Where the Shells Come From? A New Methodology for Establishing Collection Areas Applied to Upper Palaeolithic and Mesolithic Shell Middens From Northern Iberia

Abstract Shellfishing was a common activity among prehistoric hunter-gatherers living in coastal areas in Iberia. Interpreting shellfish collection strategies is crucial to understand the lifeways of these coastal hunter-gatherers. Among collection strategies, the estimation of collection areas is essential for interpretation of mobility and subsistence strategies. In this paper we present a new methodological procedure to identify mollusc collection areas using a Technical Scoring Matrix (TSM). A TSM is a qualitative tool that infers the origin of one or more objects based on probability categories that can be quantified using a scoring system. First, a TSM must be built for a given area, including the range of mollusc species identified in archaeological sites, and considering the type of coastline, substrate and the littoral zone where they currently live. The scoring system is then applied to archaeological molluscs recovered from shell middens to establish collection areas. The application of a TSM to Upper Palaeolithic, Epipaleolithic and Mesolithic shell middens from northern Iberia showed that mollusc collection was focused on rocky substrates of exposed and sheltered coastlines during the Magdalenian and the Azilian, with an increase in diversification of collection areas through time, including important shellfishing activity in soft-bottom areas, such as estuaries, during the Mesolithic. From the Azilian onwards, the lower mesolittoral replaced the upper mesolittoral as the most heavily harvested zone. Higher diversification in collection areas and larger collection in the lower zones over time suggest that intensification started at least in the Magdalenian and increased in the Mesolithic, which aligns with previous interpretations based on the decrease in shell size.