Abstract
ABSTRACT Background: The common octopus, Octopus vulgaris, is an ecologically and economically vital cephalopod species in the Mediterranean; however, its biological characteristics remain unstudied in Libyan waters. Aim: This study provides the first comprehensive analysis of growth patterns for this species along the western Libyan coast. Methods: A total of 390 specimens (172 males, 218 females) were collected monthly from January 2021 to January 2022. Results: Dorsal mantle length (DML) ranged from 5 to 25 cm, and body weight (BW) ranged from 63 to 3376 g, with no significant difference between the sexes. A strong seasonal pattern was observed, with the minimum average size recorded in August (~11 cm, ~340 g) and the maximum size recorded in January (~18 cm, ~1450 g). The length– weight relationship revealed negative allometric growth (b = 2.85) for both sexes, with a strong correlation (R² > 0.94) and no significant sexual dimorphism. The von Bertalanffy growth function estimated asymptotic lengths (L∞) of 30 and 28 cm for males and 28 cm for females, consistent with other Mediterranean populations but lower than those of the Atlantic ones, suggesting biogeographical constraints. The condition index showed significant seasonal variation, with lows in March and peaks in June, likely linked to reproductive cycles. Conclusion: These results characterize a population with typical Mediterranean growth dynamics. A pronounced seasonal recruitment pulse in late summer highlights the vulnerability of juveniles to fishing pressure. We recommend the implementation of fisheries management strategies, such as seasonal closures during this critical period, to ensure the sustainability of this valuable Libyan resource. Keywords: Octopus vulgaris, Length–weight relationship, Fisheries management, Libya, Mediterranean Sea.