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User Icon     Posted 3 months ago     by Jim Hook     

Signal Crayfish - another tasty invader

Pacifastacus leniusculus doesn’t sound like a very American name so lets go with its more easily pronounced alias - Signal Crayfish. You might not know it, but we have been invaded by this eco damaging bully since the 1970s when a US spy in the UK Government thought it would be a good idea to introduce these little critters to farm for export for the Scandinavian market. OK, that might be a bit too John le Carré, but the fact remains that a government once again thought it could outsmart nature in order to generate financial gain. You won’t be surprised therefore to discover that, like its US friend the grey squirrel, this American aquatic thug decided to wage a war against its smaller UK cousin, the white-clawed crayfish, using biological warfare. Ironically, one of the decisions to import the Signal Crayfish was due to the European crayfish populations being ravished by a crayfish plague, but unfortunately the American variant also had this plague and promptly passed it onto the UK’s native white-clawed species. Added to that, the US interloper is a voracious eater and doesn’t really care what it eats. Furthermore it sometimes lives in holes it burrows out of the river banks causing further eco damage.

Some think it’s now too late to remove this alien from our waterways. This is in part due to a study conducted in the Yorkshire Dales which determined that Signal Crayfish densities could be as much as 110 per square meter and that only 2.5% of those populations were large enough to be trapped in legal traps. Those are sobering statistics but doing nothing isn’t an option. If it were simply a case of replacing one crayfish species with another then it might be something that we would have to accept, but the fact is that the US version causes widespread damage to other species along our waterways and as a result acceptance isn’t an option.

Trapping is by and large the only practical option for the time being. However, trapping in itself can be damaging to the environment and there have been cases of otters dying after getting caught in traps, along with white-clawed crayfish who can then be mistaken for their unwelcome American counterpart and tragically destined for the pot. Traps can also offer a free form of transport for other invasive species or disease from one waterway to another if the trapping devices and tools aren’t meticulously cleaned after every use.

For now therefore, with trapping our only weapon in this war, we have to ensure we do not cause any collateral damage when employing it to catch the target species. To do that there are a number of safety mechanisms in place, but none better than your own self enforced standards when out fishing. The following check list may assist you in hunting out the ‘surf’ element to your next family ‘surf and turf’ BBQ as well as ensuring you don’t contribute to the problem at the same time.

  • Identify waterways that do not host white-clawed crayfish but do hold signal crayfish (Signal crayfish can be found in rivers, streams and lakes)
  • Ensure the waterway is not located in an SSSI
  • Get permission from the landowner to fish for the crayfish - commercial fishing lakes are likely to be supportive, if infested, as they are damaging to their operation
  • Apply for a license to fish for crayfish from the Environmental Agency - they will refuse if they know white-clawed crayfish are also present at your chosen location (The application form can be found here https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/936387/Application_to_trap_and_or_remove_crayfish_in_England.pdf)
  • Buy a UK legal trap that is proven not to cause harm to other species such as otters. A good option can be found here https://www.fishkit.co.uk/crayfish-traps.html
  • Set your traps at your intended location and leave for 24 hours. They are most effective at night.
  • Return with a bucket into which to deposit your captured quarry
  • Once home make sure you disinfect your fishing equipment, and clothing that may have been in the water, to ensure none of the tiny juveniles, or disease, are transferred to another waterway on your next outing
<p>A rewarding harvest of an invasive aggressor</p>

A rewarding harvest of an invasive aggressor

Signal crayfish are delicious. They are a perfect accompaniment or starter to a ‘surf and turf’ menu. For me, they most certainly count as a game species, and just as with other invasive species its our duty to try and manage their populations without negatively impacting the surrounding environment or species. Getting rewarded for your efforts with a tasty meal is fair recompense.

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