Michael D. Yard, GCMRC, Flagstaff, AZ

Josh Korman, Ecometric Research, Vancouver, BC

GCDAMP - Annual Reporting Meeting

January 2017

A Synthesis - What we 

have learned about 

rainbow trout 

movement, growth, 

survival over the study 

period that has 

implications to 

management Dustin Patar

Natal Origin Project 
Adult Humpback Chub A 

Adult Abundance (Age 4+)

Year

19891990199119921993199419951996199719981999200020012002

0

2000

4000

6000

8000

10000

12000

Decline in adult Humpback chub

Coggins et al. 2006
RAINBOW TROUT ABUNDANCE

Findings:

• Efficacy of Mechanical 

Removal

• RBT abundance was high 

and variable, partially 

offset by trout 

immigration

• BNT were more 

predaceous than RBT

• RBT were more 

numerous than BNT

• Predation risk is a 

function of both density 

& predatory behavior 

Coggins et al. 2011

Yard et al. 2011
RAINBOW TROUT ABUNDANCE

Questions:

• What controls trout 

abundance?

• Where were RBT 

migrants originating 

from?

Questions:

• What controls trout 

abundance?

• Where were RBT 

migrants originating 

from?

• How many sub-adult HBC 

move into the mainstem?

• How variable was subadult HBC survival?

• Was there a relationship 

between HBC survival & 

RBT abundance?

? Chub

Coggins et al. 2011

• Trout were not removed 

from the control site 

• 80% decline over 4 years

• Major truncation occurred 

between 2004 & 2005

• Similar to 2014 & 2015
Questions:

• What controls trout 

abundance?

• Where were RBT 

migrants originating 

from?

• How many sub-adult HBC 

move into the mainstem?

• How variable was subadult HBC survival?

• Was there a relationship 

between HBC survival & 

RBT abundance?

RAINBOW TROUT ABUNDANCE Outcome:

• Develop alternative 

sampling methods for 

determining:

• Abundance

• Vital rates

• Natal Origin Project

• Movement

• Trout dynamics

• NSE/JCM Projects

• Juvenile HBC survival

• Regulating factors

Coggins et al. 2011
Movement Distance (km)

-4 -2 0 2 4

Lower 2.5% = -2.7 km

Upper 97.5% = 2.9 km

Movement Based on Tag Recoveries

N=16,379

• Majority of rainbow trout exhibit limited 

movement based on differences between 

release and recapture locations.

• Taggable size is ≥ 75 mm FL

• Moderate to large sizes

• 95% of recaps moved no more than

• -2.7 km upstream

• 2.9 km downstream

Upstream Downstream

Korman et al. 2016 & and 

unpublished data
Movement Probabilities

• There is a low probability for an individual 

fish to move large distances.

• More fish upstream – more fish will move 

downstream

• Abundance is a key factor

Korman et al. 2016

-15 -10 -5 0 5 10 15

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Movement Distance (km)

Probability

I

II

III

IVa
Reach-wide trout abundance and range: estimates between 2012-2014

• Dispersal from upstream sources depends on the trout 

abundance(s) in each of the upstream reaches.

• The number of migrants decrease in relation to increasing 

distance from point of origination. 

Distance from Glen Canyon Dam (km)

Abundance ('000s per km)

0 20 40 60 80 100 120 140

0

5

10

15

20

I II III IVa

Korman et al. 2016

Below the LCR: IVb

Lees Ferry Houserock

Buckfarm

Above the LCR: IVa
Modeled comparisons

• Equivalent results between two independent models

• Recruitment in the reach below the LCR can be accounted 

for solely by immigrants from upstream sources 

0

2,500

5,000

7,500

10,000

12,500

15,000

Across-Reach

Movement Model - IVb

Jolly-Seber

Model - IVb

Predicted Immigration Results 

Below the LCR (IV b)

Reach IVa (122-124 rkm)

Reach III (72-122 rkm)

Reach II (25-72 rkm)

Reach I (0-25 rkm)

Korman et al. 2016

Estimates reflect the reach below the LCR
0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

30-3940-4950-5960-6970-7980-8990-99

100-109110-119120-129130-139140-149150-159160-169170-179180-189190-199200-209210-219220-229230-239240-249250-259260-269270-279280-289290-299300-309310-319320-329330-339340-349350-359360-369370-379380-389390-399400-409410-419420-429

