The potential use of scales for estimating age and growth of Mediterranean albacore (Thunnus alalunga)

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Abstract
The ability to accurately estimate the age of fishes is critical for conducting stock assessments and developing fishery management policies. Scales were collected from albacore, Thunnus alalunga, caught in the Mediterranean Sea during the years 1989–1995 to estimate their age and growth. Ages, which ranged from 1+ to 6+ years, were estimated from the interpretation of the concentric rings on the scales of 473 individuals that ranged in fork length from 55.5 to 89 cm. Males reached a greater size and age than females. The relatively close agreement in the mean lengths at ages estimated by scales and other techniques constituted a preliminary verification of the method. The von Bertalanffy growth model was fitted to mean lengths at estimated ages, resulting in the following growth parameters for the combined sexes: L∞ = 86 cm, K = 0.4, to = −0.8 years. Parameter estimates were in agreement with what is known about life history of the species in the Mediterranean. Moreover, the growth rates were consistent with length increment observations from five tag returns, which lend support to our working hypothesis that the scale-rings are annual structures. When the Mediterranean albacore growth parameters were compared with those of Atlantic Ocean albacore using scale age estimates, there were significant differences between the two populations, and Mediterranean albacore remain significantly smaller than Atlantic Ocean albacore.