Carbon and nitrogen stable isotope ratio analysis of freshwater, brackish and marine fish from Belgian archaeological sites (1st and 2nd millennium AD)

Abstract

Carbon and nitrogen stable isotope ratios were measured in 157 fish bone collagen samples from 15 different archaeological sites in Belgium which ranged in ages from the 3^rd to the 18^th c. AD. Due to diagenetic contamination of the burial environment, only 63 specimens produced results with suitable C : N ratios (2.9–3.6). The selected bones encompass a wide spectrum of freshwater, brackish, and marine taxa (N = 18), and this is reflected in the δ¹³C results (−28.2‰ to −12.9%). The freshwater fish have δ¹³C values that range from −28.2‰ to −20.2‰, while the marine fish cluster between −15.4‰ and −13.0‰. Eel, a catadromous species (mostly living in freshwater but migrating into the sea to spawn), plots between −24.1‰ and −17.7‰, and the anadromous fish (living in marine environments but migrating into freshwater to spawn) show a mix of freshwater and marine isotopic signatures. The δ¹⁵N results also have a large range (7.2‰ to 16.7‰) indicating that these fish were feeding at many different trophic levels in these diverse aquatic environments. The aim of this research is the isotopic characterization of archaeological fish species (ecology, trophic level, migration patterns) and to determine intra-species variation within and between fish populations differing in time and location. Due to the previous lack of archaeological fish isotope data from Northern Europe and Belgium in particular, these results serve as an important ecological backdrop for the future isotopic reconstruction of the diet of human populations dating from the historical period (1^st and 2^nd millennium AD), where there is zooarchaeological and historical evidence for an increased consumption of marine fish.