Relative Frequency

Size Classes

July 2016 - Lees Ferry Size Distribution

2016 Cohort

32% 2015 Cohort & Previous Cohorts

N = 1,282

Provisional data

• July 2016 – Length 

frequency distribution

• Age0 comprised 32% of 

total catch

• Moderate recruitment 

event compared to previous 

years 

Age0 Age1 

Age1 + Age1

∞
0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

30-39

40-49

50-59

60-6970-79

80-89

90-99

100-109110-119120-129130-139140-149150-159160-169170-179180-189190-199200-209210-219220-229230-239240-249250-259260-269270-279280-289290-299300-309310-319320-329330-339340-349350-359360-369370-379380-389390-399400-409410-419420-429

Relative Frequency

Size Classes

July 2016 - HouseRock Size Distribution

2016 Cohort

2015 Cohort & Previous Cohorts

Age0 - 6%

N = 788

• Age0 comprise 6% of 

HouseRock’s July 2016 catch

• Reach morphology and 

hydrology are not 

considered suitable for 

reproduction 

Provisional data
0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

30-3940-4950-5960-6970-7980-8990-99

100-109110-119120-129130-139140-149150-159160-169170-179180-189190-199200-209210-219220-229230-239240-249250-259260-269270-279280-289290-299300-309310-319320-329330-339340-349350-359360-369370-379380-389390-399400-409410-419420-429

Relative Frequency

Size Classes

July 2016 - Buckfarm Size Distribution

2016 Cohort

2015 Cohort & Previous Cohorts

N = 341

Preliminary data

• July 2016 - Age0 comprise 

1% of Buckfarm’s catch

Age0 - 1%
0

0.05

0.1

0.15

0.2

0.25

0.3

30-3940-4950-5960-69

70-79

80-8990-99

100-109110-119120-129130-139140-149150-159160-169170-179180-189190-199200-209210-219220-229230-239240-249250-259260-269270-279280-289290-299300-309310-319320-329330-339340-349350-359360-369370-379380-389390-399400-409410-419450-459

Relative Frequency

Size Classes

September 2016 - Lees Ferry Size Distribution

2016 Cohort

2015 Cohort & Previous Cohorts

N = 4063

• Age0 comprise 90% of Lees 

Ferry’s September 2016 

catch

• In two months this size class 

dominated the total catch 

• Total catch doubled 

• 1st strong year class since 

2011 

Provisional data

Age0 - 90%
0

0.05

0.1

0.15

0.2

0.25

0.3

30-3940-4950-5960-6970-7980-8990-99

100-109110-119120-129130-139140-149150-159160-169170-179180-189190-199200-209210-219220-229230-239240-249250-259260-269270-279280-289290-299300-309310-319320-329330-339340-349350-359360-369370-379380-389390-399400-409410-419450-459

Relative Frequency

Size Classes

September 2016 - HouseRock Size Distribution

2016 Cohort

2015 Cohort & Previous Cohorts

N = 2,004

• House Rock Reach

• Unlike other downstream 

reaches, Age0 trout are rarely 

part of the catch

• Age0 catch proportion went up 

from 6% to 76%

• This reach rarely detects Age0 

trout in EF catch 

Preliminary data, do not cite

Age0 - 76%
0

0.05

0.1

0.15

0.2

0.25

30-3940-4950-5960-6970-7980-8990-99

100-109110-119120-129130-139140-149150-159160-169170-179180-189190-199200-209210-219220-229230-239240-249250-259260-269270-279280-289290-299300-309310-319320-329330-339340-349350-359360-369370-379380-389390-399400-409410-419450-459

Relative Frequency

Size Classes

September 2016 - Buckfarm Size Distribution

2016 Cohort

2015 Cohort & Previous Cohorts

N = 441

• Age0 catch proportion went 

up from 1% to 60% of catch

• Why didn’t we see a higher 

proportion of age0’s in July?

• Length frequency 

comparisons made between 

Lees Ferry and all of the 

downstream reaches 

indicate similar size and 

likely hatch date. 

• 2011 Age0 cohort was 

substantially larger than 

2016 cohort

• This strongly suggests that 

Lees Ferry Age0 recruits 

move downstream and 

repopulate Marble Canyon. 

Age0 - 60%

Preliminary data, do not cite
Movement of RBT > 75 mm

• Dispersal from upstream sources depends in part 

on the trout abundance(s) in each of the 

upstream reaches.

• Only 1.9% of recaptures were from reaches other 

than the one they were released in.

• Number of migrants decreases in relation to 

increasing distance from point of origination.

Recruitment is strongly linked to: 

• Flow 

• Equalization-2011 [1997 ? ]), - Korman et al. 2016

• Spring HFE – 2008 [1996 ? ]) - Korman et al. 2011, 2012 

• LSSF [2000 ? ]

• Growth (2016) - Yard al. 2017 

Age0 Recruits

Adult 

Population 

High Growth

&

Condition

Movement

• Growth-dependent movement

• Density-dependent movement

Increase in Abundance

Uncertainties

• Are the number of migrants that move into 

Marble Canyon proportional to number of 

recruits in Glen Canyon?

