Michael D. Yard 1 

Josh Korman 2 

1 U.S.G.S., Southwest Biological Science Center

 Grand Canyon Monitoring & Research Center

 Flagstaff, AZ., USA

2 Ecometric Research Inc.

 Vancouver, B.C., V6S 1J3, Canada 

 

Rainbow Trout Growth, 

Condition, Population Dynamics 

and Modeling in Glen Canyon 
Overview- Glen Canyon (2012-2014). 

1. Rainbow trout Abundance

2. Capture probabilities and Catch rates

3. Survival, Recruitment, and Biomass

4. Possible metrics and prescriptive measures 

5. Growth rates and Condition

6. Possible mechanisms

7. Conclusions
Total Abundance ('000s)

Apr12Jul12Sep12Oct12Dec12Jan13Apr13Jul13Sep13Oct13Dec13Jan14Apr14Jul14Sep14Oct14Dec14

0

200

400

600

800

1000

1200

100,000 age-2

+
Capture Probabiltiy

Apr12Jul12Sep12Oct12Dec12Jan13Apr13Jul13Sep13Oct13Dec13Jan14Apr14Jul14Sep14Oct14Dec14

0.00

0.02

0.04

0.06

0.08

0.10

0.12

100

150

200

250

300
-15 -10 -5 0

0

5

10

15

Oct-2013

-15 -10 -5 0

0

5

10

15

Dec-2013

-15 -10 -5 0

0

5

10

15

Oct-2014

-15 -10 -5 0

0

5

10

15

Dec-2014

River Mile

Catch Per Minute

(5.0) (227,000) (3.8) (192,000)

(3.6) (381,000) (2.2) (354,000)

(CPUE) 
Jul12-Sep12

100 150 200 250 300

0.0

0.2

0.4

0.6

0.8

1.0

Jul14-Sep14

100 150 200 250 300

0.0

0.2

0.4

0.6

0.8

1.0

Size Class (mm)

90 Day Survvival Rate

Preliminary findings, do not cite

Glen Canyon Rainbow Trout Fishery

2012

2014
Recruitment('000s)

Apr12Jul12Sep12Oct12Dec12

Jan13Apr13Jul13Sep13Oct13Dec13Jan14Apr14Jul14Sep14Oct14

0

50

100

150

200

Glen Canyon Rainbow Trout Fishery

2012

351,000

2013

66,000

2014

36,000

Combined Annual Recruitment
75-125 125-175 175-225 225-275 >275

Oct-2012

0

10

20

30

40

50

75-125 125-175 175-225 225-275 >275

Dec-2012

0

10

20

30

40

50

75-125 125-175 175-225 225-275 >275

Oct-2013

0

10

20

30

40

50

75-125 125-175 175-225 225-275 >275

Dec-2013

0

10

20

30

40

50

75-125 125-175 175-225 225-275 >275

Oct-2014

0

10

20

30

40

50

75-125 125-175 175-225 225-275 >275

Dec-2014

0

10

20

30

40

50

Size Class (mm)

Biomass (metric tons)

(90 MT) (85 MT)

(70 MT)

(46 MT) (32 MT)

(67 MT)

WHERE’S THE BEEF ? Glen Canyon Rainbow Trout Fishery

2012

2013

2014
Nt1 = Nt0 * S + R

Total Abundance ('000s)

Apr12Jul12Sep12Oct12Dec12Jan13Apr13Jul13Sep13Oct13Dec13Jan14Apr14Jul14Sep14Oct14Dec14

0

200

400

600

800

1000

1200

Recruitment('000s)

Apr12Jul12Sep12Oct12Dec12Jan13Apr13Jul13Sep13Oct13Dec13Jan14Apr14Jul14Sep14Oct14

0

50

100

150

200

Abundance (N)

Recruitment (R)

R = Ndesired * (1 – S

^4)

Survival (S)

Glen Canyon Rainbow Trout Fishery
0 200 400 600 800

-60

-40

-20

0

20

Oct2013-Dec2013

Size at Release (g)

Growth per Month (g)

