Standardized age - Length key for east Atlantic and Mediterranean bluefin tuna based on otoliths readings.

This paper presents an age-length key (ALK) based on age estimates from otoliths following a recent standardized reading criterion. Sampling of Atlantic bluefin tuna (Thunnus thynnus) otoliths comes from the “Biological and genetic sampling and analysis" (GBYP) project and was complemented with some samples from the Spanish institute of Oceanography. Using 2010 to 2012 data improves length range and monthly sampling coverage. Variability in length at age from ALK seems acceptable and although it was developed from data pooled over three years, the bias is likely to be small. Final age was adjusted to account for the date of capture and the timing of bands formation throughout the year. Monthly formation of edge type, translucent or opaque, was inconclusive and did not allow establishing an annual formation pattern. The confidence interval of the von Bertalanffy growth model curve fitted to ALK data included currently adopted growth function for eastern bluefin stock and western stock function up to age 8. From age 9, this last western function predicts slightly older ages than the present ALK growth model.Postprint0,000

The Role of Microplastics in Marine Pathogen Transmission: Retrospective Regression Analysis, Experimental Design, and Disease Modelling

Marine wildlife and aquaculture species can accumulate large amounts of marine microplastic debris (MMD) (<1 mm) carrying pathogens, thus threatening the health of marine ecosystems and posing a risk to food safety and human health. Here, we outline a theoretical three-perspective approach for studying the relationship between MMD and disease. First, we provide a framework for retrospective analysis of MMD and pathogen loads in marine animal tissues to assess the relationship between these and other environmental variables in order to decide whether a compound or pathogen should be considered an emerging substance or organism. Second, we describe an experimental design for testing the effects of a variety of microplastics on infection intensity in two model species (oysters and zebrafish). Finally, we create a theoretical susceptible–infected microplastic particle and pathogen transmission model for bivalves and fish. Overall, the experiments and models we propose will pave the way for future research designed to assess the role of MMD as a vector for marine and human pathogens. This multi-faceted approach needs to be an urgent priority of the EU Strategic Research Innovation Agenda for addressing marine disease challenges related to MMD.This work was conceived under the research framework outlined by the National Science Foundation Evolution and Ecology of Infectious Diseases (EEID) Program, grant OCE-1216220. Funding was provided by the University of the Basque Country (UPV/EHU, GIU19/059) and the Basque Government (PIBA2020-1-0028). We appreciate this support

