# Presentation: 379438

## Differential Estimates of “Survival” for PIT Tagged Fish – Evidence and Causes

**Jason Vogel Nez Perce Tribe**
**Department of Fisheries Resources Management**

**LSRCP Annual Meeting March 4, 2008**

## Outline	

**Part I**
**Ensure marking is necessary**
**Focus on PIT Tag marking**
**Filling critical research gaps**
**Benefits vs. risks**
**Part II**
**Effects of actual PIT tag **
**What does PIT tag information give us?**
**Effects of actual PIT tag**
**Representative or not?**

## Nez Perce Tribe Department of Fisheries Resources Strategic Management Plan

**Vision**
**Manage aquatic resources to provide for healthy self-sustaining fish populations of historically present species and for harvest opportunities**
**Guiding Principles**
**Minimizing intrusive marking and handling of fish supports cultural and spiritual beliefs, respect for the fish, and maximum survival**

## PIT Tag Marking is it Necessary?

**Baseline monitoring**
**Fill critical data gaps**
**Information needed on groups of fish**
**Marking fish comes at a cost**
**Initial and Delayed Mortality**
**Information gained needs to outweigh the cost of decrease adult returns**
**How do we determine if marking is necessary and at what level?**
**Science? **
**Policy?**
**Social and Cultural?**

## Juvenile Passage Routes Through Hydrosystem

**Juvenile Passage Routes Through Hydrosystem**

**Percentages vary by species and hydro operations**

## Choosing Where the Fish Go

**Bypassed = default action for PIT tags**
**Survival estimates of fish to and through the hydrosystem**
**Monitor Mode (mimic unmarked)**
**Representative SARs **
**Johnson Creek and Imnaha River for NPT**
**Separation by Code**
**Comparative Survival Studies (CSS) = 70% transported: 30% bypassed**
**Smolt to adult return rates of bypassed, transported, and undetected juveniles**

## Differences in Chinook SARs by Passage Route

**Differences in Chinook SARs by Passage Route**

- Data from CSS 10-year Retrospective Report

## Bypassing Fish Equals Lower Adult Returns for Spring/Summer Chinook

**Bypassing Fish Equals Lower Adult Returns for Spring/Summer Chinook**

**N=405**

## Summary

**Benefits of PIT tagging fish**
**Comparison of groups/filling in critical gaps**
**From release to facilities (treatment groups)**
**Within the facilities treatment groups (barged, bypassed, others)**
**Tests of hydro actions (RSW’s, others) **
**Risks/Costs****	**
**PIT tagged fish treated differently**
**Decreases adult returns **

## Part II – Effects of PIT Tags

**Current uses of PIT tags**
**SAR calculations (LGR:LGR, Stream:Stream)**
**Adult run predictions**
**In season adjustments of harvest and broodstock take and allocations**
**Side by side comparisons of groups **

## John Williams unpublished data

## John Williams unpublished data

## Snake River Chinook Salmon

**Snake River Chinook Salmon**

## Snake River Chinook Salmon

**Y = 0.817 * X - 0.0047**
**r2 = 0.941, P = 0.006**

**Snake River Chinook Salmon**

## John Williams unpublished data

## What information do we have?

**Lostine River (4 Broodyears)**
**PIT tagged conventional underestimate SARs by 27%**
**PIT tagged captive brood underestimate SARs by 48%**
**Captive Program (1994-2003)**
**Raise fish from parr to adult in captivity**
**Fish shedding PIT tags**
**Catherine Creek 3.6% loss**
**Grande Ronde 2.3% loss**
**Lostine River 3.4% loss**
**Johnson Creek (2 Broodyears)**
**Monitor mode PIT tagged fish underestimate SARs by 39%**

## What information do we have?

**Knudsen et al. (in review) 5 Broodyears**
**PIT tagged fish underestimate SARs by 25%.  **
**Average of 18.4% fish lost their PIT tags.  **
**After correcting for PIT tag loss, PIT tagged fish had 10.3% lower SAR than untagged fish (Mortality)**

## Summary 

**PIT tags are very useful for specific side by side experiments when absolute survival is not necessary**
**PIT tagged fish do not represent an unbiased absolute measure of SARs**
**Need to design specific experiments to look at mechanisms to test for differences**
**PIT tag loss/shed**
**Mortality caused by PIT tagging**
**Malfunction of PIT tag or inability to read**

## Conclusions

**Ensure the benefits outweigh costs when using PIT tags**
**In terms of decreased adult returns**
**PIT tagged fish tend to underestimate SARs compared to untagged fish**
**Be very careful when utilizing PIT tags for absolute measure of SARs for groups of fish**
**Current methods are conservative**
**Setting and modifying harvest seasons and broodstock management**
**Determine mechanisms for differences in PIT vs. unmarked fish**

## Acknowledgements

**John Williams – NOAA**
**Fish Passage Center - CSS**
**Curt Knudsen – Oncorh Consulting**
**NPT Staff**

## Questions?