2013 Glen Canyon Rainbow Trout Fishery

Basal metabolism

(11 – 12.5o

C)
0 200 400 600 800

-60

-40

-20

0

20

Oct2014-Dec2014

Size at Release (g)

Growth per Month (g)

2013 (Oct-Dec)

2014 Glen Canyon Rainbow Trout Fishery

(13.5 – 14oC)

DO - low

Basal metabolism
-15 -10 -5 0

0.6

0.8

1.0

1.2

1.4

2012 75-124 mm

October

December

River Mile

Relative Condition Factor

Glen Canyon Rainbow Trout Fishery 2012

(10.5 – 11.0oC)
-15 -10 -5 0

0.6

0.8

1.0

1.2

1.4

2013 75-124 mm

October

December

River Mile

Relative Condition Factor

Glen Canyon Rainbow Trout Fishery 2013

11-12.5

o

C
Glen Canyon Rainbow Trout Fishery 2014

13.5-14.5

o

C
-15 -10 -5 0

0.6

0.8

1.0

1.2

1.4

2012 275-1000 mm

October

December

River Mile

Relative Condition Factor

Glen Canyon Rainbow Trout Fishery 2012

(10.5 – 11.0oC)
-15 -10 -5 0

0.6

0.8

1.0

1.2

1.4

2013 275-1000 mm

October

December

River Mile

Relative Condition Factor

Glen Canyon Rainbow Trout Fishery 2013

11-12.5

o

C
-15 -10 -5 0

0.6

0.8

1.0

1.2

1.4

2014 275-1000 mm

October

December

River Mile

Relative Condition Factor

2014

13.5-14.5

o

Low DO (6-5)

Glen Canyon Rainbow Trout Fishery
Glen Canyon December 2014
INTERGILL RAKER SPACING - FISH SIZE 

RELATIONSHIP

0.3 – 1.2 

mm (0.6 ) 

0.3 – 1.5 

mm (1.0)

0.3 – 5 

mm (2.5)

Prey Size Increase
Conclusions

1. Glen Canyon rainbow trout population levels have declined since at least 2012 (April 2012), from 

1.1 M to 200 K (December 2014). 

2. Growth rates have declined in recent years, particularly for medium to large sized trout. 

Paradoxically, small fish have higher and more stable growth.

3. Survival rates for the largest size class (>275 mm FL) has declined (late summer & fall-2014). 

4. Condition factors are highly variable (amongst size classes, spatially, and among and within years).

5. Trout biomass in Glen Canyon has declined by 2/3’s.

6. The bio-energetic demand is not being met for larger fish. 

Possible Explanations: 

• Top-down effect on food resources from high trout densities & recruitment events (2011 & 

possibly 2008-2009 [increased survival??]) may have negatively affected the invert- community

• Longitudinal differences in food resources and fish condition cannot be explained by flows or 

water quality alone. One possibility is localized sediment inputs (August 2013) were then 

redistributed during the HFE’s and may have influenced the downstream benthos 

(November 2013 & 2014). 

• Low invertebrate diversity, favoring small prey may be effecting feeding inefficiencies (small 

prey size & allometric relationship of the inter-gill raker spacing) and foraging efficiencies

• Water quality differences between years (elevated temperature and depressed oxygen levels 

during the fall season) have likely increased bioenergetic demand when food was limited.
Conclusions (cont.)

7. Large recruitment events (2011 and 2008-2009 [high survival?]) are the likely 

cause for instability in population. 

8. Reduce instability in trout population cycles by actively managing for recruitment.

• Recruitment can be determined for any desired population size.

• Use trout management flows to reduce excessively large Age-0 cohorts

• Reduce trout biomass levels (focused on catchable sizes) through managed fish 

harvesting

• Change fishing regulations in response to changes in biological conditions, 

(unlimited take (narrow time window), encourage use by other types of anglers, 

fishing derbies, etc..)

10. Future monitoring will be improved by determining abundance, survival, 

recruitment, and growth

• Capture probabilities are highly variable (across size classes, trout densities, seasons, 

and turbidity levels), which influences standard fishery metrics.

• This will influence the observed catch rate metrics (CPU) and catch proportions.