North Fork Stillaguamish and the loss of its "bugs"

[SilverFly]

Although nitrogen and phosphorus are necessary for algal productivity, it is also really helps to have limestone (i.e., calcium) somewhere in the bedrock for high insect productivity that feeds trout (e.g., Montana in map below, and notable areas in midwest and eastern US). The presence of Ca-rich bedrock becomes less critical in aridland rivers (e.g., eastern WA/OR), where high evaporation can also concentrate calcium in waters.




View attachment 105978

Forgive the following layman's terminology and thoughts to a legit, and very enlightening, scientific discussion.

On the topic of "nutrient minerals", the lack of such in PNW volcanic geology, would seem to highlight the historical importance of nutrient transport from salmon.

Specifically, how would two similar streams respond to the flood/siltation impacts being discussed. Where one had high input of salmon carcass nutrients, and the other limited to "ambient stream nutrients" (< insert proper edumicated term here).

Basically, how much do salmon nutrients affect the resilience of insect abundance and diversity?

 

[G_Smolt]

Forgive the following layman's terminology and thoughts to a legit, and very enlightening, scientific discussion.

On the topic of "nutrient minerals", the lack of such in PNW volcanic geology, would seem to highlight the historical importance of nutrient transport from salmon.

Specifically, how would two similar streams respond to the flood/siltation impacts being discussed. Where one had high input of salmon carcass nutrients, and the other limited to "ambient stream nutrients" (< insert proper edumicated term here).

Basically, how much do salmon nutrients affect the resilience of insect abundance and diversity?

This is a bit outside my wheelhouse, but I'll take a stab at it - there are winners and losers in the aquatic insect community in streams with high salmon production. Displacement via redd-building plays a role in insect populations, and affects various taxa in different ways. Similarly, the bounty of salmon carcasses is a boon to some taxa and a bane to others.
I seem to recall a case study of MDN effects on aquatic insect communities in SE AK which used a few above-barrier reaches as controls for a multi-year study. I'll have to dig around for it, if I find it I'll post it up. Interesting "nerd food", at the very least

 

[SSPey]

This is a bit outside my wheelhouse, but I'll take a stab at it - there are winners and losers in the aquatic insect community in streams with high salmon production. Displacement via redd-building plays a role in insect populations, and affects various taxa in different ways. Similarly, the bounty of salmon carcasses is a boon to some taxa and a bane to others.
I seem to recall a case study of MDN effects on aquatic insect communities in SE AK which used a few above-barrier reaches as controls for a multi-year study. I'll have to dig around for it, if I find it I'll post it up. Interesting "nerd food", at the very least

The literature agrees with all this, the answer is “it depends” in many ways … on when, where, how, and which organisms are considered. Context-dependent is the usual caveat. The whole salmon-nutrient story eludes over-simplification.

 

[Salmo_g]

I hope the combined intelligentsia on the post will forgive my ignorance, but it’s something I always felt was due to the dearth of bug diversity: why do Rocky Mountain rivers hold more trout than Puget Sound rivers? Is it the anadromous populations that affect the non-anadromous? Colder summers affecting bug populations? What is it?

SSPey described the over-riding consideration factor. Limestone. Our westside streambeds are mostly metamorphic and granitic rock and basalt with very low mineral nutrient content. Salmon carcasses can deliver a lot of nitrogen and phosphorus to western WA streams, but that can do only so much without the critical calcium carbonate that limestone provides for dense insect populations. Salmon carcasses are the backbone of stream productivity in Alaska and so provides an indication of what our western WA streams were once like. Younger volcanic soils are usually nutrient rich, but our wet, steep gradient streams erode those nutrients away very rapidly compared to our eastside and inland streams.

 

[Smalma]

Forgive the following layman's terminology and thoughts to a legit, and very enlightening, scientific discussion.

On the topic of "nutrient minerals", the lack of such in PNW volcanic geology, would seem to highlight the historical importance of nutrient transport from salmon.

Specifically, how would two similar streams respond to the flood/siltation impacts being discussed. Where one had high input of salmon carcass nutrients, and the other limited to "ambient stream nutrients" (< insert proper edumicated term here).

Basically, how much do salmon nutrients affect the resilience of insect abundance and diversity?

Salmon based nutrients can be a important piece of a river's ecosystem. Salmon based nutrients can provide direct benefit food) to the local fish populations, as down the line benefits to other portion of the ecosystem including in stream and above the high-water line as predators and scavengers drag carcasses from the river.

