Nearshore Ecology of Juveni

Fish in Grand Canyon

Central Objectives and Key C

Bill Pine, Mike Yard, 

Josh Korman, Karin Limbu

Mike Allen, Tom Fraze
Central Study Objective and R

Questions

• Understand how river flow, through i

with physical habitat structure, influesurvival rates of juvenile native fish i

• RQ1: Do steadier flows during summ

increase survival rates?

• RQ2: To what extent does physical h

and backwaters), in conjunction with period, influence survival rates.
Approach

• Estimate site occupancy (pres/abs) and 

abundance of juvenile natives over foutrips (July, Aug, Sept, Oct).

• Survival and growth can then be estim

intervals:

– July-Aug: summer flows (high Q flu– Aug-Sep: transition from flux to ste– Sep-Oct: steady flow

• Examine relationships between occupa

physical site characteristics. Do relatiowith flow regime?
0

50

100150200

July Aug Sep 

Age-0 HBC Abundance 

Flux Flows Stead

Approach (con’t)

transition
Challenges

1. Estimates of growth, occupancy, abu

survival rate may be uncertain due to 

(low numbers and low detection prob

2. Very limited replication (n=3 yrs), sin

modest flow treatment (steady 10 kcfunder fall ‘control’ (ROD) flow (ca. 5

3. Uncertainty in relating flow-depende

meaningful demographic parameters 
4. Change in mainstem abundance throu

solely dependent on physical factors imainstem survival rate 

• recruitment from LCR (otolith microchemist

marking)

• density-dependence in mainstem survival rat• non-native abundance in mainstem

5. Timing of summer-fall flow changes 

changes in other factors that will influand survival

• Fish growth declines through time (water tem• Densities decline through time, which will in
What Can be Learned Over Th

• Will define accuracy and precision of estima

(occupancy), abundance, and survival rates. Nestablishing efficacy of long-term monitoring

• Improved understanding about growth and fa

emigrants to mainstem via otoliths and tagginyoung/small emigrants survive?).

• Improved understanding about habitat use th

and temporal sampling intensity (e.g., backwfluctuating and steady flows).
Long-Term NSE Monitoring Embed

Sensible Long-Term Experimenta

• Real value of an NSE-type project comes from 

growth, occupancy, abundance, and survival ovtime period under contrasting conditions. 

• Although the nature of future experiments is un

likely be differences in mainstem physical condpurposeful experiments or natural variation (e.g

• Initial insights from current NSE project may h

experiments and increase the probability of coninformative experiments.

• Although the scope of this type of long-term pr

it is essential to relate changes in adult HBC abconditions in the mainstem.
Common Characteristics of NSE P

Monitoring of Early Life Stage Surviv

Trout in the Lee’s Ferry Reach (R

• Two well-supported assumptions justify monitori

– Early life stages are more sensitive to changes in habitat 

– Survival of early life stages determines abundance of ad

• Similarities in flow-habitat hypotheses (flow-habi• Many similarities in sampling and analytical meth

experimental design challenges

• Long-term versions of these projects could be use

of both purposeful and natural flow experiments (

any one test)

• Both efforts should be considered core projects if 

understand effects of dam operations on fish popu
2007

2006

2004

0

50,000

100,000150,000200,000250,000

0 500 1000 1500 2000 2500 3000 

Redds

July Age-0 Population Size viable 

• High winter fluctuations killed 25 and 50% of eg

experimental years 2003 and 2004, respectively.

• Strong compensation in early survival rates (e.g., 

that this flow-dependent mortality at moderate ledeposition (# redds) will not effect juvenile abun

Effects of Density Dependence in Su
2008

0

200,000400,000600,000800,000

0 500 1000 1500 2000 2500 300

Redds

July Age-0 Population Size

v

to

Post-HF

? 2009

• Survival of age-0 rainbow trout in the few few mont

30-40 mm) in the Lee’s Ferry Reach after the 2008 Hca. 5-fold higher than before (03-07).

• In the absence of juvenile monitoring, would be unc

large 2008 and 2009 cohort seen in adult monitoring flows, the HFE, or higher egg deposition.

