Impact of the natural mortality (M) variability on the evaluation of the exploitable stock of sardine, Sardina pilchardus (Actinopterygii: Clupeiformes: Clupeidae) of the central region of the Algerian coast

Abstract

Background. The landings of sardine, Sardina pilchardus (Walbaum, 1792), captured by purse seiners in the central region of the Algerian coast, Mediterranean Sea have been decreasing over the last decade. The catch was 22 580.28 t in 2001 but fell to 5600 t in 2011. To better understand the above decline, we found it useful to evaluate the impact of the change of the natural mortality (M) on the estimation of the exploitable stock of this species. Material and methods. To study the exploitation of sardine, a total of 4476 individuals of both sexes were sampled monthly in 2010. All sardines were taken from the landings of purse seiners operating in the central region of the Algerian coast between Tenes and Bejaia. The study of biological parameters and mortality were undertaken by the software recommended by FAO (FISAT II 1.2., FISHPARM 3.0 T, and the New VONBIT for Excel). Finally, VIT Software 1.2 was used for the evaluation of virtual population analysis (VPA), yield and biomass per recruit. Results. The analysis of yield and biomass per recruit using two approaches for estimating the natural mortality, namely the method of Pauly and that of Djabali et al., shows that the state of the sardine stock in the central region of the Algerian coast changed totally from a state of not overfished and not overfishing to a state of overfished and overfishing. The choice between these two scenarios, for which is important to advise and guide the management of the fisheries focuses on the case of overfishing and overfished. This choice is motivated by the geographical origin of the biological material used for the equation of natural mortality. Conclusion. The reduction of the current fishing effort factor (FC  = 1) to the factor of fishing mortality rate at which the marginal yield-per-recruit constitutes only 10% of the marginal yield-per-recruit on the unexploited stock (F0.1 = 0.23) would permit in the long term, a maximum sustainable production of sardines of the central region of the Algerian coast which will increase from 5600 to 5999.7 t, while ensuring the renewal of its stock in sea which will rise from 3987 to 12 487.8 t. Finally, it would be interesting to extend this study for all major pelagic species captured along the Algerian coasts.

Keywords

• Exploitation
• F0.1
• overfished
• overfishing