Age and growth of yellowfin tuna (Thunnus albacares) in the western equatorial Atlantic, using dorsal fin spines

Lengths of 6758 yellowfin tuna, Thunnus albacares (T albacares), were measured (42-191 cm FL) from 1992 to 2000 off northeastern Brazil (0-12degreesS/30-41degreesW). Age and growth were estimated from seasonally formed bands on the first dorsal spines of 380 specimens (45-191 cm FL) obtained from 1998 to 2000. Von Bertalanffy growth parameters were estimated from the observed length-at-age, from back-calculated lengths, and from a combination of back-calculated lengths and observed lengths. This last method was chosen for describing the species' growth; parameters were L-infinity = 230.7 cm, K = 0.267, and t(o) = -0.081 year. Marginal increment ratio and spine edge characterization suggested the annual deposition of two bands. Mean MIR values increase from November to April and from June to September, whereas translucent edges predominate in May and October, when new band formation is supposed to start. Overall, spines showed one to six complete bands with a well-developed absorbed area. The estimated reading error (IAPE) between two examiners was 9% for the overall sample. Size at maturity corresponded to an age of 3.4 years and the oldest individual in the sample was 6.5 years (191 cm FL). Fish lengths (35,469), taken from the International Commission for the Conservation of Atlantic Tuna-ICCAT database and measured in the area 20degreesS-05degreesN from 1975 to 1994, were analyzed leading to results similar to those produced from reading spines. Comparisons with von Bertalanffy parameters from the literature indicated statistical differences among all growth curves, with exception of that presented for the northern Atlantic, Average fish lengths decreased from 1975 to 1994, and only 25% of individuals in landings were larger than the size at maturity. (C) 2004 Elsevier B.V. All rights reserved.