In 31 years of monitoring the condition index of temperate northeast Pacific oysters (Crassostrea gigas), the lowest annual index value was recorded during the 1982--1983 El Ni¿o--Southern Oscillation (ENSO) event. Cross-spectral analyses of monthly fluctuations of the condition index with seal level height indicate that there are significant correlations between them, although out of phase. Coherent signals with an approximately 2-year period have been detected in the data in the interval between ENSO events. We conclude that sea level height fluctuations may indirectly influence oyster growth, through alterations in productivity, and the availability of planktonic food resources. ¿ American Geophysical Union 1987