Predation by hatchery-reared steelhead on natural salmonid fry in the upper‑Trinity River, California 2005

1. Predation by hatchery-reared steelhead on natural salmonid fry in the upper‑Trinity River, California 2005 Seth W. Naman Yurok Tribal Fisheries Program

2. Introduction

3. Trinity RiverLewiston Dam to Old Lewiston Bridge Middle of study reach

4. Key features of study reach • In any given year over 50 % of all salmonid redds, upstream of the NF Trinity, are created here…extremely important spawning and rearing zone • Coho salmon are listed under ESA and CESA • In 1991, local business owners successfully lobbied CA F&G Commission to change fishing regulations to fly only and catch and release only

5. Predation risks • Spatial and temporal overlap of predator and prey • High concentrations of predator and prey • Size overlap of predator and prey • Low turbidity • Limited fry rearing habitat (TRFE)

6. Methods

7. Basic study approach • Pump stomachs of hatchery steelhead to estimate the amount of salmon fry per stomach • Estimate the number of hatchery steelhead in the study reach • Multiply the two

8. Definitions Residuals = Hatchery steelhead that spent one or more years in the river Juveniles = Hatchery steelhead released in March of 2005

9. Study timeline February-March (residuals) March-May (juveniles and residuals)

10. Hook and line Invertebrate fly patterns

11. Smoltification ratings 1 2 3

12. Pulsed gastric lavage

13. Residual population estimates • Mark-recapture • - Upper caudal clip • - Schnabel estimator • Snorkel expansion • - Three divers • - One pass

14. Juvenile population approximation 792,861 × 0.8 = 634,289

15. Juvenile population approximation 792,861 × 0.04 = 31,714

16. Juvenile population approximation

17. Number of fry consumed

18. Statistical analyses • T-tests, chi square, ANOVA, etc. performed using Minitab and SAS • Fry per stomach data modeled using WinBugs • -non-informative priors • -Used DIC to compare models

19. Results

20. Some results briefly • Differences in fork length between all smoltification groups were significant, non-smolting juvenile were larger (ANOVA, F2, 2,476 = 24.13, P < 0.001) • No difference in the number of piscivors between smoltification groups (χ2 = 0.202) • No difference in fork length between juvenile piscivores and non-piscivores (T = 0.90; P = 0.815) • Significant difference in fork length between residual piscivores and non-piscivores (T = 3.83; P < 0.001)

21. Residual steelhead predation rates

22. Juvenile steelhead predation rates Mean = 0.062 (0.049-0.077)

23. Hatchery STH predation studies Lewis R. = 1.08, n = 48

24. Residual population estimates

25. Juvenile population approximation

26. …

27. Steps taken to minimize estimate • Chose a conservative gastric evacuation model • 158,572 (20%) hatchery juvenile steelhead not included in calculations • Used twilight hours instead of 24 hours in calculations (correction of ~ 0.5)

28. What if? What if the starting number for these calculations was 60% of total smolts released?

29. What if? • What if the starting number for these calculations was 60% of total smolts released? • 241,259 (95% CI = 153,990 – 357,683)

30. What if? • What if the starting number for these calculations was 60% of total smolts released? • 241,259 (95% CI = 153,990 – 357,683) • 40%?

31. What if? • What if the starting number for these calculations was 60% of total smolts released? • 241,259 (95% CI = 153,990 – 357,683) • 40%? • 189,900 (95% CI = 116,765 – 268,779)

32. Bias of Hook and Line?

33. Bias of Hook and Line? • Used SRS to sample 75% stomach contents data (~ 1850 records)

34. Bias of Hook and Line? • Used SRS to sample 75% stomach contents data (~ 1850 records) • Replaced 25% with zeros (~ 650 records)

35. Bias of Hook and Line? • Used SRS to sample 75% stomach contents data (~ 1850 records) • Replaced 25% with zeros (~ 650 records) • 119 fry consumed for 2,479 records

36. Bias of Hook and Line? • Used SRS to sample 75% stomach contents data (~ 1850 records) • Replaced 25% with zeros (~ 650 records) • 119 fry consumed for 2,479 records • Overall mean of 0.048

37. Bias of Hook and Line? • Used SRS to sample 75% stomach contents data (~ 1850 records) • Replaced 25% with zeros (~ 650 records) • 119 fry consumed for 2,479 records • Overall mean of 0.048 • 215,661 (95% CI = 129,474 - 344,024)

38. Does it matter? Chinook 3889 redds × 3000 eggs × 0.4 survival =4,606,800 Coho 1041 redds × 3000 eggs × 0.4 survival =1,249,200 312,802/5,856,000 × 100 = 5.3% Remember, this doesn’t include eggs, competition, etc.

39. Conclusions Predation and competition are likely important forces of mortality on naturally produced salmonids, which program partners are trying to recover

40. Conclusions Maintaining residualized hatchery steelhead conflicts with stated goals of TRRP, CalTrout, CDFG, and others CA F&G Commission policy: “Resident fish will not be planted or resident fisheries developed in drainages of steelhead waters, where, in the opinion of the Department, such planting or development will interfere with steelhead [or salmon] populations.”

41. Conclusions • Almost no naturally produced adult steelhead in this reach • High proportions of hatchery steelhead spawning in river and 100% hatchery broodstock are concerns…domestic selection

42. Recommendations • Better integration between TRRP and TRH • Reexamine mitigation goals and consider releasing fewer steelhead • Change fishing regulations • Explore possibilities for downstream release site

43. Thoughts…it’s not about 300,000 fry • Consider the cumulative effects of competition and predation over a year, or a decade, from • Residuals (individuals consumed up to 60 eggs), • plus smolts • plus anadromous hatchery steelhead (1.12 fry/stomach) • plus brown trout. Incremental effects add up!

44. Thank You Jeremy Alameda Loren Everest Bill Pinnix BOR Aaron Martin Howard Stouffer Tim Hayden Questions?