U.S. Department of the Interior

U.S. Geological Survey

Foodbase monitoring and 

research: response to PEP
Outline

 Core Monitoring Information Needs (CMINs)

 Research findings in relation to CMINS

 Proposed foodbase monitoring and research 

in FY12-14
Core Monitoring Information Needs

 1.1.1 Determine and track the composition 

and biomass of primary producers below 

Glen Canyon Dam in conjunction with 

measurements of flow, nutrients, water 

temperature, and light regime.
Flow operations and turbidity control algae production 

in Grand Canyon 

Hall et al. in prep
Turbidity strongly controls algae 

production in Grand Canyon

Hall et al. in prep
Increase in 

summer flow 

lowers GPP, 

likely by 

burying algae 

underwater

Hall et al. in prep
Monitoring Strategy

 Continuous metabolism at water quality 

monitoring sites (RM 0, RM 30, RM 61, RM 87, 

RM 165, RM 225, and in LCR)

 Changes in response to PEP

 Organic matter budgeting scaled back relative to 

original proposal
Core Monitoring Information Needs

 1.2.1 Determine and track the composition 

and biomass of benthic invertebrates below 

Glen Canyon Dam in conjunction with 

measurements of flow, nutrients, water 

temperature, and light regime.
Invertebrate production exhibits stepped 

declines below the Paria and LCR, and 

production below the LCR is extremely low 

relative to other streams and rivers

Cross et al. in prep
High flow events can exert a strong control on 

invertebrate assemblages and secondary 

production in the tailwater reach

Cross et al. (2011)
Proportion of Production 0.0

0.2

0.4

0.6

0.8

1.0

River Mile

0 30 60 125 165 225

0.0

0.2

0.4

0.6

0.8

1.0

2007

2008

Detritus 

Cladophora 

Terrestrial plant material 

Chironomidae 

Simuliidae 

Other aquatic invertebrates 

Terrestrial invertebrates 

Potamopyrgus 

Other 

Fish

-Midges and black flies

- 45-61% of production

-Diatoms

Additional 20-40% of 

production at ‘native fish sites’

Diatoms

Midges

Black flies

Donner and others, in prep

The production of native and non-native fishes through 

the river is fueled principally by two aquatic insect 

taxa—midges and blackflies
2007

River Mile

0 60 225

Production/Demand (g AFDM/m2/yr)

0.0

0.5

1.0

1.5

2.0 2008

0 60 225

Production 

Demand 

*

- Black fly (and midge, not show) production ≈ or < demand by fish

Fish production throughout the river appears limited by 

the availability of high quality prey and fish may exert 

top-down control on these prey
Monitoring Strategy

 Benthic sampling throughout Glen and Grand 

Canyon

 Comprehensive survey once per year (starting in 

FY13)

 To occur when hydropeaking is relatively low and 

benthic biomass is high (May?)

 Cobble habitats in Glen, Marble Canyon, and LCR 

confluence will be sampled quarterly in 

cooperation with natal origins & NSE project. Will 

yield benthic production estimates

 Changes in response to PEP: 

 Benthic production monitoring in key reaches was 

added.
Monitoring Strategy

 Monitoring emergent insects throughout 

Grand Canyon using citizen scientists 

 9 commercial river guides equipped with light trap 

sampling kits that will be deployed from April 

through October

 Anticipate ~1500 samples from throughout Grand 

Canyon

 Changes in response to PEP:

 Strategy completely changed. Original proposal 

called for month long sticky trap deployments at 6 

fixed sites.
Core Monitoring Information Needs

 1.3.1 Determine and track the composition 

and biomass of drift in the Colorado River in 

conjunction with measurements of flow, 

nutrients, water temperature, and light 

regime.
Drift abundance strongly related to 

benthic abundance
Some Taxa More Prone to Drifting 

Than Others
Discharge Regime Does Not Appear 

to Have Strong Affect on Drift 

Biomass
Time of Day is a Big Lever for Some 

Taxa
Drift is direct measure of food 

available to drift feeding fishes 
Monitoring Strategy

 Invertebrate drift measurements in Glen 

Canyon, Marble Canyon, and Diamond Creek

 Collected from thalweg using boats

 Midday and nighttime

 Every 6 weeks

 Quarterly in Marble Canyon and near LCR in 

cooperation with natal origins & NSE

 Changes in response to PEP: drift sampling 

will be done from boats only
Research

 LCR food web study

 In cooperation with FWS 

 Will assess potential for food limitation and 

explore role of LCR hydrology in driving juvenile 

humpback chub dynamics

 Changes in response to PEP: need to study 

tributaries to understand relative importance 

of mainstem
Summary of key points

 FY12-14 monitoring and research is 

integrated into other ongoing projects (natal 

origins, NSE, aggregation monitoring)

 Allows for more rigorous sampling (boat-based 

instead of hike-in)

 Makes use of citizen scientists to monitor 

emergence

 Builds onto GCMRCs water quality 

monitoring program

 Benthic invertebrate production will be 

monitored in key reaches
Update

 Drift rates in Glen Canyon are very low 

(similar to days immediately after 2008 HFE 

when system had been scoured)

 Predation rates on the available drift are very 

high, on order 2-10/day or higher, particularly 

in 2012

 Drift entry rates are likely high (2%+) enough 

to allow depletion of the benthic biomass for 

at least some invertebrate species 

(chironomids, simulids, gammarus)
Update

 Factors that stimulate trout recruitment 

(steady flows, HFEs) likely lead to trout 

densities high enough to cause sustained 

periods (2+ yr) of depletion for those 

invertebrate species

 This implies high probability of trout collapse, 

preceded by increased downstream dispersal of 

juvenile trout (a predator-prey cycle effect)
Update

 It is unlikely that there is an endogenous 

predator-prey cycle between trout and the 

main invertebrates; that cycle would have a 

period of less than 10 yrs, but observed trout 

peaks are about 13-14 yrs apart.

 Low drift densities, lack of large emergence 

hatches, and low swallow abundance all 

indicate that the LF insect foodbase is 

perilously low in 2012.