Abalone boom 'like lottery win' for NZ fishermen
Abalone are marine snails much sought after for their meat in Asia, and also for their decorative shells.
Fossil records suggest abalone have changed little over millions of years.
But their simple, largely static lifestyle, and preferred habitats of relatively shallow areas along the coastline mean they are easily caught; their only means of defence is to stick tightly to rocks.
New Zealand is home to several unique species of abalone - known by the Maori name paua.
Their nacre (mother of pearl) shells have been a traditional component in Maori art and their flesh has been eaten since New Zealand was first settled.
But the depletion of local stocks in Asia, especially China, means a lucrative export market from New Zealand has developed.
In the 1980s, New Zealand's government recognised stocks were shrinking and introduced fishing quotas for paua.
"Holding the quota, it's a bit like winning the lottery," David Baker who fishes from Picton on New Zealand's South Island, told the BBC World Service programme Discovery.
Now in his 60s, David began fishing paua as a teenager to substitute income from farming. At that time, the shells were more valuable than the meat.
The method of catching paua is very simple, dive down in shallow waters and prise them off the rocks. David's son Jason now does most of the diving, and tight rules mean he has to rely on holding his breath.
"It's illegal to take paua using scuba equipment. Any sort of underwater breathing equipment is illegal," Jason Baker told me.
Fresh paua in their shells cost around NZ$40 wholesale per kilo at the time of writing. In some places, it's possible to catch a kilo's worth of the snails on just one dive.
While the paua fishing industry is one of new Zealand's smaller fisheries, in 2011 it was worth approximately NZ$57m compared to NZ$220m for lobster.
The relative ease of the catching method means the quota holders have a guaranteed income.
The Bakers had their main boat specially built at a cost of around NZ$1m more than 10 years ago. The boat can carry thousands of dollars' worth of paua on a single trip.
However, the way the abalone are brought up is not how they will usually end up in the Chinese market.
The Asian varieties of paua have a white foot and the main New Zealand one Haliotis iris is black. Prior to export much of the abalone catch is bleached, sliced and tinned.
In contrast to the low tech fishing technique, digital technology is now playing a big part in ensuring catches are sustainable.
It's something the Bakers have been keen to embrace.
"We're keen this will continue for future generations. That's why we're involved in this digital stock assessment and programmes to re-seed paua," says Jason.
Each dive for paua is now monitored via satellite.
"Each wetsuit is fitted with a GPS tracker linked to a data logger," he explained.
"These little units that stick on the back of the wetsuit: Underwater they collect depth information and at the surface, GPS information."
Ed Abraham runs Dragonfly Science in Wellington, the country's capital. His organisation is number crunching this data from these digital catch records to produce a paua map.
"For the first time, they can see where the catch is happening reef-by-reef. That's really exciting - that simple visualisation of where the fish are coming from," says Mr Abraham.
"But we're also able to pick into what's the status of the fishery that's being reported for each individual reef."
The abalone live on rocks along the coast line, though often in areas that lack beaches, roads or land access, and are therefore difficult to reach.
From their large boat, the Bakers get into a small inflatable dinghy and head for these areas. The GPS unit on Jason's wetsuit tracks his movements. When he surfaces, David records each paua catch on a digital data logger in the dinghy.
"It's been a big project to get right and to have it working on a diver's back, to make the link to the satellite has taken a bit of doing," David Baker explains.
"The goal is to moderate fishing from month to month, to see where fishing has occurred before, to reduce the stress on the paua, so you don't go back to the same spot again and again," says Ed Abraham.