Rick Wilder & Jack Ingram

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 salmon • (Hiscock et al. 2002; Johnston et al. 2004) • Chum salmon • (Ericksen & Marshall 1997) • Coho salmon • (Johnson & Johnson 1981) • Pink salmon • (Godin 1981) • Rainbow trout/Steelhead • (Johnson & Johnson 1981; Bolliet et al. 2001) • Sockeye salmon • (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 FishMonitoring Program • Year-round fish monitoring • 30 years of data • For the State Water Project and Central Valley Project

5. Sampling periods

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

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

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

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. Day Crepuscular Night Sherwood Harbor (Spring) ANOVA: P < 0.001, (Day=Crepuscular)>Night for all

11. Day Crepuscular Night ANOVA: P < 0.001, (Day=Crepuscular)>Night for all

12. Day Crepuscular Night Fall sampling periods ANOVA: P< 0.0001, (Night=Crepuscular)>Day for both

13. Summary table

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

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

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

17. Potential mechanisms

18. Potential mechanisms • Water temperature During the day: • Foraging efficiency is greatest • Predation risk is greatest

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

21. Water temperature ANOVA result: P = 0.96

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

24. Studies observing nocturnal activity in salmonids

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

28. Fish size ANOVA result: P < 0.001**

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

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

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