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

Abstract

Isotopic, tagging and diet studies of modern-day teleosts lacked the ability to contextualise life-history 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. Nonetheless, 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, the authors serially-sectioned four vertebral centra of the highly migratory Atlantic bluefin tuna (Thunnus thynnus; BFT) captured off Sardinia (Italy) and analysed their isotopic composition. They show how carbon (δ 13 C), nitrogen (δ 15 N) and sulphur (δ 34 S) isotope values can vary significantly across BFT vertebrae growth-axes, revealing patterning in dietary life histories. Further, they find that similar patterns are revealed through incremental isotopic analysis of inner and outer vertebrae centra samples from 13 archaeological BFT vertebrae dating between the 9th and13th centuries CE. The 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.fish bone turnover, historical ecology, life histories of fishes, serial sectioning, stable isotope analysis | INTRODUCTIONRetrospective ecological studies are increasingly analysing the stable isotopic composition of teleost vertebrae due to the predominance of these bones in the archaeological records and potential to reveal how trophic dynamics respond to environmental, ecological and cultural shifts (Barrett et al., 2011;Ólafsd ottir et al., 2017). Nonetheless, little is known about how tissue turnover influences

Exploitation shifted trophic ecology and habitat preferences of Mediterranean and Black Sea bluefin tuna over centuries

“…Since BFT bone is likely to record multiple years of foraging behaviour (Andrews et al, 2023), the observed significantly different Black Sea isotope values and low NE Atlantic and Mediterranean overlap proportions suggest that most Black Sea BFT migrated consistently to–or were resident in–this region over multiple years for foraging while NE Atlantic and Mediterranean BFT seldomly used this region as a foraging habitat. Indeed, high‐site fidelity has been reported in BFT (Block et al, 2005; Cermeño et al, 2015) but our findings would go further, supporting tagging data (De Metrio et al, 2004) to suggest that current Atlantic foraging behaviours are probably not characteristic of all BFT, even at large body size (Rouyer et al, 2022).…”

“…Isotope signatures from multiple years prior to catch are retained across the growth axes of BFT vertebrae (Andrews et al, 2023). Therefore, to obtain averages of foraging across seasons and avoid overrepresenting potential sporadic seasonal changes or foraging behaviours, we aimed to (1) sample the same element (vertebrae), whenever possible, and (2) represent roughly equal portions of acellular (cortical) and cellular (spongy) bone across the growth‐axis, between samples.…”

“…Isotope signatures from multiple years prior to catch are retained across the growth axes of BFT vertebrae (Andrews et al, 2023).…”

“…Some degree of temporal variation can be accounted for, like the long‐term decrease in oceanic 13 C following industrialisation (Suess Effect: Gruber et al, 1999), while tissue type can also improve temporal inferences. For instance, BFT vertebrae retain multiple years of isotopic foraging signatures across their growth axes (Andrews et al, 2023) and therefore bone isotope values dampen out intra‐ and inter‐annual variation, providing an average across years of foraging prior to capture.…”