Pest Projects on Great Barrier Island  - three steps forward and two back
Environmental News Issue 24 Summer 2011

Pest management projects at Glenfern Sanctuary, Motu Kaikoura, Windy Hill Rosalie Bay, Katherine Bay, Mohunga Peninsula, the Flat Islands, and Okiwi School are all working to keep rats at zero or low levels so that native species have a better opportunity to survive. Each project uses different methods and all have the goal of finding the most efficient, cost effective, and socially acceptable way of eliminating or minimising the impact of rats on native flora and fauna.

Glenfern Sanctuary continues to battle with kiore reinvading and colonising within the 230 hectare pest-proof fenced area. Interesting dynamics between ship rats and kiore are being observed with kiore responding more quickly to the opportunity to reinvade and re-establish in this habitat. Rabbits have also managed to reinvade but have been contained by gassing their burrows. A new pest- proof fence has been added inside the Sanctuary in an effort to prevent rats coming across from Fitzroy. Rat numbers within the Sanctuary are still low compared to unmanaged areas however, so despite reinvasion biodiversity gains are still being made.

Bird counts taken in October have shown a dramatic increase in many of the native species over the last counts done in 2006. Additionally four new black petrel burrows all with chicks in the nests have been located.

The Motu Kaikoura Trust has not been able to sustain its eradication of two years ago. The Island is suffering from significant rat reinvasion and long- term management will be needed to maintain the benefits of reduced pests. Over 600 trap and bait stations are deployed on the island and on the ‘mainland’ property closest to the island. Rat tracking tunnels stood at 17% density in November.

DNA sampling of rats has not clearly indicated whether some of the rats present are survivors of the eradication process or if all are re-invaders. However, one ship rat sampled was clearly identified as having come from the Flat Islands so those pesky ship rats are still travelling by boat!

Since the Flat Island (Rangiahua) rat eradication two years ago there have been two reinvasions that have been quickly detected by trap catches or residents seeing evidence of rats. These have been responded to and the invaders dealt with by the Biosecurity team at Auckland Council (formerly the ARC), the residents, and local business EnviroKiwi. There are 100 stations with traps, bait, and tracking tunnels spread between the four islands and these are checked regularly to detect any further reinvasion.

These three projects illustrate the difficulty in achieving their goals of eradication when rats are within swimming distance and boats are travelling short distances between areas with and without rats.

Okiwi School tamariki are kaitiaki for its grounds, adjoining bush and wetlands with the goal of managing pests at low levels. This is important work as the area supports a number of native species including the kakariki and pateke. Tamariki operate tracking tunnels and collect data to calculate rat density, and evidence of indicator species such as weta and lizards. The tamariki gain a greater understanding of the impact of rats and the resulting benefits of controlling their numbers.

Mohunga Peninsula Restoration Trust maintains a virtual fence consisting of a buffer zone of bait stations across the base of the peninsular. These stations also control rat densities in areas of native bush, which are of course important food sources for a wide range of fauna. The Abercrombie shore line is also controlled recognising the considerable rodent activity over tidal areas. Residents are steadily extending the areas of predator control so that now a major percentage of the peninsular is covered. This year we are looking forward to the results of lizard and seabird surveys.

The Katherine Bay Restoration Trust has been established in the Bay area with local Peter Hoey coordinating the establishment and management of 40 trap and bait stations along trapping routes. Pre-management tracking tunnels stood at 100% in Dec. 2009. Cages are used to trap feral cats and a local hunter keeps pig numbers down.

The 620 hectare Sanctuary in the Windy Hill Rosalie Bay Catchment now has 4800 trap and bait stations and seven either part or full-time employees. Both plant and animal pests are targeted with a recent focus on reducing rabbit numbers. Using a professional contractor 32 rabbits were shot and 8 burrows gassed in February. The rat tracking tunnel results for January from the four project areas within the sanctuary varied from 0 to 20%. Following the significant discovery of an adult Duvaucels gecko in a rat trap in January a comprehensive monitoring programme is now underway with the hopes of finding a live speciman of this highly secretive gecko. Monitoring is also underway for short and long tailed bats using specialized equipment on loan from DoC. The North Island robins in the catchment had a moderately successful breeding season with 13 young fledged with four of these remaining in the Sanctuary area.