ASSESSING THE SEASONALITY AND INTENSITY OF SHELLFISH EXPLOITATION IN THREE WESTERN CANARY ISLANDS OVER THE LAST ~2000 YEARS

This study assesses the seasonality and intensity of human harvesting practices of limpet assemblages (Patella candei crenata) from three western Canary Islands (Tenerife, La Palma, La Gomera) since pre-Hispanic times (~2,000 yrs ago) to recent. We predict that shellfishing practices were intensified during the warmest part of the year, when inland agriculture was inhibited by drier conditions during the summer. We also assume that harvesting practices were relatively intense during prehistoric times, but less so than today. To test these hypotheses, we combine shell margin oxygen stable isotope data (δ¹⁸O), which reflect the sea surface temperature (SST) closest to shell collection date; and body size variations, which inform about intensity of human exploitation. A total of 100 shells from ten radiocarbon-dated cultural shell middens were isotopically measured at the shell margin and each shell was also measured to quantify shell dimensions. Calculated SSTs were derived from the shell margin δ¹⁸O and compared to the modern SST range in the Canary Islands (18-25 °C). Shell margin δ¹⁸O results demonstrate that shellfish harvesting occurred primarily in the summer months, with all analyzed shells being collected at temperatures above 21°C. Interestingly, SSTs estimated from these shells corresponded with well-established Holocene rapid climate events in the Northern Hemisphere such as the Vandal Minimum and Medieval Warm Period, which suggest that these shells can provide Holocene climate information in future studies using isotope sclerochronology. Body size measurements demonstrated a significant decline in overall body size from pre-Hispanic times to present-day, illustrating a notable increase in the intensity of shellfish collection through time. This work suggests that combining isotope geochemistry and body size data from archaeological mollusks offer more informed conditions of anthropological and climatic interactions.