Glen Canyon Upper Marble Canyon Preliminary data, do not cite Eastern Grand Canyon
System-wide Decrease in Abundance

Movement of adult RBT (> 75 mm FL) • Reduced abundance in upper reaches reduces the 

number of downstream movers

• Episodic movement occurs under periods of 

environmental stress (reduced growth & condition).

• Boom-bust cycle begins again

Glen Canyon Upper Marble Canyon Eastern Grand Canyon

Adult 

Population 

Age1

+

Preliminary data, do not cite
2002-2006 Reach Iva & IVb

• We have previously reported on substantial decreases in abundance over 

time on a system-wide scale between 2012-2015.

• Temporary increase above and below the LCR, due to influx of migrants

• It is likely, a system-wide collapse in trout occurred between 2002-2005.

• Note the truncation, resulting from poor condition and low survival

Trout abundance

Korman et al. 2016

Yard et al. 2016

Korman et al. 2017 Coggins et al. 2011

Reach I

0

5

10

15

20

25

30

35

Apr12Jul12Sep12Jan13Apr13Jul13Sep13Jan14Apr14Jul14Sep14Jan15Apr15Jul15Sep15Jan16Apr16Jul16Sep16

Reach IVb

0.0

0.2

0.4

0.6

0.8

1.0

Apr12Jul12Sep12Jan13Apr13Jul13Sep13Jan14Apr14Jul14Sep14Jan15Apr15Jul15Sep15Jan16Apr16Jul16Sep16

Abundance ('000s per km)

2012 - 2014

Preliminary data, do not cite
Rainbow Trout Condition System-wide

• We have reported on reduced trout 

growth, condition, and survival.

• This resulted in declining trout 

densities without sufficient 

recruitment to maintain trout 

abundance. 

Reach I

0.8

0.9

1.0

1.1

1.2

1.3 233

6

1683

27

1629

292

838

78

1217

34

1198

88

1423

383

1072

83

1632

38

1458

52

296

Reach II

0.8

0.9

1.0

1.1

1.2

1.3 324

1

1110

87

2876

57

891

60

1672

78

973

78

2497

61

1424

80

2454

83

1488

218

156

Reach III

0.8

0.9

1.0

1.1

1.2

1.3

Apr2012Jul2012Sep2012Jan2013Apr2013Jul2013Sep2013Jan2014Apr2014Jul2014Sep2014

275

8

1057

138

2412

92

1114

90

830

96

848

121

1902

86

1272

113

1393

129

1124

157

108

Reach IVa

0.8

0.9

1.0

1.1

1.2

1.3 133

17

293

59

311

37

367

53

349

57

378

65

604

51

574

43

416

67

470

83

494

Reach IVb

0.8

0.9

1.0

1.1

1.2

1.3

Apr2012Jul2012Sep2012Jan2013Apr2013Jul2013Sep2013Jan2014Apr2014Jul2014Sep2014

76

6

139

12

233

39

320

37

93

29

339

39

361

29

393

49

166

32

387

49

369

Observed (all samples)

Observed (recaptures only)

Predicted (recaptures only)

Relative Condition Factor

Preliminary data, do not cite
• Bioenergetic model estimated a large 

decline in prey consumption, 

• 92% reduction in the amount of 

invertebrate prey consumed

• This suggests a decline in the prey base 

and its availability

• Prey limitation lead to the collapse in 

the trout population, and by extension 

also likely happened in the downstream 

reaches.

• What might be responsible for the 

invertebrate prey decline?

0

10

20

30

40

50

60

70

Dec-11 Jun-12 Dec-12 Jun-13 Dec-13 Jun-14 Dec-14 Jun-15 Dec-15 Jun-16 Dec-16

Prey Intake (Kg AFDM da-1)

75-124

125-174

175-224

225-274

275-324

>325

Lees Ferry Trout Fishery (2012 to 2016)

Provisional analysis
• Reconstructed abundance estimates 

from AGF monitoring data, with 

confidence levels based on a densityindependent model (Korman et al. 2017)

• Lake Powell reservoir storage is 

correlated with the boom-bust cycles.

• Inflow hydrology and reservoir 

limnology likely govern the quality and 

quantity of nutrients supplied to the 

downstream river segments. 

