Over fed and over here! Was the description given to American GI’s during the 2nd World War, now I think we should be saying the same about one of fishing’s biggest threats in this country? The American Signal Crayfish.

Crayfish are not a new species to this country, we have a native species that for centuries have lived in our rivers and contributed to the natural balance of river ecology. But the American Signal Crayfish was considered to be a superior table species it grew bigger and quicker and high prices could be paid for a regular supply.

You can tell the American Crayfish from our native species simply as the underside of the American Crayfish claws have a strong red colour. This is where it gets the signal part of its name, because as soon as it is threatened it sits back on its rare legs and displays its red claws.

Stocked into overcrowded and confined ponds they soon escaped able to walk across fields they soon started to set up colonies in rivers. The American Crayfish carries a bacterium that it is immune to, but native Crayfish were not, they soon succumbed to the bacteria. Lacking any competition or predators, they have spread across our river system so that in a lifetime our native crayfish have become rare and limited to small colonies, while their American cousins thrive.

Young Crayfish can be occasionally taken while molting by Chub etc, but later in life move like locusts across the river bed eating all in sight, especially fish eggs and small fry. This means at present we are experiencing a golden age of river fishing, without competition from smaller fish, the older fish grow large; we should all be concerned about the future of our native river fish stocks.

So far, I have not heard of one instance where American Crayfish have been removed from a lake or river successfully, although many have tried. I suspect in the long-term nature will be able to recover from this invader, but wonder how many lean years river fishermen have to endure first.

Note:- It is against Environmental Agency byelaws to use Crayfish as live bait.

The photo in this article shows an American Signal Crayfish, the disc by it is a Standard English Pound coin.