Archaeologists have traditionally assumed that proportional variability in the types of shellfish remains found in middens can directly inform arguments about prehistoric coastal and island diets. We explore this assumption by comparing an analysis of three shellmidden sites on the Meriam Islands (eastern Torres Strait, Australia) with data on contemporary Meriam shellfishing strategies. We present tests of hypotheses drawn from behavioral ecology about factors that influence prey choice and differential field processing and transport, and compare these results to variability displayed in the shell assemblages. We find that while prey choice is predictable ethnographically, it is not reflected in the midden remains. Variability in the middens only begins to make sense with reference to the tradeoffs that foragers face in attempts to maximize the rate at which they can deliver resources to a central locale. This result should be of interest to all researchers concerned with reconstructing and explaining variability in prehistoric subsistence practices, especially in coastal or island settings.