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Campbell Island Ra T Eradication Information Sheet

Background
Campbell Island is 11300 ha, situated 700km south of Bluff at 520 35’ south and 1690 10 east in the area known as the furious fifties for their predictable strong winds. It is predominantly covered in tussock with areas of herbfields (megaherbs such as Pleurophyllum, Anisotome and Stilbocarpa, which can grow up to a metre in diameter. Dracophyllum (turpentine scrub or grass tree) is increasing in the sheltered areas following the burning of the island during the farming period. The high winds that are common on the island mean that only low scattered herbs can keep a foot hold on the exposed ridges. Campbell was discovered in 1810 by Captain Hasselburgh of the Perseverance, which ironically is the only ship to have been wrecked around the island when it returned several years later. The Perseverance was the first of many sealing ships to visit the island hunting both the fur seal and Hooker’s (New Zealand) sealion. Both were nearly exterminated but have since built back up in numbers. The island was farmed from 1895 until 1931 with sheep and cattle being released and large areas of the island being burnt to improve the grazing, many of the fence lines put in at that time are still obvious. It was also the site of 2 whaling stations, which hunted the slow moving Southern right whale around the island with the last one also closing in 1916. Campbell Island was made a Nature Reserve in 1954 and a National Nature Reserve in 1986. All New Zealand’s subantarctic islands were made a World Heritage Area in 1998.

Of the introduced animals on the island cattle and sheep have been eradicated. Following a lack of sighting for several years and 2 checks in 1999 using specially trained dogs, it is believed that feral cats have died out, possibly as a result of changes in the vegetation after the removal of stock. This leaves Norway Rats (Rattus norvegicus) as the sole remaining introduced animal (excluding self-introduced birds such as blackbirds, dunnock, redpoles and mallard ducks) and more notably the sole introduced predator. Norway rats are the largest of the three rat species found in New Zealand and the densities recorded on Campbell are among the highest in the world. Norway rats are believed to have made it to the island soon after its discovery in 1810 on one of the many sealing boats that visited the island. They, along with cats have lead to the extinction on the main Island of at least three landbird species – snipe, pipit and a flightless teal, along with many small seabirds – storm petrels, diving petrels and prions which are now restricted to one or more of the small islands offshore. Most of the larger petrels eg grey petrels and sooty shearwaters have also nearly been wiped out on the main island. The rats have also had a significant effect on vegetation and invertebrate fauna of the island wiping out many larger insects.

The eradication of rats on Campbell is the culmination of many years of trials and experiments by dedicated people who believed that eradicating rats from islands was possible. It is only 12 years since the first major success when rats were eradicated from 170ha Breaksea Island in Fiordland. Other recent steps in the learning curve have been 1300ha Whenua Hou (Codfish Island) and 2200ha Kapiti Island. There have now been over 20 successful Island rat eradications.

The eradication will take place in winter as this is when food is the scarcest, rat numbers are at their lowest – giving more bait per rat and the rats aren’t breeding, all of which increases the chances of success.

As some of the techniques to be used on Campbell are quite different to those used on other eradications ie less bait per hectare (6kg c/f the standard 12kg) and only one bait drop compared to the standard two drops, a large scale trial of the techniques to be used was carried out in August 1999. This used bait with a red dye in it instead of toxin dropped over 600ha of the island. This showed that the technique should work if we can get bait spread over ALL of the island. The change from the standard technique is required to make the project logistically feasible. Using 2 drops at the higher bait rate would have meant impracticable amount of bait would need to be transported and stored on this isolated island and at east twice as much helicopter time would be required to drop it. Given the unpredictable and generally unpleasant weather likely at the time of the drop this was more than could reasonably be expected. At the same time as the trial drop, work was carried out to confirm the most suitable bait type and size and to learn more about the rats behaviour eg territory size and food caching sites.

Campbell receives only 650 hrs of bright sunshine a year (compared to Invercargill at about 1620 hrs, Christchurch at 2000 hrs and Auckland at 2100 hrs) and it can expect less than an hours sunshine on 215 days (59%) of the year, frequently the tops of the island are under cloud which would prevent helicopters from dropping bait. The annual rainfall is 1450 mm with rain falling on an average of 325 days a year, fortunately this is mostly drizzle or light showers. 5mm of rain should have little effect on the bait but a major rain event (20mm +) is likely to break down any bait on the surface meaning that large areas may need to be redone. Light snow falls are common in winter and spring but they are usually not heavy ie < 150mm and melt within a few days. While the rats are still active under the snow the bait does absorb the moisture from the snow and breaks down more rapidly. . Wind gusts of over 50 knots (96kph) occur on at least 100 days a year while those of over 35 knots (63kph) occur on about 280 days per year. This is a major issue when any thing over 30 knots (58 kph) means that the helicopters can not accurately drop the bait, this is particularly true for the cliff areas where the wind is particularly strong and turbulent. Unfortunately the largest cliffs are in the western quarter which is also where the predominant wind comes from, reaching hurricane force at times. Annual and daily temperature variations are small with a mean annual temperature of 6 C and rarely rising above 12 C although extreme of 21C has been recorded. While this may make life less comfortable for the team on the island it means that there is less chance of the bait going mouldy than there is in warmer climates. From this it is not hard to see that the biggest obstacle to the success of this operation is the weather, and that it is possible that, even with the best planning and most experienced team in the world overseeing the operation, it could fail, simply because there is not a suitable amount of fine weather during the period that the operation must be carried out. Those factors are beyond the control of mortal men. While less than 150 hours of helicopter flying is needed to drop the bait (ie a total of 7 fine days given that we will be using 3 helicopters to compensate for the short daylight hours on the island at that time of year.). the team has to plan on being on the island for up to 3 ½ months to be reasonably sure of getting the job done. Even then there is no guarantee.

Of the factors we can control the keys points for the success of the whole operation come down to planning. There will not be the opportunity to pop back and pick up anything that is forgotten so all contingencies must be covered. The helicopter pilots are also pivotal because their skill ensures that there are no gaps left in the bait spread, when even a single potentially pregnant female rat could escape to recolonise the island.

The Project Leader for the operation is Pete McClelland (Programme Manager Biodiversity Southern Islands Area) who also lead the rat eradication operations on Whenua Hou (Codfish), Putauhinu and Raratoka (Centre Island). His back up is Andy Roberts who was also heavily involved in the above operations and is carrying out the consents process for the project.


Facts
Budget –
Year one $1,394, 000
Year two - $1, 025,000
Year three - $140,000
Year Four - $140, 000

Total - $2,699,000

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