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Lentic habitat preferences of juvenile Chinook salmon in experimental arenas

Lentic habitat preferences of juvenile Chinook salmon in experimental arenas. Chris Sergeant. R.Tabor. Habitat and salmon. In both streams and lakes, salmon are often found in shallow, nearshore zones Functions of nearshore habitat: Foraging Refuge Migration corridor

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Lentic habitat preferences of juvenile Chinook salmon in experimental arenas

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  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

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