It is a f**king joke we have had similar problem here on my local water, I caught one with carp in a carrier bag tied to the platform leg, still in water.
I explained that you must release alive and that retaining them is not allowed he made on that he could not understand, so told him to leave in a language he would understand, with my bull cross next to me growlin he was soon off.
in another instance a bailiff saw them placing carrier bags in the boot of car Angel got registration I reported to police who traced the car to an address 30 miles away, they gave culprits verbal warning