Abundance and operating area by benthic trawl of Atlantic horse mackerel in the central Mediterranean

Trachurus trachurus [Linnaeus C (1758) Systema Naturae. Ed. 10th, 1: 824 p. (reprint 1956, London)] is abundant in Tunisian catches, with landings varying according to region and season. Due to its quantitative importance and economic contributions to the fishing sector, it is crucial to assess its biomass and locate its areas of concentration. Exploration and experimental trawling operations are conducted aboard the oceanographic vessel O/V “Hannibal” throughout the entire Tunisian sea. However, this study focuses on the findings in the north and east of the Tunisian sea. In the east area, the depth prospected varied from 40 m to 227 m with 49 hauls, while in the north area, the depth ranged between 30 m and 512 m with 53 hauls. Three important areas of Trachurus trachurus concentration were identified in the eastern waters, particularly in the Gulf of Hammamet, above Korba banks, Mamoura and Hallouf. The overall biomass index varied from 100 kg/km2 to 455 kg/km2 depending on the location. In the northern Tunisian waters, four specific areas of concentration of this species were noted, particularly toward the northeast of the Gulf of Tunis, above El Hawaria Bank at a depth of 100 m. The three other areas were located north of Bizerte, above the Cani Islands Bank; above Stafette and Fratelli benches; and toward the extreme northwest of Tunisia, south of Galite. The estimated biomass index ranges from 118 kg/km2 to 532 kg/km2. The statistical chi-squared test was applied to analyze and identify the difference between the two areas, using the Statistica 7 software. The findings revealed a variation in the length distribution between the northern and eastern Tunisian waters.