U.S. Department of the Interior

U.S. Geological Survey

Foodweb Update

By: Theodore Kennedy, Jeff Muehlbauer, 

Charles Yackulic

Email: tkennedy@usgs.gov

Originally presented January 28, 2014 at Annual 

Reporting Meeting in Phoenix, AZ
Outline

 1) Previous findings—food limitation of fishes

 2) Why are fish food limited?

 Invertebrate assemblage is IMPAIRED

 3) Evidence that normal dam operations 

affect extant prey base

 Drift studies

 Emergence studies

 4) Conclusions 
Previous findings

From: Kennedy et al. 2013, 

Cross et al. 2013

Invertebrate production

-Downstream decline

-Shift towards aquatic 

insects

Fish production

-No pronounced decline

-Shift from trout to bottomfeeding suckers 
Previous findings

--Fish populations are food limited. 

--Food web in Glen Canyon is simple and unstable.

--Midges and blackflies key prey items everywhere.

--Midges and blackflies are the only aquatic insects. 

From Kennedy et al. 2013,

Cross et al. 2013
But is having only two types of 

insects unusual for a tailwater?

 %EPT: Nationally accepted metric for 

assessing stream health

 DIRECT measure of the ability of a stream to 

support aquatic life

Ephemeroptera (mayflies) Plecoptera (stoneflies) Trichoptera (caddisflies)
But is having only two types of 

insects unusual for a tailwater?

 %EPT: Nationally accepted metric for 

assessing stream health

 DIRECT measure of the ability of a stream to 

support aquatic life

 EPT = 

# oooo EE,PP,TT

tt tttttt # oooo iiiiiiiiii iiiiii iiii

Ephemeroptera (mayflies) Plecoptera (stoneflies) Trichoptera (caddisflies)
Yes, having only two types of insects 

(and no EPT) is unusual

Key: 1) Colorado River, 2) Kootenai River, 3) Flathead River, 4) Green River, 5) Madison River, 6) San Juan 

River, 7) Bright Angel Creek, 8) Shinumo Creek, 9) Havasu Creek. Grand Canyon tributary data courtesy of Brian 

Healy, NPS. Regulated rivers data courtesy of Kim Dibble, USGS. 

Glen Canyon 

invertebrate 

assemblage is 

IMPAIRED

Grand Canyon 

tributaries

Regulated 

Rivers

Glen Canyon

Dam tailwater

Preliminary data, subject to revision, do not cite
U.S. Department of the Interior

U.S. Geological Survey

(Bright Angel, Havasu, Shinumo Creeks)

(Colorado River below Glen Canyon Dam)

Scuds (Gammaridae)

Bladder Snails (Physidae)

 Clams (Sphaeriidae)

Snailcase Caddisflies (Helicopsychidae)

Blue-Winged Olive Mayflies (Baetidae)

Netspinning Caddisflies (Hydropsychidae)

Dance Flies (Empididae)

Riffle beetles (Elmidae)

Microcaddisflies (Hydroptilidae)

Midges (Chironomidae)

Blackflies (Simuliiidae)

Worms (Oligochaeta)

Flatworms (Planariidae)

Mites (Hydracarina)

New Zealand Mud Snails 

(Hydrobiidae)

Blue Quill Mayflies (Leptophlebiidae)

 Winter Stoneflies (Capniidae)

 Green Stoneflies (Chloroperlidae)

Little Sedge Caddisflies (Philopotamidae)

 Dobsonflies (Corydalidae)

 Damselflies (Coenagrionidae)

 Grass Moths (Crambidae)

 Soldierflies (Stratiomyidae)

 Horseflies (Tabanidae)

 Spiny Crawler Mayflies (Ephemerellidae)

 Flatheaded Mayflies (Heptageniidae)

 Little Stout Crawler Mayflies (Leptohyphidae)

Humpless Caddisflies (Brachycentridae)

Saddlecase Caddisflies (Glossosomatidae)

Green Sedge Caddisflies (Rhyacophilidae)

Scuds (Hyallellidae)

Craneflies (Tipulidae)

 Pond Snails (Lymnaeidae)

Grand Canyon 

Tributaries

Upper Basin

Grand Canyon

(Flaming Gorge, Navajo 

Dams)

Aquatic Invertebrate Families in the Colorado River Basin

Grand Canyon tributaries

more similar to Upper Basin tailwaters

than the mainstem

Preliminary data, subject to revision, do not cite
U.S. Department of the Interior

U.S. Geological Survey

Colorado River in 

Glen Canyon: 

Genera Richness= 7, 

EPT= 0

Green River below Flaming Gorge 

Dam: Genera Richness =29, 

EPT=14

Grand Canyon Tributaries 

(Bright Angel, Shinumo, Havasu): 

Genera Richness= 28, EPT= 14

San Juan River below 

Navajo Dam: 

Genera Richness= 13, 

EPT=5

Preliminary data, subject to revision, do not cite
Why are there so few aquatic insects in 

the Colorado River?

