ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Chinook salmon The fall-/late fall-run of Chinook salmon is currently the largest run of Chinook salmon in the San Joaquin River system. Because fall-/late fall-run Chinook salmon represent the greatest proportion of all four runs in the Central Valley,they continue to support commercial and recreational fisheries of significant economic importance. On September 16, 1999 (64 FR 50393),NMFS determined that listing was not warranted for the Central Valley fall- /late fall-run Chinook salmon ESU. However,the ESU was designated as a candidate for listing due to concerns over specific risk factors. On April 14,2004(69 FR 19975)the ESU was reclassified as a species of concern. The ESU includes all naturally spawned populations of fall-run Chinook salmon in the Sacramento and San Joaquin River Basins and their tributaries, east of Carquinez Strait. Chinook salmon adult migration—In general, adult fall-/late fall-run Chinook salmon migrate into the Sacramento River and its tributaries from July through December,with immigration peaking from mid-October through November(Exhibit 4.13-2). Fall-/late fall-run Chinook salmon spawn in tributaries of the San Joaquin River, including the Stanislaus River, Tuolumne River, and Merced River, several miles upstream of the project site. Optimum water temperatures for adult Chinook salmon migration have been reported to range from approximately 49 to 58 degrees Fahrenheit(°F),with adult migration continuing to occur at temperatures up to approximately 68°F (Bell 1973). Optimal temperatures generally range from 507 to 59°F for adult Chinook salmon migration and pre-spawning activity. Consistent temperatures of 60°F to 64°F are considered acceptable for migration by NMFS and U.S. Environmental Protection Agency(EPA), and EPA's criteria for migration is 68°F if there are thermal refuges in the system allowing fish to migrate and hold in cooler areas for some part of the migration period. This suggests a relatively slow increase in adverse thermal effects from 60°F to 68°F,where several types of low chronic stress have been documented(Berman 1990;Marine 1992; Poole et al. 2001), including potential for reduced swimming speed, increased disease, and reduced fecundity. There is reasonable agreement that consistent temperatures in the 64°F to 68°F range are somewhat stressful and create stress even with short-term exposure times of days to weeks. Above 68°F, disease rates have been documented to be quite high, including 100%mortality from disease outbreaks (Berman 1990). Because disease is a significant concern, and higher temperatures are clearly related to increased disease incidence and lethality, it is reasonable to assume that the adverse effects curve begins to steepen rapidly at higher temperatures and longer exposure times. Based on available information,the following temperature guidelines have been identified for adult Chinook salmon: ► Optimal range: 50°F to 60°F ► Range of increasing adverse effects: 61°F to 68°F ► Lethal effects: >68°F ► Behavioral avoidance: reported at 68°F Chinook salmon juvenile rearing and migration—Juvenile fall-run Chinook salmon emigrate from San Joaquin River tributaries (e.g., Stanislaus,Merced, and Tuolumne rivers)and other river tributaries to the delta during the late winter and spring(February—mid-June) (San Joaquin River Group 2001,2002, 2003,2004, 2005; CDFG unpublished data). Within a range of approximately 50°F to 60°F,warming temperatures appear to increase growth rates of rearing Chinook salmon and temperatures in this range are considered optimal or acceptable. Low-level stresses such as smolting problems may occur within and outside of this range,but high growth rates may be sustained in the 59°F to 66°F range, somewhat offsetting potential disease problems. Bartholow and Henriksen(2004)evaluated fall-run Chinook salmon mortality over a range of mean weekly water temperatures(constant daily mean temperature exposure, assuming variation throughout the day). Their analysis is consistent with an optimum high threshold of 60°F,where they find daily mortality rates are very low. They EDAW Manteca WQCF and Collection System Master Plans EIR Fisheries and Aquatic Resources 4.13-6 City of Manteca