Quote:
Originally Posted by Lornce
During the 70's when I first moved here, there were massive spring hatches of not only Salmonflies but Squalas and march browns in the spring—followed by a good variety of mayflies, etc. There has been a slow decline in streamside insect life ever since. Some of my old haunts north of Calgary have suffered from the drought and other factors to the point where it is hard to find much under rocks.
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Critical discussion
As reports continue to continue to come in from anglers who say the numbers of rainbows in the Bow is declining. It has me wondering what the impacts of reduced phosphorus in Alberta streams would have on trout populations.
I would postulate that phosphorus inflow is not significant in the mountain and foothill streams and rivers and that it may be more of a closed system.
We have evidence based upon experience of sewage inflow into both the Bow River and the Crowsnest River that the eutrophication caused by phosphorus dramatically increased bug populations and thereby dramatically increased the trout and fish carrying capacity of those rivers.
Since the elimination of nutrient release due to improved sewage treatment technology, the side affect has been the negative consequences in the slow decline on fish populations on sport fishing. The Bow and Crowsnest Rivers have been a major tourist draw for years and the decline in the fishery will eventually impact tourism. At the same time the local pressure continues to build on all water bodies.
When examining some key facts we can see that in a closed system or limited nutrient renewal system that removing nutrients over time will compromise the carry capacity of the stream or river.
I personally reviewed hundreds and hundreds of historic F&W reports in my past job roles and the fact is our foothills and mountain streams historically contained not only more fish but larger fish. There are photos of streams harvested of very large bull trout, and streams so full of spawning mountain whitefish that it looked like you could walk across their backs and keep your feet dry. We don’t see this anymore. One could say it’s a result of fishing regulations and fishing pressure but maybe it’s a deeper issue. Maybe if harvest was stopped completely that those rivers may take thousands of years to recover due to nutrient limitations.
The historic harvest of all this fish biomass as well as continued harvest since has likely reduced the phosphorus in the rivers and streams enough to significantly limit not only population recovery but also the maximum carry capacity. How much phosphorus is interesting. Some reports on perch for instance shows 1% of weight is in phosphorus. For trout is is likely similar so over time has more phosphorus be removed that comes into the system? Do we know? Do we care? Can we imperially or scientifically prove that this isn’t significant?
We have seen that populations in the Bow are falling hard… and phosphorus inflow is low and available phosphorus from past sewage diacharge may of been flushed from the system due to successive floods. As a result we see a reduction in eutrophication of these systems.
In this day and age… is adding nutrients to streams and rivers even possible as society seems to feel its taboo to mess with nature? At the same time can it be considered correcting an imbalance caused by people, so to inoculate our rivers and streams with nutrients to replace over a hundred year is the best thing to do.
Let’s face it. Angling pressure is climbing. Native streams and rivers are limited in Alberta. Our waters along the mountains and foothills are glacier and spring fed and aren’t productive like a prairie river.
It may take some strong leadership in Alberta to understand this and consider some research.
I think it is worth a discussion.