North Fork Stillaguamish and the loss of its "bugs"

[Smalma]

Over the decades my causal observation is that the diversity and density of various hatches (stonefly, caddis and mayflies) have changed dramatically. Currently the only "hatches" that I see somewhat regularly (though at depressed densities) are October caddis and BWO. I suspect that a decreased biomass of aquatic insects could have a significant impact the recovery of the basin's ESA listed salmonids. In freshwater the juvenile Chinook and steelhead's diet is largely insects.

I also suspect that this apparent decline in insect abundance is influenced by a variety of flood impacts. Currently the basin has experienced massive floods, 14 since 2000 that compared to a 1929 to 1980 base period would be considered to be once a 500-year (or larger) events. During these events it can be expected that bed scour and deposition would be measured in feet (perhaps as much as 5 or more feet). In addition, there is significant gravel movement of sediments with an overall reduction in the size of bed material with lots of fine material. There also has been an increase in summer temperatures with late summer afternoon temperatures in the upper 60s to upper 70s.

While I feel the above would seem to indicate a problem I don't really know much about the "bugs" so with this post I'm reaching out to the extensive knowledge of this board, especially @Taxon and @Mark Melton. Am very interested in any input about the potential loss of diversity (I assume the stone flies, many of the may flies, and many of the caddies would be wiped out by the churning gravel in such floods). Any insights on what the recovery time for the various species?

Any thoughts?

Curt

 

[Gyrfalcon22]

I can't speak for that region but my family has been on the lower tidewater of the Chehalis river on coastal WA for over 100 years. I have been on the river for about 50 years. It is a mucky silty river with just an occasional gravel bar. I remember in my youth a much more rocky substrate and we had lots of chinook spawning here. And, there were insect hatches I recall. Now I rarely see chinook spawn here and been many years since I have seen the giant yellow mayflies I used to see.

My grandfather was on the river from 1906-1984 and said that the river used to be all rock up and down both sides and no mud bars. He also said the floods were not big brown muddy messes. High slightly off colored water at worst.

Logging on this big watershed has no doubt changed this river forever and the choking silt-beyond the water temperature changes, has had to make big changes the fauna. I see far less freshwater clams than in my youth for another example.

I fish for trout on an upper small tributary off my home river and I have seen the stream go from rocky to surprising silt bars appearing now even far up.
But, it is logging country as well. Still lots of caddis in there.

 

[Mark Melton]

The increase in silt and other small particulates contributes to less species being in areas previously being rocky or gravelly. It also lessens chances for redds in that fry will not get enough oxygen. Insects will not have rocks or gravel to hide in, or to feed off of (algae, diatoms, etc.), or in the case of caddis to pupate on. Silt also contributes to stones and gravel becoming embedded and removes habitat previously available to insects.

Silt usually shows up when large floods wash it out of the surrounding land and deposit it in the river. A good deal more will show up in areas that have been logged off.

As far as insects are concerned large floods in and of themselves might reduce numbers of insects in rivers but it is more likely the after effects (silt, reduction of the hyporheic zone https://en.wikipedia.org/wiki/Hyporheic_zone, etc.) that keep numbers down. Recovery will probably depend on the silt being lessened or removed. May be a long time.

 

[Smalma]

Mark -
Thanks for joining the discussion and providing valuable insights in the processes limiting the abundance of those aquatic insects.

Would it be fair to say that those large floods depress the insect abundances, and the post flooding siltation prolongs impacts by extending the time needed the time needed for the various insects to bounce back?

Would those species with longer nymph stages (multiple years) would be more effected?

Curt

 

[Taxon]

Over the decades my causal observation is that the diversity and density of various hatches (stonefly, caddis and mayflies) have changed dramatically. Currently the only "hatches" that I see somewhat regularly (though at depressed densities) are October caddis and BWO. I suspect that a decreased biomass of aquatic insects could have a significant impact the recovery of the basin's ESA listed salmonids. In freshwater the juvenile Chinook and steelhead's diet is largely insects.

