U.S. Department of the Interior

U.S. Geological Survey

Project F: Aquatic ecology 

and food base monitoring

Ted Kennedy1 & Jeff Muehlbauer2

1-US Geological Survey, Southwest Biological 

Science Center, Grand Canyon Monitoring and 

Research Center, Flagstaff, AZ

2-US Geological Survey, Alaska Cooperative 

Fish and Wildlife Research Unit, Fairbanks, AK
Natural Processes

 LTEMP Goal 2

Restore, to the extent 

practicable, ecological patterns 

and processes within their 

range of natural variability, 

including the natural 

abundance, diversity, and 

genetic and ecological integrity 

of the plant and animal species 

native to those ecosystems.

This talk

John Wehr

3p talk

Bridget Deemer

330p talk

Anya Metcalfe

345p talk

Unpublished data, subject to change, 

do not cite.
Why Bug Flows?

~80% of aquatic insects

have cementing egg laying

strategies that are 

vulnerable to artificial tides

Year-round hydropower 

fluctuations do not support 

natural processes essential to 

diverse and resilient 

invertebrate assemblages

Photos of aquatic insects (top) and eggs cemented on various substrates (bottom).

From Miller and others 2020, Freshwater Science

From Kennedy and others 2016, Bioscience
Why Bug Flows?

Not enough insect prey for fish

Low diversity, inherently unstable

Food webs built on algae

Colorado River downstream of Glen Canyon Dam 

only 1/3 the invertebrate genera of other tailwaters.

From Kennedy and others 2016 BioScience. 

Food webs of the Colorado River circa 2006-2009.

From Kennedy and others 2014 USGS Fact-Sheet. 
Why Bug Flows?

High and low flows eliminated

Hydropower production creates tides

 Favors desiccation tolerant invertebrates

 Disfavors ~80% of aquatic insect species

NZ Mudsnail

1937 Hydrograph, Colorado River at Lees Ferry

Natural Flows

2017 Hydrograph, Colorado River at Lees Ferry

Regulated Flows

https://www.gcmrc.gov/discharge_qw_sediment/station/GCDAMP/09380000
What is a Bug Flow?

 Give bugs the weekends off

 Weekend stable low flows from May-August

 34-36 days/years

 Tested 2018-2020

 Eggs laid on weekends never dry

https://waterdata.usgs.gov/az/nwis/uv?site_no=09380000

May-August

Unpublished data, subject to change, do not cite.
Results circa October 2021

Bug Flows-Key Findings

 Enhanced natural processes 

and improved food base

 More egg laying substrates

 More insect emergence

 More caddisflies (but not midges)

 More GPP

 Enhanced rainbow trout fishery

 Higher catch rates

“Objective: Improve food base productivity 

and abundance or diversity of mayflies, stoneflies,

and caddisflies” LTEMP Table 4.

Unpublished data, subject to change, 

do not cite.
Results circa October 2021

Bug Flows-Key Findings

 Enhanced natural processes 

and improved food base

 More egg laying substrates

 More insect emergence

 More caddisflies (but not midges)

 More GPP

 Enhanced rainbow trout fishery

 Higher catch rates

“Objective: Improve food base productivity 

and abundance or diversity of mayflies, stoneflies,

and caddisflies” LTEMP Table 4.

Unpublished data, subject to change, 

do not cite.
Results circa October 2021

Bug Flows Objective: ↑ midge abundance

 Unchanged after 3 years

 Model predicted ↑ 27%

(long-term)

9 Unpublished data, subject to change, 

do not cite.

SA Review

Limitations of experimental design: 

“This [experimental] design presents great 

challenges for drawing confident conclusions 

from the experimental manipulation. That is, 

investigators are denied direct means for 

dismissing alternative hypotheses.” 

–B. Downes
UPDATED RESULTS

 Cessation of Bug Flows 

associated with ~50% 

decline in midges

10 Unpublished data, subject to change, 

do not cite.
Results circa October 2021

Bug Flows Objective: ↑ EPT diversity

 Highest 3 year average 

on record

 Predicted longer-term

11 Unpublished data, subject to change, 

do not cite.
UPDATED RESULTS

 Cessation of Bug Flows 

associated with modest 

decline in caddisflies

12 Unpublished data, subject to change, 

do not cite.
Results circa October 2021

Extreme climatic variation in Bug Flows years

Wet Spring: late emergence Dry Fall: high abundance

13 Bug Flow Years are bookends (extreme high 

and low years)...complicates results

Unpublished data, subject to change, 

do not cite.
UPDATED RESULTS

2021 underperforms 2021 underperforms

14 2021 underperforms (later emergence, lower abundance) than 

expected based on 2012-2020 relation

Unpublished data, subject to change, 

do not cite.
UPDATED RESULTS

2021 underperforms 2021 underperforms

15 2021 underperforms (later emergence, lower abundance) 

expectation based on 2012-2020 regression line

Unpublished data, subject to change, 

do not cite.

lower 

abundance

2012-2020

regression line

updated

regression line

later emergence

2012-2020

regression line

updated

regression line
Conclusions

-The best available science continues 

to indicate that Bug Flows was 

effective at enhancing Natural 

Processes of the Colorado River 

ecosystem

Bug Flows

Conceptual Model

Bug Flows Hydropower Fluctuations

From Kennedy and others 2016 BioScience. 

Unpublished data, subject to change, 

do not cite.