Year 2 of Bug Flows

Ted Kennedy & Jeff Muehlbauer

13 January 2020

Grand Canyon Monitoring and Research Center

Southwest Biological Science Center

U.S. Department of the Interior

U.S. Geological Survey
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

3
Theory behind Bug Flows

Egg mortality 

from “tides” 

limits insects

Kennedy et al. 2016 BioScience 4
Purpose of Bug Flows Experiment

Improve egg-laying conditions 

for insects!

Therefore:

- Increase midge abundance

- Increase sensitive EPT abundance/diversity 

(longer term?)

Ultimately:

- Improve fish food base

5
Design of Bug Flows

 “Give bugs the weekends off!”

 May – August 2018, 2019

 Stable, low flows on summer weekends

 Eggs laid on weekends won’t dry/die

Tu Wed Th Fri Sat Sun Mon

10,000

17,000 Discharge (cfs)

6
Unpublished data, subject to 7

change, do not cite.

Predicted Responses (long-term)

Smoothing

of spatial pattern

More midges

throughout Canyon
Predicted Responses (long-term), cont.

Smoothing

of spatial pattern

More midges

throughout Canyon

More caddisflies

(EPT)

2012 2014 2016

Catch rate

(per hour of light trap)

0

500

Year

Unpublished data, subject to 

change, do not cite.

8
Unpredicted Responses

Anglers Bug Flows

“The bug flows are 

providing great 

weekend fly fishing 

activity....”

leesferrybackhaul.com
Bug Flows = Better Fishing

Metcalfe et al. 2020 Boatman’s Quarterly Review
2019 Light Trap Caveat

 Only 569 / 959 light traps processed

 40% left

 Numbers can still change (dramatically!)

11
Midge Catch

 2017: ~5 years 

of stability

 2018: Stability 

continues

 2019: Stability 

continues?

2012 2014 2016 2018

Year

500

0

Catch rate

(per hour of light trap)

Unpublished data, subject to 

change, do not cite.

12
Caddisfly Catch

 2017: Slow 

increase

 2018: Explosion!

 2019: Back to 

Earth?

2016 2018

Year

2012 2014

200(per hour of light trap)

0

Catch rate

Unpublished data, subject to 

change, do not cite.

13
Caddisfly Spatial Pattern

 2018: canyonwide increase

 2019: still 

impressive?

Unpublished data, subject to 

change, do not cite.

14
Caddisfly Phenology

 2018: early

 2019: late

1.5 months

Unpublished data, subject to 

change, do not cite.

15
Midge Phenology

 2018: very early

 2019: very late 3.5 months

Unpublished data, subject to 

change, do not cite.

16
Midge Spatial Pattern

 2018: Sine wave 

breaks down

 2019: ??

Unpublished data, subject to 

change, do not cite.

17
Conceptual Model

Unpublished data, subject to 

change, do not cite.
Muddying The Waters

 2018: Lots of algae, average temperatures

 2019: Very little algae, warm temperatures

Credit: B. Deemer, USGS Credit: K. Dibble, USGS

Unpublished data, subject to 

change, do not cite.

19
Summary

 Both ‘18 and ‘19 were exceptional years

 Both years complicated by other factors

20
Conclusions

21

BUG FLOWS 2020