Inter-annual fluctuations of the population structure, condition, length-weight relationship and abundance of sardine, Sardina pilchardus (Walb., 1792), in the nursery and spawning ground (coastal and open sea waters) of the eastern Adriatic Sea (Croatia)

Abstract

         This paper presents inter-annual fluctuations in the population structure, condition, lengthweight relationship and abundance of sardine, Sardina pilchardus (Walb., 1792), the most important fish species in the Adriatic Sea. The random samples were obtained from the nursery ground (Zrmanja River estuary, n=2 893) and spawning ground (off Dugi Otok, n =1 628) of the sardine. Representative samples of catches obtained by purse seine fishing were collected during the 2002- 2006 period. Total lengths ranged from 5.0 to 19.5 cm (mean lengths between 7.35±1.005 and 13.87±1.102 cm; Zrmanja River estuary) and 11.5 to 19.5 (mean lengths between 15.22±1.826 and 16.19±0.854, off Dugi Otok). The length-weight relationships of sardine from the Zrmanja River estuary and off Dugi Otok point to positive and negative allometry, respectively. A comparison of the allometric condition factor (K_a) of sardine specimens, which ranged from 13.0 to 16.0 cm, showed higher values in the area off Dugi Otok (K̅_a =0.467) than in the area of the Zrmanja River estuary (K̅_a=0.331), especially during 2003 (K̅_a =2.653). In terms of the fish abundance index, seasonal fluctuations were noticed. The highest values were observed in the area off Dugi Otok during autumn and in the Zrmanja River estuary during spring.