The problem of Signal Crayfish and whether to trap them

The White-Clawed Crayfish is a fresh water crustacean native to Britain, that has become a protected species in more recent times. This was due in-part to ‘crayfish plague’ which took its toll on the population.

To supplement the population and keep the Crayfish on the menus of British restaurants, the bigger and darker coloured American Signal Crayfish was imported by the UK goverment in the 1970s. However, these more voracious Signal Crayfish turned out to be a carrier for the disease while not succumbing to it, posing a severe danger to the native population of White-Clawed Crayfish here in Britain. 

Signal Crayfish make their homes in the same places as our native species, on the banks of fresh-water rivers. They are particularly prominent in the south-east of England and Wales to the extent that there are only four known remaining populations of  native White Clawed crayfish in the Thames catchment: on the River Loddon and in a few streams in the Cotswolds.

Signal Crayfish cause a lot of damage to the river eco-system, consuming much of the plant and animal life including larval stages of riverfly like mayflies as well as fish eggs and invertebrates.

During the winter they can burrow up to two metres deep in to river banks, causing enhanced erosion and bank collapse and a dropping of water levels.

Does trapping help keep signal crayfish population under control?

In 2008 ARK (Action for the River Kennet) ran a two week intensive crayfish trapping experiment with Hugh Fearnley Whittingstall and the River Cottage team. They set 20 traps in a 40 metre stretch of mill stream. Amazingly, although they caught over 140 crayfish there was no reduction of the size of the crayfish, suggesting that there are hundreds of thousands of crayfish in the upper Kennet. To have any real impact they concluded that more than 100 traps in a similar length of river would be required.

“Sadly we don’t believe trapping is the solution to control their population,” explains Charlotte Hitchmough from ARK. “You can’t get enough out this way and if you remove one crayfish, a smaller one just moves into its place. There is a risk that trapping might accidentally introduce signal crayfish to more water courses. They walk big distances overland too so they are hard to safely contain.

“And unless the trap is well designed with an exit for water voles or baby otters, it is possible to accidentally drown creatures you didn’t mean to trap. I have seen this happen myself and as well as being illegal its upsetting.

“The good news is that we have recently seen evidence of otters making Signal Crayfish a big part of their diet, which might help control the population. Increasingly we find piles of crayfish shells left by otters after a crayfish feast.”

If maintenance is required on a waterway that is home to our protected native White Claw crayfish, a licence is required to trap and relocate them to a non-contaminated habitat.

Eating Crayfish

Having said all that, crayfish are good to eat (that’s why they were introduced) free and have low food miles. With the right licence, the right trap and permission from the landowner it is legal to trap and eat them.

ARK recommends:

1. Use a well designed trap with an exit for water voles or baby otters.
2. Check traps regularly.
3. Cleanse the crayfish by leaving them in a tank of clean water with par-cooked potatoes for them to eat before you cook them.
4. Kill the crayfish by freezing them as this is believed to be the most humane method.

Recipes

Crayfish Bisque

On the project with ARK, Hugh Fearnley Whittingstall fried up baby crayfish, shells and all, to create a base for the delicious bisque to which he added whole cooked crayfish tails and claws.

Gordon Ramsey’s Crayfish Salad 

Gordon catches crayfish on the River Pang and shows how to prepare them for a delicious salad.

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