Overweight, oversexed and over here? Will Grundy has discovered that someone is trapping signal crayfish on his patch of the Am. We asked the Environment Agency for information about this American invader.
American signal crayfish first arrived in the UK's rivers in the 1970s after escaping from fish farms. They have since wiped out the native white-clawed crayfish from many of the rivers they invaded by out-competing them for food and habitat, and because they carry a fungal disease - crayfish plague - which is deadly to the native population.
Native white-clawed crayfish now only survive in a few rivers, notably in the northwest. They are endangered and protected.
Signal crayfish may also upset the balance of our aquatic ecosystems, through preying on aquatic invertebrates and fish eggs. They can also be a serious nuisance to anglers by repeatedly taking bait intended for their catch.
Several other non-native crayfish have also become established in UK rivers.
Trapping and regulation
Prized for their tasty flesh, signal crayfish are trapped on a commercial basis, as well by the general public for domestic consumption.
Anyone who wishes to catch signal (or other non-native) crayfish must first obtain an authorisation from the Environment Agency. This allows us to make sure that trappers do not fish in native crayfish strongholds and know to return any native crayfish they accidentally catch.
We can ensure that they only use traps that will not accidentally catch otters and other wildlife, and know to disinfect their traps when moving between waters, to avoid spreading crayfish plague.
It is illegal to catch the native white-clawed crayfish. Anyone caught trapping them may be prosecuted.
To avoid non-native crayfish spreading further, it is illegal to introduce them into the wild.
Although trapping may seem like an effective way to control signal crayfish, this is not always the case. Trapping with just a few traps and only removing the larger crayfish may have little effect or may even result an increase in numbers, as the smaller ones are no longer eaten by larger specimens. However, with sustained and intensive trapping, crayfish populations may be suppressed.
Keri Davies is an Archers (and Ambridge Extra) scriptwriter and web producer.
- More advice is available from the Environment Agency
- Picture shows a native white-clawed crayfish (left) and a non-native American signal crayfish. Image supplied by the Environment Agency