There's a whole claw war taking place in rivers up and down the country. The team at River Cottage tell us how our native crayfish is being threatened.
What's the problem?
The American Signal Crayfish was imported back in the 1970s for the restaurant trade. They cause a whole host of problems not only for our native species, the White Claw Crayfish, but for rivers up and down the country.
The American Signals introduce a crayfish plague which spreads amongst the natives, killing them and leaving only the Signals behind. This breed is bigger and much more aggressive than the native species, which it out-competes, and can climb and walk considerable distances. The Signals are also damaging to plant, fish and invertebrate life and can have a devastating effect on river banks.
Can we get rid of them?
Unfortunately it is a difficult job getting rid of these 'alien' crayfish due to their incredible breeding rates. The best approach is to try and reduce their numbers to levels where they are not a nuisance - the most important thing is to prevent them from spreading any further.
Some leading scientific groups and conservationists feel any publicity is bad publicity but with dedication and the right guidance there is progress to be made. Some groups suggest the best way of saving the native crayfish populations in the UK is to completely ban the sale of the Signal.
How can we help?
Trapping is considered the best plan of attack when attempting to deal with a crayfish problem in areas where Signals are dense and natives are absent. The important thing to remember is that it must be continuous and intensive. All crayfish must be removed and killed, no matter how small. Leaving the small and taking the larger male crayfish could create a population explosion.
It is great to want to make a difference to the crayfish problem in your area but try and do it responsibly. Continual, aggressive trapping will reduce numbers but if you stop the process or engage in occasional trapping you may make things even worse as you will have altered the balance in that area of river.
Before you begin you will need a trapping licence from the environment agency. It is illegal to trap without one. And although crayfish can be fun to catch and tasty to eat, a common preconception is that there is money to be made out of trapping them. The reality is that trapping is a huge effort and the only results you will have are hopefully ones that dent the population.
NOTE: Unless previously agreed in writing with the Environment Agency, the opening or entrance to any trap should not exceed 95 mm in diameter. All traps where the trap entrance is greater, up to 200mm, must be fitted with an otter guard.
What do I do with the ones I've caught?
Freezing is generally the preferred method of killing any crayfish you catch and every last one caught must be killed. Once you have removed them from the water there is no going back - in fact, it is illegal to put them back.
Although the large crayfish make a hearty meal there is concern that the smaller crayfish will not get disposed of properly once they are removed, and this could allow them to spread into other water systems. All should be disposed of - large and small.
If you want to trap you must first contact your local Environment Agency. They will put you in touch with their fisheries officer who will know everything about the area and the river.
Remember, what may work for one river may not work for another. You must also have permission from the landowner.
Crayfish trapping advice packs are available from the National Fisheries Laboratory. Or contact the Fish Movements Authorisation Team on 01480 483968.