Grand Canyon Monitoring and Research Center

Southwest Biological Science Center

U.S. Department of the Interior

U.S. Geological Survey

Ted Kennedy and Jeff Muehlbauer

Annual Reporting Meeting, Phoenix, AZ

12 March 2019

Bug Flows Implementation 

and Resource Response
• Project F: Aquatic Invertebrate Ecology

• F.1: Influence of dam operations on the food base

• F.2: Aquatic food base status at humpback chub monitoring 

locations

• F.4: Glen Canyon aquatic food base monitoring and research

• Project Objectives: “To determine how the aquatic food base 

responds to LTEMP flow experiments such as 

macroinvertebrate production flows”

• Funding Amount and Source: GCDAMP $811,000 (for all of F)

• Cooperators: None for this presentation

• Products: Next slide

Workplan Project Summary
3

Products/Reports
4

Summarized by Kennedy, et al 2013

http://pubs.usgs.gov/fs/2013/3039

 Cross, et al. 2013 Ecological Monographs

 Fish in River are food limited

 Not enough “bug meat”

 Unstable, low-diversity

food base

Groundwork for Bug Flows
5

Camp 30, August 8, 1940. 69 1⁄2 Mile: 

“I am seated on a rock ledge above the 

river in the Grand Canyon with dozens of 

the most pestiferous of all insects, the 

May fly, hovering around my head...”

Barry Goldwater

From Goldwater 1970,

Delightful Journey down the Green and Colorado Rivers

Evidence pre-dam

Unpublished data, subject to 

change, do not cite.

Evidence elsewhere in West

Grand Canyon 

tributaries

Regulated 

Rivers

Kootenai R.

FlatheadR.

Green R.Madison R.

San Juan R.

Bright Angel

Ck.

Shinumo

Ck.

Havasu

Ck.

EPT % abundance

(Mayflies, stoneflies, caddisflies)

 Likely not! 

Should the River have so few insects?
6

From USFWS 5-year review 

SSA on Humpback Chub

 The main 

issue for 

Humpback 

Chub in 

Grand 

Canyon 

Does it matter to have so few insects?
7 From Kennedy, Muehlbauer, and others, 2016, BioScience

 Citizen science program:

 Light traps for adult 

insects

 Typical insect life cycle

 Studying multiple life stages yields insight

But WHY so few aquatic insects?
8

 Kennedy, et al. 2016 BioScience

 Light trap data

 Throughout Canyon:

Spatial pattern in midges

 High midge counts:

low water at dusk

 Low midge counts: 

high water at dusk

Groundwork for Bug Flows
9

Data synthesized from Statzner & Beche 2010, 

Freshwater Biology

 Kennedy, et al. 2016 BioScience

 Midges (and most other aquatic insects):

‘Cement’ eggs on river edges

Groundwork for Bug Flows
10 Data from Scott Miller, BLM/USU BugLab

Desiccation time (hrs)

0 (control) 4 8 12 0 (control) 4 8 12

Hatch successHatch success

 Kennedy, et al. 2016 BioScience

 Midges (and most other groups):

Lay eggs on river edges

 Eggs dry out, die after ~ 1 hour

Groundwork for Bug Flows
11

 Kennedy, et al. 2016 BioScience

 Midges (and most other groups):

Lay eggs on river edges

 Eggs dry out and die after ~1 hour

 Eggs laid at high water die 

 Explains spatial pattern

 Explains low production/diversity

Groundwork for Bug Flows
12

 Improve egg-laying conditions 

for insects!

 Therefore:

 Increase midge abundance

 Increase sensitive EPT abundance/diversity 

(longer term?)

 Ultimately:

 Improve fish food base

Purpose of Bug Flows Experiment
13

 “Give bugs the weekends off!”

 May – August 2018

 Stable, low flows on summer weekends

 Eggs laid on weekends won’t dry/die

Design of Bug Flows
Unpublished data, subject to 14

change, do not cite.

