Isn't there two sides to this, one, what impact have anglers and their baits had/will have and two, what impact will the business of angling have.
To put some fine points on this, I don't think barbel eating luncheon meat will have any effect unless it contains some weird genes that get into their bloodstream. They, along with carp eating boilies, may simply get fatter, but denied of these treats, their offspring may well grow as their forefathers did. No change.
However, the business of providing good angling to us may well change things, such as the Thames barbel are now mixed with Trent barbel. If there is a difference at all, the fish may change in subsequent recruitment and over time who knows, but it may not be a big change.
The larger question is, what impact will the introduction of new species have on our rivers. As has been mentioned, escapee carp in our rivers now make up a large proportion of the biomass. But what of the stupid idiots (some may well be pike livebaiters) introducing a alien specie into a water that has never had them before, such as wels catfish into the Thames. Fine if all you want to catch are big catfish and carp over 20lbs, but disastrous for all other anglers and fish species.
It's a multi-faceted question that has no simple answer.
So I'm sitting on the fence.
---------- Post added at 12:58 ---------- Previous post was at 12:56 ----------
How about cormorants which for millenia roosted and nested on sea rocks; moving inland nesting and roosting in trees - previously unheard of, at least in the British Isles.
Q./ What brought them inland?
A./ Easy - Stocked lakes and reservoirs - artificially stuffed to the gills with rainbow trout and coarse fish.
More likely cross breeding with it's Turkish cousin actually, Carbo Sinensis, a more inland bird. To tell the difference count the white feathers on it's throat, sinensis has 33 more than the indigenous specie.