• Nutrient limitation is hypothesized as 

being the “BIG HAMMER” to the riverine 

ecosystem, which needs to be evaluated 

in greater detail in future research

-0.1

0.1

0.3

0.5

0.7

0.9

1.1

1.3

 -

 5

 10

 15

 20

 25

 30

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

Abundance in Glen Canyon (millons)

Average Annual Reservoir Volume 

(Millon acer feet)

Lake Powell Storage

Mean abundance: density-dependent model

Korman et al. 2017

Lees Ferry Trout Fishery & Lake Powell Storage
CONCLUSIONS

Trout Movement

• There is a relationship between the Lees Ferry sport fishery and LCR inflow area 

• Recruitment is strongly linked to flow, and growth

• Out-migration is related to density- and growth-dependent conditions

• Migrants (Age-0, untaggable sized fish) repopulate upper Marble Canyon between July & September 

• Narrow window of time for conducting experimental TMF

• Trout density in upper reaches determines the number of larger migrants dispersing to the LCR

• Uncertainties –

• Are the number of migrants that move into Marble Canyon proportional to number of recruits in Glen Canyon?

• What causes Age0 movement out of Glen Canyon, growth or density?

Variability in fish abundance and vital rates

• Trout population dynamics appear to be driven by prey availability (bottom-up effects)

• Upper Basin inflow hydrology and reservoir limnology likely linked to trout boom-bust cycles.

• (Nutrients  Primary Producers  Secondary Producers  Fish Communities)

• FUTURE MONITORING and RESEARCH – Need to better understand the reservoir limnology and nutrient supply, delivery, 

and cycling in the river.

Control BNT

(Objective based)

Decision Making Tree 

Controlling BNT in Lees Ferry

STOP

Short-term Implement Physical 

Control Measures

(Y/N) Y/N

Determine 

Efficacy

Adjustment 

(+ or -)

Mechanical Removal

Directed Netting

Focused Angling

REDD Disturbance

YY Male BNT broodstock

Kitchen Sink

Public 

Outreach

Determine 

Efficacy

Adjustment 

(+ or -)

STOP

Trout Management 

Flows

(Y/N) Y/N

Hydrology

Timing

Magnitude

Frequency

Prolonged 

Maintenance

Y/N

Long-term Long-term 

Plan

RECONSIDER IMPLEMENTATION

Y/N
Don’t perform CPR on distal 

extremities 

LCR

TMF

transfusion
0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

30-3440-4445-4950-5455-5960-6465-6970-7475-7980-8485-8990-9495-99

100-104105-109110-114115-119120-124125-129130-134135-139140-144145-149150-154155-159160-164165-169170-174175-180

Relative Frequency

Size Classes

Size Distribution of 2011 Super-cohort

Nov 2011 - Lees Ferry

Korman et al. 2016

Lees Ferry 

November 2011 
0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

30-3440-4445-4950-5455-5960-6465-6970-7475-7980-8485-8990-9495-99

100-104105-109110-114115-119120-124125-129130-134135-139140-144145-149150-154155-159160-164165-169170-174175-180

Relative Frequency

Size Classes

Size Distribution of 2011 Super-cohort

Nov 2011 - Lees Ferry

April 2012 - Lees Ferry

Lees Ferry 

November 2011 April 2012 

Korman et al. 2016

• Minimal growth over a 6 

month period in Lees Ferry

• Differences in movement 

rates are often related to 

variation in energetic 

condition, essentially 

growth
0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

30-3440-4445-4950-5455-5960-6465-6970-7475-7980-8485-8990-9495-99

100-104105-109110-114115-119120-124125-129130-134135-139140-144145-149150-154155-159160-164165-169170-174175-180

Relative Frequency

Size Classes

Size Distribution of 2011 Super-cohort

Nov 2011 - Lees Ferry

April 2012 - Lees Ferry

April 2012 - HouseRock

April 2012 - Buckfarm

November 2011 April 2012 

et al. 2016, Yard et al. 2016

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

30-3440-4445-4950-5455-5960-6465-6970-7475-7980-8485-8990-9495-99

100-104105-109110-114115-119120-124125-129

130-134

135-139140-144145-149150-154155-159160-164165-169170-174175-180

Relative Frequency

Size Classes

Size Distribution of 2011 Super-cohort

Nov 2011 - Lees Ferry

April 2012 - Lees Ferry

April 2012 - HouseRock

April 2012 - Buckfarm

Lees Ferry

November 2011 

Upper Marble Cyn

April 2012 

• The 2011 cohort in Upper 

Marble Canyon grew 

substantially more than in 

Lees Ferry

• Minimal evidence of 

recruitment have been 

observed in subsequent 

years 

• It is likely this cohort 

migrated into Marble 

Canyon prior to initiating 

the NO study

Korman et al. 2016