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This study aims to clarify some aspects of the growth of Atlantic bluefin tuna, Thunnus thynnus (L.), (ABFT) mainly regarding parameters of the growth equation and of relative growth, in this case length-weight relationships. There is a great volume of literature on these matters and there is a danger that the resulting confusion may give rise to mistaken decisions. In spite of the publication of 55 articles on absolute growth (FL > 50 cm), which contain a total of 43 growth equations, no consensus has yet been reached within the ABFT assessment group (AG) of the SCRS on parameters such as Lmax and L∞. The results of the present study indicate that the L∞ = 314.9 cm of the growth equation used for the western stock by the AG from 2010 (Lt = 314.9 [1 - e-0.089 (t+ 1.13)]), which was discarded in 2016, lies within the confidence limits of the maximum Ls presented in this study (Lmax= 321.4 ± 8.7 cm), confirming that this equation fit the biology of the ABFT growth. With regard to the length-weight relationships, 38 articles (FL > 50 cm) have been consulted containing a total of 71 equations, but in spite of this the models adopted by the AG in 2014 underestimate the weight of spawners (>2 m) in high fattening phase by up to 23%. The coincidence of the length-weight model for the ABFT western stock, discarded by the AG in 2014, with that of Pacific bluefin tuna, Thunnus orientalis (T & S), (PBFT) indicates that both species must have the same growth, something that is not surprising since both were the same species until 2003. Other coincidences, such as the trend of condition factor K in adults and the growth in the first months of life, could ratify it. In the Pacific Ocean, where far fewer growth studies have been made on PBFT than on ABFT in the Atlantic and Mediterranean, the management of growth models for the purposes of stock assessment in the International Scientific Committee (ISC) makes more sense than that carried out by the SCRS on this matter. [ABSTRACT FROM AUTHOR]

The recently adopted model by ICCAT Standing Committee on Research and Statistics (SCRS) for the western Atlantic bluefin tuna (ABFT),Thunnus thynnus(L.)(RW= 0.0000159137SFL3.020584,WEST), together with the model used to date (RW= 0.0000152 SFL3.0531,Ec1) is analyzed in using a bi-variant sample (SFL(cm),RW(kg)) of 698 pairs of data (K= 2.02 ± 0.23 SD) in order to validate them and to establish the model that fits best the reality represented by the sample and, therefore, will have the greatest descriptive and predictive power. The result of the analysis indicates that the adopted modelWESTclearly underestimates the weight of spawning ABFT being modelEc1 that best explains the data of the sample. The result of the classical statistical analysis is confirmed by means of the quantile regression technique, selecting the quantiles 5%, 25%, 50%, 75%, and 95%. Other biological and fisheries indicators also conclude that the modelWESTgradually underestimates the weight of ABFT spawners (of 2–3 m) by 11–13%, does not meet the criterion that forRW= 725 kg (Wmax),SFL= 319.93 ± 11.3 cm (Lmax), and the average value ofK(1.77) obtained for a wide range of size–weight values, usingWESTmodel, represents ABFT in low fattening condition. [ABSTRACT FROM PUBLISHER]

Following an extensive description and review of the bibliography of the overall situation of the bluefin tuna,Thunnus thynnus(L.), ABFT, from ancient times until the present, the eastern Atlantic fisheries that traditionally caught ABFT spawners (traps of the Strait of Gibraltar and northern European fisheries) are described with the aim of explaining the reasons behind their decline from the 1960s. The study includes the fishery of the Bay of Biscay, an area where small and medium-sized spawners migrated towards areas of trophic concentration in the north of Europe. The fisheries of ABFT juveniles began to develop in the eastern Atlantic at the end of the 1940s (Bay of Biscay) and the middle of the 1950s (off the coast of Morocco). The results of an analysis of the juvenile ABFT population of the eastern Atlantic part between 1949 and 1962 reveal that under different scenarios the high fishing mortality exerted on the juvenile fish groups (<5 years) in the period studied may have been one of the main factors behind the decline of the north eastern Atlantic fisheries of spawners from 1963. Juvenile catches of that magnitude (6,879,967 ABFT) may have given rise to the limited recruitment from juvenile age to spawning stocks. The analysis has also been made for the periods 1970–2006 and the present (2009). In the first of these two cases, fishing mortality (F) fell as a result of a fall in the catch of juveniles, mainly the fishery of Morocco. Nevertheless, during these years, over 4 million specimens of 1 year were caught illegally in the Atlantic part of the eastern stock. The fall in F is now even greater due to the practically entire disappearance of the juvenile fisheries as a result of the implementation of the Pluriannual Recovery Plan (PRP) of theInternational Commission for the Conservation of Atlantic Tunas(ICCAT), which began in the fisheries of the eastern stock in 2007. [ABSTRACT FROM AUTHOR]

