Public concern over wildlife deaths in Hauraki Gulf

You may be concerned about recent reports of dog and marine wildlife deaths in the Hauraki Gulf. DOC is also concerned and has been working as part of an inter-agency group led by the Auckland Regional Council (ARC) to investigate the deaths.

The agencies involved are confident that the dog and marine wildlife deaths and the use of brodifacoum are not related. Those agencies are Auckland Regional Public Health, MAF Biosecurity, ARC, North Shore and Auckland City Councils.

Testing by independent scientists, veterinary surgeons and pathologists quickly ruled out brodifacoum poisoning. Brodifacoum is an anticoagulant - signs that could indicate brodifacoum poisoning are bruising, internal bleeding and haemorrhaging. None of these signs were found in the dolphins, penguins and dogs.

Because of the ongoing level of public concern, DOC commissioned further tests on dolphin, penguin and pilchard samples that specifically looked for brodifacoum poisoning. These results confirmed that brodifacoum was not the cause of any wildlife deaths. The results of all tests to date are summarised below.

Summary of investigation results

Dogs

• Tests done by the Cawthron Institute identified the toxin found in the vomit of a dog that died after visiting Narrow Neck Beach as tetrodotoxin. This toxin was identified as the cause of death.
• Tetrodotoxin (TTX) is a naturally occuring substance found in tropical puffer fish, and has also been found in sea slugs taken from the beach. Its presence in sea slugs found at Narrow Neck and Cheltenham beaches where the dog deaths occured has not been previously described.
• Independent toxicology tests that DOC commissioned on vomit from one of the dogs that died at Narrow Neck beach were negative for brodifacoum.

Dolphins

• Post-mortems confirmed the dolphin deaths were not related to brodifacoum.
• Independent laboratory tests on dolphins have come back negative for brodifacoum, tetrodotoxin and domoic acid – an algal toxin known to be a common cause of dolphin deaths.
• Massey University marine biologist Dr Karen Stockin says that the number of carcasses has returned to what we would normally expect at this time of year, suggesting that whatever caused this issue in the dolphins is no longer a threat.
• Massey University has conducted post-mortems of dolphins as part of a long-term research programme since 2002. Monitoring of common dolphin mortality will continue as part of the research programme.
• We have now exhausted all lines of enquiry. Post-mortems on the dolphins have given us no further clues as to what else we could test for, so unfortunately we may never know how these dolphins died.

Penguins

• Penguin mortalities have been reported in the Far North, Rodney, Auckland, Coromandel and Bay of Plenty regions. Penguin mortalities in winter, particularly following storms, are not uncommon.
• The New Zealand Centre for Conservation Medicine (NZCCM) initially carried out post-mortems on six penguins. They found that the birds were in poor body condition and that starvation was the likely cause of death. Histology on two of these birds showed no evidence of acute poisoning.
• John Potter, who carried out the penguin post-mortems, says that “none of the birds showed any signs of haemorrhagic effusion consistent with rodenticide poisoning. Each of the birds was very thin and their stomachs were empty, consistent with starvation as being the cause of death.”
• DOC also commissioned Landcare to carry out toxicology tests on nine penguins from Long Bay. Low level traces (ranging from 0.005 parts per million to 0.17 parts per million) of brodifacoum were found in the livers of three of the penguins, but this has been ruled out as the cause of death.
• Further test results from NZCCM indicate that starvation is the likely cause of death of penguins from the region.

Fish and shellfish

• Tests on pilchards samples and further pilchards taken from dead dolphins’ stomachs, mussels and pipis have come back negative for brodifacoum.

Despite the results of investigations being widely publicised, a number of reports in the media have attempted to link the deaths with the aerial application of rodent bait on Rangitoto and Motutapu. This has included some inaccurate reporting, and we would to clarify the following points:

• The pest control agent used in the Rangitoto/Motutapu restoration project was brodifacoum in cereal baits, not 1080 (sodium monofluoroacetate). Brodifacoum and 1080 are entirely different chemicals. Brodifacoum is a commonly used rat poison and is easily available at the local supermarket.
• It was expected that a small amount of bait would enter the marine environment. This was necessary to ensure complete coverage of the coastal area critical to the success of the operation. Approval for this was granted as part of the Resource Consent.
• DOC went to considerable effort, using aerial GPS technology, to ensure the bait containing brodifacoum was accurately targeted.  In total, DOC dropped 147 tonnes of cereal-based bait over Rangitoto and Motutapu. The toxin content of that 147 tonnes was only 2.9kg.
• The amount of toxin assimilated into the marine environment is many orders of magnitude lower than the lethal limits known to be toxic to fish.  No traces of brodifacoum have ever been detected in shellfish or fish following past aerial application of baits for rodent control on offshore islands. 

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