Analysis and validation of annual increments in otoliths of European hake (Merluccius merluccius) in the central Mediterranean Sea

Back-calculated length-at-age data derived from otolith measurements were used to estimate the growth parameters in European hake of the central Mediterranean Sea. The otoliths showed a significant sexual dimorphism in the relationship between dorsal otolith radius and fish length. The sexes had no significant differences in growth up to their second year of life, but older females grew faster than males. In samples of recent commercial catches the oldest females were 16 years old and attained more than 85 cm in length, while no males were observed exceeding the age of 6 years and 42 cm in length. The estimated parameters of the von Bertalanffy function were: in females: L∞ = 93.2; K·year-1 = 0.13; to = -0.35; in males L∞ = 45.7; K·year-1 = 0.40; to = 0.1. The age determination was validated by analyzing the changes in the type of otolith margin and in marginal increments, which coincided with periods of slow growth during the winter and fast growth during the summer. However, false rings of physiological origin are often deposited during the first two years of life. A validation of the otolith interpretation up to the age of 3 years was additionally obtained through the analysis of a time series of length frequency distributions recorded during trawl surveys.