Chemical signatures in fin spine edge of Atlantic bluefin tuna (Thunnus thynnus) can serve as habitat markers of geographically distinct marine environments

Chemical fingerprints in otoliths are commonly used as natural habitat markers in fishes. Alternatively, the first dorsal fin spine can provide valuable chemical information and may be more suitable for studying (i) endangered fish species that cannot be sacrificed for their otoliths or (ii) fishes for which otoliths might not be available because of management or commercial reasons. Here, we studied multi-element chemistry of fin spine edges collected from Atlantic bluefin tuna (ABFT; Thunnus thynnus) (Linnaeus, 1758) to investigate the utility of the fin spine edge as a natural habitat marker. We determined stable isotopic δ18O and δ13C ratios, as well as concentrations of the tracer elements Mg, Mn, Li, Ba, and Sr, at the edge of ABFT fin spines, and then we used these measures to discriminate ABFT individuals among capture regions (i.e., the eastern Atlantic Ocean or Mediterranean Sea). Isotope ratios and tracer element concentrations, and especially a combined multi-element approach, were able to effectively discriminate individuals by capture region. The Mg, Mn, Li, and δ18O concentrations were the strongest variables driving this discrimination. Overall, our results demonstrate that chemical signatures are consistently retained in the ABFT fin spine edge and support the use of fin spine edges for discerning habitat use. The fin spine chemistry as a minimally invasive sampling method, combined with otolith chemistry, genetic markers, and tagging efforts can help us to reconstruct fish movements, providing a deeper understanding of the spatial population dynamics of this iconic fish species.The authors also wish to thank the many people who were involved in the collection of the fin spine samples used for this study under the provision of the ICCAT Atlantic Wide Research Programme for Bluefin Tuna (GBYP), which an ICCAT special research program funded by the European Union, several ICCAT CPCs, the ICCAT Secretariat, and other entities (see https://www.iccat.int/gbyp/en/overview.asp). The content of this paper does not necessarily reflect ICCAT's point of view or that of any of the other sponsors, who carry no responsibility. In addition, it does not indicate the Commission's future policy in this area. Special thanks to Pedro Lino and Ruben Muñoz-Lechuga from IPMA - Portuguese Institute for the Ocean and Atmosphere (Portugal), as provider of samples from the South of Portugal. Fulvio Garibaldi from UNIG - University of Genoa, Dept. of Earth, Life and Environment Sciences, for samples collected in the Ligurian Sea (Italy); Piero Addis and Rita Cannas from UNIC - Department of Life Science and Environment, University of Cagliari, for samples collected around Sardinian coast; F. Saadet Karakulak from ISTA - Department of Fisheries Technology and Management, Faculty of Aquatic Sciences, Istanbul University, for provider samples collected in the Levantine sea (Turkey); Antonio Celona from NECT - Necton Marine Research Society, for samples collected around Sicily (Italy), and Leif Nottestad from IMR - Institute of Marine Research, for providing samples collected in the Norwegian waters. We are so grateful for their efforts in collecting biological samples. Femtosecond Laser Ablation (fs-LA) analyses at the Institut des Sciences Analytiques et de Physico-Chimie pour l’Environnement et les Matériaux, Université de Pau et des Pays de l’Adour/CNRS (Pau, France) were conducted by Gaelle Barbotin as the engineer and under the supervision of Research engineer Dr. Christophe Pécheyran. We thank them for their help and assistance with technical issues. Stable Isotopes Analysis were conducted at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and we are grateful for their assistance. The contents of this manuscript do not necessarily reflect the point of view of ICCAT or of the other funders, neither do they necessarily reflect the views of the funders and in no ways anticipate the Commission's future policy in this area. Editing help was provided by Science Journal Editors, Inc