Lentic habitat preferences of juvenile Chinook salmon in experimental arenas

1. Lentic habitat preferences of juvenile Chinook salmon in experimental arenas Chris Sergeant R.Tabor

2. Habitat and salmon • In both streams and lakes, salmon are often found in shallow, nearshore zones • Functions of nearshore habitat: • Foraging • Refuge • Migration corridor • Little is known about juvenile Chinook salmon that rear in lakes before migrating to saltwater

3. Lake Washington nearshore habitat and Chinook salmon • L. Washington Chinook listed as threatened under the ESA • Human-induced habitat changes: a main cause of salmon population decline? • Shoreline restoration projects • Does nearshore habitat affect the productivity of Chinook salmon in Lake Washington?

4. Cedar River juvenile Chinook: Life history patterns Emergence: January - March Ship Canal River Lake Littoral Pelagic/Littoral: May - July Salt Migration: June – Sept. Cedar River

5. Field observations of lake-rearing chinook (Tabor and Piaskowski 2001) • Temporal movement • Littoral zone: January – June • Pelagic zone: Mid-May - July • Habitat use patterns • Low bottom slope • Sand, gravel substrate • Shallow water < 0.5 m Try isolating the habitat variables! R.Tabor

6. 2004 objectives • Examine effects of physical habitat factors • Slope • Substrate • Substrate-cover combinations • Examine effects of biotic factors • Predator presence • Ontogenetic shifts

7. Slope experiments Substrate experiments N = 80 Y = % fish in each slope; water column location; location within slope patch N = 20 Y = % fish in each substrate Substrate/Cover experiments N = 60 Y = % fish in each substrate/cover combination Observe over 3 diel periods, repeat for 2 life stages

8. Methods cont’d • Source of fish: WDFW Issaquah Creek hatchery • Fish were fed daily in holding tanks, but not during experiments • Before experiments: • Naïve fish chosen randomly • Holding cage within arena • Acclimation period • After acclimation period, observations were made over the following 24-hour period

9. Slope arena 10% 20% 15% 5%

10. Slope experiments Fry • No diel or predation effects • Deep neutral area most preferred • 20% slope least preferred • Cutthroat most often in 5% or neutral area

11. Slope experiments Presmolts • No diel or predation effects • Strong preference for deep neutral area • Both 15% and 20% slopes avoided

12. Substrate arenas

13. Substrate experiments Fry • Substrate preferences shift with diel period • No predation effect • Sculpin mainly in cobble, rarely in sand

14. Substrate experiments Presmolt • Similar, but looser, trends than fry • No predation effect

15. Substrate-Cover arenas

16. Substrate-Cover arenas

17. Substrate-cover experiments • No cover, cobble most used by fry • No patterns in presmolt data • Note small y-axis scale

18. Conclusions • Experimental findings support Lake Washington field observations of Tabor and Piaskowski (2001) • Slope experiments: • No strong selection for slope • Steep slopes avoided • Substrate experiments: • At night, fry preferred finer substrate • No strong preference during day and crepuscular • Substrate/cover experiments: • No strong preference for any particular substrate/cover combination • Diel and predation effects were not usually present

19. Directions for future experimental research • Larger arenas • Examine substrate/cover combinations • Cruising predators • Predator density thresholds • Combinations of predators

20. UNIVERSITY OF WASHINGTON Acknowledgements • Committee: Dave Beauchamp, Tom Quinn, Roger Tabor • Seattle Public Utilities: Julie Hall, Keith Kurko • USGS – Sand Point: Jeff Duda, Reg Reisenbichler • UW Hatchery: Dave Rose, Jon Wittouck • WDFW Issaquah Creek Hatchery • Beauchamp group: Alison, Angie, Erik, Hilary, Jen, Jim, Liz, Mike, Nathanael, Sarah, Steve

21. How many docks are out there? Figure courtesy of J. Toft

22. Slope experiments: Water column location Fry • Top of the water column rarely used • Bottom of the water column used heavily at night, especially around predators

23. Slope experiments: Water column location Presmolt • Top of the water rarely used • No predation effect

24. Slope experiments: Patch location Fry • No diel or predation effect • Cruising fish most common

25. Slope experiments: Patch location Presmolts • No diel or predation effect • Offshore and cruisers most common

26. Slope experiment summary • The presence of cutthroat trout and effect of diel period had minimal effects on slope preferences • Deep neutral area most preferred habitat patch by fry and presmolts • Steep slopes avoided • At night, most fish move to bottom of water column • Most presmolts used offshore regions of slope patches or cruised • No strong preference for any slope patch