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Stable isotope signatures in dorsal fin spines as a non-invasive and non-lethal alternative to otoliths for reconstructing fish life and environmental history

Periodic Reporting for period 1 - SIFINS (Stable isotope signatures in dorsal fin spines as a non-invasive and non-lethal alternative to otoliths for reconstructing fish life and environmental history)

Reporting period: 2017-07-03 to 2019-07-02

Tunas often undertake large oceanic migrations crossing international jurisdictions or management boundaries during their lifetime, which makes the sustainable management of these species a complex and urgent challenge for scientists and of considerable policy and societal concern. The Atlantic bluefin tuna (Thunnus thynnus) is a well-known highly migratory species, and their long lifespan and high market value contribute to their vulnerability to overfishing and population collapse. As such it is essential to resolve juvenile migration pattern to effectively guide management of the resource for a long-term sustainability. Stable isotopes analysis preferentially performed in fish otoliths (ear stones) have been largely used in fish ecology, providing useful information about population dynamics, movement patterns, habitat use and connectivity. However, otolith removal is not practical for commercially valuable species like Atlantic bluefin tuna since it greatly affects the appearance of a fish diminishing their market value. The SIFINS project overall aims to investigate the ability of the dorsal fin spine bone (fin spine hereafter), in preserving isotopic signatures of ecological value as environmental proxies to infer migration patterns, habitat use, and other life history events of highly migratory tuna species. SIFINS uses the Atlantic bluefin tuna as a model species and sentinel of ocean health. The fin spine is also particularly attractive for rare and/or endangered species that cannot be sacrificed for their otoliths and a non-lethal alternative sampling method is preferred to complement otolith analysis promoting its applications in conservation issues.We conclude that there has been deviations from planned tasks and deliverables. However, it has definitely allowed Luque to acquire new competencies and skills, assist her in developing new long-term collaborations with high level researchers working in several institutions around the world, and has reinforced her career as a highly competitive, well-connected and influential scientist. Besides, it provided a competent tool to the Fisheries Research Community working on endangered and/or protected species, opening new research avenues to improve their management and conservation.
The SIFINS project has meant a step forward in the current knowledge of the fin spine chemistry necessary to trace movement, habitat use, and other fundamental aspects of fish life history throughout their lifetime. This knowledge connects the fields of microchemistry, bio-chronology and population structure to synergize how physiology may influence biomineralization and subsequent inference of fish life history. Task 1.1. “Revision of state-of-the-art of the fin spine chemistry and its biomineralization” has evidenced our deep gap knowledge of the ability of fin spine to incorporate elements and associated isotopes into its cellular matrix. Lastra Luque considered this as a priority task and crucial for a reliable biological interpretation of the isotopic signal using this novel structure. As such, a new Task 1.2. “To characterize and analyze the mineral component of fin spine bone of bluefin tuna” was included and has resulted in a publication the Peer J journal. The confirmation that the mineral matrix regularly showed carbonate ions that substitute for phosphate (B-type) support the suitability of fin spine for SIA. Task 2.1. “Compilation of methodology approaches and revision of current state and progress of analytical techniques of isotopic composition of biomineralized structures” has resulted in an extensive review to evaluate the appropriate methodology to apply to the fin spine for microchemitry. Two micro-sampling techniques were evaluated onto bluefin tuna fin spine: Task 2.2. “The secondary ion mass spectrometry (SIMS)” and Task 2.3. “The micro milling-Isotope gas-ratio mass spectrometry (GRMS)” commonly used in the analysis of oxygen isotope ratios of fish otoliths. Experimental trials have resulted in the publication of an optimal standard protocol in the Frontiers Marine Science supporting the micro-milling as the most appropriate technique for isolatin annulus across fin spine for stable isotope analysis . Task 2.4. “Contingency Plan: Fin spine microchemistry analysis (trace elements)” has resulted in the suitability of Femto-Laser technique FS-LA-ICPMS as an alternative high-resolution method to complement the work focused on stable isotope analysis to address main questions of SIFINS project. A publication is at the last stage before submitting at the ICES Journal. the Task 3.1. “Analysis of highly resolved profiles of δ18O and δ13C” obtained across fin spine growth trajectory from nucleus (early ages) to edge (age to death) confirmed that fin spines retained oxygen isotopic ratios of sea water surface where the fish inhabited supporting the use of fin spine chemistry as an alternative method to trace and characterize tuna movement in a predictable manner as it has been hypothesized in otoliths. The publication is at the last stage and results will be presented in the ISOBAY symposium innJune 2021. Task 3.3. “Exploring the suitability of combining isotopic and trace element concentrations across annuli to determine any seasonal pattern that can be used as chemical clocks”. This task is ongoing and will result in a publication. Also two abstracts have been presented at the International World Fisheries Conference in Australia, Sep 2021. During the SIFINS, two workshops have been organized.
The SIFINS project (1) has delivered a more refined understanding of the fin spine crucial for the application of isotopic signatures of ecological value to fisheries management of tunas, in particular, the Atlantic bluefin tuna as a sentinel of ocean health, (2) has provided an original perspective of the chemical archives in fishes beyond otoliths, particularly relevant to support the management of endangered, rare and commercially valuable species under the EU Biodiversity and Fisheries policies priorities, (3) has offered to the research community a valuable complement approach to the otolith and conventional tag and recapture approaches to effectively explore and characterize oceanic migration (i.e. seasonal migration, ontogenetic habitat shifts, and aperiodic immigration) of large pelagic predators as it is likely applicable to all life history stages, (4) has provided the international fisheries community a more refined understanding of the tuna migration ecology across their distribution range in the eastern North Atlantic and Mediterranean sea waters. Such an interdisciplinary project has built protocols and models to better assess population structure of commercial fish species of interest for the EU fishery industry, but also for endangered or protected species due to the non-lethal nature of the fin spine removal. The SIFINS project (5) has also provided new training to the Fellow in a range of analytical techniques, statistical tools and professional skills, (6) has fostered international collaborations between Europe and overseas institutions (JAMSTEC, University of St Davis, CNRS,etc., (7) is resulting in a series of high impact research articles in open access journals which are currently either being peer-review or under development; and finally (8) has raised societal awareness through effective communication of the benefits of healthy oceans for the well-being of humanity.
Goals and fundamental questions addressed by SIFINS