# Presentation: 118592

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

***Core Area**** *

**Prehistorical Metapopulation**
**- Subyearling ocean entrants **

**Contemporary Subpopulations **
**-Subyearling and yearling ocean entrants**

##      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.

**     ****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.**

**Notes:**
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. 

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

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

-  **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.

**Prevalence of yearling ocean entry increases**

##  Fall transport175-200 mm FL

**Summer transport****75-100 mm FL**

** ****Fall transport****175-200 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**

##           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.

**05/01/2006**

**06/16/2006**

**08/01/2006**

**09/16/2006**

**11/01/2006**

**12/17/2006**

**02/01/2007**

**03/19/2007**

**Passage date at Lower Granite Dam**

**0**

**20**

**40**

**60**

**80**

**100**

**120**

**Estimated number passed**

**Radio tags**

**Clearwater**

**Dewatering**

**PIT-tag detection**

**system typically**

**dewatered**

**Snake**

**Mostly**
**subyearling**

**Mostly**
**yearling**

**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.

**      ****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.**

**Subyearlings**
**prevalent**

**Yearlings**
**prevalent**

**Yearlings**
**prevalent **

**Yearlings**

##   Yearling inriver 200-225 mm FL

**Subyearling inriver****100-125 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.

**95% of Smolts**

**5% of Smolts**

**Avg.**
**SAR**
**0.4%**

**Avg.**
**SAR**
**3.4%**

## 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?**

## Conclusions

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