1. Seasonal shifts in diel patterns of juvenile Chinook salmon catch rates in the Sacramento-San Joaquin River Delta Rick Wilder & Jack Ingram Delta Juvenile Fish Monitoring Program, US Fish & Wildlife Service, Stockton, CA

2. Diel patterns in activity level of juvenile salmonids Atlantic salmonAtlantic salmon (Hiscock et al. 2002; Johnston et al. 2004) Chum salmonChum salmon (Ericksen & Marshall 1997) Coho salmonCoho salmon (Johnson & Johnson 1981) Pink salmonPink salmon (Godin 1981) Rainbow trout/SteelheadRainbow trout/Steelhead (Johnson & Johnson 1981; Bolliet et al. 2001) Sockeye salmonSockeye salmon (Steinhart & WurtsbaughScheuerell & Schindler 2003) (Steinhart & Wurtsbaugh 1999; Scheuerell & Schindler 2003)

3. Purpose of the study To determine whether juvenile Chinook salmon in the Sacramento-San Joaquin River Delta exhibit seasonal changes in diel activity patterns.

4. Delta Juvenile Fish Monitoring Program Year-round fish monitoringYear-round fish monitoring 30 years of data30 years of data For the State Water Project and Central Valley ProjectFor the State Water Project and Central Valley Project

5. Sampling periods Season Study site Dates Spring Georgiana Slough 4/29/96-5/2/96 Walnut Grove 4/29/96-5/2/96 Jersey Point 4/29/97-5/15/97 Sherwood Harbor 5/15/03-5/16/03 4/15/05-4/16/05 4/29/05-4/30/05 Fall Sacramento River, RM 27 10/29/01-11/1/01 Delta Cross Channel 10/29/01-11/1/01

6. Jersey Point Delta Cross Channel Sherwood Harbor Walnut Grove Sac. River RM 27 Georgiana Slough Study sites

7. Each sampling period 10 to 20 minute trawls ≥24 hours of nearly continuous sampling Photos: P. Voong

8. Photo: C. Hagen Kodiak trawl Midwater trawl Photo: J. Hanni

9. Data Analysis Categorized each trawl into 1 of 3 times of day: “Day,” “Night,” or “Crepuscular” For each sampling period separately, compared mean CPUE among times of day across entire sampling period –non-parametric ANOVAs and post-hoc multiple comparisons tests

10. Sherwood Harbor (Spring) ANOVA: P Night for all Day Crepuscular Night

11. ANOVA: P Night for all Day Crepuscular Night

12. ANOVA: P Day for both Fall sampling periods Day Crepuscular Night

13. Summary table SeasonStudy siteDatesResult SpringSherwood Harbor5/15/03-5/16/03(Day = Crepuscular) > Night Sherwood Harbor4/15/05-4/16/05(Day = Crepuscular) > Night Sherwood Harbor4/29/05-4/30/05(Day = Crepuscular) > Night Georgiana Slough4/29/96-5/2/96(Day = Crepuscular) > Night Walnut Grove4/29/96-5/2/96(Day = Crepuscular) > Night Jersey Point4/29/97-5/15/97(Day = Crepuscular) > Night FallSacramento River, RM 27 10/29/01-11/1/01(Night = Crepuscular) > Day Delta Cross Channel 10/29/01-11/1/01(Night = Crepuscular) > Day

14. Caveats 1.Many fish are likely hatchery production fish Photo: CNFH

15. Caveats 1.Many fish are likely hatchery production fish 2.Only two fall samples, and from same date close to one another Delta Cross Channel Sac. River RM 27 Photo: CNFH

16. Additional studies in Fall/Winter showing nocturnal activity patterns Atlantic salmon (Hiscock et al. 2002)Atlantic salmon (Hiscock et al. 2002) Chum salmon (Ericksen & Marshall 1997)Chum salmon (Ericksen & Marshall 1997) Chinook salmon at RBDD (Gaines & Martin 2001)Chinook salmon at RBDD (Gaines & Martin 2001) Photo: CNFH

17. Potential mechanisms

18. 1.Water temperature During the day: Foraging efficiency is greatestForaging efficiency is greatest Predation risk is greatestPredation risk is greatest

19. Potential mechanisms Low water temperature low metabolism, low mobility,low energy requirements low metabolism, low mobility, low energy requirements Nocturnal (low predation risk, low foraging efficiency) → Nocturnal (low predation risk, low foraging efficiency)

20. Potential mechanisms Low water temperature low metabolism, low mobility, low energy requirements High water temperature high metabolism, high mobility, high energy requirements Nocturnal (low predation risk, low foraging efficiency) →Nocturnal (low predation risk, low foraging efficiency) Diurnal (high foraging efficiency, high predation risk) →Diurnal (high foraging efficiency, high predation risk)

21. Water temperature Season Study site Mean temp (C) (± 1 SE) Spring Sherwood Harbor 17.87(0.03) 15.31(0.04) 16.82(0.04) Georgiana Slough 16.90(0.12) Walnut Grove 16.76(0.10) Jersey Point 17.97(0.13) Fall Sacramento River, RM 27 15.57(0.02) Delta Cross Channel 18.21(0.03) ANOVA result: P = 0.96

22. Potential mechanisms 2.Gear efficiency Photo: J. Hanni

24. Studies observing nocturnal activity in salmonids StudyMethod Fraser & Metcalfe 1993Infrared camera Hiscock et al. 2002Radiotelemetry Scheuerell & Schindler 2003 Hydroacoustic echosounder

27. Potential mechanisms 3.Fish size Photo: P. Voong

28. Fish size Season Study site Mean FL (mm) (± 1 SE) Spring Sherwood Harbor 80.77(0.47) 68.72(0.92) 76.49(0.81) Georgiana Slough 82.11(0.14) Walnut Grove 80.90(0.28) Jersey Point 84.19(0.15) Fall Sacramento River, RM 27 96.45(0.54) Delta Cross Channel 95.14(2.35) ANOVA result: P < 0.001**

29. Fish size Larger fish are: less active, no need to forage during dayless active, no need to forage during day active at night active at night physically able to avoid net when visiblephysically able to avoid net when visible catch rates higher at night catch rates higher at night → →

30. Future directions Look at federal salvage dataLook at federal salvage data Sample multiple times of yearSample multiple times of year Observe net avoidance in situObserve net avoidance in situ Experimentally manipulate physical factorsExperimentally manipulate physical factors Photo: Alamy Images

31. Implications Our sampling scheduleOur sampling schedule Water operationsWater operations Photo: J. Hanni