Matt Sloat and Gordon Reeves

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Influence of changing thermal regimes on
steelhead growth and life history expression
Matt Sloat and Gordon Reeves Fisheries and
Wildlife Management Oregon State University and
USFS PNW Research Station, Corvallis, OR
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Climate change will alter the thermal regimes of
aquatic ecosystems How will aquatic organisms
with complex life histories respond to these
alterations?
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O. mykiss life cycle
J. Tomelleri
Boughton et al.
J. Tomelleri
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O. mykiss life histories

• Males exhibit alternative mating tactics

FW resident- mature early at small size
Anadromous- delay maturation and mature at large
size
photos J. McMillan
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Probability of early maturity
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Length-at-age
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McMillan et al. (2011) Env. Bio. Fish.
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Probability of early maturity
Length-at-age (mm)
Redrawn from McMillan et al. (2011) Env. Bio.
Fish.
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(No Transcript)
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Colder
Warmer
Probability of early maturity
0
Length-at-age
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Study objective Determine the influence of
thermal regimes on energy allocation and life
history expression in O. mykiss
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Overview of experimental design

• 2 thermal regimes
• 12 replicates per thermal regime
• 24 tanks total

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Overview of experimental design
30 individually marked fish per tank post hoc
analysis sex ratio 11

• 30 fish per tank
• 24 tanks total
• 720 individually marked fish

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• Methods
• Monthly growth measurements (FL, mass) of
  individual fish

• Life history categorization
• Assessment of smolt status April June 2011

• Assessment of maturity Aug 2011

• Retrace growth trajectories of fish within life
  history categories

• Whole body lipid analysis (forthcoming)

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Results
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Male growth trajectories length
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Male growth trajectories mass







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Smolts
Mature males
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Male life history expression for steelhead
offspring reared under different thermal regimes
Smolts 46
UN 5
Mature 49
Cold thermal regime
Warm thermal regime
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Male growth trajectories by life history type
length
Cold regime
Warm regime




Length (mm)


Month
Month
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Male growth trajectories by life history type
mass
Cold regime
Warm regime



Mass (g)






Month
Month
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Warm regime
Cold regime
smolt
smolt
mature
mature
smolt
smolt
mature
mature
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• Conclusions
• Despite higher rates of somatic growth, fish
  experiencing warmer
• temperatures had lower rates of maturation

• Temperature may alter energy allocation in
  important ways that
• are not captured by measuring somatic growth
  alone

• A mechanistic understanding of physiological
  responses to altered
• thermal regimes is needed to forecast effects
  of climate change

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Acknowledgments Funding provided by USFS PNWRS
with additional support from USGS FRESC,
Corvallis, ORAFS Carl Bond Memorial
Scholarship. Thanks to Jason Dunham, India
Sloat, Jill Pridgeon, Haley Ohms, Amy Lindsley,
Stephanie Saunders, Matt Stinson, and staff at
ODFW Clackamas Hatchery.
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photo Becky Sloat