Flatfish and the origins of European marine fishing

During the Early Medieval period, most fish consumed in areas around the southern North Sea were taxa which could have been caught in freshwater habitats. From around the 11th century CE significantly more marine species appear in inland archaeological deposits — the so-called ‘marine fish event horizon’. As flatfish are ecologically varied, they could have been amongst the first marine taxa exploited, but so far, their role in this economic transition has been unclear due to difficulties in identifying marine, estuarine, and riverine flatfish morphologically.
To assess the role of flatfish in the marine fish event horizon, a timeline is constructed for the frequency of six species from thirteen sites around the southern North Sea to explore how flatfish fisheries changed per region during the Medieval period (6-16th centuries CE).
Firstly, flatfish identifications are refined via morphological and molecular approaches. It is found that comparative osteology and geometric morphometrics have limited applicability on archaeological material, however, a more thorough understanding of flatfish morphology is described. ZooMS identifications (n=467) using eight newly described peptide markers, reveal a relative decrease of flounder (Platichthys flesus) and an increase of plaice (Pleuronectes platessa) throughout the Medieval period.
Secondly, multi-isotope analysis of a substantial dataset (δ13C, δ15N, δ34S; n=476) indicates an early onset of marine fishing and a continuation of freshwater fisheries of flatfish throughout the Medieval period. Changes in isotope values and species abundances could be linked to a more marine-oriented fishing practice across the southern North Sea in the High Medieval period.
This first multi-disciplinary study of flatfish remains has revealed species-specific interpretations about where and when people exploited flatfish, providing insight into economic, social and environmental changes in the North Sea area during a key period of economic transition in the Medieval period.