Migration pathway, age at ocean entry, and SARs for Snake River Basin fall Chinook prior to summer spill at LGR, LGS, and LMN dams

Snake River

Columbia River

Salmon

Grande Ronde

Imnaha

0 50 100 Km

N

Clearwater

MONTANA

Swan Falls

Estuary

Core Area

Prehistorical Metapopulation- Subyearling ocean entrants

Snake River

Columbia River

Salmon

Grande Ronde

Imnaha

0 50 100 Km

N

Clearwater

MONTANA

Swan Falls

Estuary

Contemporary Subpopulations -Subyearling and yearling ocean entrants

Brownlee

McNary

Bonneville

OREGON

WASHINGTON

IDAHO

Oxbow

Hells Canyon

John Day

The Dalles

Ice

Har

bo

r

Lo

wer

Gra

nit

e

Lo

wer

Mo

nu

men

tal

Lit

tle

Go

ose

Dw

ors

hak

1998

Return Year

0

10

20

30

40

50

60

70

80

90

100

Per

cen

tag

e o

f an

nu

al s

amp

le

1999 2000 2001 2002 2003 2004

(2)

(101) (55)

(6)

(65)(92)

(305)

Subyearling inter-annual mean 59%Yearling inter-annual mean 41%

2005 2006

(126)(444)

Fig 1. - Age at ocean-entry for random samples of wild Snake River Basin full-term fall Chinook salmon adults (i.e., II-Salts) collected at Lower Granite Dam.

Briefly explore the complex and diverse juvenile life history of Snake River Basin fall Chinook salmon;

1) Describing migration pathways and the subyearling and yearling tactics (a.k.a., ages at ocean entry)

2) Summarizing the limited information on SARs for the migration pathways and subyearling and yearling tactics

Data Collected during Non-spill years (1992 to present)

Validated scale pattern analysis

PIT-tag detection histories

A complete data set describing migration pathway, age at ocean entry, and SARs for wild Snake River Basin fall Chinook Salmon does not exist

Therefore, existing data are subject to interpretation and this requires some generalization and speculation

#1 Migration Pathway = Transportation

• Subyearling ocean entrants winter at sea (prevalent in summer barged groups)

• Yearling ocean entrants winter below Bonneville Dam (prevalence increases in fall trucked groups)

• Subyearling ocean entrants are numerically dominant

Fig 2.- Smolt-to-adult return rates (full-term adults detected at LGR / number of smolts transported system-wide) for surrogate and run-at-large Snake River subyearlings (brood year 2001) transported from a collector dam in 2002.

Summer transport Fall transport

Migration pathway

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

3.5%

4.0%

4.5%

5.0%

5.5%S

mo

lt-t

o-a

du

lt r

etu

rn r

ate

81 / 17,282

32 / 875

Prevalence of yearling ocean entry increases

Summer transport75-100 mm FL

Fall transport175-200 mm FL(or larger)

Size and Timing of Release Downstream of Bonneville Dam

#2 Migration Pathway = Inriver Migration

• Subyearling ocean entrants winter at sea (prevalent for Snake River subpopulation)

• Yearling ocean entrants winter above or below Bonneville (prevalent for Clearwater River subpopulation)

• Active subyearling migrants are numerically dominant

05/01/200606/16/2006

08/01/200609/16/2006

11/01/200612/17/2006

02/01/200703/19/2007

Passage date at Lower Granite Dam

0

20

40

60

80

100

120E

stim

ated

nu

mb

er p

asse

dRadio tagsClearwater

Dewatering

PIT-tag detectionsystem typicallydewatered

SnakeMostlysubyearling

Mostlyyearling

All yearling(reservoir types)

Never detected group(reservoir types)

Fig 3.-Seasonal migration patterns in 2006-2007 for wild fall Chinook salmon juveniles (brood year 2005) from the Snake River Basin upstream of Lower Granite Reservoir.

Fig 4.- Smolt-to-adult return rates (full-term adults detected at LGR / smolts detected and bypassed system-wide) for surrogate subyearlings released into the Snake River in 2002 (i.e., brood year 2000) that migrated to the sea inriver.

Summer inriver

Migration pathway

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

3.5%

4.0%

4.5%

5.0%

5.5%S

mo

lt-t

o-a

du

lt r

etu

rn r

ate

8 / 3,310

Fall inriver

4 / 178

Spring inriver

56 / 1,229

ND inriver

72 / ?

Subyearlingsprevalent

Yearlingsprevalent

Yearlingsprevalent

Yearlings

Subyearling inriver100-125 mm FL

Yearling inriver 200-225 mm FL

Size at Bonneville Dam Passage

Fig 5.- Smolt-to-adult return rates for surrogate and run-at-large subyearlings by migration pathway in 2002 (i.e., brood year 2001) given with the percentage of smolts detected using each migration pathway.

Summer inriver

Migration pathway

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

3.5%

4.0%

4.5%S

mo

lt-t

o-a

du

lt r

etu

rn r

ate

Fallinriver

Summertransport

Falltransport

Pe

rcen

tage o

f smo

lts5.0%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%95% of Smolts

5% of Smolts

Avg.SAR0.4%

Avg.SAR3.4%

Discussion

Diversity increases fitness

There will be a “Darwinian Debt” to pay if the population evolves completely to the yearling tactic (e.g., Williams et al. in press; Evolutionary Applications)

Discussion (Cont)

Summer spill (2005 to 2007)

Will summer spill increase the SARs of active inriver migrants destined to enter the ocean as subyearlings, thereby balancing

juvenile life history diversity in the population?

Summer inriver

Migration pathway

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

3.5%

4.0%

4.5%

Sm

olt

-to

-ad

ult

ret

urn

rat

e

Summertransport

Percen

tage o

f smo

lts

5.0%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Conclusions

1. The juvenile life history of Snake River Basin fall Chinook salmon is complex and diverse; unlike Snake River Basin spring Chinook salmon, this complexity and diversity is exhibited within the hydropower system and the estuary

2. The relatively large number of active early migrants destined to become subyearling ocean entrants likely compensates for the relatively low SARs for active early migrants

3. The relatively high SARs for late migrants destined to become yearling ocean entrants compensated for the relative small number of fish that likely survive to become yearling ocean entrants

4. Consequently, both the subyearling and yearling tactics contribute largely to the return of full-term adults