Age and growth of early life stages of European pilchard (Sardina pilchardus) from the western Adriatic Sea

Abstract

      Age and growth of early life stages of sardine, Sardina pilchardus, were investigated by microincrement counts on sagittal otoliths. Postlarval and juvenile specimens were collected in the coastal waters off Ortona (central Adriatic Sea) from December 1996 to May 1997. Otolith microstructure analysis was conducted on 286 specimens ranging from 30 to 68 mm TL. Age estimates ranged from 65 to 151 days. The precision of age estimates was tested by applying both the average percent error (APE) and the coefficient of variation (CV). The hatch date distribution, back-calculated from the date of capture, was spread over a long period lasting from September to March, with two main
cohorts hatched in autumn (October) and winter (February), consistently with a long spawning season reported for this species. Applying the Gompertz growth model to the age-length data set, a growth curve was obtained for each cohort. The mean absolute daily growth rate was 0.33 mm day^-1 and 0.22 mm day^-1 for the autumn and winter cohorts, respectively. Otolith growth increment patterns was rather similar in the two cohorts, but they differed for the amplitude and timing of increment width deposition, being otoliths accurate proxies of larval fish growth rate. Strong seasonality of environmental features, such as water temperature and food resources, and endogenous factors linked to the larval ontogeny, largely contributed to affect the early life history stages of sardine.