Red Signal Crayfish are native to North America and Canada and were originally imported to areas of Scandinavia to boost native crayfish stocks devastated by a ‘crayfish plague’. Ironically, the new imports were found themselves to be carriers of the plague without actually being susceptible. That is irony, isn’t it? I often find myself forgetting the point at which coincidence becomes irony. They can live around 20 years and are able to breed after 2 or 3.
The main impacts on native species are on the White Clawed Crayfish, which have suffered dramatically since the introduction of Signal Crayfish in the 1960’s, dropping by an estimated 95%. Disease is the main reason, although there is also an argument that the more aggressive Signal can out-compete the White Clawed and is more tolerant of pollution.
So is there a solution in this case? There are a lot of variables to deal with and it currently doesn’t look too great for the White Clawed Crayfish. Cleaning up our waterways to improve potential habitats would help, but that’s a much larger problem. The plague is the main issue here and it does not seem as though the White Clawed Crayfish can offer any opposition. Mortality rates are nigh on 100% in European crayfish species and other options are limited. One glimmer of hope may be gleaned from the very vector of their devastation. Signal Crayfish and other North American species have developed resistance to the crayfish plague, so theoretically the chances are that this could also occur in European crayfish species, however as yet no incidents have been recorded. Is there any way we can realistically intervene to save the species? Small breeding colonies are being promoted in areas of Yorkshire and Bristol, but as the Signal crayfish becomes more and more ubiquitous in our waterways, is this an occasion where we are throwing away resources against an irresistible force?
It would be negligent of us as conservationists not to try, and there are ways in which we can co-opt the public into helping us. And after all that dry information about plague resistance and lifecycles, here is the interesting bit: They’re incredibly tasty, and easy to catch.
A few years back, when I was a volunteer with a wildlife charity in London, we started to find Signal and Turkish crayfish in the Regents Canal. In a waterway already packed with its share of invasive species (Aesculapian snakes, Red-eared Terrapins, and, apparently now snapping turtles) this wasn’t really a surprise. In fact it would have been a much greater surprise to find the native White Clawed Crayfish in a polluted, stagnant waterway such as the Regents. Still, we devised a number of methods to catch them, ranging from bacon on the end of a piece of string to willow-weaved constructions resembling old eel traps. They were all pretty ineffective, but there are much better DIY ideas out there if you have a look around. In other places I’ve found it much more straightforward and you can sometimes literally scoop them up out of the water (if you are careful). It is definitely recommended that you purge any you catch by keeping them in fresh water for a few days. I have previously done this in a reconfigured steel bin in the back yard. My wife was not impressed.
So could we ever remove it? With many of our waterways to polluted or eutrophied to sustain populations of native crayfish, would there be any point in trying to remove the interloper? It’s a long shot, but when conservation can be this tasty, it’s worth a go.
If you are thinking of fishing for Red Signal Crayfish, which I thoroughly recommend, then be sure to contact the Environment Agency first to gain permission.