U.S. Department of the Interior

U.S. Geological Survey

Foodbase Update
Outline

 FY12 Publications

 Major findings of Foodbase research project 

(2006-2009) and outcomes of PEP 

 Choose your own foodbase adventure:

1. Effects of discharge and benthic abundance on 

invertebrate drift at Lees Ferry

2. Invertebrate drift and rainbow trout diets—Glen and Marble 

Canyon

3. Harnessing the power of citizen science—emergent aquatic 

insect monitoring using light traps

4. Drift distances—characterizing invertebrate drift 

throughout Glen Canyon

5. Identifying controls on algae production at Diamond Creek
 Hall, Kennedy, and Rosi-Marshall. 2012. Air-water oxygen exchange in 

a large whitewater river. Limnology and oceanography: fluids and 

environments 2: 1-11.

 Kennedy, Baxter, Hall, Rosi-Marshall. 2012. A summary of research 

conducted in support of the Glen Canyon Dam Adaptive Management 

Program’s Goal 1—Aquatic Foodbase—Including Proposed Monitoring 

Protocols. Administrative Report provided to TWG and PEP

 Kennedy. In press. Identification and evaluation of scientific 

uncertainties related to fish and aquatic resources in the Colorado 

River, Grand Canyon: summary and interpretation of an expert 

elicitation questionnaire. USGS Scientific Investigations Report.

 Wellard-Kelly, Rosi-Marshall, Kennedy, Hall, Cross, Baxter. In press. 

Macroinvertebrate diets reflect tributary input and turbidity-driven 

changes in food availability in the Colorado River downstream of Glen 

Canyon Dam. Freshwater Science

 Cross, Baxter, Rosi-Marshall, Hall, Kennedy, Donner, Wellard-Kelly, 

Seegert, Behn, and Yard. In revision. Foodweb dynamics in a large 

river discontinuum. Ecological Monographs.
Foodbase Research—Brief Methods

Developed quantitative food 

webs for 6 sites across 3 

years (2007-2009)

Quantitative food webs 

describe how energy moves

through the web 
Findings

As distance from Dam

increases we see: -Increasing eco-trophic

efficiency

Invert production

Fish consumption
Findings

As distance from 

Dam increases we 

see:

-Increasing reliance 

on organic matter

-More incorporation

of detritus into food

web
Findings

As distance from Dam

increases we see:

-Increasing complexity

in food webs:

1) greater number of 

interactions

2) higher number of 

interactions per species
Findings

As distance from Dam

increases we see:

-Native fishes dominate

-Food webs have a higher

proportion of ‘weak’

interactions

-Fish trophic position 

decreases
Food web metrics—Summary 

Metric Glen Canyon Grand Canyon

Eco-trophic Efficiency Low High

Complexity Less Complex More Complex

Resource Base Algae Algae and Detritus

Proportion of weak 

interactions

Low High
Food web stability

 What is it?

 “The likelihood of the persistence of some set 

of interacting species.” (Rooney and McCann 

2012)

 Why does this matter?

 Complex > Simple

 Algae + detritus > algae alone

 Strong and weak > strong only
Food web response to 2008 HFE

The 2008 artificial flood 

caused a larger shift in the 

structure and function of 

Glen Canyon food web 

relative to downstream 

food webs

In other words, the Glen 

Canyon food web appears 

less resistant to 

perturbation than Grand 

Canyon food webs
Conclusions

 Based on theory and other studies, Glen 

Canyon food web appears relatively unstable

 Food webs as stock portfolios:

 Glen Canyon food web has a small number of very volatile 

stocks

 Downstream food webs have a larger and more balanced 

portfolio of stocks

 In the absence of changes in food web 

structure (i.e., more diverse invertebrate 

assemblage), it is possible that rainbow trout 

populations will continue to fluctuate through 

time 
PEP review

 Timeline

 PEP convened Jan 2012

 Panel Chair and Kennedy Report at April 2012 TWG

 Outcomes/recommendations incorporated into FY 13-14 

workplan

 Outcomes

 Focus on invertebrate drift as monitoring metric, but need a 

better handle on spatial and temporal variation

 Continue integrating information on prey base with 

information on fish feeding habits

 Evaluate emergence monitoring as a surrogate for benthic 

monitoring
Technicians

 Adam Copp (natal origins river trips, 

database)

 Joshua Smith (natal origins river trips, diet 

samples)

 Moriah Evans (drift samples)

 Connor Phillips (drift samples)

 Thomas Quigley (drift samples)

 Anya Fayfer (light trap samples)

 Eric Kortenhoeven (light trap samples)
Outline

 Choose your own foodbase adventure:

1. Effects of discharge and benthic abundance on 

invertebrate drift at Lees Ferry

2. Invertebrate drift and rainbow trout diets—Glen and Marble 

Canyon

3. Harnessing the power of citizen science—emergent aquatic 

insect monitoring using light traps

4. Drift distances—characterizing invertebrate drift 

throughout Glen Canyon

5. Identifying controls on algae production at Diamond Creek
Invertebrate Drift at Lees Ferry

 Goal: Identify relative roles of discharge and 

benthic density on invertebrate drift rates in 

Glen Canyon

 Data: Monthly measurements of benthic and 

drifting invertebrates (Dec 2007—May 2009)

 Benthic—20 samples per month from all habitat types (from 

RM-8.5 to -3.5)

 Drift—15 samples per month across a range of discharges (at 

boatramp only)
The Data Drift (# m-3)

Benthic (# m-2)

Drift

Benthic
Modeling Drift

C = Drift concentration (#/m3)

B = benthic density (#/m2)

Q = Discharge (m3/s)

a = intercept (estimated)

f and g = exponents (estimated)
Model Output
Model Summary

Taxa f (benthic ) g (discharge)

