Here you go Daemo, this is a copy of a post I made on another forum a while ago, hope it is of some use to you and others interested in trapping the signal crayfish:
It sounds obvious, but you will need somewhere where there is actually a population of foreign crayfish, not english ones as they are heavily protected. The most common type of invasive crayfish currently found in the UK is the American signal crayfish but there are actually 6 different species currently found. They are:
Marbled crayfish (also known as Louisiana red swamp)
Australian (Spiny cheeked) crayfish
White clawed (English) crayfish
The Environment Agency (EA) have produced a map that a lot of people take to be the distribution of signals found in the uk, it is actually a map of areas where you need a license (or not) to hold non-native crayfish. The areas where you do not need a license are areas where a significant feral population is established, this does not mean they are in every pond or river but that if you had a tank full and the tank smashed and they all escaped, it would not be an ecological disaster in that area as there are already so many crayfish there that it would not make a difference. For example, I live in Lincolnshire and although they are found in many ponds and rivers round here I must have a license from CEFAS to hold any non-native crays at my yard as if a ton of crayfish was to escape, it would be a local environmental disaster as although there are some locally, there are not as many as are present in other areas of the country.
Here is a link to the map:
Why is there a licensing system then?
Signal crayfish (most commonly found) are a threat on many levels, they carry a fungus called crayfish plague that is harmless to them but will kill the now endangered White clawed crayfish.
They eat fish eggs and fry, so although the crayfish provide a high protein source of food to fish such as Chub and Barbel (you may know that the British records have been broken pretty regularly in the last few years), the numbers of crayfish means that very few eggs and fry survive to adulthood, so although there are currently lots of big fish, there will be very few to come through and replace them once they die of old age.
They burrow into banks upto 1 metre, this undermines banks, causing them to collapse and causes trees to fall into water courses, the trees then need removing which costs money. If the water course is bunded, they may drill a hole straight through the bank and drain the water away.
They are a nuisance to anglers as they get to such a level that you can't put a bait into the water without a cray taking it within seconds. Stretches of water literally become unfishable, fish weights drop as there is no food available to them and members leave clubs and syndicates as they are unable to put a bait in the water.
Not only is there a licensing system for holding crayfish, there is also a licensing system to go through before you can trap crayfish. You must apply to the EA by filling in an FR2, here's another link:
To fill in this form you will need permission from both the owner of the water and/or the club that has the fishing rights and a 6 figure grid reference that relates to the centre of the piece of water you are planning to fish. The form is pretty self-explanatory. You may also want to ask the EA for a crayfish trapping pack which includes a copy of the FR2 form and information on identifying diffent species of crayfish etc. The EA are not keen on so called "piecemeal trapping" which basically means putting in a few traps to catch some for yourself as what often happens is you catch the dominant males first, they are fairly canniballistic and so keep the population in check to a certain extent, when you take them out and eat them, the young ones have fewer predators so in a couple of years the population actually grows as a result of removing just a few. Once permission has been granted, you will recieve your numbered tags through the post, these must be attached to the top front of the trap (how you decide where the top is on something that is round and falls through the water to settle is anyones guess).
Right then, that's all the legal side covered so how do you catch them?
Various methods can be used including drop nets and handlines but if you are serious about getting a few without putting in much effort then the pot has to be the way to go. There are many different designs of pot, the 2 most common being the "trappie" and the collapsible net traps you can find on e-bay etc. The trappie costs around £8, is made of plastic mesh and includes a bait box so that the crays can't eat all the bait, this means the trap shoud keep catching for longer. The collapsible net trap also contains a netting pouch with a zip on to do the same job and costs around £4. Be warned, the zips do not last long! Weigh up the pros and cons of each design, the main plus of the collapsibles is that you can fit around 15x as many traps into the space you'd need for the trappies.
