Creepy cannibal river creature Brits should kill on sight by stabbing its brain

Brits are being asked to kill a tiny foreign invader on sight, because of the deadly threat it poses to native species.

Fishermen or walkers that see an American Signal Crayfish – a ten-legged miniature lobster that’s common in many UK waterways, are asked to humanely kill it.

The best method is to stick a knife into its brain, but that’s not always practical.

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“We realise not everyone will have a knife with them,” crayfish expert Helen Carter-Emsell told North Wales Live. “The alternative is to squash them under a rock, though we recognise some people might find this unpleasant.”

Helen is wellbeing officer for the North Wales Resilient Ecosystems pilot project, an initiative that’s been set up to tackle invasive non-native species such as the US Signal Crayfish.

The American Signal Crayfish, which can grow to lengths of up to 12 inches, has menacing claws, and a voracious appetite. The female of the species can carry up to 250 eggs.

They were originally imported to the UK as a replacement for dwindling stocks of the native crayfish, which was being decimated by disease.

The American Signal Crayfish was originally believed to be immune to crayfish plague, and was introduced from the US in the late 1970s, to be reared in farms for restaurants and food shops, the species quickly became established in the wild. Since then they have decimated populations

Some scientists estimate 90% of White-clawed crayfish have been wiped out by their larger US rivals in parts of the UK. As well as predating on native crayfish, Signals are immune to the crayfish plague they carry, but which causes 100% mortality in White-claws.

Establishing exactly where Signals are present in North Wales is an ongoing exercise for Helen and her colleagues.

Focusing on the Dee catchment in north east Wales, eDNA testing found one river completely devoid of White-claws. And even in rivers where no Signals were found, crayfish plaque was detected in some, indicating wider prevalence.

Earlier this month, the team descended on a Flintshire river when Signals had been reported. It was astonished by the sampling results. “In four visits, we found 140 of them in a quarter-mile stretch,” said Helen. “That’s about one caught every five minutes.

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“Along this section, the riverbanks were badly eroded and were collapsing where people walk along a footpath. We didn’t find a single fish along the whole stretch, and the riverbed was covered in sediment, disrupting spawning grounds.”

If you see one of the Signal crayfish you’re asked to kill it on sight – after making sure that it’s not one of the now-endangered white-clawed native ones.

Differences in size can be obvious but this is not always a reliable indicator. A key difference is claw colour – Signal claws are red underneath with a white or bluish blotch below the fingers – the “signal” patch.

In contrast, native crayfish have claws that are a pale colour, hence their name. They are also less aggressive if caught.


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