Analysis of the length weight relationships for the Atlantic bluefin tuna, Thunnus thynnus (L.)

Abstract

The recently adopted models by ICCAT Standing Committee on Research and Statistics (SCRS) for the Atlantic bluefin tuna (ABFT), Thunnus thynnus (L.) (RW= 0.0000159137 SFL^3.020584, WEST; and RW= 0.0000315551 SFL^2.898454, EAST ), together with the models used to date (RW= 0.0000152 SFL^3.0531, for western stock; and RW= 0.000019607 SFL^3.0092, for eastern stock) and an alternative model for the eastern stock (RW= 0.0000188SFL^3.01247), are analyzed in using bi variant samples (SFL (cm), RW (kg)) of 698 pairs of data (K= 2.02 ± 0.23 SD, western stock) and 474 pairs of data (K= 2.03 ± 0.15 SD, eastern stock) with the aim of validating them and establishing which model best fit the reality represented by the samples and, therefore, will have the greatest descriptive and predictive power. The result of the analysis indicates that the adopted models WEST and EAST clearly underestimates the weight of spawning ABFT being the models used to date, as well as the alternative model presented in this paper, that best explains the data of the samples. 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 models WEST and EAST gradually underestimates the weight of ABFT spawners (of 2 3 m) by 8 14%; the average value of K (1.78 and 1.82) obtained for spawners (> 140 cm), using the adopted models, represents ABFT in low fattening condition; and the evolution of K throughout the year, by using the monthly L-W adopted models, does not represent the significant increase in weight that ABFT experiences in nature between August and December.