I also suspect that this apparent decline in insect abundance is influenced by a variety of flood impacts. Currently the basin has experienced massive floods, 14 since 2000 that compared to a 1929 to 1980 base period would be considered to be once a 500-year (or larger) events. During these events it can be expected that bed scour and deposition would be measured in feet (perhaps as much as 5 or more feet). In addition, there is significant gravel movement of sediments with an overall reduction in the size of bed material with lots of fine material. There also has been an increase in summer temperatures with late summer afternoon temperatures in the upper 60s to upper 70s.

While I feel the above would seem to indicate a problem I don't really know much about the "bugs" so with this post I'm reaching out to the extensive knowledge of this board, especially @Taxon and @Mark Melton. Am very interested in any input about the potential loss of diversity (I assume the stone flies, many of the may flies, and many of the caddies would be wiped out by the churning gravel in such floods). Any insights on what the recovery time for the various species?

Any thoughts?

Curt

Hi Curt-

Just discovered your post. Can't really add anything of value regarding your and others observations, nor to Mark's analysis, other than to agree with everything that has already been said.

 

[Mark Melton]

Mark -
Thanks for joining the discussion and providing valuable insights in the processes limiting the abundance of those aquatic insects.

Would it be fair to say that those large floods depress the insect abundances, and the post flooding siltation prolongs impacts by extending the time needed the time needed for the various insects to bounce back?

Would those species with longer nymph stages (multiple years) would be more effected?

Curt

Curt-
I don't know If the large floods in and of themselves would be enough to lower insect populations very much or over long periods but the siltation certainly would. Although over a longer period of time you might end up with a relatively large population of different species that favor silt such as chironimids, Callibaetis, Siphlonurus, Tricorythodes, and assorted worm species.

I don't think those species with longer developmental stages would be affected differently other than having a population that had a large number of a particular age for a year.

 

[Matt B]

Puget Sound Stream Benthos

All Streams health calculated from benthic macroinvertebrate samples.

pugetsoundstreambenthos.org

If you weren’t aware, you might be able to glean some more info on benthic macroinvertebrate trends from the PSSB database. Though, the period of record likely doesn’t extend back to members’ childhoods. Water quality and habitat composition seem to drive these critters populations more than hydrography which still certainly plays a role.

 

[Dave M]

Could be the combo of flooding and continued decline of all species of salmon that provide the nutrients for the food chain.

 

[DerekWhipple]

I'm sure that river has it's own specific problems, but people are starting to notice macroinvertebrates have been decreasing all over the country.

Dude, Where’s My Hatch? - Patagonia Stories

The decline of aquatic insects should bug everyone. https://playlist.megaphone.fm/?e=PTA3967760177 Trout anglers speak reverently of the “evening rise,”

www.patagonia.com

 

[Pink Nighty]

In my very limited experience its beyond the NF stilly. It seems outside of mosquitoes there are very few bugs around the nooksack or Skagit anymore either. I have to imagine it's a combination of many factors with the usual suspects at play. Hydrography, ag practices, logging, not enough of the right nutrients, too much of the wrong nutrients, invasives.....

It's a wonder we have anything left at all

 

[DimeBrite]

The DeForest Creek/Deer Creek slide wasn't kind to insect life.

 

[Cabezon]

