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Estimates of Coho Spawners in Lower Cowlitz River Tributaries

Estimates of Coho Spawners in Lower Cowlitz River Tributaries. Mara S. Zimmerman, WDFW Presentation to the Cowlitz FTC May 3 2016. Lower Cowlitz River Coho. 421 miles of tributary habitat Goal from FHMP – Appendix J is to estimate NOS (natural-origin spawners )

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Estimates of Coho Spawners in Lower Cowlitz River Tributaries

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  1. Estimates of Coho Spawners in Lower Cowlitz River Tributaries Mara S. Zimmerman, WDFW Presentation to the Cowlitz FTC May 3 2016

  2. Lower Cowlitz River Coho • 421 miles of tributary habitat • Goal from FHMP – Appendix J is to estimate • NOS (natural-origin spawners) • HOS (hatchery-origin spawners)

  3. Data Collection - Weirs • 4 resistance board weirs • Daily check • Fish data • Species, HOR/NOR, J/M/F, CWT, length, direction of travel, previous tag • Fish fate • HOR surplused • NOR coho passed in direction of travel • Upstream maiden NOR coho are tagged & released

  4. Data Collection - Surveys • Continuous spatial index reaches • Above Ostrander, Delameter weirs • Below Ostrander, Delameter weirs, Arkansas • GRTS index reaches • 1-mile length • 30 reaches or 30%

  5. Data Collection - Surveys • Oct – Jan • 7 to 10-day interval • Fish data • Redds(New, Still Vis., Not Vis., GPS) • Carcasses (Species, HOR/NOR, J/M/F, length, tag, CWT) • Live (Species, J/A, tag) • Clarity Photo: Bryce Glaser

  6. Analysis Overview • Tributary M-R Estimate (above weirs) • + • Redd-based Estimate (outside weirs) • Surveyed Reaches • Non-Surveyed Reaches • Total Spawners

  7. Tributary M-R Estimate (above weirs)Data Summary • n1 = Tagged live fish released upstream • n2NOR = All NOR carcasses (surveys, weir) • n2HOR = All HOR carcasses (surveys, weir) • m2 = Carcasses with tags (surveys, weir)

  8. Tributary M-R Estimate (above weirs)2014 Example n1 = Tagged live fish released upstream n2NOR = All NOR carcasses (surveys, weir) m2NOR = Carcasses with tags (surveys, weir) n2HOR = All HOR carcasses (surveys, weir)

  9. Tributary M-R Estimate (above weirs)2014 Example

  10. Redd-Based Estimate (outside weirs)Data Summary • Step 1: Estimate total redds • Redds in census reaches • Redds per mile in GRTS reaches • Surveyed miles, non-surveyed miles • Step 2: Estimate total spawners • Redds per female • Proportion female • HOR/NOR recoveries (weir arrivals, surveys)

  11. Redd-Based Estimate (outside weirs)2014 Example • Step 1: Estimate total redds Non-surveyed miles 208

  12. Redd-Based Estimate (outside weirs)2014 Example • Step 2: Estimate total spawners MR est, M/F at weir, redds above weir M/F at weir, carcasses HOR/NOR at weir, carcasses

  13. 2014 Coho Spawner EstimateTributary MR Estimate (above weirs)+Redd-Based Estimate (outside weirs) 15,995 NOS (11.9% CV) 405 HOS (20.3% CV)

  14. Tributary M-R EstimateHave we met estimator assumptions? • Population is closed (re-ascensions?) • Equal catchability in first or second sample (tag/no tag in surveys vs. weir washups, male vs. female) • Tag loss (double vs. single tag) • Tag detection (training!) • Handling mortality (observations)

  15. Tributary M-R Estimate2014 Example 1Recaptures in Ostrander were too few to conduct a mark-recapture estimate. Redundancy in survey methods is important backup!

  16. Tributary M-R EstimatePutting the data together NOR Spawners HOR Spawners Total Spawners

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