lentic habitat preferences of juvenile chinook salmon in experimental arenas chris sergeant r.tabor
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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