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?

Bypassed = 3-10% Undetected = 20 – 40 % Transported = 55-75% 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 Data from CSS 10-year Retrospective Report

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John Williams unpublished data

Snake River Chinook Salmon

Y = * X r2 = 0.941, P = 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 ( ) –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?