Colin...I think it is important to keep protesting to the authorities and show the evidence at the damage being caused to the fish stocks, wildlife and wildfowl.
There is no real answer for the individual to stop it at the moment unless you are willing to be banged up inside!
The otters as you know are only doing what comes naturally and it therefore comes down to whether the authorities should have sanctioned the otter re-instatement/releases without proper scientific research and impact assessment regarding to the consequences of such actions. Someone, somewhere may well be found to be liable for not researching in the first place!
Personally speaking, I think there will be a turnaround by the authorities 'eventually' when the evidence becomes clear and more apparent to themselves, and when they are made to 'open their eyes' and look at what is happening!
Only then will the law regarding otters be changed!
At present, they don't want to look, and the heads are buried to the carnage being caused. They know already, in my opinion, but don’t want to admit it!
In the end, Otters will probably be classed just as mink are now and controlled in some way or possibly Nuetered/Spayed so they can’t breed in such numbers!
Basically, if anglers are not prepared and afraid to voice the issue now, then you must expect fisheries to decline and your own fishing (and barbel populations) to be lost.
Best regards...Ray