Bug Flows

Jeff Muehlbauer, 

Ted Kennedy 

20 January 2021

Grand Canyon Monitoring and Research Center

Southwest Biological Science Center

U.S. Geological Survey

U.S. Department of the Interior
Workplan Project Summary

• 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 $779,000 (for Project F)

• Products (FY20): 9 presentations, 5 articles. See Annual Report

Upshot: We study bugs. 

AKA “Foodbase”

2
Why Bug Flows? (1) 

1. River dominated by 1 taxon (midges)

 Low diversity = low resilience

2. Total insect abundance low

 Not enough “bug meat” for fish

3. Insect abundance not distributed evenly

 Peaks/troughs of “bug meat”

 Not where we want it 

(for fish)

Cross et al. 2013 Ecol. Monographs;

Kennedy et al. 2016 BioScience

3
Theory Behind Bug Flows (1)

 Daily hydropower flows create “tides”

 Insects lay eggs at water line at dusk

 When tide drops, eggs dry, die

Want to 

avoid 

this

Kennedy et al. 

2016 BioScience

4
Theory Behind Bug Flows (2)

 Daily hydropower flows create “tides”

 Insects lay eggs at water line at dusk

 When tide drops, eggs dry, die

 Mechanism to explain:

 Low diversity

 Low abundance

 Peaks/troughs 

Kennedy et al. 

2016 BioScience

5
Goals of Bug Flows

Improve egg-laying conditions for bugs!

 Thus:

 Increase abundance of midges

 A couple years?

 Increase abundance/diversity of EPT

 (mayflies, stoneflies, caddisflies)

 A few years?

 Improve fish condition

 Several years?

Midge 

(Chironomidae)

Caddisfly

(Trichoptera)

Yum

6
Design of Bug Flows

 Give bugs the “weekends off”

 Stable, low flows on weekends, May-August

 Eggs laid on weekends won’t dry/die

Tested at Glen Canyon Dam 

2018, 2019, 2020 7
How we monitor Bug Flows (1)

 Citizen science light trapping

 Give river guides a light trap

 1 hr, at dusk, nightly

 Typical year:

 757 samples

 April to September

 Canyon-wide

8
How we monitor Bug Flows (2)

 Citizen science light trapping

 Give river guides a light trap

 1 hr, at dusk, nightly

 Typical year:

 757 samples

 April to September

 Canyon-wide

 2020 (COVID closures):

 355 samples

 Mid-June to September

 Unusual focus on Lees 

Ferry, Phantom Ranch

9
What have we learned? (1)

Let’s unpack these...

10
What have we learned? (2)

Caddisflies enter the scene

 ...but why so 

quickly?

Unpublished data, subject to 

change, do not cite.

11
What have we learned? (3)

 Midges counts unchanged

 Predicted 27% 

increase

 ...but do we 

trust 2020?

Unpublished data, subject to 

change, do not cite.

12
What have we learned? (4)

 Midges counts unchanged

 Predicted 27% 

increase

 Total aquatic 

abundance

increases 

~20%

Unpublished data, subject to 

change, do not cite.

13
What have we learned? (5) 

 Midge spatial “sine wave”

 2018: Breaks down

 2019: More typical

 2020: Too few samples (COVID)

Unpublished data, subject to 

change, do not cite.

14
What have we learned? (6) 

 Midge spatial “sine wave”

 2018: Breaks down

 2019: More typical

 2020: Too few samples (COVID)

 Caddisflies 

go where 

chub live

2018-2020

Hydropsychids (Fall Cyn)

~0 abundance pre-2018

2012-2017

Hydroptilids (LCR)

2018-2020

Unpublished data, subject to change, do not cite. 

Courtesy of Anya Metcalfe.

15
Bug Flows is about more than eggs (1)

Increased weekend GPP (algae growth)

 See Deemer and Yackulic’s presentation!

FY21-23 TWP,

Project F.

16
Bug Flows is about more than eggs (2) 

 Increased weekend GPP

 Increased weekend emergence

Unpublished data, subject to change, 

do not cite.

17
Bug Flows is about more than eggs (3) 

 Increased weekend GPP

 Increased weekend emergence

 Improved weekend fishing

Metcalfe et al. 2020 

Boatman’s Quarterly Review

18
Bug Flows aren’t the only driver (1) 

Spring “mud”

 Affects midge and 

caddis timing 

(and size?)

Unpublished data, subject to change, 

do not cite.

19
Bug Flows aren’t the only driver (2)

Fall “mud”

 Affects caddis 

(but not midge) 

survival?

Cumulative suspended silts and clays 1 Sep to 1 Nov (year prior; mg/L)

With thanks to Craig Ellsworth! Unpublished data, subject to change, 

do not cite.

20
Bug Flows aren’t the only driver (3)

Temperature, nutrients, substrate

 See Michael Cavallaro’s 

poster about Davis Dam!

FY21-23 TWP,

Project F.

21
What can Bug Flows still teach us? (1)

Links to fish

2018-2020

2018-2020

Unpublished data, subject to change, do not cite. 

Courtesy of Anya Metcalfe.

22
What can Bug Flows still teach us? (2)

Links to other 

drivers

Cumulative suspended silts and clays 1 Sep to 1 Nov (year prior; mg/L)

Unpublished data, subject to change, 

do not cite.

23
What can Bug Flows still teach us? (3)

 Definitive spatial change

 Is egg-laying hypothesis 

viable?

2020? +?

Unpublished data, subject to change, 

do not cite.

24
What can Bug Flows still teach us? (4)

Long-term trajectories

FY21-23 TWP,

Project F.

25
Why Bug Flows? (2)

1. River dominated by 1 taxon (midges)

 Low diversity = low resilience

2. Total insect abundance low

 Not enough “bug meat” for fish

3. Insect abundance not distributed evenly

 Peaks/troughs of “bug meat”

 Not where we want it 

(for fish)

Cross et al. 2013 Ecol. Monographs;

Kennedy et al. 2016 BioScience

26
Why not Bug Flows?

 Tangible weekend benefits

 GPP (algae), fishing, bug emergence

 Possible caddisfly benefits

 Into chub reaches, population increase

 Critical uncertainties: Insects

 Spatial “sine wave”, egg-laying success

 Interaction with sediment/other conditions

 Critical uncertainties: Fish

 Feeding/diet link to insect increases?

 Hydropower cost

Unpublished data, subject to change, 

do not cite.

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