Following extensive review, a model of the Atlantic bluefin tuna (ABFT),Thunnus thynnus(L.), length–weight relationship for the eastern Atlantic and Mediterranean (RW= 0.0000188SFL3.01247;Ec 1) is presented on the basis of samples of ABFT spawners, with an average value of indexK= 2.03 ± 0.15SD, collected by the Atlantic traps of Portugal and Spain in the Strait of Gibraltar (1963; 1996–1998; 2000–2012), and a set of samples of juvenile fishes from ICCAT–GBYP (n= 707). The resulting model (Ec 1), together with the model used for the eastern stock assessment (RW= 0.000019607SFL3.0092;Ec 2) and a recently adopted by ICCAT Standing Committee on Research and Statistics (SCRS) (RW= 0.0000315551SFL2.898454;EAST) are analyzed in using a bi-variant sample [SFL(cm),RW(kg)] of 474 pairs of data with the aim of validating them and establishing which model(s) best fit the reality represented by the sample and, therefore, will have the greatest descriptive and predictive power. The result of the analysis indicates that the modelEASTclearly underestimates the weight of spawning ABFT and that modelEc 2overestimates it slightly, being modelEc 1that best explains the data of the sample. The result of the classical statistical analysis is confirmed by means of the quantile regression technique, selecting the quantiles 5, 25, 50, 75, and 95%. Other fisheries and biological indicators also conclude that the modelEASTgradually underestimates the weight of ABFT spawners (of 2–3 m) by 9–12.5 %, and does not meet the criterion that forRW= 725 kg (Wmax),SFL= 319.93 ± 11.3 cm (Lmax). [ABSTRACT FROM AUTHOR]

The growth equation currently used for Atlantic bluefin tuna, Thunnus thynnus (L.), eastern stock (Lt = 318.85 [1-e-0.093 (t + 0.97)]) is validated using several approaches. The first method involved a comparison of studies with von Bertalanffy parameter estimates in which, different methods for the age estimation are utilized, taking as references the maximum size of this species (Lmax = 319.93 ± 11.3 cm) and the growth equation of the western Atlantic stock (Lt = 314.90 [1-e-0.089 (t + 1.13)]). The result of this analysis showed that the growth equation used by ICCAT's Standing Committee on Research and Statistics Atlantic bluefin tuna assessment group for the eastern stock perfectly fits Lmax. Second, an analysis was realized from first dorsal spine rings, 578 samples (age groups 0 to 3) of ABFT collected from the Bay of Biscay and the Mediterranean Sea, enabled the interpretation of the wide opaque bands (fast growth), formed during the boreal late spring and completed by autumn (June to November), and the translucent rings (hyaline rings, slow growth), formed during boreal autumn to late spring (November to May-June). In addition, first dorsal spine sections bands of two recovered fish that had carried conventional and electronic archival tags are also consistent. The chronological analysis of the opaque bands and hyaline rings of one fish tagged with an archival tag and recovered in the Bay of Biscay (the first time such a spine had been available for such analysis) revealed that transatlantic migrations may lead to double hyaline ring formation in the spine. Finally, the validation of the ABFT growth equation is made by superimposing tag-recovery data from tagging surveys in the Bay of Biscay, western Mediterranean and western Atlantic (N = 131) and spine readings (N = 299) to the eastern stock ABFT growth equation and analysing residuals. The coefficient of determination (R² = 97.98) and the residual's distribution indicated good performance of the model. Although no important differences between the growth model of the eastern stock and that of the western stock are found, in all cases studied, the predictive accuracy indicators are better for the eastern model. [ABSTRACT FROM AUTHOR]