OPINION PIECE - High poison residues in New Zealand wildlife

Kathy White

The Department of Conservation is proposing a brodifacoum poison drop on Rakitu Island, near Great Barrier Island. Here are some of the reasons they shouldn't do it:

The entire western weka population was exterminated in a brodifacoum drop on Tawhitinui Island (1984); Nearly 60% of the Tawharanui Regional Park dotterel population died through eating brodifacoum baits and poisoned sand-hoppers (2004); Brodifacoum residues continued to be found in wildlife more than 24 months after the brodifacoum poison drop in and around the Rotoiti Nature Recovery Project in Nelson (2005); Dolphins, penguins, fish, numerous dogs and birds mysteriously died after the Rangitoto and Motutapu brodifacoum drops. Vast numbers of dead horseshoe mussels washed up on Waiheke Island up to five months after the poison drop. Hundreds of dead birds also washed up on Coromandel Peninsula beaches in the months following (2009); More than 10,000 seagulls were killed in Shakespear Regional Park (2011).

Blue cod, mussels, limpets and birds had brodifacoum residues in them after the Ulva Island drop, prompting restrictions on harvesting. Dead robin nestlings on the island were found to have brodifacoum residues, indicating that poisoned invertebrates had been fed to the young birds. Nearly 90% of the weka population was also killed (2011); Brodifacoum and other anticoagulant residues were found in freshwater fish, eels and sediment in Southland (2012); After Great Mercury Island was poisoned, 16 dead seals and a multitude of birds and fish washed up dead on Coromandel beaches (2014);

A Landcare Research study of road-killed harrier hawks revealed 78% of those tested had at least one anticoagulant rodenticide in them. Some had as many as four different types. Brodifacoum was common.

It’s dangerous stuff, no doubt.

I asked Auckland Council for the results of their monitoring of feral pigs on islands in the Hauraki Gulf as part of our investigation in the Environmental Performance Committee at Waikato Regional Council. The Auckland Council reply stated that 13 out of 14 pigs tested positive for brodifacoum residues. Most of the pigs were on Great Barrier Island.

Brodifacoum has now been confirmed in fish, shellfish, pigs, bats, deer, eels and birds across New Zealand, which is a concern for those who hunt and fish. There’s also concern for those who commercially harvest wildlife. MPI notified a restricted procurement area for feral pigs in Marlborough due to high levels of brodifacoum residues in pig livers in 2004.

Why would we use brodifacoum when our own scientists have expressed concern about residues persisting in the environment?

Penny Fisher said in 2013 in her Overview/Summary – Environmental Residues of Anticoagulants Used for Pest Control, 10 June 2013.
“There is increasing evidence that uses of anticoagulants for both household rodent control and field pest management are resulting in widespread contamination of both terrestrial and aquatic wildlife. The latter is presumably through carcasses of poisoned animals entering waterways ….”

According to MPI, brodifacoum is the most inhumane toxin we’ve got, causing pain and suffering for days to weeks before an animal succumbs to internal haemorrhaging. Apart from the lethal effects, brodifacoum also causes sub-lethal reproductive and developmental damage. Would you choose to use brodifacoum if you knew it was also going to harm and kill the native species you’re trying to protect?

Personally, I hope DoC chooses to use methods of pest control on Rakitu Island that are less harmful to the wider environment long-term. And I'd like the government to stop making money out of manufacturing these poison baits through their company Orillion. It's a huge environmental and financial conflict of interest that finally needs addressing.

Kathy White is the Waikato Regional Councillor for Taupo-Rotorua and the current Chair of the Environmental and Services Performance Committee. This is her personal view.
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