Koura in Forestry Ponds

July 2013

Earnslaw One is a forestry company diversifying into freshwater crayfish production

Ernslaw One, the fourth largest forestry company in NZ, has introduced freshwater crayfish, called koura, to its forest fire ponds in Otago and Southland, and built a aquaculture facility at Naseby for breeding stock and juveniles, in order to diversify the income from within their forests. The ponds are essentially unused except for insurance in case of fire. Ernslaw intends to be a large volume producer of koura, which are a high-priced delicacy on the local market and have a huge export potential.

About five years ago Greg Kendall, forestry manager for Ernslaw One in Naseby, suggested diversifying into growing freshwater crayfish (koura), within the Douglas Fir forests of Otago and Southland. The growing of koura in the forestry fire ponds appeared a good prospect as the ponds were largely devoid of fishlife and provided a suitable koura habitat. John Hollows was retained initially as a consultant and then as aquaculture manager. Permits to harvest seed stock from rivers, lakes and ponds were obtained from MPI and about 18 months ago, buildings were relocated to Naseby to form a hatchery. These have been lined with old freezing works panels from Burnside. A heat exchange system has been installed, along with the tanks and reticulation system. This is the first large-scale koura farming venture in NZ, although there are smaller private operations in centres such as Alexandra and Blenheim.

John Hollows, aquaculture manager and former Wanaka butcher, studied freshwater crayfish for his masters degree in zoology from Otago University. He graduated in 2000 and followed with a diploma in environmental science. He has worked for environment consultants, Fish & Game and has consulted to various small koura ventures because of his academic knowledge and practical experience. He was retained by Ernslaw One when it began investigating the large-scale rearing of koura in forest ponds and the need for a hatchery soon became obvious, because permits to capture koura from the wild would not provide enough brood fish to stock the large number of ponds within the Ernslaw forest estate. He now works full time as aquaculture manager which is a job that suits his unique qualifications.

Southern Koura (Paramephrops zealandicus) live in freshwater streams, lakes, ponds and swamps. Their colour can be variable but generally matches the bottom of their habitats. The preferred temperature range for optimum growth is around 15C for this species, although P. plnifrons can tolerate warmer temperatures. They can also survive much colder temperatures, even down to freezing level when the water above has turned to ice. The maximum age is thought to be greater that 30 years although they are hard to age as the retain no annuli. They are harvested at around 40gms after three years of growth and packed into chilled boxes with some wet greenery for live transport to the market. In the wild they feed on zooplankton, algae, decaying vegetation and other material, and are true omnivores, feeding on older, larger fish, and any meat or fish source. Predators include trout, eels and shags. For harvesting, ideally the pond would be drained, but if not they can easily be attracted with baits and netted.

The Ernslaw Hatchery was built on Wet Gully Rd, Naseby, within the Naseby Forest Recreation Area which surrounds the town and is located within the 2000ha forest. New forest ponds have been dug along Wet Gully Rd, which fill with either rain or artesian water and remain full year-round. Ernslaw also buys water from the Mt Ida water race from the local Hawkdun-Idaburn irrigation scheme. Temperatures above 10C are needed for steady growth and regular moulting and the heat exchangers ensures water temperarue is kept above this over the winter. Lower water temperatures during the colder months restricts fish growth. The hatchery is home to the female brood stock, each of which carry between 100 and 400 eggs under the tail. It takes seven months of development before juveniles drop off and start feeding themselves. The hatchery uses enhanced salmon pellets for feeding.

The first release of 3000 juvenile koura (at about 1cm length) occurred last August in representative forest ponds around the Ernslaw forests in Otago and Southland. They were stocked at various densities in ponds with different aquatic environments to monitor growth rates. Some were recaptured in January and they had already trebled in size. They are expected to grow to a harvestable size (40g, around 14cm total length) in two to three years, when they might fetch $80-$90/kg. The hatchery should be able to supply >100,000 juveniles a year to the ponds and after two to five years a sustainable harvest of marketable fish could be taken. However it is going to take many years to build up these indicated numbers. The local market has high demand by restaurants for entre-type fish and exports have not even started yet.