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It’s a rock … rock lobster

Dean Stotter and Jeff Forman wade out to the rocks to survey puerulus. PHOTOS/LANA YOUNG, NIWA

For over 20 years researchers from the National Institute of Water and Atmospheric Research have been travelling from Wellington to Castlepoint and Riversdale once a month to survey populations of puerulus [the young, translucent post-larval stage of the spiny red rock lobster].

The prized delicacy, rock lobster is at the centre of a highly lucrative industry in New Zealand worth more than $200 million in exports annually.

The aim of the research was to understand the year-to-year settlement of puerulus on the coasts which helps to shape the management of the fishery.

Dean Stotter counts the young lobster on a rock.

Dean Stotter and Jeff Forman’s work in Wairarapa is part of a wider study investigating puerulus settlement at seven key sites around New Zealand, including Gisborne, Kaikoura and Stewart Island.

Established in the late 1970s, the project is one of New Zealand’s longest running marine surveys.

NIWA communications and marketing adviser Sam Fraser-Baxter joined researchers Stotter and Forman out at the beaches as they counted once again the baby lobsters.

Each month, the scientists have a three-day window to choose from as the count can only be carried out at low tide when the puerulus collectors sit in about a metre of water.

Despite the wild conditions in the Wairarapa region, Forman said the pair have a pretty good track record.

“Since Stotter and I have been doing the surveys, we’ve only missed one month due to bad weather.”

‘Collectors’ were developed at the start of the project, consisting of plywood boards attached to a metal weight.

A sample of puerulus in Wairarapa.

The boards sit closely together, creating a perfect place for puerulus to safely settle and hide from predators.

“The first thing they want to do is hide,” Forman said.

“They’re looking for an ideal habitat and that’s what we’re providing with these collectors.”

A long knife is used to scrape out the puerulus into a catch bag for counting.

Stotter sorts through the weed, crabs and other marine species to count the puerulus before releasing them back into the water.

“It’s a no-frills kind of science”, with equipment that has hardly changed since the survey started, Fraser-Baxter said.

Jeff Forman at work on one of New Zealand’s longest running marine surveys.

Using the same collectors maintained scientific consistency over decades, so researchers can accurately compare year-to-year trends in puerulus settlement.

They described the life cycle of spiny red rock lobster as a journey of epic proportions.

The number of individuals that survive the journey to puerulus and grow into legal sized crayfish will determine the size of the fishery in years to come.

“There can be big differences annually,” Forman said.

“That’s what we’re trying to detect.”

There is a phenomenal amount of puerulus settling on the southeast coast of the North Island.

Wairarapa has a huge anti-clockwise rotating current 200km offshore which is believed to be the reason, larvae are trapped and held as they grow into puerulus.

Since joining the study in the 1990s, Stotter and Forman have seen fluctuations in puerulus settlement.

A range of factors including ocean storminess and climate can impact the number of puerulus surviving the journey to the coast.

Recently, puerulus settlement has been very good in Wairarapa.

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