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Monster in the Meadows

May 3, 2013

As usual I was out walking the dogs, when I saw one of them sniffing at something in the grass by the weir. When I looked down what did I see? An absolute monster of a Signal Crayfish Pacifastacus leniusculus.

Signal CrayfishThe Signal crayfish is a non-native species to the UK. It is a North American species that was introduced to the UK in the 1970s and sold to farmers looking to diversify into new markets. The crayfish escaped into the wild carrying with them the crayfish plague, this has had huge implications here in the UK. All North American species are capable of carrying crayfish plague to which European crayfish are highly susceptible.

There are six non-native species of crayfish in England and Wales. The most common species – and the one that causes the biggest problem – is the signal crayfish. This six-inch-long killing machine has already annihilated the smaller native White-Claw crayfish Austropotamobius pallipes which is now an endangered European species, by out-competing it and spreading the fatal plague. A voracious predator the Signal will eat almost anything it finds including plants, invertebrates, snails, small fish and fish eggs. It is also a cannibal that
makes a meal of its own young. The signal is often bluish-brown or reddish-brown, with very large and heavy claws that are red on the underside with a turquoise or white patch on the upper side in the joint (you can see this clearly in the photo).

The Signal also digs burrows up to three feet long in river banks where each year it lays more than 250 eggs at a time. At a time of increased flooding risk the numbers and size of the burrows is increasingly causing river banks to collapse.

So what can we do?

All non-native crayfish caught must be humanely destroyed and to catch them you must have a licence and contact the Environment Agency before doing so.

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