Preliminary Update to 

November 16, 201

Grand Canyon Monitoring 

Research Center – USG

Ecosystem Modeling Work

Mesa, AZ

October 13-15, 2010
Workshop Objectives/F

• Review of recent development in native and nonn

population and food production assessments

• Update and evaluate Lees Ferry reach model (Ko

• Update and evaluate LCR reach model (Walters e• Evaluation of LCR model fits, hypotheses (Walter• Policy gaming: use of the models to explore altern

management and non-native fish control policies 

• Development of recommendations for monitoring 

policy tests based on the policy gaming results (W
Food Web Presenta

• Discussion about basal resources of food 

energy flows to native & nonnative fish (RKennedy, Cross, Baxter)

• Discussed New Papers on New Zealand 

(Cross et al., 2010) and 2008 HFE respoal. in review)

• New Production estimates from team we

into ecopath modeling (Walters et al.)

• Discussions about Native and Non Native 

interactions & competition for 3 high qual
Lees Ferry Rainbow Trout Model 

(Korman et al. in prep)

OBJECTIVES : Lees Ferry RBT Modeling • Estimate Inter-annual Trend in Recruitment in Lees Ferry

– Relate to GCD operations and other factors (e.g., basin h

• Estimate extent of outmigration from Lees Ferry to Marble Ca

– evidence for outmigration– # of fish that leave– size and season when outmigration occurs– Inter-annual variation in outmigration (what causes it)

• Estimate Inter-annual trend in recruitment in Marble Canyon

– Is there evidence of substantial local recruitment?

• Estimate inter-annual trend in total abundance in Lees Ferry a

– Relate to management objectives (100 k in LF, 0 in MC)– Support other research objectives (evaluation of LF food 
Main findings from wo

• Severe food limitation in both L

reaches limit total fish abundan

• Food production strongly linked 

LF and downstream turbidity/trinputs in LCR

• Downstream food resources ar

mix of allochthonous and autoc
Main findings from Mo

• Upstream RBT control options stron

by compensatory responses in growsurvival (as per 2003-2005 RTELSS 

• Downstream non-native control of R

would not prevent HBC decline; con

would; this is based on observation 

50% of predation is by each predatresulting in about 50% total mortalitjuvenile HBC when trout are near 2

• Impacts on native fish involve both 

and predation with trout
Where & when to contro

Above Lees Ferry

Lees Ferry to Badger

Eggs and fry

Ineffective due 

to compensatory survival (when by 0

2, flow)

NA 

Juveniles (100-200 mm)

Might be ineffective, 30 days for 75% removal

2011 experime

Larger fish Would be ineffective

(increased compensation)

NA 
How to control rainbow 

• Mechanical removal variants OR Tr• Harvest netting, contract fishing, we• Flow controls, e.g. fast downrampin

severe e.g. 2,500 cfs trout suppressand/or load following (pre-MLFF sty

• Sediment curtain (operate dam to e

natural turbidity OR import fines)
TAKE HOME #1 - It would be hugely 

informing future policy not to control trout at the Little Colorado (LCR) iAdaptive Strategy Concept: We now 

years of reference data from the NeaEcology (NSE) research study showinjuvenile survival rates of native fish in mainstem (preliminary finding), during 

when trout abundances have been thdecades.
TAKE HOME #2 - Our (ecopath) mod

predict that the arrival of large numberainbows will NOT result in substanreduction in survival rates of native measured by NSE sampling already sbecause: (1) turbidity below LCR will rainbow numbers and efficiency; and have low rates of piscivory due to facwarm water. This prediction will fail, irates will be lower than in last two yea(1) water is clear (and/or cold) so manmove down and feed below LCR, and predation-competition interactions leapredation rates than predicted.
TAKE HOME #3 - Further, a High Flo

Experiment (HFE) before summer 20impair our ability to interpret survivestimates, since it is possible that neof sand filling along rocky shorelines reduced carrying capacity of these hajuvenile humpback chub (HBC). Evepoor survival rate in 2011, long term ithe HBC population would not be sevproportion of HBC recruits produced inatural variation in HBC juvenile survrecruitment, long lived species for whrecruitment variation is “normal”).
NOTE: A Presentation by Josh Korm

Progress of Lees Ferry RBT Modeling for the January 2011 Annual ReportinPhoenix, AZ