The among of benefit a given ecosystem benefit from the carcasses can depend on a number of factors besides the obvious number of spawners/carcasses. The ability of a particular river system to capture those nutrients can be highly variable. A classic is the differences in Washington streams is the important differences between east and west stream hydrographs. On the west side much of the mountain snow melt is associated with rain on snow type events which produce those fall floods (late October to early February). On the east side the much of the run-off is associated with spring snow melt. While both sides of the Cascade on the East side nearly all the largest floods occur in May and June while on the West side they typically November, December, and January. With all of our salmon being summer/fall spawners the west side streams have less time to capture those salmon-based nutrients before they are potentially washed downstream.

Another important that comes into play again more so on the west is the simplification of the stream channel(s). With a century of wood removal from the streams, armoring of stream banks, dikes, etc. many of the in stream factors that capture and retain carcasses are now greatly reduced.

Bottom line to better advantage of those salmon based nutrients that currently reaching the spawning grounds the need is improve the complexity of the stream resulting in those features that are carcasses traps.

Curt

 

[Matt B]

Another important that comes into play again more so on the west is the simplification of the stream channel(s). With a century of wood removal from the streams, armoring of stream banks, dikes, etc. many of the in stream factors that capture and retain carcasses are now greatly reduced.

Don't forget a century and a half of logging off the potential new large wood supply.

Bottom line to better advantage of those salmon based nutrients that currently reaching the spawning grounds the need is improve the complexity of the stream resulting in those features that are carcasses traps.

And a lot of those carcass-trapping features, like forested islands, large wood jams extending into the channel, highly sinuous channels with complex margins and intact riparian forests, are unpopular with the adjoining landowners, as they affect their use of the floodplain, or are nearly impossible to permit as features of restoration projects, as they raise water surface elevations during high flows. It's a long road...

 

[Mukman]

What a great community this is. Thank you all for your erudition and patience. I have learned more in the past several posts than I have in 30 years of asking “Why?” Just looking in the wrong places I guess.

To summarize the question “why doesn’t the South Fork of the Stilly have as many trout as the Blackfoot?”, the elevator answer would be:

1). Not enough nutrients due to the underlying strata of rocks. The relative “newness” of the Cascades results in the dominant metamorphic river beds instead of softer limestone. The lack of critical calcium carbonate prevents plant and therefore bug production.

2). The gradient of the rivers adds to the issue by sweeping away any nutrient opportunity.

3). The benefits of anadromous “fertilizer” has been negatively impacted by the reduction in biomass as well as man-made effects of river channel disruption.

Have I got it about right?

 

[SSPey]

a final nutrient treatise (this is my sub-specialty in science)

Across multiple studies in WA, OR, ID, and BC where nutrients (nitrogen, phosphorus) have been added experimentally to streams, there have been inconsistent responses of algal growth. Many sites show more algal growth, but 1/3 of streams show no response. Those that do respond depend primarily on ambient nutrient levels and sunlight. Many watersheds have been affected by humans and show elevated nutrient concentrations already, and natural factors like alder can increase stream nutrients, very radically in some cases. The trophic cascade of increased production from nutrients to algae to insects to fish is tenuous in these streams, not well studied, though it has been seen in a few ultra-low nutrient settings.

Arguably the primary ecological importance of “marine derived nutrients” is that adult salmon are made of meat. Meat pumps calories directly into an ecosystem. Dislodged salmon eggs are especially important for juvenile fish, they’re hard-wired to eat the things. Got beads?

So why is there so much emphasis on “marine derived nutrients” like nitrogen and phosphorus? Partly because it is logically sound, even if not always observed to occur, and it is a cool story about the circle of life. And scientifically, it has taken hold partly because enriched nitrogen isotopes have been used to trace nutrients from dead adult salmon into freshwater food webs, leading to the assumption that the nutrients matter. But, just tracing a nutrient is not a demonstration that it is limiting ecologically. There are 20+ essential elements in organismal tissues that have isotopes, that’s no guarantee they matter to algae over background levels.

Restoration of fish and healthy ecosystems is multi-pronged effort. All the parts. And I’m all in. But, if I had to vote blind on random PNW stream X, I’d prioritize physical habitat and the key processes that sustain it every time.

 

[Smalma]

A fishing report -
"Took fine catch second day - 19 fish averaging 1 1/2 to 2# on dark caddis #10 peacock body, brown legs, dark bucktail"

Skagit river in BC, July 1935 by Letcher Lambuth from his angling diary as reported by Steve Raymond in his forward in the book "The Angler's Workshop".

Some context, the Skagit is a freestone stream above anadromous use (even if salmon historically had access? they would have been excluded by Gorge dam more than a decade earlier) and those rainbows could not have had an ad fluvial life history. Access to the river at that time would have been difficult.

In a later chapter in that book Lambuth writes- "We catch many rainbows weighty one to two and half pounds, occasional we take one weighing up to four pounds."

Later he writes- "We fish quit regularly on Saturdays during the summer season. Our practice on most streams is to drive to the end of the road, walk three- or four-miles additional miles, and fish two or three miles of the stream. On the return we have 5 to seven miles of trial and a drive of fifty to seventy-five miles home." (My kind of angler!)

