Age composition and average annual growth rates were determined for a geoduck clam (Panope abrupta) population located in Ladysmith Harbour, British Columbia. Acetate peels were made from cross-sections of the right shell portion of each clam. The number and distances between the annuli in shell cross-sections were used to determine age and growth. Analysis of the growth measurements suggested the annual growth of individuals within this population in any year t was approximately 80% of the annual growth in year t − 1. This estimate does not appear to be a function of age. An average annual index of standardized geoduck growth was constructed for the period 1907–1980. Abrupt changes in mean annual growth were detected near 1919 and 1962. Intervention analysis was employed to quantify changes in mean standardized growth at these two points in time. An 8% increase in geoduck mean annual growth was coincident with an increase in mean annual temperature around 1920. A 27% decrease in growth occurred soon after the initiation of log booming and storage in Ladysmith Harbour (about 1960). The results of this study suggest measurements of growth from geoduck shells may be useful in identifying and quantifying changes in the marine environment.