Six sampling sites were selected along the flanks of the lower 14 km of the estuary where clams were found. Approximately 20 clam shells ≥10 cm with obvious external growth lines and patterns were selected at each site in total for internal growth line analyses , and two shells from each site were selected for the oxygen stable isotope analyses (del18O). One valve of each clam shell was used for delineation of internal growth lines and the other valve was then used to transcribe internal lines onto the shell surface in order to estimate size for each year of growth. For internal growth line analysis, the valves were first embedded in epoxy resin (to prevent shell fracture during sectioning . The valves were sectioned from the umbo to the ventral margin using a rock saw .The cross-sectional surface was ground with 240, 320 and 600 abrasive papers and polished using a Buehler Grinder-Polisher . We periodically observed the cross-section under a microscope during the grinding-polishing process and continued the process until the internal growth lines became apparent. Annual growth lines were identified, marked and counted under the microscope .The internal growth lines were transcribed onto the shell surface of the matching valve and then shell length was measured for each year of age . Shell length was measured as the maximum distance across the shell surface, typically perpendicular to the cross-sectional cut The measurements were made to the nearest 0.01mm using digital vernier calipers. For oxygen stable isotope analysis, we collected sequential shell-carbonate samples from two shells from each site (total twelve shells). Two to five samples were collected between presumed growth lines and on the growth lines by grinding a strip approximately 1 cm long by 1 mm of shell width with 0.5 to 1 mm intervals between samples from the ventral margin to umbo . The samples were ground with a dremel. When grinding the shell, the entire shell from inner surface outwards was collected, as opposed to only layers corresponding to specific times when new shell material was laid down. Therefore each sample from shell edge to chondricle included growth from all prior years in addition to new group, blending seasonal data. Prior to analysis, we cleaned the shell surface and the inner shell layer several times to remove organic matter. The samples were muffled in a muffle furnace for 1 h at 380° C to further remove organic contaminants. Collected grindings were powdered in a mortar and pestle, and stored in sample vials for submission to an isotope analysis laboratory (Colorado Plateau Stable Isotope Laboratory at Northern Arizona University.)