invasion are the island’s three main wharves which is where current biosecurity measures are targeted.

If rats and feral cats were removed from the island, this current biosecurity programme area would most likely be extended to other entry points, like the Okupu wharf and the wharf at Orama, as it is the freight and vehicle carrying boats that pose the most likelihood of harbouring an invasive species. There have been some meetings with Sealink to discuss this – currently the company has a private contractor that maintains rat bait on their vessels and the Auckland Regional Council assists with pest control around their yard environs. It would only take the addition of rat and/or mustelid sniffing dogs to check all cargo and vehicles on the Auckland side (including Fullers) to improve detection. Not unlike what happens at Auckland airport with the beagles sniffing bags and cargo. Pest-specific sniffer dogs are already used in New Zealand.

Private boats also pose a risk, albeit a relatively low one, of harbouring an invader. It’s very obvious when you have a rat on board a boat. Of the large number of private boats that visit each year, a relatively small number actually dock, most people come in by small craft to the wharf areas. An unnoticed rat or mustelid in such craft is unlikely and directions for reporting such an incursion would be publicized. Large numbers of private boats land on the beach at Tiritiri Matangi every year, but they have never had a rat jump ship there.

The Auckland Regional Council and Department of Conservation are working together on ideas and options for appropriate signage to the Hauraki Gulf islands emphasizing their unique environments that need to be kept free of unwanted pests. It advertises in local boating magazines and the like, giving the same message.

It is considered that a pest incursion by air poses a pretty low risk, however monitoring and baiting provisions could also be established around the two airports. The cost of extending biosecurity measures for Barrier should not be expensive and DOC, Auckland Regional Council, and Auckland City would be looking at ways they can plan for these costs in the long term.

Rats being rats we must assume that there will be incursions – it’s how we provide for that event that is important. A single rat or two does not mean that the whole island would need to be eradicated again. Even if a breeding population re-established it would certainly be detected, and could be dealt with before it spread over the whole island. The current Open sanctuaries like Tawharanui and Tiri provide well thought out plans for dealing with these events and there is current research being carried out at Auckland University and Landcare Research on the behaviour of rats when they first arrive in an environment free of rats. So far there is early evidence that ship rats, our most likely invader following an eradication, stay close to the place where they land for a number of days. Practically this means that ensuring that monitoring and control measures are established in places where rodents are most likely to come ashore will likely be most effective. Monitoring and control measures do not need to be in extensive grids throughout the island nor does every property owner need to be involved. Identifying and having measures around the areas of highest risk as stated above is likely to be all that is required.

All mainland areas and islands that are pest-free face the risk of re-invasion. Ulva Island, off Stewart Island, has had three rat incursions because they can swim to it from the main island. All incursions have been spotted through monitoring and the rats dealt with.

No rat free island out of swimming range has been re-invaded to date.