Orepuki Beach was littered with toheroa shells late last week – the consequence of an as-yet-unidentified die-back that has struck the endangered shellfish.
Representatives from Environment Southland, Otago University and Te Ao Marama converged on the beach yesterday (Saturday) to collect samples and try to quantify the extent of the deaths.
Hungry birds had eaten most of the molluscs by the time the agencies learned of the die-back, but a small number of intact toheroa were gathered and will be sent to the Cawthron Institute for analysis.
Ironically, Environment Southland and Te Ao Marama are about to adopt a protocol for responding to just such an event involving the toheroa. Unexplained die-backs have historically been few and far between. The last such mass death in Southland was at Oreti Beach in the early 1990s. Saturday’s response was the first time that a scientific approach has been taken to quantifying the die-back as it happens.
Toheroa are significant kai moana to Ngai Tahu and the iwi resource management agency Te Ao Marama Inc has been working with Environment Southland to find sustainable ways of managing the three declining populations – Oreti, Orepuki and Bluecliffs.
Kaumatua Michael Skerrett said that he was concerned at the deaths. “It’s a real blow, and the big concern is that this could be just the start.”
Associate Professor Henrik Moller from Otago University’s Centre for the Study of Agriculture, Food and the Environment, said there were an estimated 58,000 toheroa living on Orepuki Beach. Judging by the number of empty shells strewn along the beach, several hundred had died last week. But it was too early to know whether more toheroa were already dead under the sand and whether this was the beginning of an ongoing impact on the molluscs.
“In scientific terms we call this an ecological catastrophe – a short, sharp event that comes out of the blue,” Professor Moller said. “We will be trying to find out how many have died and what has killed them.” Without wanting to speculate on the cause, he said the likely scenarios included starvation, a biotoxin or an algal bloom.
Speaking as a conservation biologist, the Southland toheroa are really important because there are only two other toheroa strongholds in New Zealand – around Kapiti and in Northland. They are also of great cultural significance to iwi.
Environment Southland Senior Planner Dallas Bradley said that the Council was collaborating with Te Ao Marama and Professor Moller’s team, and the swift response was a result of the draft protocol that had just been developed.
Mr Bradley said that so far, the extent of the die-back on Orepuki Beach was small numerically compared with the last known event, where thousands of toheroa died on Oreti Beach. He expected that Environment Southland would monitor the beach over the next week to see whether more toheroa were exposed.
He hoped that more would be known once the Council received the analysis of the samples collected over the weekend.

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