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This study deals with important methodology issues that affect age estimates of eastern
Atlantic bluefin tuna Thunnus thynnus using dorsal fin spines. Nearly 3800 spine sections
were used from fish caught in the north-east Atlantic Ocean and western Mediterranean
Sea over a 21 year period. Edge type and marginal increment analyses indicated a yearly
periodicity of annulus formation with the translucent bands (50% of occurrence) appearing
from October to May. Nucleus vascularization seriously affected specimens older than
6 years, with the disappearance of 40-50% of the presumed annuli by that age. An alternate
sectioning location was a clear improvement and this finding is an important contribution
to the methodology of using this structure for ageing the full-length range of eastern
T. thynnus. Finally, there were no significant differences between the coefficients
of von Bertalanffy growth model estimated from mean length at age data (L∞ = 327.4;
k = 0.097; t0 = -0.838) and those estimated from the growth curves accepted for the
eastern and western T. thynnus management units.