briefing goals
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Age at ocean entry of Snake River Basin fall Chinook and its significance to adult returns prior
to summer spill at LGR, LGS, and LMN dams
Briefing Goals
1) Describe age at ocean-entry for the Snake River Basin population of full-term wild adults (i.e., II salts)
2) Describe age-at-ocean entry for transported subyearlings
3) Describe age-at-ocean entry for inriver migrants
4) Summarize the limited information on SARs
• Both subyearling and yearling ocean entrants made substantial contributions to the return of full-term wild Snake River Basin adults
• Subyearling and yearling ocean entry has been evident in full-term adults from summer and fall transport groups as well as inriver migrating groups
• The tendency to become a yearling ocean entrant and SARs increased as the migration season progressed
Key Points
Method A: Trapped random samples of adults at Lower Granite Dam and used scale pattern analyses to identify origin, age at ocean entry, and ocean age
Finding 1: Age at ocean-entry for random samples ofwild Snake River Basin full-term adults
1998Return Year
0
10
20
30
40
50
60
70
80
90
100
Perc
enta
ge o
f ann
ual s
ampl
e
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)
Method B: Same as method A, but we targeted adults that were PIT-tagged as juveniles
Method B (Continued): Use juvenile PIT-tag histories to determine migration pathway and location of first year wintering
Summer and fall transport
Subyearling entrants winterin the ocean
Yearling ocean entrants winterbelow Bonneville Dam
Inriver migration
Subyearling entrants winter in the ocean
Yearling ocean entrants winter above or below Bonneville Dam
Finding 2: Age at ocean entry for summer and fall transport groups (N = 32 adults collected in 2005; pooled 2001-2004 migration years)
Summer FallTransport season
0
20
40
60
80
100
Perc
enta
ge o
f int
er-
annu
al s
ampl
es
n = 15 n = 17
SubyearlingYearling
33% 47%
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
120
Estim
ated
num
ber p
asse
d
Radio tagsClearwater
Dewatering
PIT-tag detectionsystem typicallydewatered
SnakeMostlysubyearling
Mostlyyearling All yearling
(reservoir types)
Never detected group(reservoir types)
Finding 3: Age-at-ocean entry for inriver migrants (e.g., wild)
Never detected
Summer 02transport
Jun-Oct 02bypassed
Spring 03(reservoir type)
Fall 02transport
0
1
2
3
4
5
72 /?????
98/16,284 21/3,990
55/1,190
80/2,500
Smol
t-to-
adul
t ret
urn
(%)
Finding 4-1: Smolt-to-adult return rates for surrogate subyearlings released into the Snake River in 2002
02 02 mortalityunknown
Jun 02 Jul 02 Aug 02 Sep 02 Oct 02 Spring 03(reservoir type)
0
10
20
30
40
50
60
0
1
2
3
4
5Juveniles
SAR
Last PIT-tag detection
Perc
ent o
f mig
rant
sSA
R (%
)Finding 4-2: Seasonal trend in SARs for bypassed surrogate subyearlings released into the Snake River in 2002
Summer transport75-100 mm FL
Fall transport 175-200 mm FL
Subyearling inriver100-125 mm FL
Yearling inriver 200-225 mm FL
Finding 4-3: Size after passing Bonneville Dam and at ocean entry likely affects SARs
Both subyearling and yearling ocean entrants made substantialcontributions to the return of full-term wild adults regardless ofof how they reached the sea because:
1. The relatively large number of early migrants destined to become subyearling ocean entrants likely compensated for the relatively low SARs for early migrants
2. 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
Conclusions
Research Needs
• Summer spill (2005 to 2007)
• Surrogate subyearlings were provided for research in 2005 and 2006, but not in 2007
• Support for research in 2008 is needed to evaluate spill and its influence on SARs of early inriver migrants destined to become subyearling ocean entrants
Jun 02 Jul 02 Aug 02 Sep 02 Oct 02 Spring 03(reservoir type)
0
10
20
30
40
50
60
0
1
2
3
4
5Juveniles
SAR
Last PIT-tag detection
Perc
ent o
f mig
rant
s
SAR
(%)
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