Energy dynamics and growth of Chinook salmon (Oncorhynchus tshawytscha) from the Central Valley of California during the estuarine phase and first ocean year

The greatest rates of energy accumulation and growth in subyearling Chinook salmon (Oncorhynchus tshawytscha) occurred during the first month following ocean entry, supporting the importance of this critical period. Data from an 11-year study in the coastal ocean off California and the San Francisco Estuary revealed that juvenile salmon gained 3.2 kJ.day(-1) and 0.8 g.day(-1), representing 4.3%.day(-1) and 5.2% day(-1), respectively, relative to estuary exit values. Little gain in energy (0.28 kJ.day(-1)) or size (0.07 g.day(-1))occurred in the estuary, indicating that the nursery function typically ascribed to estuaries can be deferred to initial ocean residence. Calculated northern anchovies (Engraulis mordax) equivalents to meet energy gains were one anchovy per day in the estuary (8% body weight.day(-1)) and about three per day immediately following ocean entry (15% body weight.day(-1)). Energy content in the estuary was positively related to higher salinity and lower freshwater outflow, whereas in the ocean, cooler temperatures, lower sea level, and greater upwelling resulted in greater gains. These results suggest that greater freshwater flows, warmer sea temperatures, and reduced or delayed upwelling, all of which are indicated by some (but not all) climate models, will likely decrease growth of juvenile Chinook salmon, leading to reduced survival.