MACROINVERTEBRATE OVIPOSITION HABITAT SELECTIVITY AND

EGG-MASS DESICCATION TOLERANCES: IMPLICATIONS FOR

POPULATION DYNAMICS IN LARGE REGULATED RIVERS

Freshwater Science. 2020

Scott Miller1,2, Matt Schroer1,2, Jesse Fleri2,

Theodore Kennedy3

1BLM National Aquatic Monitoring Center

2Department of Watershed Sciences, Utah State University

3USGS, Grand Canyon Monitoring and Research Center
Introduction

...the potential for loadfollowing flows associated 

with hydroelectric power 

production to act as a 

population bottleneck for 

aquatic insects via reductions 

in the availability and 

temporal persistence of 

optimal oviposition habitats.

Theory behind the Bugflows 

Experiment at Glen Canyon.
Introduction

Why Flaming Gorge?

Why USU Buglab?

Why WAPA?

• Flaming Gorge has the bugs.

• USU Buglab has a long history of

studying the aquatic foodbase in

the Flaming Gorge tailwater.

• WAPA has been a key player in

the management of the

tailwater fishery.
Hypothesis and research questions

Hypothesis: Load following limits recruitment success of 

aquatic insects, thus altering assemblage composition.
Hypothesis and research questions

Hypothesis: Load following limits recruitment success of 

aquatic insects, thus altering assemblage composition.

Research questions:

1. Are egg masses randomly distributed or differentially 

located in habitats impacted by load following?

2. Does load following reduce the availability of optimal 

oviposition habitats? 

3. What are the implications of artificially high or low 

flows for insect recruitment? 
Study area

Flaming Gorge tailwater

• Green River

• Northeastern Utah

• Load following flows
Study area

Selected three segments for study to represent 

a gradient of hydro-geomorphic conditions 

Tail Race Little Hole Taylor Flat Bridge
Objectives

• Characterize the egglaying habits of four 

widely distributed insect 

taxa, 

• Experimentally 

manipulate substrate 

depth and distance from 

river margins, 

• Quantify oviposition 

habitat availability, and 

• Conduct comprehensive 

laboratory desiccation 

trials.
Oviposition habitat availability and utilization

Three 1.5 km river segments

Flow

= 1.5 km study segment
Oviposition habitat availability and utilization

1.5 km river segments: 

Delineated fast- and slow-water habitats 

Randomly select two of each

Flow = Fast Water (FW) Reaches

= Slow Water (SW) Reaches

= 1.5 km study segment
Oviposition habitat availability and utilization

2 stage sampling 

1st stage (availability)

5 transects with 10 sample pts. per transect
Oviposition habitat availability and utilization

2 stage sampling – 2nd stage (use): 

Stratification to sample rare habitats (15 pts. per stratum)

Total points per reach: 75 - 100
Oviposition target taxa

Surveys conducted for:

• Mayflies (Ephemeroptera): Baetis spp. 

• Caddisflies (Trichoptera):

• Brachycentrus occidentalis 

• Hydropsyche occidentalis 

• Midges (Diptera): Chironomidae Orthocladiinae (likely Eukiefferiella spp.)
Oviposition habitat utilization – RF model results

Predictor B. occidentalis H. occidentalis Orthocladiinae

Distance from bank X X X

Substrate size X X X

Emergent area X X X

Water depth X X X

Embeddedness X

Velocity X

Segment X X

Habitat unit X

R 2 51% 25% 67%
Preference for large, emergent substrates

Ln substrate size (mm)

Ln emergent area (cm2)

Baetis spp. B. occidentalis Chironomidae

Ln Egg abundance

H. occidentalis

Oviposition habitat utilization – RF model results
Oviposition habitat utilization – RF model results

Water depth (cm)

Edge specialists

Open-water 

specialist

Bank distance (m)

Ln Egg abundance

Baetis spp. B. occidentalis Chironomidae H. occidentalis
Oviposition habitat utilization results summary

Egg masses for 3 of 4 taxa located in habitats affected by load following: 

Emergent rocks in the varial zone

Edge specialists

Open-water 

specialist
Load following effects on habitat availability

Load following significantly reduced the availability of optimal 

oviposition habitats – emergent rocks 

800 cfs 1800 cfs
Load following effects on oviposition

Experimental substrate manipulations: 

egg density f(submerged and emergent substrates) 

Load following: high Q Load following: low Q

Caddisflies getting 

ready to oviposit
Load following effects on oviposition

High flows have the potential to reduce egg densities 

by reducing emergent substrates

0

0.5

1

1.5

2

2.5

3

Orthocladiinae Baetis spp.

Egg abundance

Emergent Submerged
Oviposition habitat utilization
Load following effects on egg viability

Low flows have the potential to desiccate eggs and 

reduce hatching success
Consequences of load following for river biodiversity

Load following may limit edge specialists 

that use large, emergent substrates

Edge specialists Open-water 

specialist
Conclusions

• Large river macroinvertebrates disproportionately use edge 

habitat for oviposition

• Large emergent mineral substrates

• Load following can reduce the availability of optimal oviposition 

habitats

• During load following, high and low flows have the potential to 

reduce population recruitment, but by differing mechanisms 

• High: loss of emergent substrates

• Low: egg desiccation

• Timing of load following, both seasonally and within day, could 

be managed to increase recruitment
Publication

• Miller, S.W., M. Schroer, J.R. Fleri, and T.A. Kennedy. 2020. 

Macroinvertebrate oviposition habitat selectivity and egg-mass 

desiccation tolerances: Implications for population dynamics in 

large regulated rivers. Freshwater Science. 39(3):584–599

• https://www.journals.uchicago.edu/doi/pdf/10.1086/710237