ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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show daily mortality rates rising slowly as temperatures approach 68°F and then rising rapidly from 68°F to 77°F, at which time mortality is considerable. They note that this mortality is not necessarily a result of direct thermal effects,but may be related to disease, predation, and other indirect effects. Their continuous relationship,therefore,provides a basis for establishing a continuous criterion that reflects indirect effects as well as direct effects. They compare their projections to relationships for rearing and smoltification,which include acclimation effects. Given the potential for downstream thermal effects on emigrating fry and smolts, a regime of rising temperatures in the spring,up to 60°F,may be considered beneficial, and temperatures from 61 OF to 68°F should be considered acceptable,with low levels of stress offset by growth rates that may not decline significantly until about 68°F. Based on available information,the following temperature guidelines have been identified for juvenile Chinook salmon: ► Optimal range: 50°F to 60°F ► Range of increasing adverse effects: 61'F to 68°F(low); >68°F (rapidly increasing) ► Lethal effects: >77°F ► Behavioral avoidance: change(delta-T) of 16°F above ambient Steelhead On March 19, 1998,NMFS listed the Central Valley Steelhead as threatened(63 FR 13347). Central Valley steelhead are all considered to be winter-run steelhead(McEwan and Jackson 1996). Similar to salmon,these fish mature in the ocean before entering freshwater on their spawning migrations. Steelhead adult migration—The timing of river entry is often correlated with an increase in river flow, such as occurs during freshets and precipitation events with the associated lowering of ambient water temperatures. Moyle (2002)notes that steelhead have been observed in migration,holding, and spawning over a wide range of temperatures (33°F to 77°F),but he considers an acceptable range is 39°F to 73°F. Estimates of optimum temperature regimes are correspondingly wide ranging, and estimates of optimal conditions are: 39°F to 51°F (IEP 1999); 44°F to 51°F(USFWS 1997); 50°F to 59°F (Moyle 2002). EPA(2003) applies its general salmonid criteria to steelhead,with an acceptable seven day average of the daily maximum temperature of 64°F (or 68°F with thermal refuges).USFWS (1997) suggests there is chronic low stress at 51°F to 59°F, and higher stress above this range. Given the potential for high diel(24-hour daily)temperature variation, an optimal mean daily temperature range for steelhead migration may be 44°F to 53°F,with low stress effects between 54°F and 68°F. Temperatures in excess of 68°F should be assumed to be stressful,with a lethal threshold of 69°F to 73°F, depending on assumptions regarding disease(LWA 2006). Based on available information,the following temperature guidelines have been identified for adult steelhead: ► Optimal range: 44°F to 53°F ► Range of increasing adverse effects: 54°F to 68 F ► Lethal effects: >69 OF ► Behavioral avoidance: reported at 65°F Steelhead juvenile rearing and emigration—Moyle(2002)notes that juvenile Steelhead have been observed rearing in temperatures from 33°F to 77°F,but that a survivable range is probably 37°F to 71'F. Steelhead are thought to have marginally higher thermal tolerances than Chinook salmon. This would reflect steelhead life history,which includes the potential for progeny of anadromous steelhead to rear in freshwater for an extended period of time pending parr maturation and a return to the sea. Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.13-7 Fisheries and Aquatic Resources