The freshwater crayfish or koura (Paranephrops planifrons and P. zealandicus) is an inquisitive animal that is always ready to scavenge should the opportunity arise. It is therefore generally easy to catch with a baited trap. Maori used to trap koura as a minor food item.
For the purpose of learning about these native animals which are both culturally and ecologically important it is useful to catch some.
Catching koura to estimate their abundance can be used as a measure of the health of a stream.
After counting and measuring the animals, they should be returned to the stream.
Transferring a couple of specimens for study in a classroom aquarium can be very useful in allowing students to observe movement and feeding. Return them to the stream after completing the classroom studies.
Try some of the trapping methods below to see which are the most effective and develop some other methods or refinements. When trapping, it is vitally important not to allow the traps to remain longer than overnight. They must also be will tied off and their location marked exactly to prevent their being lost. A lost trap might continue to catch Koura and although they usually will find their way out again, some might starve in the trap.
Rough treatment can easily harm koura, making them lose their nippers or legs. Be sure the students know to be gentle with them. Convincing the koura to be gentle with little fingers may require some thought, especially as they are covered with sharp spines. Gloves are a good idea for those who will handle the koura.
Crayfish in Berry
Like many crustaceans, female koura carry their eggs under the abdomen attached to hairs on the swimmerettes. In this condition the females are said to be "in berry".
If crayfish in berry are trapped, be sure to return them to measure them first and return them to the water as quickly as possible to ensure that the eggs are not harmed by drying out because future stocks of crayfish in the stream depend on a good supply of juveniles.
Koura are attracted to the scent of raw meat. Place a piece in the centre of a bundle of slender ti tree sticks and bind the bundle fairly tightly.
----- For overnight traps it is a good idea to place the meat in a polythene bag with holes punched in it. This allows the scent of the meat to escape to attract the koura but prevents them escaping with the meat.
----- The bundle must be pegged or weighted down firmly on the stream bed.
----- Run a slack security line from the bundle to the trunk stream bank bush so the trap is easily recovered and cannot be carried away downstream.
----- Leave the trap set for a set time, ideally in a fairly deep pool.
----- When recovering the bundle, raise it gently and move a wide mouthed net underneath to catch crayfish that drop free before you get the trap to the bank.
----- Shake the trap over a plastic or material sheet to collect the crayfish that have been trapped in the bundle.
A similar trap can be made from fine wire chicken mesh - the type with hexagonal holes about 2 cm across.
----- Roll up a piece about half a metre wide by one metre long with the bait tied securely in the centre, and flatten the roll ends.
----- The crayfish find their way into the netting roll but cannot escape easily as it is hauled out.
----- Using pieces of meat the same size and similar sized bundles compare the effectiveness of traps made the traditional way with small sticks and those using modern materials - chicken wire.
Koura will hang on tenaciously to a baited line with their pincer claws.
----- Fine wire makes a good line that is easy to twist around the bait and will sink to the bottom.
----- You need to find a position on the stream bank where you can squat or lie comfortably and where the water is overhung by trees so there is no bright reflection off the water's surface to reduce visibility to the bottom.
----- When you see a koura take a firm grip of the bait lift it out gently slipping a small net underneath in case it releases its hold.
Koura can be used as biological indicators of the health of a stream. Keeping an annual record of the number and size of koura caught from the same stretch of water will give good baseline data.
Select a number of sites along a stream bank (6 to 10) appropriate to the size of the class. Identify each exact site by driving a small permanent numbered peg into the bank.
Each site should be safe for a group of 3 or 4 children to release and recover their traps. (See Risk Management section)
All sites should be within view of the teacher in charge and or teacher aids at all times.
----- All traps should be identical and suitable for storage from one year to the next.
----- Use a standard type and size of bait in each trap and on each survey.
----- Traps should be left down for a standard time, either one to two hours of a study trip or ideally overnight if the stream is within walking distance of the school.
----- Release all koura from each trap, on to a collecting sheet .
----- Count the crayfish and measure the length of each one against a ruler. Measure the total length of the carapace - without the tail - from the tip of the rostrum (the sharp spine on the front of the koura to the center of the back end of the head section, just before the segmented tail section).
----- Record the data on a standard sheet.
b. Anchor line
d. Map of trapping sites.
f. Hand net
h. Collecting sheet
i. Clip board
j. Data sheets
k. Pencil / pen k.
Crayfish are interesting animals to keep in the classroom but more than two in a small aquarium may result in aggressive territorial behaviour.
----- They will need a sandy bottom and some rocks to hide under
----- Well aerated water
----- A small amount of water weed and some decaying fallen leaves from their natural riverbed.
----- For animal food, they will be happy to take small pieces of minced beef, one small piece per day. Do not overfeed or the water will quickly become cloudy with bacteria. If in doubt, it is better not to feed at all than have food rot in the aquarium.
----- Place the aquarium in the classroom in a position where it is never in direct sunlight and not close to a heater (or radiator).