Bacteria likely cause of pipi devastation

A bacterial infection could be behind the mass pipi deaths at Ngunguru Estuary.

A bacterial infection appears to be responsible for mass pipi deaths at Ngunguru Estuary nearly three months ago.

Signs warning the public not to eat from the shellfish beds will remain in place while authorities find out more. The Ministry for Primary Industries (MPI), charged with testing dead shellfish collected on May 22, said the deaths reported by the public were associated with a "Rickettsia-like" bacteria that was present in all specimens tested.

Northland Regional Council's environmental management committee was told this week that, while the bacteria had been found in New Zealand shellfish before, this was the first time they had been associated with a die off.

Signs warning people not to take shellfish from Ngunguru Estuary have been in place for more than three months.

The infection likely occurred due to the pipi being put under stress, though the cause of this stress was unknown, the committee heard. While the bacteria were "host specific" and did not appear to harm humans, people could get sick from eating shellfish that were dying and putrefying. MPI staff were still trying to establish the significance of the detection, the report to the committee stated. The exact number of shellfish that died is not clear, but witnesses at the time said it appeared a large number had died over the course of a day and that Ngunguru Estuary smelled strongly of rotting seafood.

Committee member Ann Court said the public may need a reminder about the ban on gathering, as signs had been in place for so long and people were likely to "take the law into their own hands".

"Until we know more, even though you might be tempted, please don't [gather]."

A second decline at Ruakaka's Mair and Marsden Banks is similarly mysterious, with MPI informing NRC via letter that "the cause of the mortality event may never be confirmed".

In March, the Northern Advocate reported that the number of pipi on the sandbank jutting into the Whangarei Harbour entry off Marsden Pt had fallen from an estimated 10,000 tonnes to less than 100 tonnes since 2005. This was following a ban on collecting at the spot, known as Mair Bank, in late 2014.

That ban came three years after local hapu Patuharakeke imposed a similar rahui at the smaller Marsden Bank, which is adjacent to the shore and accessible by foot or vehicle. The ban was based on concerns the Marsden Bank was being over-harvested before juvenile shellfish could grow. MPI deputy director general Scott Gallacher told the NRC such declines were relatively common among shellfish populations.

"The recovery of such shellfish beds can take many years and there are limited options to stimulate a rebuild."