Flatfish (Pleuronectidae) on the menu in 16th century Abbeville (France). The contribution of osteometrics and stable isotopes to species and fishing origin identification

Pleuronectidae (flatfish) are not always identifiable to the species level on the basis of isolated bones found in archaeological assemblages, and one of the most targeted species in northwestern Europe, flounder (Platichthys flesus), has an extremely large plasticity in habitat use. These issues limit the interpretation of the presence of flatfish bones with regard to fishing ground exploitation and fish trade in the past. This study aims to infer the fishing grounds of flatfish consumed at the site of Abbeville Chaussée du Bois, in northwestern France, dated to the 16th century, based on the analysis of examples of two unpaired bones, the first anal-fin pterygiophore or “os anale” and the urohyal. The city of Abbeville was an important port during Middle Ages and the Early Modern period. We used an integrated approach combining osteology, osteometrics (n = 84), and stable isotope analysis of bone collagen (n = 31). We were able to confirm the presence of both flounder and plaice (Pleuronectes platessa). We estimated their size and age at capture thanks to metric models that we developed for modern plaice (n = 34) and flounder (n = 55) from in- and offshore environments in the Somme estuary. The presence of only adult fish remains at the site and the ethology of the two species exclude exploitation of only the immediate vicinity of the city, i.e., the River Somme itself or the very non-saline part of the estuary close to the river outlet. Although the δ13C and δ15N values of the flounder and plaice from the site partially overlap, the two groups present distinctive δ13C and δ15N values and bi-isotope variability. Their isotope signatures were compared with those of archaeological marine (n = 14) and freshwater (n = 26) fish remains used as references. The flatfish identified from the site had spent time living in habitats ranging from marine to brackish or even freshwater. Our combined approach suggests the contemporaneous exploitation of several fishing grounds or alternatively marine waters at spawning time to provide the menu served at the site. Our approach appears a promising means to explore the trade in flatfish inland during historical times.