Date: 02 September 2009
The Department of Conservation is concerned about recent dolphin deaths in the Hauraki Gulf, and has commissioned toxicology tests to try to determine how they died.
Necropsy tests on the dolphins to date indicate that the deaths were not related to the rat poison, brodifacoum, used by DOC in its recent restoration programme on Rangitoto and Motutapu islands.
Massey University holds samples from the dead dolphins and DOC is working with Massey marine biologist Karen Stockin on further testing to try to identify the cause of the dolphin deaths.
Brodifacoum poisoning has already been ruled out by scientists and veterinary surgeons. Brodifacoum is an anticoagulant - signs that could indicate brodifacoum poisoning are bruising, internal bleeding and haemorrhaging. As none of these signs were found in the dolphins, penguins and dogs, brodifacoum poisoning has been ruled out by all the agencies involved – Auckland Regional Public Health Service, MAF Biosecurity NZ, Auckland Regional Council, North Shore City Council, Auckland City Council.
“While we are confident that brodifacoum has been ruled out as a cause of death, we are conscious of the level of public concern surrounding this issue. As a result, we have commissioned further chemical tests on the dolphin, penguin and pilchard samples that will specifically look for brodifacoum poisoning,” said DOC Auckland Area Manager, Brett Butland.
Independent toxicology tests that DOC commissioned on vomit from one of the dogs that died at Narrow Neck beach has already proved negative for brodifacoum.
Tests done by the Cawthron Institute have identified the toxin found in the vomit of a dog that died after visiting Narrow Neck Beach as tetrodotoxin. Tetrodotoxin 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, as found at Narrowneck and Cheltenham beaches where the dog deaths occurred, is unusual and has not been previously described.
Penguin mortalities have been reported in the Far North, Rodney, Auckland, Coromandel and Bay of Plenty regions. Penguin mortalities in winter, particularly following winter storms, are not uncommon for this time of year.
The New Zealand Centre for Conservation Medicine has post-mortemed six penguins to date, and has found that the birds were in poor body condition and that starvation was the likely cause of death. Histology on two of these birds has shown no evidence of acute poisoning.
John Potter, who carried out the post-mortem on the penguins that were sent to the New Zealand Centre for Conservation Medicine, says that none of the birds showed “any sign of a haemorrhagic effusion consistent with rodenticide poisoning.”
“Each of the birds was very thin and their stomachs were empty, consistent with starvation being the cause of death.”