Peter and Francie Diver, owners of Sweet Koura, have been raising koura (freshwater crayfish) near Alexandra since 1990. Fewer than one in 1000 is blue, ranging from a pale icy colour through cobalt to almost purple.
The couple, acknowledged as pioneers in the koura-farming business, are so busy with the day-to-day operations of their venture that they don't have time to develop a market for these striking anomalies.
However, the blue koura escape the fate of their brown cousins destined for top-end restaurants.
They are thrown back into the pond. Peter says he knows where to find them again, although Francie laughingly says it's not that simple.
If they quarrel with the other inmates they tend to leave home in the dead of night, migrating to the next pond.
That can cause headaches when they are needed in a hurry, if for instance Dave Bradshaw, operations manager of Southern Encounter Aquarium and Kiwi House in Christchurch, calls for a replacement for their resident blue koura.
The blue coloration, known to occur in freshwater crayfish and marine lobsters in many parts of the world, seems to come about in two different ways: environmental (a change in diet or habitat can change a brown crayfish to blue and vice versa) or genetic via a recessive gene.
Dave is pretty sure the koura he gets from the Divers are the latter. They arrive blue and stay blue.
It's pretty hard to hide when you're bright blue, but North American studies have found no difference in mortality between blue and regular crayfish.
It has been suggested that evolution has endowed the blues with an extra dose of aggression to compensate for their high visibility. Francie Diver's anecdotal evidence backs the theory. ‘‘We have an enormous blue in the pond near the road, and every time we're in there he goes for us.''
The risk of getting nipped is minor compared to the hardships the Divers have endured. In their first season they had a contract to supply a Christchurch restaurant year round. If there was ice on the ponds they broke it with an axe and at night, when the koura were active, donned all the clothes they owned and a pair of waders for the harvest.
‘‘We took turns, one in the water, the other on the bank with the spotlight,'' Francie remembers.
‘‘If the spotlight wasn't in the right place and you slipped over there would be screaming and yelling and the dogs would start barking. When you started to mumble it was time to get out - hypothermia was setting in.''
You live and learn, says Francie. Koura farming in New Zealand is uncharted territory. From the start they have been guided by trial and error.
As a land management officer with the Otago Regional Council for 29 years, Peter was always on the lookout for alternative uses for Central Otago's rabbit-ravaged land, and tried a few out on his own 2.5ha beef, sheep and mixed-cropping operation.
A nudist colony fell flat and gold mining was less a business venture than an addiction.
When he couldn't interest local farmers in koura production (‘‘no takers, they were merino men'') he decided to try it himself, and in 1990 was granted the relevant resource consents.
Peter and Francie got a permit to catch 2000 koura in local streams - the species found in most of the South Island, Paranephrops zealandicus - and introduced them to specially made ponds.
‘‘You have to give the koura what they want and the stocking rate is important. You can't push them or they eat each other. We're ranching rather than battery farming,'' Peter explains.
So what do koura want? Not what you might expect. ‘‘Deep, dark, manky water'' according to Peter, and a muddy or stony bottom with pond weed and dead vegetation, lots of hiding places and a temperature not exceeding 20degC.
The picturesque trees overhanging the ponds are a working part of the production unit. Apart from pellets specially made in Timaru, the koura eat plant matter and insects.
In the wild, koura prey on juvenile fish and eels, but as the larger fish and eels return the favour they are not welcome at Sweet Koura.
An infestation of perch that got in through open irrigation waterways was a major disaster that set the couple's plans back between three and five years.
Establishing the operation, now comprising 40 ponds with aeration and drainage systems, has been an uphill struggle.
‘‘We've succeeded through bloody-minded persistence. A lot of physical work was involved in set-up but it should be much lighter from now on. I hope we're at the crest of the ridge,'' Peter said.
‘‘We spread the breeding stock last year and harvested maybe 200kg which we've been spoon-feeding to top-end restaurants around the country. We're hoping to double production each year, aiming at 2 tonnes in three years. And that will meet only a fraction of the demand.''
The easiest harvesting method is trapping. Mesh traps baited with bacon or ham usually lure a dozen koura in a couple of days.
But for short orders Peter and Francie sweep the weed off the surface of the pond and wade in with a net. Startled koura flick their tails to shoot themselves backwards; the water disturbance spells their doom. Others can be seen sitting on the pond bottom.
Twelve to 15 koura are needed for a 1kg order worth $80 plus freight costs. They are packed into polystyrene boxes with a freezer pad, a sprinkling of water and a nest of ferns and other vegetation to protect and keep them apart. Air-freighted throughout New Zealand, they can live in a restaurant chiller for three weeks.
The Divers sell almost entirely to restaurants these days. Apart from the Christmas-New Year period when a holding tank is kept stocked with koura, members of the public are likely to be lent a trap and directed to a nearby dam.
There are plenty out there in the wild if you know where to look: Peter estimates there are 20 million koura in a 20-mile radius.
Koura are a feature of healthy waterways and an important food source for Maori.
Peter says most people - Maori and Pakeha - who knock on the door at Sweet Koura have been fishing for them. It's a favourite Central Otago family holiday activity.
Although the commercial harvest of wild koura is prohibited, amateur fishers can take up to 50 a day. And they can get pretty big, as evidenced by a photo on a hunting and fishing forum of a koura caught in an undisclosed Otago stream which spanned a dinner plate.
The Department of Conservation lists koura as a threatened species ‘‘in gradual decline'' in some parts of the country. There is debate in Doc circles about whether fishing should be restricted.
Francie says a decline in Central Otago would be understandable given the area's increasing population. Peter disagrees, saying a single flash flood can do more damage than heavy human predation.
‘‘I don't believe there is a decline in numbers in Central. I've heard reports of ponds with clouds of juveniles".
Increasing rural use of fertilisers and pesticides has been bad news for koura, he says, but they are a resilient species and bounce back readily when farmers modify their practices.
‘‘There are people who grew up in the DDT years who never saw one, but they're coming back to the streams now".
The controlled environment at Sweet Koura has its advantages.
With bore water and a flushing system for controlled temperature, and water quality and hard-earned knowledge about the breeding habits and requirements of Paranephrops zealandicus, these pioneers of New Zealand's aquaculture industry are set, finally, to arrive in the black. Or sometimes in the blue.
- Meg Davidson is a freelance writer.
