Do the yabbies get any natural food in dams?
The first winter rains each year provide future food for yabbies in the next growing season. The runoff carries crop stubble, pasture debris and sheep droppings into a dam. This organic matter from outside the dam (“allochthonous” material) can often be seen for a time floating in the corners of a dam. Eventually it sinks and is gradually decomposed by bacteria to form “detritus”, a protein-rich feed for crayfish. Organic matter is also produced in a dam (“autochthonous” material), from sunlight and nutrients by plant growth, usually as surface “blooms” of minute single cells of suspended green algae. Various small animals, many microscopic, feed on the algae and detritus, providing natural food chains for yabbies. On these natural feeds, the richer farm dams can maintain a total “biomass” (living weight) of crayfish of up to 1500 kilograms per hectare of surface area of water. However, most dams average only 300-400 kilograms per hectare, without additional hand feeding.