Next you must bait your trap, crayfish will eat almost anything, including plants but the best bait is something dead. Roadkill or what ever you shoot/catch is free, any household scraps will do and if you puncture a tin of dog or cat food, the smell will waft out but the crays will be unable to eat all the bait, the best baits are all fish based in my opinion. Don't be shy with the bait, put plenty in as the crays are attracted in by the scent.
Crays are mainly nocturnal although you will be able to catch plenty in the daytime. If you aren't leaving the traps in for long, an overnight soak will produce more that a dawn till dusk soak. If you are leaving them in for longer, they will catch as long as there is still bait in the trap. Not every cray that goes into the trap will stay there, they can and do find their way out so you are working on net gain all the time, you are aiming to lift the trap when most have gone in and least have found their way out; if you leave a trap in too long then you may find that so many crays have gone in, they have suffocated each other, NEVER eat a crayfish you have found dead. Crayfish are affected by the water temperature, the warmer it is, the more active they become so the best catches are to be had in July/August when the water has had chance to warm up (it is always lagging behind the air temperature by a couple of weeks or so). The main season commercially runs from around March until November, after that, the water is generally too cold to make a worthwhile catch.
Once you've decided on the trap to use, which bait to put in and how long to leave it for you must decide where in the water course you will put them and how to secure them. The best place to put a trap is generally as close to the bank as you can get it without any passers by being able to see it and lift the lot. Pick a feature such as a set of tree roots or rocks and set by them, crays like to have something touching them on all sides so love crevices in roots and rocks. If you are just running a few traps for your own use the easiest ways are tying to a buoy, although this draws attention to the trap, or tying a monofilament line to a piece of thicker rope, sunk by leads and remebering where you left them, not easy when you're running as many traps as I do. You simply pull the monofil until you get to the sunken rope, then pull the trap in.
Now then, lets assume that it's all worked well and you've got a pot with 100 crays in it, on the plastic trap, you just twist the front and it comes off so you can tip the crays out although eventually the lugs snap off and the trap won't shut without cable ties. On the net traps you can either open the zip and tip them out, or you can collapse the top half of the trap in one hand and take the crays out by as many as you feel you can get in you hand at once without being bitten. So now for 2 good tips: 1:take the crays out backwards from the valve as this way their spines on the pincers and above the eyes don't snag on the netting, 2:when a cray bites you, and it will happen, if you are really in pain and it is going to through your skin (they can get down to the bone), snap the pincer off at the shoulder, the grip doesn't tighten but relaxes straight away.
Where do you put the crays from the trap? Not in water as it will drown them, there's not enough Oxygen going into the water to replace what they'll take out so keep them dry, either in a bucket or leave them in the trap until you get home if you're only laying you traps once. Once you get home, they should really be purged to get the food out of the intrestine (which runs through the tail). To do this you can either keep them in fresh water for a week or if you want them to eat the same day, kill them by putting a knife into the head and cutting the head section in half (leave the tail intact), the tail has 5 rays, take the middle one, push it parallel with the others one way, then the other, you will feel it click both ways, the pull it out along the length of the tail gently and it will have the intestine attached. If you purge them for a week, the recommended way to kill them is to put them in the freezer for 1/2 hour to slow them down, then put them into rapidly boiling water. Obviously don't try and do loads at a time or it cools the water down and they don't die quickly. I normally cook them for 5 minutes after the water has come back to the boil. There are so many different recipes I'm not going to go into them as that's not the purpose of this topic and there's loads available on the internet. Once they've purged and they're out of the water, they will keep alive in a fridge for at least a week, I've seen them survive 2 weeks with no problems.
I hope this has helped anyone interested in trapping crays. If I've forgotten anything, taken it for granted or it's unclear then ask and I'll try and help although I've tried to steer clear of commercial methods deliberately as my knowledge has been hard learned and this is not meant to be a "how to make a living out of trapping" kind of post. If you get so good at trapping them by reading this that you come up with a few hundred kgs then contact me and I'll have them off you!