Depending on the type and suitability of the available land, two common methods of yabby farming have developed.
These methods are:
This type of farming is the easiest as it utilises pre-existing farm dams and watercourses. Although being the easiest, it is the most fickle when it comes to consistent yield, size, weight and cleanliness of product farmed.
"The yabby is susceptible to insecticides and herbicides, crop runoff sometimes carries pesticides into a farm dam, making it uninhabitable to crayfish. Runoff from roads may kill whole populations in dams…In a natural population, with limits to space and food, only a few of the 500 to 1000 young produced by each mature female during a breeding season can survive to 2 or 3 years of age to replace the parents. Therefore, a juvenile has only one chance in a thousand of surviving to old age. Studies of wild populations show that mortality is highest (perhaps 95 to 99 per cent) during the first year of life, but as a yabby ages and grows its chances of survival to old age increase. Mortality during the second year is somewhat lower (perhaps 50 to 80 per cent), and lower still during the third year. Survival could be kept much higher in tanks or ponds where predators could be removed or controlled, sizes graded, shelter provided, diseases treated, sufficient food and additives supplied, and water quality monitored…In farm dams the density of yabbies can be as high as 5 per square metre, and standing stocks of up to 340 kilograms per hectare have been recorded". (NSW Fisheries Publication DF 10, DF.)
This method of farming requires a great deal of habitat development where five areas of environmental conditions need to be addressed (air, food, temperature, water quality and shelter). These dams are also built so they can be emptied periodically and a thorough harvest and cleanout can be done. This procedure is quite costly due to the large volume of water being emptied by the use of petrol pumps. Semi-intensive farming offers a greater yield than extensive farming. However, considering the costs involved (pond construction, predator vigilance, dam maintenance, etc) the increased yield hardly justifies the hectares required.
"In the semi-intensive ponds we produce 1,200 to 1,600 kgs/hectare per year". (Pg. 90 The Yabby Farmers Handbook Crayhaven Aquaculture Industries)
Harvesting yabbies is the same with both methods of farming. Harvesting is a dangerous time for any surviving yabbies, due to fighting within the traps for available bait. Drag-netting, wire traps, opera house and ring nets are the four most common forms of harvesting. All four have advantages and disadvantages, but it is important to note that unless great care is taken when harvesting, many yabbies can die.
A large net strung across a dam and pulled through it from end to end. This technique, while allowing maximum yield from least effort can kill quite a few yabbies.
"In summer when you drag a pond 15% of your yabbies are berried (carrying fertilised eggs). The rough handling in the net causes considerable stress and damage to these females and eggs. Also 15% are fresh moulted and soft shelled – all these become crushed and killed when drag netting. Even healthy yabbies get crushed as the weight of other yabbies builds up in the net". (Pg. 159 The Yabby Farmers Handbook Crayhaven Aquaculture Industries)
These are the main tools used by existing industry. They may hold only a kilogram or so at any time and are quite bulky and difficult to transport reasonable quantities.
Opera houses and ring nets are smaller but need more vigilance and physical work. Harvesting yabbies via manual traps labour-intensive and constant care must always be taken so that the quantity already caught does not kill or maim one another whilst awaiting transport to processing.
Throwing net in"When you haul a trap it disturbs the bottom, stirring up the black, oxygen deficient (anaerobic) mud, so the yabbies in the trap are pulled through this bacterial-laden water. As the trap is pulled out of the water, the yabbies in it stop pumping water through their gill chambers and close the chambers at the bottom to stop the water running out. As a result, their gills are surrounded by bacterial-laden water. If you now keep the yabbies out of water for some time, they become infected internally by the bacteria. Over the next few days the bacteria multiply in the yabbies, no matter how clean their subsequent tank holding conditions (purging tanks) may be, and then the yabbies die." (Fisheries Western Australia)
Processing requires the yabbies be graded via size/weight and purged (cleaned). Grading requires that yabbies be sized because differing markets require different sizes varying between 60 to 120 grams. Markets have also been identified for 40 gram yabbies as well. This process is labour-intensive and great care must be taken to ensure survival of yabbies. Purging cleans the yabby’s intestinal tract and cleans the gills from the mud obtained via the harvesting procedure. This process requires yabbies to be kept in large tanks of clean aerated water for two to three days. The holding, grading and purging facilities required to generate a profit in traditional yabby farming can be quite expensive, not to mention labour-intensive.
"This is one of the most time consuming jobs… once all yabbies are sorted, we then sort each size again". (Pg. 117 The Yabby Farmers Handbook Crayhaven Aquaculture Industries)
"If you intend to start a farm then remember you need lots of land. A viable farm needs at least three hectares of water and preferably ten. You need good quality water holding soils and access to large amounts of good quality water, as well as closeness to markets or freight routes." (Pg. 22 The Yabby Farmers Handbook Crayhaven Aquaculture Industries)
We thought there must be a better way. That is why we developed the EDU system of aquaculture providing extreme density farming.