Otolith morphology and age and growth of Trachurus mediterraneus (Steindachner) in the Eastern Mediterranean

Abstract

Otolith morphology and age and growth of Mediterranean horse mackerel, Trachurus mediterraneus (Steindachner), in the Eastern Mediterranean (Gulf of Saronikos, Greece) were studied during the years 1989–1992. Length frequency of a total of 4612 specimens was followed by month; ages were determined based upon otolith microstructural interpretations ( n=1611). The otoliths were classified into four types on the basis of differences in the presence, number and appearance of pseudo-annuli in the first year of life. These seasonal rates of formation of pseudo-annuli and the true annuli were examined in samples collected monthly. Successive hyaline rings were interpreted as annuli on the basis of their formation at progressively greater distances from the nucleus, while the opaque rings were not always visible. The time of annulus completion was estimated by the study of monthly marginal increments. This time was found to be around the end of autumn and coincided with the end of the spawning period. The spawning period was identified by following the seasonal changes of gonadosomatic index. Different growth rates of otoliths for each otolith type may have been the result of differences in spawn-date. Mean lengths at age from otolith reading (all types combined) in the monthly samples were applied to the von Bertalanffy equation and growth parameters were estimated: L inf=37.24 cm, k=0.326, t 0=−0.842.