Technical Memo #2 Simulating Fall Redistribution and Overwinter Survival of Klamath River Coho Cramer Fish Sciences Nicklaus K. Ackerman Steve Cramer

Purpose Present an approach to simulate fall redistribution and overwinter survival of coho in the Klamath Basin. Approach Klamath data for this portion of the life- cycle were limited. We outlined an approach based largely on information presented in peer reviewed and gray literature. Tech Memo 2

Fall Redistribution Estuary - Trinity

Fall Redistribution Coho Catch at the Big Bar Trap in Fall 2005

Fall Redistribution 3651,71711K45K39K441,

How Do We Simulate Fall Redistribution with limited information? We reviewed literature to find studies that presented data that would provide insight into the proportion of coho populations that move to or from tributaries during fall freshets. Ebersole et al. (2006) Rodgers et al. (1987) Moring and Lantz (1975) Peterson (1982) Fall Redistribution Transferability? Effects of Assumptions?

We concluded that typically 3-11% of coho emigrate from tributaries to larger streams. Maximum range from literature reviewed was 0-38%.  Percent emigrating from a given reach partly dependent on habitat quality of that reach. Fall Redistribution We also concluded that 3-16% of the population in each mainstem Klamath reach would move into each nearby or downstream tributary.  Total exit rate from the mainstem would be % because of high number of tributaries available for overwinter rearing.

Proposed Approach: Overwinter Survival Simulate overwinter survival in each reach of the model with a hockey-stick stock-recruitment function Hypothetical Population α = 0.45 K = 50,000 K Predicted using habitat data and habitat-based capacity model

Assigning an α value to each reach: Overwinter Survival – α Value Standard α value for tributaries based on review of overwinter survival rates by Lestelle (2007). Baseline α Chose rate high among those reported by Lestelle under assumption that this would be most likely to reflect density independent survival. Baseline is similar to 3-year average survival for McGarvey Creek in lower Klamath

Habitat Quality RatingTributary ReachesMainstem Klamath Reaches High (1.0 scalar)45%32% Moderate (0.61 scalar)28%20% Low (0.22 scalar)10%7% We proposed to scale the Tributary reach α to account for habitat quality. The mainstem Klamath was assumed to be less suitable for winter rearing than tributary reaches due to confinement and lack of wood for cover. Predictions of habitat capacity would be used to assign reaches high, moderate, or low quality scalars. Overwinter Survival – α Value

Why Assume Lower Survival in Mainstem?

Simulating Effect of Size on Winter Survival Why Bother? Flow management in the mainstem affects river temperatures for a portion of the river. Temperature affects growth which determines fish size entering winter. Size entering winter affects overwinter survival. Allows us to connect effect of alternative flow operations on river temperature to relative changes in survival of fish rearing the summer in the mainstem.

Simulating Effect of Size on Winter Survival AuthorStudy GroupWinter Surv. Small Class Winter Surv. Large Class Small as % of Large Ebersole et al. 2006Moore Cr.12%52%23 Gold Cr.3%10%30 Beaver Cr.8%36%22 Brakensiek 2002Oct: Nov-Mar35%77%45 Nov: Nov-Mar20%68%29 Quinn and Peterson 1996 Big Beef Creek %44%39 Big Beef Creek %46%83 Mean39

Simulating Effect of Size on Winter Survival Bioenergetics modeling by Sullivan et al. (2000) suggests what relative effect of maximum summer temperatures on size is. Model assumed equal initial fish sizes, feeding ration, and density were equal. Extrapolation of Sullivan’s findings suggested that temperature alone may reduce fall size from 4.1 to 2.6g When MWAT increases from 12.5 to 22.5 o C. Length weight relationships for coho indicate this is a 10mm reduction in length.

Simulating Effect of Size on Winter Survival From Sullivan et al. (2000) Bioenergetics modeling shows that food rations partly determine how coho growth will respond to temperature. Higher food availability increases the tolerance fish have towards higher temperatures and shifts optimal growth to a higher temperature. Higher rations exaggerate differences in size that may be observed at a given temperature.

Simulating Effect of Size on Winter Survival Conclusions on Summer Temperature Effect on Winter Survival: Survival of fish 60mm is 39% of fish 100mm in length. MWATs ranging from may reduce end of summer length by 10mm. 10mm Reduction in length equals a 15% reduction in winter survival.

Coho Young-of-Year in 2003

Tech Memo 2