Age, growth and mortality rate of horse mackerel, Trachurus trachurus (L.), living in the eastern central Adriatic

Background and Purpose: The horse mackerel, Trachurus trachurus, is pelagic and migratory fish, common in the North eastern Atlantic and Mediterranean. In the Adriatic, it is important object of pelagic and demersal fishing. In spite of this fact, information on its biology is scarce. The aim of this study was to estimate the age, growth and mortality rate of horse mackerel in the central Adriatic. Material and Methods: Age, growth and mortality rate were analyzed for horse mackerel collected in the eastern central Adriatic from 1996 to 2000 during spawning season (March - May). A total of 2,304 individuals were collected. The total length of sampled individuals ranged from 10.3 to 37.3 cm and weight from 6.04 to 437.5 g. Age was determined by the sagitta otolith rings reading. The commonly used length-weight relationship W = aL b was applied. Length and age data were used to estimate growth parameters (L ∞ K, t 0 ) of von Bertalanffy growth equation Lt = L ∞ (l - e - K ( t - t ) 0 ). Total mortality rate (Z) was calculated from the length-converted catch curve using FiSAT program. Natural mortality (M) was estimated using L ∞ , K and annual mean water temperature. Exploitation rate was calculated by the equation E = F/Z. Results and Conclusion: Age ranged from 1°-8°. The length-weight relationship, which differs between sexes, was estimated for males b = 2.9929, a = 0.0087 (N = 599); females b = 3.0598, a = 0.0069 (N = 560) and whole sample b = 3.0198, a = 0.0080 (N = 1454), indicating isometric growth for males and whole sample and positive allometric growth for females. Growth parameters for males L ∞ = 38.11 cm, K = 0.215, to = -0.39; females L ∞ = 38.16 cm, K = 0.203, t 0 = -0.40; whole sample L ∞ = 37.68 cm, K = 0.230, t 0 = -0.30 were calculated. Natural mortality was found to be M = 0.46 1/year, fishing mortality F = 0.27 1/year and total mortality Z = 0.73 1/year (Z/K = 3.174). The exploitation rate E = 0.38 suggests that the stock was relatively highly exploited.