Biological study and stock assessment of boops boops (Linnaeus, 1758) and diplodus Sargus Sargus (Valenciennes, 1830) and biological study of the invasive species Lagocephalus Sceleratus (Gmelin, 1789) in Lebanon

Abstract

The purpose of this study was to carry out a biological study and a stock assessment of the two commercial species Diplodus sargus sargus (Valenciennes, 1830) and Boops boops (Linnaeus, 1758), as well as a biological study of the Lessepsian invasive Lagocephalus sceleratus (Gmelin, 1789) in Lebanon. This research was undertaken to lay the basis for future fisheries management. The methodology adopted was a length-based single species stock assessment. Stocks of B. boops and D. sargus sargus were assessed based on length frequencies and the landings collected by the MRCZM-IoE-UoB within the context of the FLOUCA initiative. The biological studies evaluated parameters related to reproduction, maturity, and growth of the three species. Stomach contents and feeding intensity were only investigated for L. sceleratus. The stock assessment showed that the stock of B. boops is overfished, with an exploitation level of 0.55, higher than Emax (=0.517). The stock size totals 50,993 kg, with a total catch of 28,046 kg, and a commercial value of 107,000 USD/year. The exploitation rate must decrease to Emax (=0,517), E0.1 (=0.455), or E0.5 (=0.342), depending on management objectives. For Emax, total catch must decrease by 6% to 26,363 kg, equivalent to 100,000 USD/year. For E0.1, total catch should decrease by 18% to 23,202 kg, with a commercial value of 88,000 USD/year. For E0.5, total catch should decrease by 38% to 17,440 kg, with a commercial value of 66,000 USD/year. B. boops spawns between February and April and it reaches maturity at 13.5 cm in males and at 12.7 cm for females. Therefore, fishing seasons should extend from October to January and from May to July with a minimum harvesting size of 12.7 cm. The exploitation level of D. sargus sargus is 0.4, lower than Emax (=0.42). The stock size totals 323,173 kg, with a total catch of 129,269 kg, corresponding to a commercial value of 686,000 USD/year. It is advisable to reduce it to E0.1 (=0.355) corresponding to a total catch decrease of 11% to 114,726 kg with a commercial value of 609,000 USD/year or to E0.5 (=0.278) equivalent to a decrease of 30% to 89,842 kg with a commercial value of 477,000 USD/year. D. sargus sargus spawns between February and April and reaches maturity at 18.5 cm and 18.4 cm for males and females respectively. Fishing seasons should extend from October to December and from May to July with a minimum harvesting size of 18.4 cm. L. sceleratus spawns between April and June and reaches maturity at 40 cm. It feeds mainly on fish, but its diet is supplemented by a wide range of other organisms. Feeding intensity, it is lowest in March and highest in April and May.