GEODUCK AQUACULTURE MONITORING IN NEAH BAY AND SEAWATER ISOTOPIC ANALYSES

Makah Fisheries Management (MFM) has conducted a monitoring program at the Neah Bay geoduck aquaculture beds since 2013, and obtained water samples and environmental parameters (e.g., temperature, salinity. pH, dissolved oxygen and pressure) in situ on a weekly basis. The water samples were analyzed for dissolved inorganic carbon (DIC) for δ¹³C and ¹⁸O/¹⁶O ratios. The two-year water quality data reflect patterns of natural variation: a clear seasonal shift in both temperature and salinity. The DIC ranged from 0.7‰ to 4.2‰ while the δ¹⁸O ranged from -4.5‰ to -0.6‰. The pH showed a range from 7.5-8.4 in the first year, but much lower (6.4-7.5) in the second winter. The pH variation appeared consistent with the seasonal change of temperature. In contrast, the DIC variations were correlated with temperature and the δ¹⁸O correlated with salinity. There were no clear patterns of variation for dissolved oxygen, or significant correlations with environmental parameters. These results indicated that our sampling scheme is viable and can provide valuable input for the MFM projects with geoduck, mussels, and scallops. Once stable isotope data from shell material (mainly for δ¹³C and δ¹⁸O) have been obtained, the shell and seawater δ¹⁸O allow us to create a predictive model of past temperatures that the animal has been exposed to; whereas the shell and seawater δ¹³C can allow us to track the animal's sources of carbon that are changing through time.