The above report is not dissimilar to other from the early decades of the 1900 I have seen or heard. I believe that those 14-to-18-inch fish were the historic norm. The fact that those streams no longer have that kind of productivity is a state of how we collectively changed those waters and the fish that live in them.

Curt

 

[krusty]

Water Quality Atlas - Map

Washington State Water Quality Data

apps.ecology.wa.gov

WA Department of Ecology has interesting WQ databases to explore.

 

[Smalma]

Krusty -
Thanks for the link!
Though dated (2001) I found stream max. NF basin temperatures across the basin (Upper, middle and lower NF, upper and lower Deer Creek, Squire Cr, French Cr., Boulder Cr. and Little Deer Cr.). Tells an interesting tale.

Curt

 

[krusty]

Krusty -
Thanks for the link!
Though dated (2001) I found stream max. NF basin temperatures across the basin (Upper, middle and lower NF, upper and lower Deer Creek, Squire Cr, French Cr., Boulder Cr. and Little Deer Cr.). Tells an interesting tale.

Curt

We never step into the same stream twice....in many more ways than one!

 

[Smalma]

Yesterday (3/03/2025) I repeated my unscientific bug count on the North Fork. I visited the same 3 sites and once again turned over 20 stones at each site counting the mayflies. Saw an increase in bugs in all 3 sites.

At the Hazel site in 2024 had 2 mayflies, in 2025 I found 18
At the Grant Creek site had 24 in 2024 and 46 in 2025.
At the Lime Quarry site had 1 in 2024 and 10 in 2025

Suspect the difference in peak flood in each year contributed to the insect abundance increase. In 2024 the peak winter flood was 33,600 cfs. while in 2025 it was 17,400 cfs.. Unfortunately for the bugs and ultimately the fish over the last 25 years flows over 30,000 (10) is more common than those under 20,000 (4).

Curt

 

[Matt B]

Yesterday (3/03/2025) I repeated my unscientific bug count on the North Fork. I visited the same 3 sites and once again turned over 20 stones at each site counting the mayflies. Saw an increase in bugs in all 3 sites.

At the Hazel site in 2024 had 2 mayflies, in 2025 I found 18
At the Grant Creek site had 24 in 2024 and 46 in 2025.
At the Lime Quarry site had 1 in 2024 and 10 in 2025

Suspect the difference in peak flood in each year contributed to the insect abundance increase. In 2024 the peak winter flood was 33,600 cfs. while in 2025 it was 17,400 cfs.. Unfortunately for the bugs and ultimately the fish over the last 25 years flows over 30,000 (10) is more common than those under 20,000 (4).

Curt

Glad to hear that your observations show an increasing trend but the statisticians I've associated with in the past would probably throw a hissy fit over your relatively small sample size and sort of limited sampling technique. I'm not a statistician, though, so let's just say you're right.

Looks like the Stillaguamish basin might be a big blind spot for this type of monitoring.

Puget Sound Stream Benthos

All Streams health calculated from benthic macroinvertebrate samples.

pugetsoundstreambenthos.org

 

[justme2024]

SSPey described the over-riding consideration factor. Limestone. Our westside streambeds are mostly metamorphic and granitic rock and basalt with very low mineral nutrient content. Salmon carcasses can deliver a lot of nitrogen and phosphorus to western WA streams, but that can do only so much without the critical calcium carbonate that limestone provides for dense insect populations. Salmon carcasses are the backbone of stream productivity in Alaska and so provides an indication of what our western WA streams were once like. Younger volcanic soils are usually nutrient rich, but our wet, steep gradient streams erode those nutrients away very rapidly compared to our eastside and inland streams.

Does anyone know if supplementing unproductive stream segments with limestone has been studied? And what effects it had on fish and stream macroinvertebrates? I imagine it would be prohibitively costly and environmentally irresponsible to dump a bunch of limestone in a random river/creek, but I'm curious if it's been tried. I did a quick look on Google but couldn't find anything. Or studies of changes in macroinvertebrate densities in stream segments downstream of the few limestone mines west of the Cascades.

 

[Matt B]

Does anyone know if supplementing unproductive stream segments with limestone has been studied? And what effects it had on fish and stream macroinvertebrates? I imagine it would be prohibitively costly and environmentally irresponsible to dump a bunch of limestone in a random river/creek, but I'm curious if it's been tried. I did a quick look on Google but couldn't find anything. Or studies of changes in macroinvertebrate densities in stream segments downstream of the few limestone mines west of the Cascades.

Yeah, try searching "lime doser" or limestone doser and similar terms. https://dep.wv.gov/WWE/Programs/nonptsource/Stories/wv_threeforkcreek.pdf