Analysis of the Length–Weight Relationships for the Western Atlantic Bluefin Tuna, Thunnus thynnus (L.)

Abstract

The recently adopted model by ICCAT Standing Committee on Research and Statistics (SCRS) for the western Atlantic bluefin tuna (ABFT), Thunnus thynnus (L.) (RW = 0.0000159137 SFL^3.020584, WEST), together with the model used to date (RW = 0.0000152 SFL^3.0531, Ec 1) 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 model WEST clearly underestimates the weight of spawning ABFT being model Ec 1 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 model WEST gradually underestimates the weight of ABFT spawners (of 2–3 m) by 11–13%, does not meet the criterion that for RW = 725 kg (W_max), SFL = 319.93 ± 11.3 cm (L_max), and the average value of K (1.77) obtained for a wide range of size–weight values, using WEST model, represents ABFT in low fattening condition.

Keywords:

• Atlantic bluefin tuna
• Thunnus thynnus
• length–weight relationships
• quantile regression
• condition factor (K)

Acknowledgments

The authors thank Molly Lutcavage (Large Pelagic Research Center, University of New Hampshire, Durham, USA) and John Neilson (Canada) for the data provided for a previous publication and which have also been utilized in the present study. The authors thank Orestes Cendrero for the wording revision.