Some 500 ponds are now in varying degrees of readiness, making it an enormous opportunity for a collaborative industry.
the Outstanding NZ Food Producer Awards 2017, for its sustainable approach and conservation ideals.
Some 500 ponds are now in varying degrees of readiness. Stocking a pond takes time, which means it will be years before the company can guarantee a steady supply, let alone make a profit. Last year John harvested just 250kg for sale. That’s about half the estimated total national production from the country’s four active farms. It’s well short of the 10 tonne minimum needed to attract an overseas market.
John’s booklet, backed by the Sustainable Farming Fund, is the first attempt to collate what is known about crayfish farming in New Zealand. It’s aimed at everyone: large landowners, farm foresters, small farmers, and lifestyle block owners who want to stock a stream, irrigation canal or garden pond with a native species in need of protection.
He’s written it so people can avoid the years of trial and error experienced by the small group of pioneers who set up their own crayfish farms without guidance.
“We’re starting an industry with a blank sheet,” says John. “There is no blueprint so it’s challenging. There’s a lot of misinformation out there. This (book) is a document a lay-person can understand. In a couple of years I’d like to think we can edit it.”
The information draws on the methods used by farms in Marlborough, Kaikōura and Alexandra. These are all smaller in scale than Keewai, and semi-intensive in the use of supplementary feed and mechanical aeration of water in ponds and water races. But mostly, the guidelines are shaped by John’s own experience, honed from years of research in the laboratory and many hours in a wetsuit observing kōura in their natural habitat.
The Keewai farming system is adapted to New Zealand conditions and is unique in its hands-off approach. Other countries have more intensive systems. In Australia, yabbies and the larger marrons are farmed in dams that are drained once a year. The French écrevisse are harvested from ponds in a similar way. In China and the Southern states of America, crayfish are farmed in rice paddies.
The basics of farming crayfish
The Keewai system relies on modifying existing fire ponds, or digging new ones, to replicate the kōura’s environment. Riparian edges are planted with native grasses and watercress, which provide both foliage and insects for the kōura to feed on. New ponds are filled naturally with spring or rain water and then left for two years. By the time the kōura are introduced, each pond has developed its own ecosystem, filled with everything crayfish like to eat.
Nothing is introduced. The kōura eat everything from plankton to plants, snails, and water boatmen, but they are not at the top of the food chain.
“Eels, trout, water rats, perch, even hedgehogs. Anything you can think of will have a crack at crayfish,” says John. “They’re such a lovely thing to eat.”
To protect them, large branches of twiggy trees like coprosma are dropped into the middle of each pond. These act as natural refuges to save the kōura from harm, particularly when they moult. As a kōura grows, it sheds its outer skeleton, leaving a softer skeleton underneath that needs time to harden. During this time, they are more vulnerable to attack by predators.
The branches also give them a climbing platform from which they can gorge on the plankton that bloom on the surface water in summer.
3 reasons it’s a great idea
• this is an easy form of land-based aquaculture, sustainable, and cheap to run, with returns of $100 per kilogram of crayfish.
• there are no feed costs
• labour is minimal for most of the year
5 disadvantages to farming crayfish
Labour becomes quite intensive during the short harvest season between February and April. At Keewai, forestry workers lend a hand to set baited nets. There’s no way to drain the fire ponds so the harvest is completed with hand-held scoop nets. The catch is sorted and the kōura are either thrown back, transported to new ponds for breeding, or taken to a purging facility before being shipped out live in chilled boxes. The system is low yield because:
• it takes a great many ponds to grow a sizeable population;
• left to their own resources and with no extra feed, only five per cent of eggs make it to their second year;
• in these conditions it takes three years to raise a juvenile South Island kōura to a saleable weight of 70g-100g – the North Island species, which also occurs in the north and west of the South Island, is generally smaller and sold at around 50g;
• more intensive systems raise denser populations with faster growth and better yields, but at a higher cost.
The key ingredient: water
Water is the main consideration. Habitats can be created or modified from new or existing ponds, dams, streams or canals but they need to be clear of sediment. The water source – spring, stream or rain – must be clean. Kōura are extremely sensitive to water quality and will only live in pristine conditions.
“Herbicides and pesticides will kill within hours,” says John. “Keep spraying well away from the water and riparian areas.”
Then there are pests and diseases. New Zealand has a market advantage as it is free from the crayfish plague which has devastated stocks in other countries. There are one or two other lesser diseases to look out for, chiefly the white tail fungus. To limit predation by eels and perch, stream-fed ponds should be fenced or fitted with traps.
Prospective farmers will also need to source seed stock, dig ponds, set up purging facilities, and maybe hatcheries. All these activities require consents and permits from government agencies, territorial authorities or other groups. John warns it pays to do the homework before embarking on a commercial venture.