The isotopic differences and implications for Pacific razor clams along the Washington coast

The Pacific razor clam fishery in Washington State has been co-managed by the coastal Indian Tribes and the state, but little is known about the growth and population structure of the clams due to difficulties of tagging and monitoring. Here we report the results of a pilot study using stable isotope ratios (δ 13 C and δ 18 O) of razor clam shells collected in two groups (juvenile vs. adult) and from two sites (Kalaloch Beach and Roosevelt Beach) where distinct biological differences in clam growth and survival rates were observed. The δ 13 C values of razor clam shells ranged from -2.9 to -0.3‰, whereas δ 18 O values of the same samples ranged from -2.2 to +1.4‰. Between the two sites there were significant differences in δ 13 C values especially for juvenile clams. The δ 18 O profiles from two representative shells demonstrated similar patterns of rapid growth as juveniles and seasonal patterns throughout the life span. Profiles of δ 13 C were sinusoidal but did not show seasonality and signatures of ocean acidification. We concluded that stable isotope analysis of razor clam shells is a potential new tool in shellfish research and management.