Perilous puerulus – the epic life of the spiny red rock lobster
Sam Fraser-Baxter heads to the Wairarapa for one of New Zealand’s longest-running marine surveys – counting baby lobster.
On a calm, sunny day, Riversdale beach is a paradise.
While the rest of the Wairarapa beaches are rugged and rocky, Riversdale is a beautiful stretch of sandy coast; a reprieve from the harsh elements that characterise one of New Zealand’s wildest coastlines.
The golden sands have been a drawcard for holidaymakers for decades. Today, though, a tiny, unassuming critter hiding in the shallows is the reason Dean Stotter and Jeff Forman are visiting. The NIWA researchers have travelled to the Wairarapa from Wellington once a month for more than 20 years to survey populations of puerulus – the young, translucent post-larval stage of the spiny red rock lobster.
A prized delicacy, rock lobster is a highly lucrative industry in New Zealand worth more than $200 million in exports annually. Understanding the year-to-year settlement of puerulus on our coasts helps to shape our management of the fishery.
Dean and Jeff’s work in the 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 70s, the project is one of New Zealand’s longest running marine surveys.
At the end of October, Dean and Jeff are relieved to be working under a blue sky on a windless morning.
The survey can only be carried out at low tide when the puerulus collectors sit in about 1m of water. Two hours before or after low tide means working in water too deep to haul them. Each month, the scientists have a three-day window to choose from. The day with the least swell and wind is best.
But of course, this is the Wairarapa.
Through the winter months, surging swells and bitterly cold winds are a day-to-day reality. Even at the peak of summer, sudden shifts in the weather can turn a beautiful day ugly. Despite the wild conditions in the region, Jeff says the pair have a pretty good track record.
“Since Dean and I have been doing the surveys, we’ve only missed one month due to bad weather.”
Today, the normally relentless Wairarapa winds have let up. Jeff and Dean don their wetsuits and wade out to the collectors.
Dean lifts a collector onto a rock to count the puerulus. The collectors are rudimentary and reliable. Developed in the 70s – at the start of the project – the collectors consist of plywood boards attached to a metal weight. 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. They’re looking for an ideal habitat and that’s what we’re providing with these collectors,” explains Jeff.
A long knife is used to scrape out the puerulus into a catch bag for counting. Dean sorts through the weed, crabs and other marine species to count the puerulus. He jots down the count, releases the puerulus into the water and moves on to the next collector.
It’s a no-frills kind of science; no computers, no flashy gear, no complicated experiments. The equipment has hardly changed since the survey started. And for good reason. Using the same collectors maintains scientific consistency, so the researchers can accurately compare year-to-year trends in puerulus settlement.
When each of the nine collectors have been counted, Jeff and Dean wade back to shore, pack up the gear and hop back into the truck without changing out of their wetsuits. The tide has turned and time is ticking. With the windows down, they set off for Castlepoint, the second survey site in the region.
Life cycle of the spiny red rock lobster
The life cycle of spiny red rock lobster is a journey of epic proportions.
After mating, females carry thousands of fertilised eggs under their tails for 100-150 days. In spring, the eggs hatch as tiny larvae that are carried by currents out to sea. For the next one to two years, the larvae are at the mercy of the ocean. Some larvae will drift as far as 1000km offshore.
After developing into puerulus – about the size of a small shrimp and transparent in appearance – they begin to swim back to shore. How the puerulus navigate their way back to shore is a bit of a mystery. Following the sound of waves breaking on the coast is one theory.
At the coast, puerulus settle in cracks and crevices in shallow water where they will moult and develop into juvenile crayfish. The number of individuals that survive the journey and grow into legal sized crayfish will determine the size of the fishery in years to come.
“There can be big differences annually. That’s what we’re trying to detect,” says Jeff.
There is a phenomenal amount of puerulus settling on the south-east coast of the North Island.
The Wairarapa eddy – a huge anti-clockwise rotating current 200km offshore – is believed to be the reason, trapping and holding larvae as they grow into puerulus.
The second survey site is tucked inside Castlepoint; a dramatic stretch of coast formed by sandstone and sculpted by wind and waves. Popular with tourists and fishers, crowds come to visit the iconic lighthouse and cast a line from the steep cliffs.
As they arrive, so do the Wairarapa winds. Sheltered from the southerly breeze under the lighthouse cliff, Dean and Jeff enter the water.
Several fur seals emerge from the shade and join the researchers in the water. Dean and Jeff are unfazed – they smile and like clockwork, make their way through the site; hauling the collectors, scraping out wriggling puerulus and recording numbers.
Since joining the study in the ‘90s, Dean and Jeff 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 the Wairarapa.
When the sampling is finished, Dean and Jeff walk back to the beach, following the cliff line underneath the Castlepoint lighthouse. They peel off their thick dive-wetsuits, pack their gear and climb into the truck as the sun drifts behind the Wairarapa hills. They’ll be back again in a month.
The puerulus settlement research project is funded by Fisheries New Zealand and its predecessors.
This article forms part of our 2019 Summer Series. Read other stories in the series.