Growth Rate Variation among Juvenile Chinook Salmon (Oncorhynchus Tshawytscha) Cohorts and Rearing Conditions

The San Joaquin River (SJR) in California’s Central Valley represents the historical southern-most range of Chinook salmon (Oncorhynchus tshawytscha). In 2006, the San Joaquin River Restoration Program (SJRRP) was created to mitigate the negative effects of the Friant Dam which has caused degradation of extended portions of the SJR. The artificially changing hydrology of the SJR affects the thermal dynamics of restoration reaches which plays a significant role in growth and metabolism of juvenile Chinook salmon (JCS). Mass standardized growth rates () of SJR JCS cohorts (n=4) were compared to other wild (n=4) and hatchery (n=10) JCS populations. The estimated  of wild SJR are high compared to other wild populations and are comparable to hatchery populations, despite living in what is regarded as “poor conditions.” The temperature optima and critical level for the SJR set by the SJRRP are based on EPA Region 10 (Pacific Northwest). Using a new JCS bioenergetics model with updated parameters and accurate recorded temperatures, bioenergetic model simulations were run to examine population-specific temperature regulation of manifested and potential growth. The results suggest that SJR JCS can continue their high growth rates with ample prey. My results suggest the importance of population-specific growth rate parameters and call into question the practice of applying bioenergetic and metabolic estimates from one population to other populations of Chinook. These data can help inform both water management and salmon conservation, especially in California where river water temperatures are highly regulated by water agencies and conflicting water demands and uses.