A preliminary analysis of the state of exploitation of the sardine, Sardina pilchardus (Walbaum, 1792), in the gulf of Annaba, East Algerian

Abstract

This study was performed on 2,859 specimens of sardine, Sardina pilchardus, collected biweekly from November 2006 to October 2007. Samplings were carried out at the fishing port of Annaba where purse-seine methods are used for small-scale fishing at depths from 15 to 30 m. Data concerning the exploitation of catches were analysed by means of two software packages: i) FISAT (2004), which we used to determine the essential parameters for the study of dynamics; and ii) VIT (2000), the most suitable tool for stock assessment based on the application of length cohort analysis (LCA) together with a yield per recruit analyses (Y/R) based on a short series of data. VIT (2000) assumes steady state and functions with pseudo-cohorts, requiring knowledge of the catches over one year only instead of a historical series of several years. The results of this application revealed that the exploitable average biomass of the sardine stock, composed of 28 length sizes from 6.5 to 20 cm with a step of 0.5 cm, was around 4,778.93 tons, of which 2,513 tons (53%) were spawning stock. The size and the average age of the sardine stock were 12.5 cm and 2.7 years. Total biomass balance (D) was estimated at 5,508.64 tons. This corresponded to growth in weight of 4,453.77 tons, (80.85%), as compared to recruitment of only 1,054.86 tons (19.15%). Losses were caused mainly by natural mortality (M), estimated at 3,823.14 tons, and accounting for 69.40%. This was higher than fishing mortality (F) which was 1,685.5 tons (30.60%). We estimated the yield per recruit (Y/R) of sardine at 2.682 g. This value was lower than the threshold of maximum yield per recruit at 3.413 g. Though preliminary, these results indicate that the sardine population can be considered to be in a situation of under-exploitation in this area. The stock is moderately exploited for F0.1 a reference considered more appropriate for management. Applying the precautionary principle, fishing efforts should not increase and we recommend limiting fishing to current levels. However, we recommend monitoring the fishing strategy and the annual evolution of catches.