Updates on 

1. Bright Angel Creek Trout Removal and

2. Brown Trout Movement Modeling 

Study

Robert Schelly1, Charles Yackulic4, Emily Omana Smith1, Rebecca 

Koller1, and Brian D. Healy1,2,3

1Science and Resource Management, Grand Canyon National Park, Flagstaff, AZ 86001, 

USA 2Department of Watershed Sciences, Utah State University, Logan, UT 84322, USA 

3Ecology Center, Utah State University, Logan, UT 84322, USA

4USGS-Grand Canyon Monitoring and Research Center, Flagstaff, AZ 86001, USA
Collaborating agencies:
Project title: Bright Angel Creek Trout Removal

• Project elements: Not included in AMP workplan; relates to project H

objectives

• Project Objectives: Nonnative fish control

• LTEMP goals addressed:

• 3. Humpback Chub. Meet humpback chub recovery goals, including maintaining a self-sustaining

population, spawning habitat, and aggregations in the Colorado River and its tributaries below Glen

Canyon Dam.

• 5. Other Native Fish. Maintain self-sustaining native fish species populations and their habitats in their

natural ranges on the Colorado River and its tributaries.

• 10. Nonnative Invasive Species. Minimize or reduce the presence and expansion of aquatic nonnative

invasive species.

• Funding amount and source: FY2020 - $306,000 for brown trout control

from Bureau of Reclamation, with other funding from NPS and Grand

Canyon Conservancy

• Cooperators – see previous slide

• Products:

• Annual reports to Reclamation

• Manuscript in prep. on brown trout movement modeling with PIT-tag data
1. Bright Angel Creek trout removal update
Beneficial use
Bright Angel Creek Trout 

Removal: first 5 seasons

• Steady production 

of young-of-year 

cohorts (75-200 mm 

TL)

• Declines driven by 

reductions in larger 

size-classes, age-1 

and older fish

• No high-magnitude 

spring runoff floods 

during BNT 

emergence period

• High-magnitude, 

short-duration 

monsoonal floods 

typical July- September
Brown Trout 

resurgence in 

BAC in 2020-21

• Driven by large young-of-year

cohort, with fish 80-200 mm 

TL

• Raw numbers rival early years 

of project

• Similar large year class of 

rainbow trout, n=2607
Strong YOY Brown 

Trout cohorts 

compared

• This season’s lengthfrequency is reminiscent of 

2013-14, minus the age-1 and 

older size-classes
Bright Angel Creek hydrographs for 2019 and 2020

• High-magnitude 

early spring floods 

and a sustained 

high-magnitude 

runoff in 2019 may 

have disfavored 

newly emerged 

Brown Trout

• Lack of early spring 

floods and lowmagnitude runoff in 

2020 may have 

allowed for high 

survival of newly 

emerged trout
Reproductive 

potential in 

preceding seasons

• Presently less common to see 

a ripe female Brown Trout 

<300 mm TL

• In early years of project, rare 

to see ripe female Brown 

Trout <200 mm TL; many ripe 

females from 200 mm TL and 

larger

• Interpretation: female Brown 

Trout in their second year are 

growing larger thanks to 

lower densities

• The size of the 2020 cohort 

demonstrates the 

reproductive potential of 

even a small number of 

spawning females
Stream 

Renovation: a 

future possibility

• Renovation of BAC upstream 

of Transept Barrier would 

eliminate trout production 

from more than 5 miles of 

creek

• Reach 5 includes deep, 

electrofishing invulnerable 

pools
Potential barriers: 

Split-Rock Falls (left) and Above Transept (right)
2. Brown Trout movement: PIT-tag data
Brown Trout whitepaper modeling of Lees 

Ferry increases

• Size-class distribution flipped

• Increased immigration 

beginning in fall 2014

• Increased reproduction in 

2011, 2013, and from 2015 

onward
Colorado River at Lees Ferry Hydrograph 

(2000-2020)

• Fall HFEs: blue 

arrows (2004, 2012, 

2013, 2014, 2016, 

2018)

• BAC weir operation: 

gray bars

• Only 1 spring HFE: 

2008

• Only 1 equalization 

flow: 2011

• Winter BAC weir 

operation constant, 

and fall HFEs 

common, during 

period of Lees Ferry 

BNT increase
BAC Weir Captures
Hypotheses for increased Brown Trout 

immigration into Lees Ferry (Runge et al. 2018)

• Fall HFEs cue ripe and gravid fish to migrate. High variance

in flow and temperature triggers migration to spawning

areas (Ovidio et al. 1998)

• Bright Angel Creek rendered inaccessible by weir

• Compensatory reproduction in BAC following removals, with

upstream movement of large cohort

• System-wide reduction in food resources induces upstream

migration
Modeling BNT movement with 

20 yrs of PIT-tag recapture 

data

• Manuscript in preparation with Charles Yackulic and Brian 

Healy

• Data from GCDAMP sampling between 2000-2019:

system-wide and Lees Ferry monitoring of large-bodied 

fishes (AZGFD), near-shore ecology study (GCMRC), 

population dynamics of Rainbow Trout (GCMRC), 

salmonid suppression near LCR confluence (GCMRC), and 

Bright Angel Creek salmonid suppression (NPS), among 

others

• 207 sampling events, 2000-2019

• Brown Trout <200 mm TL excluded to reduce 

heterogeneity in capture probability and survival

• 3747 Brown Trout tagged and released, 399 recaptured 

one or more times
Multistate markrecapture model

• Cauchy distribution for movement 

probability (top right)

• Grand Canyon divided into 61 five-mile 

blocks (Lees to Pearce), with block 62 

representing Bright Angel Creek (captures 

mapped by location in bottom right)

• 4 season time-step: winter (Dec-Feb), 

spring (Mar-May), summer (June-Aug), fall 

(Sept-Nov)

• Dispersal function modified to test for 

directed movement, adding parameters 

for “homing” to Lees Ferry, into Bright 

Angel, and out of Bright Angel

• Time-varying covariates tested: BAC weir 

operation, fall HFEs, fall to winter 

transition when BNT typically spawn

• Three models with fall HFE covariate 

considered, testing influence on upriver 

change in direction of movement, change 

in scale of movemement, and increase in 

movement to Lees Ferry
Best supported 

model with Lees 

Ferry origin

• Greater movement 

into Bright Angel 

Creek in absence of 

weir
Best supported 

model with LCR 

origin

• Again, greater 

movement into 

Bright Angel Creek 

in absence of weir

• Increased 

immigration into 

Lees Ferry in years 

with fall HFEs and 

BAC weir operation
Best supported 

model with BAC 

inflow origin

• Increased 

immigration into 

Lees Ferry in years 

with fall HFEs and 

BAC weir operation
How to Interpret?

• Experimental fall floods increase rates of Brown Trout

immigration into tailwater

• This modeling helps to slightly improve our

understanding of factors driving Brown Trout ecology in

Grand Canyon

• This modeling examined movement only; does not have

bearing on increased reproduction and recruitment of

Brown Trout in Lees Ferry

• There are numerous, sometimes competing, resource

goals factoring in management decisions. Any increases

in understanding of factors influencing Brown Trout may

be helpful to managers in the context of changing

conditions.