Age Structure, Growth Parameters, and Otolith Traits of Two Species of the Genus Trachurus in the Central Mediterranean

The Atlantic horse mackerel (Trachurus trachurus) and the Mediterranean horse mackerel (T. mediterraneus) are two commercially important species whose biological traits remain insufficiently studied in the Central Mediterranean Sea. This study examines their age, growth pattern, and, for the first time, otolith morphology in both species in the Eastern Ionian Sea. The intercept of the weight–length relationship was a = 0.00599 (95% CI = 0.0050–0.0072) for T. trachurus and a = 0.00801 (95% CI = 0.0072–0.0089) for T. mediterraneus, and the slope was b = 3.121 (95% CI: 3.058–3.183) and b = 2.994 (95% CI: 2.957–3.031), respectively. Age was estimated by counting annual growth increments, visible as alternating opaque and clear bands along the axis of the left sagittal otolith from the core to the posterior margin. Von Bertalanffy growth parameters were estimated as L∞ = 34.65 cm, k = 0.31 year−1, and t0= −1.11 years for T. trachurus and L∞ = 35.98 cm, k = 0.23 year−1, and to = −1.60 years for T. mediterraneus. Otolith morphometrics showed significantly higher values (ANOVA, p-value < 0.05) in T. mediterraneus for all morphometric variables, except one, indicating larger and wider otoliths than those of T. trachurus, which can be a tool to distinguish the two species. A strong correlation was observed between the total length of the body and otolith metrics in both species. This study enhanced our scientific knowledge on the studied species’ life history traits and provides information for further ecological and stock assessment studies.