Sarah McCarthy Trophic performance of Oncorhynchus mykiss along forest gradients in the South Fork Trinity River watershed UNIVERSITY OF WASHINGTON

South Fork Trinity River Photo courtesy of J. Duda

Klamath River tributary Trinity River dam: 1962 South Fork Trinity undammed Klamath Mountains Province steelhead ESU unlisted

What factors control O. mykiss production in CA? Temperature Effects Prey Quality Feeding Rate Use bioenergetics modeling to identify effect of season, age, forest cover, and temperature on O. mykiss consumption and growth efficiency (GE).Objectives

Study Design 9 streams 3 forest cover categories 2 temperature regimes

Study Design Conifer-cool N=1 Conifer-warm N=2 Mixed-cool N=1 Mixed-warm N=2 Hardwood- cool N=3 N/A

FISH GROWTH Bioenergetics Model CONSUMPTION THERMAL EXPERIENCE DIET COMPOSITION PREDATOR ENERGY DENSITY PREY ENERGY DENSITY C = G + M + W Proportion of maximum consumption (p): C/C max G/C = Growth efficiency (GE)

Model Inputs Stream Temperature (constant temperature monitoring) Prey Quality (invertebrate drift sampling) O. mykiss Growth Measurements O. mykiss Diet Composition

Fish Sampling Electrofished 9 streams during June, August, and October 2003

Measured length & weight Fish Sampling

Electrofished 9 streams during June, August, and October 2003 Measured length & weight Collected scales Fish Sampling

Electrofished 9 streams during June, August, and October 2003 Measured length & weight Collected scales Collected stomach contents Fish Sampling

Weight Trajectories Fish Sampling Conifer-cool highest weight, but all groups had slow growth Warm streams had sharpest growth increase Hardwood-cool and conifer-cool grew most

Diet Composition Prey items: Immature aquatic sources: –Aquatic larvae (Diptera, Coleoptera, Trichoptera, etc) –Aquatic nymphs (Ephemeroptera, Plecoptera, etc) –Aquatic other (Gastropoda, Isopoda, Crustacea, Acarina, Ostracoda, etc) Adult invertebrates: –Aquatic (Ephemeroptera, Plecoptera, Trichoptera, Diptera) –Terrestrial (Coleoptera, Hymenoptera, Araneae)

Diet Composition Contribution of adult insects increased with age

Diets varied by season and age

Low proportion of maximum consumption (avg=0.25) Temperature (°C) Specific rate (g/g/d) C max Summer temps: 14-18°C Consumption Respiration Bioenergetics Modeling C = G + M + W

Simulating Increased Summer Temperature Effects Most growth occurs during winter/spring Age 0 Age 1 Age 2

Simulating Increased Summer Temperature Effects With 2 o C temperature increase, O. mykiss required to grow more over winter. 5.4% 8.9% 11.5% 18.8%

Summary Increased consumption of adult insects with age and season Higher consumption of adult invertebrates in conifer-cool category Decreased or negative growth during late summer Low feeding rates throughout summer Decreased summer growth after 2 o C temperature increase Photo courtesy of J. Duda

Summary Increased consumption of adult insects with age and season Higher consumption of adult invertebrates in conifer-cool category Decreased or negative growth during late summer Low feeding rates throughout summer Decreased summer growth after 2 o C temperature increase Photo courtesy of J. Duda

Summary Increased consumption of adult insects with age and season Higher consumption of adult invertebrates in conifer-cool category Decreased or negative growth during late summer Low feeding rates throughout summer Decreased summer growth after 2 o C temperature increase Photo courtesy of J. Duda

Summary Increased consumption of adult insects with age and season Higher consumption of adult invertebrates in conifer-cool category Decreased or negative growth during late summer Low feeding rates throughout summer Decreased summer growth after 2 o C temperature increase Photo courtesy of J. Duda

Summary Increased consumption of adult insects with age and season Higher consumption of adult invertebrates in conifer-cool category Decreased or negative growth during late summer Low feeding rates throughout summer Decreased summer growth after 2 o C temperature increase Photo courtesy of J. Duda

Conclusions Isn’t summer the “growing season”? –O. mykiss may be food-limited across the watershed –Heightens concern for effects of interannual variability and/or climate shifts –Implications for other steelhead stocks in CA high temperatures exacerbated by low prey supply even minor shifts in temperature or food supply could push population further into negative growth patterns –Recommend extending study to neighboring populations

Acknowledgements USGS: Jeffrey Duda, C. Ostberg, Dr. R. Reisenbichler, Dr. S. Rubin, K. Larsen, S. Dufrene, L. Pascoe, C. Chambers, C. Galitsky, J. Steinbacher UW School of Aquatic and Fishery Sciences: Dr. C. Grue, Dr. L. Conquest, V. Blackhurst, E. Chia, D. O’Donnell, A. Van Mason, A. Lind, C. Sergeant, S. Damm, J. Matilla, E. Duffy, A. Cross, J. Moss, M. Mazur, N. Overman, S. Wang, E. Schoen USFS Redwood Sciences Laboratory, Arcata, CA: Dr. H. Welsh, G. Hodgson, Dr. B. Harvey USFS Ranger Station, Hayfork, CA: J. Lang, J. Fitzgerald UNIVERSITY OF WASHINGTON Graduate committee : Dr. David Beauchamp, Dr. John Emlen, Dr. Thomas Quinn

Effects of Food and Temperature on Growth Energetics Temperature (°C) Specific rate (g/g/d) C max Consumption: Respiration 25% C max Consumption rate reduction = reduced optimal temperature for growth and growth potential.

Effects of Food and Temperature on Growth Energetics Temperature (°C) Specific rate (g/g/d) C max Consumption Respiration 5 25% C max Growth (g/(g*d)) Temperature (°C) % C max 100% C max Absolute growth very low when costs associated with metabolism and waste are accounted for.

Physical Stream Characteristics Stream Temperature Temperature loggers deployed April-October 2003 Temperature recorded every 20 minutes Avg daily temp >17°C = warm Avg daily temp <17°C = cool

Prey Sampling Drift Composition Drift samplers deployed before dusk; collected after dawn Evaluated relative proportion of invertebrate drift Invertebrates used for bomb calorimetry

Relative Prey Supply Drift Composition Higher volume of immature aquatic invertebrates Higher prey supply in hardwood-cool flow Stream bottom Drift sampler bias

Cumulative Consumption GE = Growth/Consumption %-2.3 – 9.7%-7.3 – 7.2% Lower growth efficiencies during late summer

Cumulative Consumption GE = Growth/Consumption -1.1 – 11%-42 – 15.2%-3.8 – 15.4% Lower growth efficiencies during late summer

Cumulative Consumption GE = Growth/Consumption 3.7 – 7.1%-2.7 – 13.2%-12.2 – 15.9% Lower growth efficiencies during late summer