Help protect koura

A freshwater koura or crayfish.

The two species of koura are found in streams, ponds, lakes and swamps but prefer slow or non flowing waterways.

They have a dark green mottled exterior, ideal camouflage as they burrow into muddy substrate, shelter between the rocks and stones or hide under logs, leaves or tree roots.

One species is found in the North Island and Marlborough, Nelson and West Coast while the other is found on the East and South of the South Island and Stewart Island, - the Alps have separated the species.

The South Island species is slightly larger (80mm vs 70mm) and has very hairy pincers.

Koura are crustaceans with four pairs of legs and a fifth pair modified as pincers.

They use these pincers for feeding, fighting and intimidation.

The four pairs of legs are for walking, and koura do not swim well.

The only type of swimming is due to a sudden forward tail flick which rapidly propels them backwards in an emergency.

Koura have gills located where the legs meet their thorax and water is pumped over these gills and out their mouth after the oxygen has been removed.

They can backflush this system if needed. Koura can be sexed from underneath.

Males have a pair of gonads protruding from the fourth leg pair while females have holes at the base of the second leg pair.

Koura are omnivorous scavengers eating any floating debris - they do not actively hunt.

Their diet consists of insects (snails, mayflies) and leaves.

They are miniature water purifiers. Their pincers grab the food and shred it into smaller pieces which are then passed to the mouth for more grinding. Only small particles are swallowed after being filtered.

Reproduction occurs between April and December but mostly May-June.

The female carries 20-200 fertilised eggs on her abdomen, stuck on with mucus.

After three to four months the eggs hatch and the mini-koura cling to the female until they are 4-10mm long, usually around December.

They will have undergone two moults by this stage and will have up to nine moults in their first year, gradually decreasing to one in their fourth year.

Koura are very slow growing, by year 4 they are only 20mm but considered an adult.

Moulting means the young koura are very vulnerable - until their new shell hardens.

They need high levels of calcium for this process, some coming from gastroliths in their stomach and some from the old shell which is eaten.

Threat to koura include anything reducing water quality, predation and harvesting.

Predators include eels, trout, perch and catfish as well as rats, kingfishers, shags, scaup, stoats and kiwi.

We can help koura by fencing stock from waterways, planting native vegetation along the water's edge and leaving them alone. Koura are now being bred for the dinnerplate.