Gammarus 1.0 3.7

Mudsnails 1.0 3.7

Oligochaete

worms

1.6 0

Black flies 0.35 -2.8

Midges 1.0 1.7
Caveats

 Only evaluated short-term effects of 

discharge on drift (i.e., what happens over the 

course of a day)

 Over longer-time scales (i.e., weeks-months)

High discharge →high drift →low benthic?
Conclusions

 Benthic density and discharge both affect 

drift densities in Glen Canyon

 Variation among taxa is consistent with other 

studies

 Black flies and midges drift at high rates relative to other taxa

 Larger taxa (Gammarus and mudsnails) show stronger 

relation with discharge 

Acknowledgements: Thanks to WAPA for 

providing funding for this study.
Invertebrate drift and RBT Diets

 Collaborating with Natal Origins project to 

estimate growth potential for RBT throughout 

Glen and Grand Canyon

 Up to 20 RBT diets from each of 5 sampling 

reaches

 stratified by fork length ( >200mm vs. < 200 mm)

 Drift—20 drift samples from each of 5 

sampling reaches

 6 midday

 14 during crepuscular period

 5 minute tows or ~50 m3 per sample
April
April
Seasonal Changes in Drift
Conclusions

 Diets mirror drift rates, with some exceptions 

 Apparently high selectivity for midge pupae, avoidance of 

tubificid worms

 Midges dominate drift and diets in April (>90% 

of diet at sites in Grand Canyon)

 Downstream increase in drift and diet 

contents defies conventional wisdom about 

prey availability in the Colorado River

 Competition?
Emergence monitoring

 One major flaw of previous invertebrate 

monitoring in Grand Canyon is inadequate 

temporal and spatial resolution of sampling

 E.g., Entire cohorts of short-lived midges and 

black flies could be missed with quarterly 

sampling

 Two dominant invertebrate prey items for fish 

are both insects—black flies and midges 

(Cross and others in review)

 Emergence flux is highly correlated with 

benthic production (Statzner and Resh 1993)
Emergence monitoring

 Goal: Evaluate whether monitoring 

emergence flux is a useful surrogate for 

traditional benthic monitoring

 Worked with 7 commercial river guides to 

pilot in FY2012

 Bob Dye NPS

 Kelsey Wogan Grand Canyon Youth

 Gibney Siemion

 Walker McKay

 Derrick Spice

 Eric Baade

 Scott Jernigan
Emergence monitoring

 Standardized light trapping conducted every 

night in camp

 2 traps per night (waters edge, 45k cfs stage line)

 Traps turned on within an hour of sunset

 Trap left on for 1hr

 River mile, air temp, substrate (e.g., grass, sand), 

and wind speed recorded

 Sampling conducted from April-October

 N= >950 samples (230 processed)
Outreach Flier
Emergence monitoring Chironomid Catch
Emergence monitoring
Conclusions

 Extremely cost effective means of sampling

 Good opportunity for public outreach

 Preliminary data appear promising
 Downstream increase in drift densities 

through Marble Canyon could arise if 

invertebrate drift distances are long (>miles)

 Interpretation of drift densities would 

therefore benefit from an improved 

understanding of drift distances

Drift distances—characterizing 

invertebrate drift throughout Glen Canyon
Drift distances—characterizing 

invertebrate drift throughout Glen Canyon

 But how can begin to get a handle on drift 

distances in a large river?

 Sample intensively along a downstream gradient starting 

from the Dam, where upstream supply = 0, to Lees Ferry

 Hypotheses: 

 Drift densities increase as a function of distance from the 

dam

 Smaller scale variation in drift densities related to local 

geomorphology and/or hydrology 
Drift distances—characterizing 

invertebrate drift throughout Glen Canyon

 Sampling done over 4 consecutive days (Oct 

10-13)

 32 locations through Glen Canyon sampled 

each day

 Sampled intensively from dam to RM-8

 Also sampled intensively in a portion of the 

natal origins reach (~RM -5 to -1.5)

 Constant 8,000 cfs discharge

 5 minute tows or ~50 m3 per sample
Drift distances—characterizing 

invertebrate drift throughout Glen Canyon

 Sampling design allows us to separate spatial 

from temporal variation in drift rates

 Day 1—top to bottom

 Day 2—middle to bottom, then middle to top

 Day 3—bottom to middle, then lost bomb 

(samples not analyzed)

 Day 4—middle to top, middle to bottom
The Data

Taxa Midge

larvae

Midge 

pupae

Midge 

adults

Worms 

(tubifici

d)

Mud 

snails

Scuds Black 

fly

Larvae

Black 

fly 

adults

Black 

fly

pupae

Catch 20,156 709 430 12,699 5,998 236 199 4 1





Conclusions

 Midges dominate the drift in Glen Canyon

 Spatial variation in drift rates of all taxa 

appear to be a function of local conditions 

(substrate, hydrology, predation?) and 

upstream supply 

 Formal analysis....stay tuned
Gross primary production at Diamond 

Creek

 Continuously monitored since spring 2009

 GPP estimated using dissolved oxygen 

budgeting

 Daily GPP estimates modeled as a function 

of:

 Turbidity

 Discharge variation

 Light (from Yard et al 2005)

 Clouds

 Temperature

* Note that several of these are interrelated
The Data
Environmental Conditions
Model output
Out of Sample Comparison
Conclusions

 Numerous factors control algae production at 

Diamond Creek

 Turbidity

 Cloud cover

 Water temperature

 Light

 Discharge variation
Food web response to 2008 HFE

The 2008 artificial flood 

caused a larger shift in the 

structure and function of 

Glen Canyon food web 

relative to downstream 

food webs

In other words, the Glen 

Canyon food web appears 

less resistant to 

perturbation than Grand 

Canyon food webs
The Data