Disease hits millions of shellfish

Millions of pipi died on the Horowhenua coast in March 2017. Photo / Ashleigh Collis

Horowhenua has been struck with a possible pathogen that contributed to the death of millions of pipi and tuatua earlier this year.

In March the Horowhenua coast had huge numbers of dead and dying shellfish that the public were warned not to eat. Dying shellfish in Waihi that same month made national headlines.

The Ministry for Primary Industries (MPI) tested live samples of the shellfish from Horowhenua.

Results released to Horowhenua Chronicle show the shellfish were heavily affected by Rickettsia-like organisms (RLOs), however, MPI is unable to confirm where the organism originated or how to prevent further infection.

MPI found RLOs in cockles, tuatua, pipi, green-lipped mussels, toheroa and scallops across New Zealand, in Northland, Auckland, Bay of Plenty, Horowhenua, Marlborough and the West Coast.

RLOs are not new but could be considered emerging pathogens as they were relatively unknown until recent years, according to scientific study.

So far this year, there have been five reported events of mass shell fish mortalities in New Zealand, four confirmed to be linked with RLOs.

MPI spokesperson Lesley Patston said given the importance of shellfish in New Zealand, RLOs have become a research priority.

More shellfish deaths were reported at Hokio Beach in May, with 10 tuatua taken for sampling. RLOs were present on seven of the 10.

Ms Patston said MPI has also taken samples from healthy beaches for comparison but tests had not been conclusive.

A strategic sampling scheme would be triggered whenever shellfish mortalities were found, aiming to better understand how RLOs, environment and other potential factors contribute to shellfish mortality.

Ms Patston said MPI was unsure if pollution from the Manawatu River had any bearing on the shellfish deaths on the Horowhenua coast but that environmental factors can stress shell fish.

"Stress can leave them predisposed to infection by opportunistic pathogens [such as RLOs]," she said.

Hokio Beach resident and a kaumatua for Muaupoko iwi Peter Huria said that it was a devastating tragedy to see the fisheries in this state.

"I'm worried about how the population will bounce back after such a loss," he said.

He believed the local deaths were closely linked with pollution of the Manawatu River and Hokio Stream.