 Smoothing

of spatial pattern

 More midges

throughout Canyon

Predicted Responses (long-term)
Unpublished data, subject to 15

change, do not cite.

Caddisflies

Midges

 Smoothing

of spatial pattern

 More midges

throughout Canyon

 More caddisflies

(EPT)

Predicted Responses (long-term)
16

#/m

3

Unpublished data, subject to 2007 2018

change, do not cite.

 Light traps

 ~ 1000 samples per year, throughout Canyon

 Data were the basis for Bug Flows

 Invertebrate Drift 

 10+ year dataset at Lees Ferry

 Correlated w/ light traps throughout Canyon

 Food directly available to fish

 Sticky traps

 Egg surveys

Bug Flows Monitoring Program
17

Early results from Glen Canyon
Unpublished data, subject to 18

change, do not cite.

Sticky traps

 May 2018: “It’s buggy out there!”

 Sticky traps: massive emergence event

 Summer 2018: Overall 

more midges than any 

other year

Early results from Glen Canyon

(other monitoring) 
19

Female 

midges

Sunday May 6, River Mile -6

Unpublished data, subject to 

change, do not cite.

Eggs

May 

weekends: 

High 

egg-laying

Early results from Glen Canyon

(other monitoring) 
Unpublished data, subject to 20

change, do not cite.

Sunday May 6, River Mile -6

Dozens of egg “ropes”, 

each with 1000s? of eggs

Eggs

May 

weekends: 

High 

egg-laying

Early results from Glen Canyon

(other monitoring) 
Unpublished data, subject to 21

change, do not cite.

Eggs

Tens of thousands 

of egg “ropes”

Sunday May 6, River Mile -13

May 

weekends: 

High 

egg-laying

Early results from Glen Canyon

(other monitoring) 
Unpublished data, subject to 22

change, do not cite.

Many emergent rocks One emergent rock

Bug Flows Load-Following

Eggs

Early results from Glen Canyon

(other monitoring) 
Unpublished data, subject to 23

change, do not cite.

Midges

(per light trap hour)

Weekdays Weekend

Light Traps

 August 2018: Weekday vs. weekend study

 More emergence on weekends:

Unexpected egg-laying benefit of Bug Flows

 More eggs to hatch

 Better fishing on 

weekends

(AZGFD Creel)

Early results from Glen Canyon

(other monitoring) 
24

Canyon-wide results
Unpublished data, subject to 25

change, do not cite.

Light Traps

 Weekdays 

vs. 

weekends:

 More 

midges 

emerging 

on 

“weekend 

water”

Canyon-wide results
Unpublished data, subject to 26

change, do not cite.

 Prediction: 

Sine wave 

flattens

 Result: 

Yes, but 

different than 

expected

Light Traps

Canyon-wide results
Unpublished data, subject to 27

change, do not cite.  Prediction: 

More midges 

canyon-wide 

(>1 years)

 Result: 

Encouraging 

initial signs 

(more drift 

after Bug 

Flows)

Drift

Canyon-wide results
Unpublished data, subject to 28

change, do not cite.

 Prediction: 

More 

caddisflies 

(>1 years)

 Result: 

Caddisfly 

population 

boom in 2018

Light Traps

Canyon-wide results
Unpublished data, subject to 29

change, do not cite.

 Bug Flows in 2018 had ecosystem-wide effect

 Flow matters!

 More egg-laying, weekend activity

 Less canyon-wide variability (↓ sine)

 More midges (maybe)

 Caddisfly explosion (definitely)

Conclusions
Unpublished data, subject to 30

change, do not cite.

 Robust, 3-year test

 Conduct Bug Flows again: 2019, 2020

 Expand experiment into other months?

 Earlier (spring): Natural life history timing?

 Later (fall): Food when critical for fish?

 Continued monitoring regardless

 Effect of 2018 Bug Flows propagates

Potential Next Steps