Growth estimation of Merluccius merluccius off the northern coast of Tunisia
Growth parameters of any species are fundamental for biological or dynamic studies. The quality of the estimation for these parameters directly impacts on species stock assessment and, as a consequence, on fisheries management. In order to improve fishery and species stock management, growth analysis, especially by sex, is recommended. In this study, otoliths were used to estimate growth parameters of Merluccius merluccius Rafinesque, 1810. Hake is well-known as being a species in which otolith interpretation is extremely difficult. To estimate growth parameters, the first daily increment was validated as the tool for age determination. Otolith interpretation was done according to the last results of ICES cooperative research report. In total, a sample of 1599 M. merluccius were examined, consisting in 638 females, 771 males and 190 immature juveniles. They were caught in southwest of Mediterranean Sea, along the northern coast of Tunisia. Transverse sections were used for the interpretation of growth (annual) increments and age estimation. Growth by sex was considered: TL = 102.850 * (1 – e –0.141 * (t + 1.345)) for females, TL = 40.700 * (1 – e –0.619 * (t + 0.992)) for males and for combined sexes. Validation of the first growth annual increment and knowledge from recent tagging studies have helped in highlighting a different growth model of M. merluccius from that previously described. Our study showed that ages previously reported were overestimated, as observed in other regions (Gulf of Lion and Bay of Biscay). Moreover, at defined length and weight, females grow at a faster rate than males. This difference was explained by the difference in performance index (Φ), which is 3.17 for females and 3.01 for males.