Since 1989 Peter Diver has been experimenting with growing the South Island fresh water crayfish (koura). By trial and error he and wife Francie have developed systems for propagating and growing koura to a size suitable for the restaurant trade. In the process they have had to overcome numerous obstacles including bureaucracy and predators, and develop production techniques for a species that little is known about.

This year they will sell around 250kg but are poised to take that up to 2 tonnes over the next few years. They estimate the local market demand to be ten times that figure.

Hunting koura in Central Otago creeks, rivers and dams has long been a local sport. Everyone goes out a couple of times a year to get a bucketful for the barbecue. Back in the 80s, Peter Diver was working for the Otago Regional Council looking at diversification of land use, and one of the ideas was freshwater crayfish farming.

“I couldn't get any of the farmers to take up the option, and as I had my own 10 acre block and good irrigation water I decided to have a go myself. In 1990 we put a few ponds in and it looked promising, so we went through the licensing procedure with DOC, Fish & Game, Ngaitahu and MAF,” says Peter.

“In those days aquaculture was not an allowable use of rural land so we had to go for specified departure from the district scheme, and it was a fair bureaucratic hurdle. The first one to try the system always gets put through the wringer, but being a bureaucrat myself I could handle it alright, and in 1992 we got the second crayfish farming license issued in New Zealand.”

The variety of koura they farm is Paranephrops zealandicus, which occurs in the southeast of the South Island and in Stewart Island, and is larger than the North Island variety. Around January or February when the first frosts hit Central Otago, the females shed their skin, and breed. They attach 50 to 200 eggs to their tails, they carry them there through the winter until about November when the water starts to heat up. The eggs then hatch and the young stay with the mother under their tails for about three weeks, and go off out into the big wide world.

They take about two years to get to marketable size, and they start breeding about year three. Peter has been harvesting at year two because the restaurants want tails about the size of a cigarette lighter for the entrée trade.

Water temperature is all important to the life cycle. They grow best between 15 and 18° C, are sluggish below 10° C. When ice forms on the ponds in winter, the water underneath it is highly oxygenated and the koura are adapted to it. They go into suspended animation, and start moving again when the ice thaws. At the other end of the scale, temperatures over 20° C make them most unhappy.

Peter says they are very sensitive to rapid temperature change and he has to be careful when moving them from one pond to another that there is not a temperature difference of more than a couple of degrees.

Over the years he has put in many ponds and now has 40, each of 200 sq.m and each with an aeration system and water supply from a high quality aquifer that is consistently at 10° C. Temperature sensors in each pond are monitored by a computer, and are adjusted up or down when necessary by pumping in more 10° C water – air temperatures can reach 38° C in summer and -15° C in winter.

Until now Peter has been focused on breeding up numbers, constructing and stocking three or four ponds a year, but now the farm is poised to increase sales of koura to restaurants substantially.

“When we were starting up we didn't have anybody to call upon for advice so we had to try out everything ourselves. Only now after 15 years have we got what we think it is the final recipe – the design of the ponds, the depth, the cover they require, managing the algae and water quality and oxygen issues,” he says.

“I have spent the last two years upgrading all ponds to a good standard so the whole operation is now ready to start production in earnest. I can also focus more on fine-tuning of management, and perhaps extend the growing season by using solar energy or ponds covers to delay the temperature fall in autumn.”

Pond design
The first ponds Peter put in were round, but he later found that the circulation of water in them from pipe coming in at one point was very poor. To overcome that he put an “island” in the middle, which resulted in better mixing and oxygenation of the water. It also had the advantage of creating more bank area – koura are mud/bank feeders and the production from pond is proportional to the amount of bank they have.

Young koura eat mainly insects, but the adults eat mainly organic matter, and a muddy bottom and bank of the ponds provides both. Mud is important, and where pond liners had to be used Peter has covered them with a layer of clay.

The natural biological life in a pond is good enough to support a population of three or four koura per square metre. Populations of commercial density require another food source, and Peter has developed a simple fish pellet mix similar to the salmon farm pellets but modified to cater for the higher calcium and lower protein requirements of the crayfish.

The other important factor is shelter and hiding places, according to Peter.

“It took us a long time to learn that the more cover you give koura, the more you of them get. We use rock rubble to line the banks of all pond margins,” he says.

“We harvest them using set pots. They are sold live, delivered by overnight courier to restaurants all around New Zealand in a chilly bin pack with a freezer bag in it and vegetation to keep them apart.”

“They can live quite happily in a fridge for about three weeks. For them it’s like what normally happens in the winter when the frosts come and the creeks dry out, they pull themselves into a damp position under a rock out of the water.”

Predators and companions
Trout, perch and eels will eat koura. Fortunately there are no eels in the area, but perch are a huge problem. Peter says he drained one pond last autumn and got only 30kg of koura but 150kg of adult perch and 4000 fingerlings.

“We should be getting 40 kg of crayfish a year from a pond, but with perch you would be lucky to get 10kg. So we have had to put in place measures to prevent perch entering the system. All water is micro-filtered because the young are very small and will get through just about anything – they are extremely resistant and durable little bastards,” he says.

“We have a real menagerie of bird life around the place, but fortunately we also have a huge population of frogs and the ponds sometimes turn back with tadpoles, so the birds gorge themselves on them and leave the crayfish alone.”

“Universities think it's wonderful and are researching the frogs because the problems affecting frogs in the rest of the country don't seem to be affecting ours.”

Peter is at pains to point out that even with the expected increases in production in coming seasons they will not be able to keep up with the demand.

“There are 18 other licensees breeding koura but there's only one other that is really serious about it, the others are just running trials at present. The market looks like it is about 20 tonnes per year and when we are fully up and running here we will supply 2 tonnes,” he says.

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