1. 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

2. Briefing Goals
Describe age at ocean-entry for the Snake River Basin population of full-term wild adults (i.e., II salts)
Describe age-at-ocean entry for transported subyearlings
Describe age-at-ocean entry for inriver migrants
Summarize the limited information on SARs

3. Key Points
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

4. 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

5. Finding 1: Age at ocean-entry for random samples of
wild Snake River Basin full-term adults
1998
Return Year 10 20 30 40 50 60 70 80 90
100
Percentage of annual sample
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)
BILLY
We sampled enough wild full-term run-at-large adults for analysis during five years.
During these five years, both subyearling and yearling ocean entrants were important to the return of full-term adults.
Oveall, 54% of the full-term adults we collected had entered the ocean as subyearlings and 46% of the full-term adults had entered the ocean as yearlings.
Migration pathway (i.e., summer transport, fall transport, or inriver) could not be determined for all of these fish.

6. Method B: Same as method A, but we targeted adults that were PIT-tagged as juveniles

7. Method B (Continued): Use juvenile PIT-tag histories to determine migration pathway and location of first year wintering
Summer and fall transport Subyearling entrants winter in the ocean Yearling ocean entrants winter below Bonneville Dam
Inriver migration Subyearling entrants winter in the ocean Yearling ocean entrants winter above or below Bonneville Dam

8. Percentage of inter-annual samples
Finding 2: Age at ocean entry for summer and fall transport groups (N = 32 adults collected in 2005; pooled migration years)
Subyearling
Yearling n
= 15 n
= 17
100 80
33%
47%
Percentage of inter-annual samples 60
BILLY
In 2005, we were able to sample adults that had been PIT-tagged as part of the transportation studies.
The sample size was relatively small and incomplete with respect to age-class distribution.
The data, however, shows that some transported subyearlings winter in freshwater (likely the estuary) and enter saltwater as yearlings.
This viloated the assumption of our 2005 paper.
However, a large portion of the full-term adults sampled had been inriver migrants and entered saltwater as yearlings.
These data are incomplete, but they point to a relatively large contribution of inriver migrants to the return of full-term adults. 40 20
Summer
Fall
Transport season

9. Finding 3: Age-at-ocean entry for inriver migrants (e.g., wild)
Mostly
subyearling
Snake
Clearwater
Radio tags
120
Mostly
yearling
100
PIT-tag detection
All yearling
(reservoir types)
system typically 80
dewatered
Estimated number passed 60
Never detected group
(reservoir types)
Dewatering 40 20
05/01/2006
08/01/2006
11/01/2006
02/01/2007
06/16/2006
09/16/2006
12/17/2006
03/19/2007
Passage date at Lower Granite Dam

10. Smolt-to-adult return (%)
Finding 4-1: Smolt-to-adult return rates for surrogate subyearlings released into the Snake River in 2002 02
02 mortality
unknown 5 55
/1,190 4 80
/2,500 3
Smolt-to-adult return (%) 2 1 98
/16,284 21
/3,990 72
/?????
Summer 02
transport
Fall 02
transport
Jun-Oct 02
bypassed
Spring 03
(reservoir type)
Never
detected

11. Last PIT-tag detection
Finding 4-2: Seasonal trend in SARs for bypassed surrogate subyearlings released into the Snake River in 2002 5 60
Juveniles
SAR 4 50 40 3
Percent of migrants
SAR (%) 30 2 20 1 10
Jun 02
Jul 02
Aug 02
Sep 02
Oct 02
Spring 03
(reservoir type)
Last PIT-tag detection

12. Subyearling inriver 100-125 mm FL Summer transport 75-100 mm FL
Finding 4-3: Size after passing Bonneville Dam and at ocean entry likely affects SARs
Subyearling inriver mm FL
Summer transport mm FL
Fall transport mm FL
Yearling inriver mm FL

13. Conclusions
Both subyearling and yearling ocean entrants made substantial
contributions to the return of full-term wild adults regardless of
of how they reached the sea because:
The relatively large number of early migrants destined to become subyearling ocean entrants likely compensated for the relatively low SARs for early migrants
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

14. 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