Cray (or should it be KRAY?) fish

The BBC carried this story yesterday about something not so nice to be found in the River Nith.

Investigation work is planned following reports of a potentially devastating invasive species being discovered for the first time in the River Nith.

Scottish Natural Heritage is to carry out surveys to see if North American signal crayfish are established in the south of Scotland river.

The crayfish were first found in Scottish waters in 1995.

Escapes from fish farms or illegal releases are thought to be the reason for their spread through the UK.

The waters of Loch Ken in Dumfries and Galloway are already infested with the species.

Dr Colin Bean, a freshwater adviser with SNH, said the latest incident would be examined closely.

“The prospects of removing signal crayfish from any water body – particularly one the size of the Nith – is likely to be difficult if not impossible,” he said.

Now, I am sure the scientist mentioned knows far better than me that in these circumstances the word impossible is not actually a synonym for unachievable but rather a synonym of very very expensive and time-consuming, which is not the same thing.

The article itself tells people to leave them alone completely (pending studies).

However, another scientist, in fact the very one I spoke to in a recent podcast had a view about possible future strategies…

Eradication may be possible using biocides but trials in Scotland have found this to be very difficult (you have to get them all and prevent reinfestation). Releasing large amounts of pesticides into water courses brings with it its own environmental problems. 

These fish are also pretty tasty.

Show people the difference between them and native crayfish and you might find locals are up for a little gourmet conservation.

Thing is, I don’t know if people eating them would keep their numbers at a level where they could coexist with the native ones.

They’re just too aggressive!

Anglers are a potential  source of transmission too, accidentally carrying eggs on their boots and kit or even using adult crayfish as bait. Realistically biocides are the most cost-effective way of getting rid of them but these are very harmful to other wildlife. Manually eradicating them is next to impossible.

Any eradication programme would also have to be very well co-ordinated, covering large areas. The benefit of eradicating the pest would have to be balanced with damage to fish stocks and other aquatic wildlife.

So there you have it, and as she also said… “Time to be makin’ some gumbo“.

The general point is that people in general have to be more careful about stopping these things before they start. Invasive species are responsible for many extinctions of native species around the world.