Toheroa die on Orepuki Beach

Scientists are calling the discovery of hundreds of dead toheroa at Orepuki Beach an ecological catastrophe.

Hundreds of the endangered shellfish were spotted by a resident last week and staff from Environment Southland, Otago University and Te Ao Marama collected samples at the beach on Saturday.

Environment Southland coastal scientist Greg Larkin said samples had been sent to the Cawthron Institute in Nelson for analysis, which might take weeks.

Shellfish deaths had happened before but it was without any identifiable pattern, he said.

"There were also reports of similar deaths back in the North Island last week."

Kaumatua Michael Skerrett said the news was a blow but the biggest concern was this could be only the beginning.

Otago University centre for the study of agriculture associate Professor Henrik Moller said estimates put the Orepuki Beach toheroa population at 58,000 and, judging by the empty shells found at the site, several hundred died last week.

It was too early to know whether more were dead under the sand and whether this was the beginning of a continuing problem, he said.

"In scientific terms we call this an ecological catastrophe; a short, sharp event that comes out of the blue."

They would try to work out how many had died and why they died, he said.

Among the possible scenarios could be starvation, a biotoxin or an algal bloom, he said.

Council senior planner Dallas Bradley said staff were collaborating with Te Ao Marama and Professor Moller's team, and the swift response was a result of a newly drafted protocol to manage this kind of event.

A few dead toheroa were also spotted at Oreti Beach but nothing like at Orepuki, he said.

"But there were a few surf crabs washed up at the north end of the Oreti, which does have us thinking a bit."

Toheroa at Bluecliffs were unaffected, he said.

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