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Age determination and validation on otoliths of the striped red mullet, Mullus surmuletus from the Adriatic Sea

There is a need to establish a method for age determination of the striped red mullet, Mullus surmuletus as target fish species of Mediterranean artisanal fisheries. In total, 387 specimens ranging in total length from 6.8 to 32.9 cm were analyzed for this purpose. Ground otoliths were used to estimate fish ages. The annual periodicity of annulus deposition was supported by the marginal increment analysis. The annual growth of otoliths was verified using edge-type analysis. The formation of growth increments followed a seasonal pattern. The proportion of otoliths with opaque margins was the highest (>80%) in the winter period (December-March). Moreover, the monthly mean marginal increment showed a single minimum in June and confirmed the formation of one annulus per year. A distance measurements analysis revealed that first regular ring appears at distance of 0.78 mm (± 0.104 SD) from otolith nucleus and fish age of about 0.83 years. The age analysis revealed 6 age classes. Predominance of age classes 1+ and 2+ in the total catch (54.3% individuals) was observed. All measured otolith morphometric parameters (length, width and mass) were linear with fish age. The linear model explained between 80.3% and 84.4% of the variation in age. The most precise age estimations of analyzed population were obtained from the otolith width, followed by the otolith length and mass. The growth parameters were estimated by the fit of the Von Bertalanffy growth function. The growth of M. surmuletus was rapid up to 2 years of age and then slowed. Considering the identified biological implications, existing management should be complemented by a more holistic, ecosystem approach to regulations, in order to assure effective conservation measures for this economically and ecologically important fish species.

Age; validation; otoliths; Mullus surmuletus; Adriatic Sea

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