Several sites in Plum Island Sound, the mainstem of the Parker River and Rowley River were selected and sampled for 2 and 4 inch clams on a monthly basis (clams selected were intertidal, meaning they were collected at low tide due to being covered by water at high tide). 20 clams 2" in length and 20 clams 4" in length were collected at each site monthly, and frozen for later isotopic analysis. In the lab, these clams were dissected and their adductor muscles removed (adductor muscles were selected because the muscle tissue would give the best representation of long term food sources rather than a brief snapshot if stomach tissue were selected). The muscles of the clams were freeze dried and then ground together using a ball mill. The tissue samples were then weighed out on a microbalance into tins for isotope analysis (deuterium (H), carbon (C), nitrogen (N) and sulfur (S)). Northern Arizona University's isotope lab performed the analyses Water samples were also filtered at several clam collection sites and plants were collected to determine their isotopic composition . Filters were sent directly to Northern Arizona University for analysis. Plant samples were freeze dried and ground in a ball mill, then weighed into tins and sent to Northern Arizona University for analysis.