Possum control operation to help maintain water quality

Maintaining a healthy forest in Wellington’s water catchment areas is the main reason for an 11,000 hectare possum control operation by Greater Wellington (GW) north of Upper Hutt this winter.

Most of the land that is being treated is the forested hills around the Western Hutt and Eastern Hutt rivers at the southern end of the Tararua Ranges.

GW Divisional Manager Water Supply, Parks & Forests Murray Kennedy says the operation is needed to maintain the region’s high quality public water supply and help protect public health.

“We collect over 40% of Wellington’s drinking water from the Hutt Water Collection Area and rely on this forest for clean water. The roots of the trees bind the soil and help to keep sediment out of the water, making it much easier and less expensive to treat. Possum browse damages our forests and makes them less effective at filtering our water.”

Mr Kennedy says possum faeces can spread water-borne organisms like giardia and cryptosporidium throughout water catchment areas.

“For this reason, the Ministry of Health recommends that feral animals, such as possums, should not be in water catchment areas.”
Two smaller parcels of land are being treated at the same time – part of the adjacent Kaitoke Regional Park and the Akatarawa Saddle area. All three areas are Greater Wellington land and have recorded possum numbers that threaten the health of the forests. The operation will use 1080 cereal possum baits distributed by helicopter and is timed for the first suitable weather window from mid-May 2009.

Mr Kennedy says native birds will benefit from this operation, as they did from a similar operation in the area in 2003.
“Birds breed more successfully and bird numbers increase following a 1080 operation. The bird numbers in the Hutt Water Collection Area have been monitored since 2002. There was an increase in bird numbers following the 1080 operation in 2003, but bird numbers are now falling, as possums numbers have built up again.
“Our native birds rely on this forest for food. Possums eat the eggs and chicks of native birds and compete with the birds for food."
Mr Kennedy says that Greater Wellington is taking a precautionary approach with 1080 where drinking water is concerned.

“We know that 1080 breaks down in the environment after rainfall.”

No water will be taken from the area for public supply until the Medical Officer of Health determines the water catchment can be used again. During that period the Te Marua Storage Lakes, the Wainuiomata and Orongorongo Catchments and the Lower Hutt Aquifer will supply drinking water for the region’s four cities.

Public warning signs to alert people of any potential risks will be placed at all main access points to the operational areas. Operational maps and information sheets will be provided to all neighbouring property owners. Letters will be written to recreation groups that use the area, police, health centres, veterinary clinics and district and city councils. The operation will be advertised in local papers and there will be updates issued to the media and posted on the GW website.

NOTE - This press release was amended on 20/3/09.

Background

Best financial option for ratepayers

• This operation covers 11,000 hectares (an area larger than Wellington Harbour - 15,700 rugby fields) of hilly and mountainous terrain with peaks up to 1300m and large areas of tight scrub. There is no vehicle access. It is not practical or affordable to do a ground control operation.
• It is costing Wellington regional ratepayers $210,000 to treat the area with 1080 poison applied by helicopters. It will take one day to complete the operation.
• Doing ground control would require 11,000 bait stations, and take 15 staff 46 weeks to complete. This would cost regional ratepayers $1.6 million. Trapping would be more expensive again.
• This operation area is too big, too hilly, too remote and much of the bush too dense for a ground control operation to be effective.
• Safety
• 1080 is a poison and is toxic to humans and pets, particularly dogs. However, it has been used in New Zealand since the 1950s and there isn’t a single recorded case of a person dying from 1080 poisoning. It is the most widely studied pest control poison that is used in New Zealand.
• 1080 was reviewed by the Environmental Risk Management Authority in 2007 and confirmed as safe to use, as long as safety precautions are followed. This operation will follow the safety precautions set out in the ERMA guidelines.
• There is a risk that a possum killed by 1080 could be washed down the Hutt River in a flood and end up on a river bank outside the operational area. A dog could then scavenge this carcass and die from secondary poisoning. GW staff will be checking the banks of the Hutt River after floods for possum carcasses following the operation and will warn dog owners to keep their dogs on a lead alongside the river. The number of possums in the catchment this time is much lower than at the time of the previous Hutt 1080 operation, so the likelihood of carcasses washing down will be lower.
• 1080 was last used to cull possum numbers in the Hutt Water Collection Area in July 2003; that operation was very successful. A post-operation trapping survey found less than one possum caught per night per 100 traps laid; a residual trap catch rate of 0.5%. The pre-operation survey had yielded a trap catch rate of 23%.