The Newbury & Port Talbot Blanker

And it gets worse! I had a similar conversation with a trapper some years ago (he was at Rainsford on the TAA ticket). He was trapping c30000 a season - circa ¾tonne of the blighters. However he noticed that his catch numbers were actually going UP year on year from the same stretches of river - though the average size was coming down (so overall tonnage staying about the same!)  - probably due to the high levels of cannibalism signals have (well they haven't got anything else to eat but themselves!) The only upside is that perch & chub sizes have increased in recent years due to this new high protien diet but there's been precious little in the way of smaller fish coming through - which is whay it's been pleasing to see quite a few 12-16oz chub appearing in my landing net this summer.....

Chris, I have today received this from the Angling Trust. 

I echo your concern for Signal crayfish and the impact that they can have on our freshwater environments. We have been working for a number of years on this issue and calling for advancements in the methods available to manage this species. 

Trapping presents one of the only ways of managing crayfish at present, however, due to its design it is biased towards catching larger individual. This results in the larger crayfish being removed which also exert a predation pressure on the smaller juveniles. This is less of a problem if trapping continues, but it is stops for any reason this can result in greater population as the juvenile population grows in the absence of those large males.  To improve the efficiency of traps, the Angling Trust did a piece of work with Cefas a few years ago exploring ways of improving their efficiency at capturing smaller individuals, and we have been supporting some work recently that is looking at male sterilisation as an alternative technique to management. The use of male sterilisation would allow some larger sterilised males to be returned to the water, allowing them to continue to predate on the younger juveniles. At present, these techniques are all focused on controlling the population rather than eradication. There have been some recent discussions around the use of gene drives which will could be used to make the entire male population sterile (I have attached a link to a talk below if you are interested), but this is very early days and will likely not be an option for 5-10 years. 

https://www.youtube.com/watch?v=y_V0bLPIgnw 

The Trust are currently calling for a national strategy to be developed which outlines steps to manage crayfish populations. We feel that only through looking at a river at a catchment scale can we develop an approach that will be effective at controlling populations. We have been successful in calling for a similar strategy for Floating Pennywort, so we hope that by showcasing the benefits of that new approach we can showcase why we need one for crayfish as well.

 

Similar rationale as to why pike culls INCREASE the pike population though here it's the big girls that are the cannibals!

The gene thing sounds scary as the gene will be in the food chain ,kill as many as I can but only the larger ones get caught by anglers and trappers as you suggest ,had hoped the otters would adapt to eat the crays but have not seen any evidence.