Over the last 40ish years, the presence/absence/relative abundances of aquatic invertebrates have been used as bioindicators of stream health and water quality (chemical, biological, and physical characteristics). The underlying rationale is that some species have very narrow tolerances and require relatively pristine conditions while other species are tolerant of degraded habitat conditions. The advantage of using aquatic invertebrates is that their relative abundances reflect long-term stream conditions, not just a single point in time (as you would have from a water sample on a single day). This is especially true for species with a long aquatic phase, such as stoneflies. Thus, which invertebrate group thrives or is absent from a stream integrates long-term conditions; however this approach doesn't pinpoint just which parameters (dissolved oxygen, fine sediment load, temperature) are causing long-term degradation.
Some assessments are qualitative, but the stronger ones are quantitative, such as the Hilsenhoff Biotic Index (HBI, a version of which is commonly used in Oregon) or Index of Biological Integrity (B-IBI, commonly used in the WA). The HBI index scores the water quality tolerance of each aquatic invertebrate species on a scale of 1 (very intolerant, such as giant stoneflies = 0, PMDs = 1, October caddis = 1) to 10 (BWO = 6, black flies = 6, midges = 8). These numerical values are derived from surveys of reference streams that have been studied in depth for their water quality. So, the invertebrate species that are found only in clear, cold, highly-oxygenated waters would receive low values while those species more commonly found from waters known to have low dissolved oxygen, high turbidity, and warm waters would receive high values. Assessments of aquatic invertebrates have been used by both professional biologists (e.g., state scientists) and citizen scientists to monitor water quality.
[I used to teach a summer workshop class at Centralia College where we sampled the upper Skookumchuck River (just below the dam) and at its confluence with the Chehalis River at Boost Park. We would measure physical (temperature, turbidity, dissolved oxygen) and chemical conditions (pH, nitrate, phosphorus, ammonia) and collect samples of stream insects to identify in the lab. Not unexpectedly, the upper river had far more stoneflies and other high-water-quality species than were found at the mouth of the river (more black flies, midges, snails, and BWOs).]
Regarding the North Fork Stillaguamish, the factors that @Smalma described (increased turbidity, more fine sediments, less heterogeneity, warmer temperatures) could certainly have major impacts on vulnerable stream invertebrates, such as stoneflies and some caddis and mayfly species. But this isn't necessarily supported by surveys of the stream invertebrates. In this study by Snohomish County, their Surface Water scientists monitors stream invertebrates from the Stillaguamish River watershed, the Snohomish River watershed, and the Cedar-Sammamish watershed. A summary report of data from 2005 - 2014 (too short a time span, in my opinion), indicated that most of the sampling sites in the first two locations scored in the low end of the "good" category, while the Cedar-Sammamish sites scored as middle of the "poor" range. The change from "excellent" (pristine reference stream) to "good" would reflect a) slight divergence from least disturbed condition, b) absence of some long-lived and intolerant taxa, c) decline in richness of mayflies, stoneflies, and caddisflies, and d) increased proportion of tolerant taxa. A score of "fair" would indicate a) total taxa richness declining, especially by intolerant stonefly and clinger mayflies, b) reduced abundance of predators, and c) increase proportion of tolerant taxa. The Snohomish County report also indicates that they could detect no significant positive or negative trends in the B-IBI scores either overall or when comparing specific sites over the time frame covered by the report.
You could argue that time scale is too short (2007 to 2014 for the Stillaguamish River sites) is far too short to address the long-term trends that @Smalma has observed. And you could argue that the B-IBI is too coarse (too much data lumping) to assess fine-scale changes in the biological communities. Finally, these aquatic invertebrate surveys are not assessing overall aquatic invertebrate biomass (mass of trout and salmon food) in these rivers, just the relative abundances of various groups. For example if the biomass of invertebrates declined by 25%, but the relative abundance of different taxa was similar, you would not pick that up in the B-IBI metrics.
Steve

 

[Smalma]

Steve -
Thanks for the excellent information. I agree with your assessment of the usefulness of the B-IBI metric in assessing overall aquatic invertebrate biomass, my largest concern with large scale flooding impacts.

Unfortunately, as part of the Stillaguamish basin study the few main stem North Fork sites were all sampled on years without major flooding the previous winter, luck of the draw. A quick look at the rates for those main NF sites they typically fell into the fair category, potentially due to impacts on the long-lived stonefly and clinger taxa.

Pink Nighty -
Speaking of the Skagit, there was mid-1970s study (Aquatic Insect Abundancein a regulated under Fluctuating and Stable Diel Flow Patterns, Gislason, 1985) where the aquatic insect abundance at water depths of 15 to 45 cm was examined in 1976 and 1977 between May and November each year. In 1976 the common practice of hydroelectric power-pecking the river was subject to diel flow fluctuating (the common practice we still see) and in 1977 that peaking was curtailed resulting in relatively stable flow pattern.

