Terran, the linked article is absolutely correct about problems with stocked fish, but, as much most such articles, it omits some research, muddies the waters (so to speak), and ignores current practices by agencies such as Washington Department of Fish and Wildlife (WDFW) which is the agency and state I know best.
As cited in the article, studies on the mountain yellow-legged frog are the most well known high lake work on the effects of fish stocking in high lakes. But there have also been studies in other states, most notably North Cascades National Park (NCNP).
In most high lakes amphibians are the top native predator. Shallow, warm lakes and ponds are the best amphibian habitat. When trout or char are introduced they become the top predator. What they found in NCNP was that when fish were either over-stocked or over-reproducing naturally they could suppress or extirpate some amphibian species with the long-toed salamander being the most sensitive species in the area. At the same time, they discovered that in lakes were fish were stocked periodically and in low densities native species were preserved. And that is exactly the philosophy that guides current stocking practices in the state of WA. For an exhaustive deep dive into WDFW’s stocking philosophies and history see “Washington Department of Fish and Wildlife’s High Lakes Fishery Management Program”.
As recently as the 1980s the NPS was saying that the best practice would be to stop fish stocking but that there would always be fishing available because in some lakes introduced fish were able to reproduce. This is backwards. When fish are able to reproduce naturally in high lakes they will, most of the time, reproduce too well and over-populate the lake. In NCNP they have gotten really good at removing these spawning populations with rotenone. At the same time, some lakes are being stocked with non-reproducing fish and effects on native vertebrate and invertebrate species are being monitored. And, of course, if you stock fish that can’t reproduce they can be removed by simply waiting. More and more we are doubly assuring fish can’t reproduce by stocking sterile triploid trout.
At this point the biggest issues in high lakes are not the lakes being stocked, but the lakes with naturally reproducing populations. It is even worse when they are a non-native species like eastern brook. These stunted populations can even change zooplankton population dynamics. In WA high lake zooplankton populations will often be dominated by large, predatory copepods (tiny red crustaceans you can see, if you look closely) but they can be grazed off by fish and the lake will become dominated by smaller grazing species. Stocking non-reproducing, fish periodically, in low densities assures these populations aren’t disrupted.
I could go on all day (I also volunteer counting amphibians in Mt Rainier national Park and I love to talk about amphibians) but this is getting long enough. Hopefully I’ve been somewhat coherent in trying to explain why articles like the one linked above can on the one hand be quite correct, and on the other make things confusing about hatchery stocking by ignoring current best practices.
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