The impact is not equal across species. Bass are different to fallfish which in turn are different to suckers etc etc. To answer the bass question directly - there is no data to show that stocking trout impacts bass (lots of data to show that bass impact everything when they are stocked into new waters) but that's not because there may be no impact but more because, as far as I can see across the literature, that specific question hasn't been asked (and notwithstanding Char_master's interesting observations). The effects of trout (or bass, or any predator at or near the top of the food chain) are well documented as having profound impacts on aquatic ecosystems when they are stocked into waters where they haven't been present before. You only have to have a quick squint at the literature to see a whole cascade of food web effects, declines in species richness, changes in nutrient cycling etc etc. That was really my point in post #10 - effects are much more profound on the other organisms in the water and might be less easily measured on our favorites like bass.
Pcray and FarmerDave's points are well made though. Stocking in short temporal windows is likely to diminish any impact. Yet the practice certainly won't have no effect on food webs. How long a pulse of stocking is felt in the ecology of a non-trout stream, how well those webs recover, whether they revert to the same state they were before are difficult to answer. But - as was my main point - in the absence of a clear answer shouldn't we treat these places on their own terms, as environments in and of themselves (and if degraded help them back to their former selves even if that means not fishing them) and not as places that we try to make look like the high street, an aquatic Starbucks on every creek corner dolling out sub-standard trout - a rather pale and pathetic reflection of the real thing. Parsing the differences between A type water and B and C and D is just another way of maintaining an extractive mentality on the 'Resource'.
Mike's point is well made too and I know the board has debated the impacts of trout on trout ad infinitum. Impacts of stocking on the wider food chain in waters that haven't had trout are easy to show. It is much more difficult to categorically show negative impacts on wild trout from stocking domestic trout into waters whose food chains have already been shaped by a standing wild trout population. I have read the literature and very few studies are unambiguous. Even the well known study from Montana that changed that States attitude to stocking, raises questions about the conclusions it draws because of the experimental design and the possible lack of meaningful controls. In addition, studies in the UK on some of their southern chalkstreams found no gross effect of stocked trout on wild populations. That's not to say there may not have been something going on but this kind of field work is inherently difficult and often short term. The more subtle effects, the effects that become apparent over longer time periods, only come out from dedicated long term study - which you know is financially hungry work. Having said that, most of the indications (if not clear conclusions) are towards the negative and so that should be a good enough reason to not f@$k around with a natural environment. No?
