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

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

River Lake

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

SlopePredator present

Predator absent

NA

5%

10%

15%

20%

SubstratePredator present

Predator absent

Sand

Gravel

Sand/Cobble

Cobble

Predator present Predator absent

SubstrateNo

coverWoody debris

Overhead cover

No cover

Woody debris

Overhead cover

Sand  

Gravel  

Sand/Cobble  

Cobble  

N = 80Y = % fish in each slope; water column location;

location within slope patch

N = 20Y = % fish in each substrate

N = 60Y = % fish in each

substrate/cover combination

Observe over 3 diel periods, repeat for 2 life stages

Slope experiments Substrate 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 experimentsFry

• No diel or predation effects

• Deep neutral area most preferred

• 20% slope least preferred

• Cutthroat most often in 5% or neutral area

0.0

0.2

0.4

0.6E

lect

ivit

y in

dex

(al

ph

a)

0.0

0.2

0.4

Slope

Neutral area 5% 10% 15% 20%0.0

0.2

0.4

Crepuscular

Night

No cutthroat

Cutthroat presentDay

Slope experimentsPresmolts

Ele

ctiv

ity

ind

ex (

alp

ha)

0.0

0.2

0.4

0.0

0.2

0.4

0.6

No cutthroatCutthroat present

Slope

Neutral area 5% 10% 15% 20%0.0

0.2

0.4

Crepuscular

Night

Day

• No diel or predation effects

• Strong preference for deep neutral area

• Both 15% and 20% slopes avoided

Substrate arenas

Pro

po

rtio

na

l us

e

0.0

0.2

0.4

0.0

0.2

0.4

0.6

Substrate

Sand Gravel Sand/Cobble Cobble0.0

0.2

0.4

Crepuscular

Night

Day

SculpinNo sculpin

Substrate experimentsFry

• Substrate preferences shift with diel period

• No predation effect

• Sculpin mainly in cobble, rarely in sand

Substrate experimentsPresmolt

Substrate

Sand Gravel Sand/Cobble Cobble0.0

0.2

0.4

Pro

po

rtio

nal

use

0.0

0.2

0.4

0.0

0.2

0.4

0.6

Crepuscular

Night

Day

Sculpin

No sculpin• Similar, but looser, trends than fry

• No predation effect

Substrate-Cover arenas

Substrate-Cover arenas

Substrate-coverexperiments

PresmoltSculpin present

Substrate

SandGrav SC Cobb0.00

0.05

0.10

0.15

FrySculpin present

Pro

port

iona

l use

0.00

0.05

0.10

0.15

PresmoltNo sculpin

SandGrav SC Cobb

FryNo sculpin

No coverOverhead coverWoody debris

No coverOverhead coverWoody debris

• 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?

0

500

1000

1500

2000

2500

3000

1940 1950 1960 1970 1980 1990 2000

Year

Nu

mb

er o

f D

ock

s

0.0

10.0

20.0

30.0

40.0

Nu

mb

er o

f D

ock

s/M

ile

Hockett DataUW Data

Figure courtesy of J. Toft

Slope experiments:Water column location

Fry0.0

0.2

0.4

0.6

0.8

1.0P

rop

ort

ion

al u

se

0.0

0.2

0.4

0.6

0.8 Cutthroat presentNo cutthroat

Water column location

Bottom Middle Top Entire0.0

0.2

0.4

0.6

0.8

Crepuscular

Night

Day • Top of the water column rarely used

• Bottom of the water column used heavily at night, especially around predators

0.0

0.2

0.4

0.6

0.8

1.0P

rop

ort

ion

al u

se

0.0

0.2

0.4

0.6

0.8Cutthroat presentNo cutthroat

Water column location

Bottom Middle Top Entire0.0

0.2

0.4

0.6

0.8

Crepuscular

Night

Day • Top of the water rarely used

• No predation effect

Slope experiments:Water column location

Presmolt

Slope experiments:Patch location

Fry

0.0

0.2

0.4

0.6P

rop

ort

ion

al u

se

0.0

0.2

0.4

Slope unit location

Nearshore Center Offshore Cruiser0.0

0.2

0.4

Cutthroat presentNo cutthroat

Crepuscular

Night

Day• No diel or predation effect

• Cruising fish most common

0.0

0.2

0.4

0.6

0.8P

rop

ort

ion

al u

se

0.0

0.2

0.4

0.6

Slope unit location

Nearshore Center Offshore Cruiser0.0

0.2

0.4

0.6

0.8

Cutthroat presentNo cutthroat

Crepuscular

Night

Day

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