Scud Soup & a Sammie

[nightfish 0]

Cache Anglers held their monthly meeting tonight at RoundRocks Fly Fishing in Logan. Dr. Mark Vinson presented information on the aquatic invertebrate population of the Green River below Flaming Gorge Lodge and what the fish are eating. Mark also gave us an update on the Logan River Salmonfly Relocation Project.

 

Let's start with the Sammies...

 

At the nymph release site, sampling has shown no nymphs present. This is a heavy water site, and it is possible the released nymphs were washed further downstream than the survey area. Last year, this site had pteronarcys exuvia present, indicating that some transplanted nymphs did hatch.

 

At the adult release site, sampling has shown nymphs present in the 1yr old age class. Looks like some of the adults got busy & did what they were supposed to.

 

 

For the Green River project, Dr. Vinson & his crew surveys several sites for aquatic invertebrates, from the dam down to the state line. For fish stomach content surveys, Vinson worked alongside DWR biologists as they electrofished locations in the A section, working the shockers by boat. Vinson collected stomach samples from 50 fish at the tailrace boat ramp (main put-in) and 50 fish at Little Hole. This is consistent with the annual data collection method dating back to 1995.

 

The biomass numbers for the Green (averaged from all survey sites) shows an average aquatic invertebrate density of 12,000/square meter. To put that into perspective, the Logan River has a density around 2,000/square meter. There are about 20 species present in the system. Of those, four species make up 93% of the overall biomass. The most prevalent is hyalella azteca (little grey scud) taking up 66% of the count. The rest of the top group include chironomidae, ephemeroptera and simuliidae.

 

The Green River fish are definitely meat eaters. 20% of the browns sampled had fish remnants in their stomachs, while 12% of the rainbows ate their cousins. Mice remnants have been found in quantities that reflect cyclical rodent populations, with some years showing as high as a 10% stomach presence, and other years (like this year) having 0% presence.

 

New Zealand Mud Snails have increased rapidly in the system, including appearance in the stomach samples. They were first found in survey fish in 2001 with a very small presence. In 2005, 60% of the fish had NZMS in their stomachs. Vinson said ingestion is likely incidental, picked up while going after other invertebrates.

 

One of every 20 fish over the life of the study is found with fishing flies in their mouth. You guys need to tie better knots & give up the 6x.

 

Historical species diversity

Dr. Vinson presented data showing that the regulated flows put in place in the mid-1990's have improved the diversity of aquatic invertebrates in the Green River. After scientists issued a biological opinion stating that Double Peak flows for power generation were adversely affecting the rivers biomass, dam operators instituted a flow schedule for power generation that more closely mimicked a natural system. Before this flow regime (ca. 1994), there were 8 species of aquatic invertebrate present in the system. In 2006 there were 20 species present, and overall biomass had increased.

 

At this time, Western Power is considering a return to the Double Flow program to generate more peak time power. There is significant scientific data that shows this would very negatively affect the river biodiversity. Insect diversity and density would decrease, juvenile fish would be frequently stranded by rapid flow changes, and fish would be stressed by the fluctuations.

 

 

 

[Taxon 0]

nightfish-

 

Extremely interesting report. At first, I wondered if 12,000 invertebrates per square meter could possibly be true, as it's a bit difficult to visualize. However, a little internet research supports that magnitude of number on the Green River. Also found the biotic sampling domination by Hyalella azteca interesting. It made me curious to know which species of Ephemeroptera, Trichoptera, and Plecoptera were identified. Anyway, thanks for taking the time share a summary Dr. Mark Vinson's report with us.

[Ethan Bright 0]

It would also be interesting to know the functional feeding groups the EPT. If there would abundant simuliids, which implied sufficient suspended organic matter and, by relation, sufficient periphyton/aufwuchs upon substrates, then I'd guess there would be a lot of net-spinning, grazing caddis (e.g., hydropsychids and philopotamids), and grazing/scraping mayflies and stoneflies (e.g., heptageniids, capniids). In terms of midges, I'd suspect a lot of Rheotanytarsus, Micropsectra, and Cricopotus/Orthocladius, depending upon the temperature/flow regime.

 

Primary and secondary productivity, as measured by dry-weight biomass, may or may not be positively correlated to biodiversity. Invertebrate biodiversity can decrease because of fish predation; the converse may be true. Another statistics mentioned - eveness - indicates just a few species dominating, which according to some ecological models indicates the lack of disturbance. The presence of Hyallela aztecta probably indicates the proximity of the reservoir, which may mirror more a lentic than a lotic ecosystem. The presence of simuliids - very often found in huge numbers immediately downstream of a reservoir, lake, or pond - may also reflect this observation. Thus, it might be argued that MORE simulated disturbance - unregulated flows - might be called for, in order for the river to fluvially act like a river. One can then look to see if rarer invertebrate species come more common, and the dominate species become less abundant, and represent less of the total per area biomass. But, of course, I'm not there, so I can only arm-chair speculate. And I don't know what the management targets that determine what's a good river from a bad one.

 

Nightfish, thanks for the interesting note!

[nightfish 0]

Here's the study info, if you're willing to take on nearly 100 pages & lots of fancy words:

 

http://www1.usu.edu/buglab/projects/project%20fgd.htm

[Taxon 0]

nightfish-

 

That's either a bad URL. or the site is temporarily down, as all I get is a page not found.

[nightfish 0]

The site is down apparently. Give it a try tomorrow.