Hi morayflyfisher,
I think we must be very carefull comparing stillwater fisheries to rivers. Rivers are a much more demanding environment, with much higher energy demand and many other challenges for a fish, that do no exist in stillwater, couseing the state of the fish to deteriorate much faster than in stillwater and the window of opportunity for the fish to adapt to river conditions, much smaller. It is also predator rich environment, which further degrades chances even of those stocked fish, that could actually make it. It is well known and admited fact over here, also by some of those, who put stocked fish in water, that their survival is miserable. One of the reasons, you get truckloads of those into the waters every year and through the season.
It takes much more than week for stocked fish to adapt, although they will take some of the natural food as well. You can find all sorts of things in their stomachs, from terrestial insects like wasps, beatles, to pieces of plants like spruce needles etc. They do get some energy with those and for example in stillwater that might actually be enough but in running water, it simply isn`t.
There is a big problem with the effect of stocked fish on wild populations, predation is onyl one of possible effects, but it simply means, that a fish, that does not belong in that water in the first place is destroying natural population, for the gain of nothing, just cousing further damage.
For example, here is a picture of wild rainbow cought in a water near me, where wild rainbows have prevailed and have seriously declined a population of brownies:
Let`s leave teh question of brownie, rainbow and protection of autochtonous species aside for the moment and just go at wild/stocked question. As you can see this fish has spawned. By my observations, that must have taken place somewhere from middle of January to middle of March, in any case spawning was spread through a longer period judging by the variation in size of juvenile fish. Spawning over a long period is actually good for wild fish as it acts as a buffer against numerous changes in evironment and enables population to adapt to those. Anyway from those eggs that made it, this is, what could be observed in that river a couple of months ago. Those are little wild rainbows:
However, stocked fish can have a serious impact on these cycle. First, they will compete with wild fish. They will couse havolc in water, cousing bigger energy losses of wild fish. They can disturb spawning. They can eat the eggs. To name just a few of the impacts they can have till we get to those little wild fish we see above. However, this is not end of the story, when we stock water, we actually artificially create a water, that has more fish, that it can actually support. There is a limited number of places in water for a fish of certain size, where it can have a positive energy balace. Limited number of places were fish of ceratin size can survive floods for example. Etc. There are many factor that can have a bottleneck effect.
However, putting stocked fish in water, destroys the "order" in that water. Not only, that there is a problem with wild fish, stocked fish shall take places that are not usual in that water and displaced fish or stocked fish lurking around can frequent, take temporary or permanent place in parts of water, that are not normaly inhabited or frequented so often by wild fish. Now that is a problem, couse those places are normaly used by juvenile wild fish. Suddenly, you can have bigger losses becouse of predation, but also becouse juvenile fish shall change its behaviour in presence of adult fish. Feeding time shall decrease, hidding time shall gol up, reducing the fitness of fish, which can lead to higher losses later in life, like overwinter survival, survival of high waters etc.
This is for example a juvenile grayling taking a shelter among cobbles:
Grayling emerge around end of April in this water and this is already a fishing season. Which means that in stocked waters, heavy stocking has already started. So little graylings swiming up from the gravel can actually find out, that spawning grounds, which are not normaly inhabited by adult fish as they simply are not an environment which could permanently support adult fish, are now either inhabited of frequently visited by those as direct result of stocking.
Of course if we go into the question of loosing population of autochtonous fish, the question is even more disturbing. Yes rainbow trouts and brownies can coexist. One population can dominate over the other as well, depending on size of population, or some factors that might tip the balance in water.
If we go at the question of stocked fish breeding with wild fish.....now there is a sea of possible problems. Wild rainbow from above is from naturalised population, and those fish beahve totally diffrent to stocked rainbows. Not only becouse they grew up in diffrent environment, but also, becouse farm raised fish are more prone to risk taking and researches have shown that breeding of farm raised fish can seriously increae losses of juvenile fish till they become adult. Even in wild populations, you do get fish, that grow faster than the others, for example, those are little graylings and you can clearly see the size difference. They were raised in artifical environment, simulated natural environment and were fed with natural food. As you can see, there is a clear size difference, although when they were cought they were more or less the same size:
But what is interesting, was to observe their behaviour. When they woudl get scared, they would all hide. But the biggest fish, was also the most aggressive or the most risk taking one. It would come out sometimes as fast as just a few second, while the most carefull fish would sometimes take up to 20min. Of course that risk taking fish was very succesfull in this artificial environment, but its chances for survival in wild would be minimal. Imagine a heron coming to such place. Fish would hide and the first one out would be the best candidate for that herons lunch. And farm raising promotes risk taking fish as they are more succesfull in such environment.
So as you said, stocking must always be done with upmost care, although unfortunately this is not always the case.
I appologize for going a bit off the topic.
Regarding the topic, i think that all fish deserve respect, but stocked fish do not belong in many wild waters and throwing them in, is actually very contraversial. They do destroy quality of fishing for those, that seek something more than just banging fish. And for this easy fun of anglers, they pay a heavy price. So as far as stocking adult fish in wild rivers goes, i do not respect them as target. I do respect them as living beings, but i do not think they should end up in a river in a first place. Becouse of their well being as well as consequences that has on wild populations/autoshtonous fish. And all that is done just so that some anglers, who are not willing to learn a bit about fishing, would catch their fish.
As said before, my opinion goes for waters capable of sustaining wild populations. I understand that many anglers do not have a chance to fish such waters close to them and i do agree that overwintered stocked fish as you call them, can be a true fishing challenge as well.
BlueOne
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