Plecoptera (stoneflies)

Trichoptera (caddisflies)

Ephemeroptera (mayflies)

Pre-dam invertebrates

Post-dam invertebrates

Preliminary data, subject to revision, do not cite
Aquatic Insects Have Complex Life 

Cycles

1 mo. to 4 years

Hours to days Minutes to 

Hours
Invertebrate drift

• Fundamental process in streams and river

• Critical to maintenance of invertebrate 

populations

• Key mechanism of resource delivery for 

many fish
Discharge < median

Discharge > median

Discharge (m3·s-1) Benthic density (#·m-2) 

Benthic < median

Benthic > median

Drift increases 

exponentially with 

discharge 

But benthic density is 

also an important 

control

Kennedy et al. 2014, supporting online information
Discharge < median

Discharge > median

Discharge (m3·s-1 Benthic density (#·m-2) )

Benthic < median

Benthic > median

Benthic→Drift Discharge→Drift

Discharge and benthic densities jointly control drift concentrations

Kennedy et al. 2014, supporting online information
Export 100%

10%

1%

0.1%

0.01%

0.001%

0.0001% Export (%/d)

Kennedy et al. 2014

Daily export of Glen Canyon invertebrates past Lees Ferry

(% of total population) 

Banking analogy:

Larval drift export = 

 withdrawals

Adult Egg laying = 

 deposits

To grow account, 

withdrawals (drift) 

must be less than

interest off principal 

(via egg laying)
Evidence for Negative Feedbacks

Benthic (# m-2

)

Drift (# m-3

)

Drift

Preliminary data, subject to revision, do not cite Benthic
Drift varies spatially, highest below 

riffles

River mile

Shear stress

(N/m

2

)

Midge drift

(#/m

3

)

0

10

20

20

0

40

60

80

Preliminary data, subject to revision, do not cite
 Advantages of this approach:

 Critical life stage for aquatic insects

 Integrated in space and time

Emergence

See poster on new 

sticky trap method
Methods

 Standardized light trapping conducted every 

night in camp

 Guides paid $10/sample to ensure high quality 

data (2013 samples cost $6,000)
Now that’s a dataset!

Because of 20+ 

dedicated river 

guides, we have a 

continuous record of 

insect emergence for 

Grand Canyon!

2012

2013

See poster on sample 

tracking

Preliminary data, subject to revision, do not cite
Preliminary data, subject to revision, do not cite

Caddisflies in Grand Canyon

Trichoptera are 

present in Grand 

Canyon!

But they are tiny and 

functionally 

equivalent to midges

And strongly tied 

to tributaries

1 mm

Preliminary data, subject to revision, do not cite
Temporal patterns

Preliminary data, subject to revision, do not cite
Midge Emergence—Spatial Patterns

Peak in lower 

Marble Canyon, 

but abundant 

throughout

Preliminary data, subject to revision, do not cite
Midge Emergence—Spatial Patterns

Abundant near 

and far from 

tributaries

Preliminary data, subject to revision, do not cite
Midge Emergence—Temporal patterns

Preliminary data, subject to revision, do not cite
Midge Emergence--Temporal patterns

Peak 

emergence 

occurs near end 

of month, and 

then declines 

precipitously 

with stepped 

changes in flow

Preliminary data, subject to revision, do not cite
Conclusions

 Invertebrate assemblage is impaired

 Trichoptera are present, but they are strongly 

tied to tributaries

 Evidence that flow management affects larval 

abundance and emergence rates

Preliminary data, subject to revision, do not cite
Why is this important to fisheries 

management?

 There are no ‘big-ticket’ items available for 

fish ANYWHERE

 The average size of EPT is >> than the average 

size of midges and blackflies

 Food web stability

 More invertebrate species = more stable food web 

and fish populations

Preliminary data, subject to revision, do not cite
Acknowledgements SBSC—funding(emergence)

BOR—funding

WAPA—funding (drift) 

NPS—permitting

USGS technicians

 Eric Kortenhoeven

 Anya Fayfer

 Adam Copp

 Connor Phillips

 Tom Quigley

 Moriah Evans

 Josh Smith

 Carol Fritzinger

Thank you Grand Canyon 

River Guides!!

 Scott Jernigan (242)

 Gibney Siemion (183) 

 Bob Dye (173)

 Walker McKay (164)

 GCY (161)

 Kelsey Wogan (124)

 Eric Baade (92)

 O. Roussis

 Kelly McGrath (46)

 Connie Tibbits (38)

And 11 others