Sex change and oscillating growth pattern of the picarel (Spicara smaris) in the saronikos gulf (Greece)

Abstract

The picarel (Spicara smaris) is an interesting species of the Mediterranean Sea fishery, yet little information is available on life history of this protogynous species. A total of 6458 picarel (4.3 to 20.7 cm total length [TL]) were sampled from the Saronikos Gulf, an important fishing area in the eastern Mediterranean, during 1998 and 1999 to assess their age structure, sex-based growth, and sex-change pattern. Marginal-increment analysis combined with otolith edge analysis (n=1694) showed that the time of annulus formation was around July (i.e., at the end of the spawning season). The length and age at sex change were estimated to be 15.3 cm TL and 3.0 years, respectively. The proportion of early maturing males, or males maturing before the length at sex change (L50), was 2.4%, whereas the ratio of L50 to maximum length was 0.74, approximating the dimensionless theory. Males were shown to become longer than females, and the decreasing growth rate noticed between summer and autumn in fish older than 2 years, resulted in a strong oscillating growth pattern, clearly attributed to the synergistic effect of sex change and to large differences in summer and winter temperatures. Additionally, an alternative method for assigning fish to age groups, based on clusters derived from length distributions, is proposed.