Robust Monitoring Tool to Evaluate 

Flow Experiments
Hypotheses of habitat u

flow sensitivity in large 

High-angle habitatPreferred by larger age-0 troutLess sensitive to variation in flow

Low-an

Preferred by smaMore sensitive to 

Daily Min. Flow

Daily Max. Flow

7 m

Low-velocity-shallow habitatsuitable for small age-0 trout
Age-0 habitat use and mov

June 

Fork Length (mm)

20406080

100

Fork Length (mm)

20406080

100

2004

0

30,00060,00090,000

120,000

Population Size

Low-AngleHigh-Angle

 Apr May Jun Jul Aug Sep Oct Nov

2008

0

100,000200,000300,000400,000500,000600,000

Population Size

 Apr May Jun Jul Aug Sep Oct Nov
Age-0 growth – habitat e

0

20406080

100120

0 30 60 90 120 150 180 210 240 270

Fork Length (mm) Low-Angle

High-Angle

2004

0

20406080

100120

0 30 60 90 

0

20406080

100120

0 30 60 90 120 150 180 210 240 270

Age from Hatch (days)

Fork Length (mm)

2007

0

20406080

100120

0 30 60 9

Ag
20

30405060708090

100110120

0 30 60 90 120 150 180 210 24

Age from Hatch (days)

Fork Length (mm) 

Age-0 growth – year effe
Age-0 mortality estimated from abu

Low-Angle

0

30,00060,00090,000

120,000

Population Size

2003 20042006 2007

 Apr May Jun Jul Aug Sep Oct Nov

High-Angle

0

30,00060,00090,000

120,000

Population Size

Apr May Jun Jul Aug Sep Oct Nov

0

5,000

10,00015,00020,00025,00030,00035,00040,00045,000

Dec Jan 

Discharge (ft3.sec-1)
Model-based estimates of tem

variation in age-0 surviva

0.00.20.40.60.81.0

JunJul Jul- Aug Aug- Sep Sep- Nov Nov- Dec Jun- Jul Jul- Aug Aug- Sep Sep- Nov 

2004 2006 

Monthly Survival Rate
0

100200300400500600700800

16 20.5 25 29.5 34 38.5 43 47.5 52 56.5 61 65.5 70

Thousands

Age-0 Population2004 2006 2007 2008

Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar

• High abundance in 2008 was apparent by summer

steady flows.

• Age-0 survival rate over fall was actually lower in 

was likely caused by higher density, rather than b

• Need comparable densities to ROD period to eval

steady flows on age-0 survival rate.

Confo

Fall s
Sample width (4 m)

Sampling at daily minimu

Daily Max. Flow

Sample width (4 m)

Sampling at daily maximum f

1) Shoreline-tracking

Permanently

submerged

zone

2) Restri

Unanticipated gains in knowledge r

high spatial and temporal samplin

River bank

A

Water surface
25% Increase in otolith growth 

in 2003 when flow was low 

8,000

10,00012,00014,00016,00018,00020,000

Discharge (ft3.sec-1)

Thursday Friday Saturday Sunday Monday

2003

2004
15oC 11oC

Otolith growth - nearshore h

Sunday ma

Daytime – Sunday (2

Daily max. flow

Daytime – Mon

Daily min. flow

Permanently su

varial zone

Permanently su

11oC 15oC
Summary

1. Flow-dependent incubation losses of 25-50% in experime

large enough to reduce abundance of age-0 trout because 

2. Some age-0 trout migrate from low- to high-angle shoreli

shorelines is considerable, and may buffer impacts of flow 

3. Age-0 growth over the summer and fall was very similar 

reasonably similar across years, and showed little density

4. Apparent age-0 mortality rates over summer and fall wer

2007, but were much higher in 2008. Density-dependent 

5. Apparent age-0 mortality was highest during periods whe

occurred (Aug-Sep, Nov. ‘04). Flow-dependent mortality 

6. More years of data are needed to better separate effects o

natural variation on early survival rates.