A review of Mediterranean albacore (Thunnus alalunga) biology and growth studies

Growth parameters are used to estimate catch-at-age data which is required as an input to many stock assessment models. In the case of Mediterranean albacore stock no assessment has ever done (ICCAT, 2009). This study presents growth information based on spine section interpretation of annual time marks. A preliminary age-length key is presented for males, females and two sexes combined, based on 249 albacore (Thunnus alalunga, Bonn.1788) spine samples caught around the Balearic Islands and Western Mediterranean sea between June and November from 2004 thru 2006. The albacore length ranged from 52 cm to 94 cm for females and from 53 cm to 96 cm for males. Available length-weight data for 138 males and 162 females was analysed separately. New estimates presented in this study were compared with assumed biological length-weight relationship for Mediterranean albacore stock. As well, mean length by age estimates derived from the age-length-key obtained by reading fin ray section were compared with other studies that used hard parts to age Mediterranean albacore.Des paramètres de croissance sont utilisés pour estimer les données de prise par âge requis en tant que valeur d’entrée pour de nombreux modèles d’évaluation des stocks. Dans le cas du stock de germon de la Méditerranée, aucune évaluation n’a jamais été réalisée (ICCAT 2009). Cette étude présente des informations relatives à la croissance en se fondant sur l’interprétation des sections des épines des marques annuelles. Une clé âge-taille provisoire est présentée pour les mâles, les femelles ainsi que pour les deux sexes combinés, reposant sur 249 échantillonnages d’épines de germons (Thunnus alalunga, Bonn, 1788) capturés dans les environs des îles Baléares et de la Méditerranée occidentale entre le mois de juin et de novembre 2004 jusqu’en 2006. La taille du germon oscillait entre 52 et 94 cm dans le cas des femelles et entre 53 et 96 cm dans le cas des mâles. Les données disponibles de longueur-poids des 138 mâles et 162 femelles ont été analysées séparément. De nouvelles estimations présentées dans cette étude ont été comparées à la relation biologique postulée longueur-poids du stock de germon de la Méditerranée. De plus, les estimations moyennes de la longueur par âge (dérivées de la clé âge-longueur) obtenues sur la base de la lecture de la section du rayon de la nageoire ont été comparées avec d’autres études qui ont recours à des pièces dures pour déterminer l’âge du germon de la Méditerranée.Se utilizan los parámetros de crecimiento para estimar los datos de captura por edad que se requieren como entradas para muchos modelos de evaluación de stock. En el caso del stock de atún blanco del Mediterráneo, no se ha realizado nunca una evaluación (ICCAT, 2009). Este estudio presenta información sobre crecimiento basada en la interpretación de marcas anuales de secciones de espinas. Se presenta una clave edad-longitud provisional para los machos, las hembras y ambos sexos combinados basada en 249 muestras de espinas de atún blanco (Thunnus alalunga, Bonn. 1788) capturado alrededor de las islas Baleares y en el Mediterráneo occidental entre junio y noviembre de 2004 hasta 2006, inclusive. La longitud del atún blanco oscilaba entre 52 cm y 94 cm para las hembras y entre 53 cm y 96 cm para los machos. Los datos disponibles de longitud-peso para 138 machos y 162 hembras fueron analizados por separado. Las nuevas estimaciones presentadas en este estudio se compararon con la relación biológica longitud-peso asumida para el stock de atún blanco del Mediterráneo. Asimismo, las estimaciones de longitud media por edad derivadas de la clave edad-longitud y obtenidas mediante la lectura de secciones de rayos de aleta, se comparan con otros estudios que utilizaron partes duras para determinar la edad del atún blanco del Mediterráneo

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

Growth of bluefin tuna (Thunnus thynnus) in the North-eastern Atlantic and Mediterranean based on back-calculation of dorsal fin spine annuli

The growth of bluefin tuna (Thunnus thynnus) in the North-eastern Atlantic and Mediterranean wasanalysed using the back-calculation of the dorsal fin spine annuli. Spines from a total of 2678 bluefin tuna,collected from 1984 and 1990–2010, were analyzed. The specimens ranged from 45 to 287 cm straightfork length (SFL). Both linear and power regression functions showed a significant relationship betweenspine radius and SFL, but power function fitted better than linear (SFL = 42.978R0.884, r2= 0.98), as also wasfound in previous studies when a wide range of sizes was available. Two back-calculation equations wereused to obtain the back-calculated SFL, Fraser-Lee and Body Proportional Hypothesis (BPH), showingsimilar results. The Von Bertalanffy growth parameters obtained with the selected BPH model were:SFL = 349.5(1 − e−0.086(t+0.814)). Back-calculated lengths and growth parameters showed similarities withthose from previous literature.Postprint1,586

JUVENILE ATLANTIC BLUEFIN TUNA OTOLITHS EXCHANGE

Otolith reading bias for juvenile Atlantic bluefin tuna was detected at its 2017 assessment. To try to reduce this bias, the current standardized reading protocol was revised. The new protocol uses age estimates from the first dorsal fin ray (spine) to identify the growth increments in the otoliths removed from the same young specimen. An exchange involving 14 experienced otolith readers was conducted to verify if the new reading procedure minimized the difference between otolith and spine readings. The results showed that there is a good agreement in the first five years, but from age 6, otoliths ages tended to be higher than spine age. Some readers had difficulty following the new protocol despite being experts, which indicates that it is necessary to improve it. The use of annual band measurements has shown to be a good tool for the control of the quality of age estimates. The results indicate that we are progressing in the recognition of the deposition pattern of the first annuli. It is recommended to carry out an ageing workshop to achieve the tasks identified as necessary