Abstract
The growth of Mullus barbatus has been widely studied using different methods, but no previous study has focused on age validation. The uncertainty in estimating the age of the red mullet by otolith reading is linked to the number of false-growth increments laid down before the annulus. The capture of red mullets in the early life stage allowed us to estimate their size at the metamorphosis from the pelagic to the demersal phase. The comparison between the metamorphosis size and the back-calculated length of the first growth increment clarified the position of the false growth increment on the otolith. Moreover, the analyses of the otolith marginal increments in adult and juvenile specimens allowed us to define the deposition patterns of their annuli. The modal components of the length–frequency distribution analysis (LFDA) were identified in the winter survey (ELEFAN and Bhattacharya methods), and they did not show significant differences from the length back-calculation of the annuli. Moreover, no significant differences were found between the growth curves calculated by otolith reading (back-calculation and direct otolith reading) and the LFDA. The agreement between the length–frequency results and the otolith age estimation either corroborated or indirectly validated the growth pattern estimated in the otoliths of the red mullet, mainly when the direct validation methods (e.g. mark-recapture, captivity, radiochemical) were difficult to implement, like the case of this species. The comparison of the results of the present work to previous Mediterranean studies showed agreement with the slow growth pattern.
Highlights
Since red mullet has a great commercial value, it is a main target species of coastal fisheries in the Mediterranean
The Marginal Increment Analysis (MIA) showed the same pattern of the Marginal Analysis (MA) with significantly higher marginal increments in the summer months (July–September) and significantly lower marginal increments in the winter and early spring (February– April) (Fig. 5)
These results showed that the growth of otolith was significantly higher during the deposition of the opaque area
Summary
Since red mullet has a great commercial value, it is a main target species of coastal fisheries in the Mediterranean. Explained by geographic variability and genetic differences Other factors, such as age estimation methods and age estimation criteria, could have contributed to this high discrepancy. One of the most important reported sources of discrepancies between readers is the identification of the first annulus[9,10] In studying this species, a main problem is that direct age validation methods (e.g. mark-recapture, captivity rearing and radiochemical dating)[13] are quite difficult to be applied, because of the high mortality after capture (stress, scale loss and wounds)[14] and the short life span of the species[15,16,17]. Uncertainty in age determination and in the estimate of growth parameters has a considerable effect on the results of stock assessments results because uncertainties about the first annulus can lead to the over- or under-estimation of one year in age determination is important in a species that has a life span of 5–8 years[15,16,17]
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