"The highest density observed in 1976 was 1,788 insects/m2 at 25 cm in July. Under stable flow conditions, the abundance in benthic insects was greatly enhanced and the densities at corresponding depts and months were 1.8-59 times higher in 1977 than an in 1976. Insect densities increased steadily from May through September in 1977 when they reached maximum level of 16,763 insects/m2 at 15 cm.

Curt

 

[SSPey]

I can’t be the only person here who learned about the IBI from Jim Karr at U WA?

Anyway, coarse compositional data from the paper noted above.

 

[Smalma]

Decided to do a little unscientific sampling today to check out my flood impact theory. Went to the Hazel area and in the first riffle above the big hole checked out 20 flattish hand size stones that I though my be hiding a mayfly. In those 20 stones I found 2 mayflies. In those rocks or in the area sampled saw no caddis or stoneflies. Next I sample Grant Creek a mid-sized tributary stream just downstream of Cicero. I again turned over 20 stoneflies in a similar size area with similar velocity. Those 20 stones yield 24 mayflies and, in that area, saw approximately 40 caddis fly larva and again no stoneflies. I then sampled the Lime Quarry area sampling the riffle above the first pool again focusing on a similar size area and velocity turning over 20 similar sized stones. That yield a single mayfly larva and say no caddis or stoneflies.

Again a very unscientific approach but I think my "findings" are enough to warrant concern.

Curt

 

[Mukman]

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?

 

[Pink Nighty]

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?

I think I know this one!! You are correct that the warmer Montana summeris a factor that enhances bug growth. You'll see more bugs on the yakima than the Snoqualmie, or the methow vs the nooksack. Montana rivers also generally follow a gentler gradient than our westside steams. Mountain peak to ocean in 80 miles is pretty common here, not so much in montana.

I think the biggest reason for the difference is nutrient load. The Rockies are geologically far older than the cascades, by tens of millions of years. Our relatively young cascade range still run over primarily sterile volcanic rock, short on the phosphorous and nitrogen required to build a large base at the bottom of the food chain. Our rivers rarely have algae or aquatic plants because there is nothing for them to work with.

In fact i think it's fair to say that without the nutrient load brought back by anadramous fish, the rivers (and forests) of the west side would be dramatically limited in their productivity.

 

[Mukman]

I think I know this one!! You are correct that the warmer Montana summeris a factor that enhances bug growth. You'll see more bugs on the yakima than the Snoqualmie, or the methow vs the nooksack. Montana rivers also generally follow a gentler gradient than our westside steams. Mountain peak to ocean in 80 miles is pretty common here, not so much in montana.

I think the biggest reason for the difference is nutrient load. The Rockies are geologically far older than the cascades, by tens of millions of years. Our relatively young cascade range still run over primarily sterile volcanic rock, short on the phosphorous and nitrogen required to build a large base at the bottom of the food chain. Our rivers rarely have algae or aquatic plants because there is nothing for them to work with.

In fact i think it's fair to say that without the nutrient load brought back by anadramous fish, the rivers (and forests) of the west side would be dramatically limited in their productivity.

Thank you!

 

[SSPey]

I hope 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?

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.

 

[Smalma]

I have to wonder how of the fishers here would be interested in fishing a river with 4,000 or more salmonids/mile. Where the fish size is measured in pounds instead of inches. At peak time fly anglers having days with double digit numbers of fish in a 4 to 10# range with some larger fish some of which could be very large.

All we need is a time machine to go back about 200 years. The above is what we would have found in many of the Puget Sound rivers of the period. That fact that we do not see that kind of abundances today is not a statement about the lack of productivity in the river but what we have done to those rivers. Just one example right now during the Skagit CnR steelhead season we would be fishing on over 10 times the current number.

Curt