Matt Sloat and Gordon Reeves Fisheries and Wildlife Management Oregon State University and USFS PNW Research Station, Corvallis, OR Influence of changing thermal regimes on steelhead growth and life history expression

Climate change will alter the thermal regimes of aquatic ecosystems How will aquatic organisms with complex life histories respond to these alterations?

O. mykiss life cycle Boughton et al. J. Tomelleri

Males exhibit alternative mating tactics Anadromous- delay maturation and mature at large size FW resident- mature early at small size O. mykiss life histories photos: J. McMillan

Probability of early maturity % 90% Length-at-age

McMillan et al. (2011) Env. Bio. Fish. Lipid storage greater in cold streams and growth (i.e., length) greater in warm streams. (Wilcoxon rank sum test, p >0.001) (Wilcoxon rank sum test, p = 0.02)

Redrawn from McMillan et al. (2011) Env. Bio. Fish. warmer colder Probability of early maturity Length-at-age (mm)

Warmer Length-at-age Probability of early maturity 1 0

Study objective: Determine the influence of thermal regimes on energy allocation and life history expression in O. mykiss Obtained fertilized eggs from a single pair of Clackamas River steelhead from the Clackamas River Hatchery Incubated at OSU Salmon Disease Lab

2 thermal regimes 12 replicates per thermal regime 24 tanks total Difference in thermal regimes represents a 2.5°C increase in mean annual water temperature Overview of experimental design

30 individually marked fish per tank post hoc analysis: sex ratio ~ 1:1 30 fish per tank 24 tanks total 720 individually marked fish VIE marks identify individual fish Overview of experimental design

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)

Results

Male growth trajectories: length * * * * * * * 20mm

Male growth trajectories: mass * * * * * * * 22g

SmoltsMature males

Smolts: 46% * Mature: 49% * Smolts: 16% * Mature: 76% * UN: 8% UN: 5% Male life history expression for steelhead offspring reared under different thermal regimes Cold thermal regimeWarm thermal regime

Cold regime Warm regime Male growth trajectories by life history type: length * * * * * * Month Length (mm)

Cold regime Warm regime Male growth trajectories by life history type: mass * * * * * * * * * Month Mass (g)

Warm regimeCold regime smolt mature smolt mature smolt mature smolt mature

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

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.

photo: Becky Sloat