Isotopic life‐history signatures are retained in modern and ancient Atlantic bluefin tuna vertebrae

Isotopic, tagging and diet studies of modern-day teleosts lack the ability to contextualise life-histories and trophic dynamics with a historical perspective, when exploitation rates were lower and climatic conditions differed. Isotopic analysis of vertebrae, the most plentiful hard-part in archaeological and museum collections, can potentially fill this data-gap. Chemical signatures of habitat and diet use during growth are retained by vertebrae during bone formation. However, to fulfil their potential to reveal life-history and trophic dynamics, we need a better understanding of the time-frame recorded by vertebrae, currently lacking due to a poor understanding of fish bone remodelling. To address this issue, we serially-sectioned four vertebral centra of the highly migratory Atlantic bluefin tuna (Thunnus thynnus; BFT) captured off Sardinia (Italy) and analysed their isotopic composition. We show how carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) isotope values can vary significantly across BFT vertebrae growth-axes, revealing patterning in dietary life-histories. Further, we find similar patterns are revealed through incremental isotopic analysis of inner and outer vertebrae centra samples from thirteen archaeological BFT vertebrae dating between the 9th-13th century CE. Our results indicate that multi-year foraging signatures are retained in vertebrae and allow for the study of life-histories in both modern and paleo-environments. These novel methods can be extended across teleost taxa owing to their potential to inform management and conservation on how teleost trophic dynamics change over time and what their long-term environmental, ecological, and anthropological drivers are.