Mysterious death of swans, eels at Napier’s Ahuriri estuary

The deaths of eels and swans have been reported at the Ahuriri estuary near Hawke's Bay Airport. Photo / Paul Taylor

The mysterious deaths of several animals at Napier’s Ahuriri estuary are being investigated, with initial test results for algal toxins proving inconclusive.

However, experts are not ruling out high water temperatures and PH levels as potential causes.

Involved stakeholders say they are working together to determine what happened to the eels and swans after members of the public raised the issue last weekend.

A post circulating on Facebook showed the dead animals in the water near Hawke’s Bay Airport.

Angie Denby, of the Ahuriri Estuary Protection Society, said one member of the group saw the dead animals and wondered whether the deaths had been caused by humans or by toxicity in the water.

“We don’t know the answer.”

She said the birds were found in an area called The Scrapes, which was enclosed and not fed by a water flow.

Department of Conservation ranger Matthew Brady confirmed that the deaths of several swans and tuna (freshwater eels) were reported to the department last weekend.

Napier City Council was leading the investigation and DoC was helping where it could.

“The Ministry for Primary Industries has also been contacted. Neither swans nor tuna are considered protected in New Zealand,” he said.

Napier City Council executive director of infrastructure Russell Bond said it was working with other organisations to determine the cause of the deaths.

“We were made aware of dead eels in the Westshore Wildlife Reserve on Monday and our environmental staff visited the area to investigate.

“The eels appeared to have been dead for some time.”

Initial testing for algal toxins proved inconclusive, meaning levels were below the detection limit.

“However, recent warmer weather leading to high water temperatures, the presence of algae leading to low oxygen levels, and a high water pH may be factors,” Bond said.

“Our staff will continue to liaise with Hawke’s Bay Regional Council, the Department of Conservation, the Ministry for Primary Industries and Mana Ahuriri.”

Senitra Nathan-March, pou taiao environmental lead for Mana Ahuiri, encouraged people to report any further deaths to MPI, the council or Mana Ahuriri.

“We’d be keen to understand what the effects are out there that are causing our taonga species to pass.”

The Ahuriri estuary has previously recorded cases of mass wildlife deaths, with one case stemming from pollution from the nearby industrial district.

More than 40,000 litres of acid-contaminated water was extracted from the Napier waterway in 2021 after a hydrochloric acid spill, which killed a significant amount of wildlife.

Mitchell Hageman joined Hawke’s Bay Today in January 2023. From his Napier base, he writes regularly on social issues, arts and culture, and the community.