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 Little is known about juvenile Chinook salmon that rear in lakes before migrating to saltwater

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?

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

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

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

Slope Predator present Predator absent NA 5% 10% 15% 20% Substrate Predator present Predator absent Sand Gravel Sand/Cobble Cobble Predator presentPredator absent Substrate No cover Woody debris Overhead cover No cover Woody debris Overhead cover Sand Gravel Sand/Cobble Cobble N = 80 Y = % fish in each slope; water column location; location within slope patch N = 20 Y = % fish in each substrate N = 60 Y = % fish in each substrate/cover combination Observe over 3 diel periods, repeat for 2 life stages Slope experimentsSubstrate experiments Substrate/Cover experiments

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

5% 15% 10% 20% Slope arena

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

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

Substrate arenas

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

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

Substrate-Cover arenas

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

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

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

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 UNIVERSITY OF WASHINGTON

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

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

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

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

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

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