Seasonal pattern of population dynamics, spawning activities, and diet composition of sardine (Sardina pilchardus Walbaum) in the eastern Adriatic Sea

Abstract

Monthly samples from commercial catches obtained with purse seiners operating in the Croatian fishing grounds (eastern Adriatic Sea) were collected throughout 2013, excluding January and December due to a fishing ban. Overall, 1010 sardine individuals were analyzed. Total body length ranged from 10.4 to 17.6 cm (mean ± SD: 13.9 ± 1.28 cm). Slightly larger individuals were caught during autumn at the beginning of the spawning season. Analysis of length–mass relationship showed that sardine specimens grow isometrically (b = 3.063). Seasonal oscillations of condition factor indicated that the examined specimens were in the best condition at the beginning of the spawning cycle. The analysis of stomach contents indicated that sardines preferred animal food (calanoid copepods, Oncaea spp., Farranula rostrata), although a plant component was also present (Bacillariophyceae). Seasonality was also observed in diet analysis, with diet changing in terms of feeding activity and prey quantity. The observed seasonal alternations of allometric condition factor and fullness index additionally confirmed that sardines were in the best condition at the beginning of the spawning season, for which they prepared themselves by higher feeding intensity, leading to higher storage of consumed energy.