Evaluating overall size selection pattern and seasonal variations for the commercially valuable cephalopod Loligo vulgaris in the Mediterranean bottom trawl fishery

Loligo vulgaris, a semelparous cephalopod of commercial importance is mainly considered as by-catch in the Mediterranean bottom trawl fishery without specific fisheries regulations. In this study, the overall size selection pattern for L. vulgaris was examined in the Mediterranean bottom trawl fishery. Specifically, the size dependent escape, discard, and landing probabilities were estimated for two seasons (summer and autumn) and for three codends of 40 mm diamond (40D), 40 mm square (40S) and 50 mm diamond meshes (50D). In addition, an exploitation indicator quantifying the efficiency of each codend and season in releasing or catching individuals below the length at first maturity (LFM) was estimated. The results showed that a large proportion of juveniles were retained in all codends and both seasons, limiting the spawning opportunities for this semelparous species. The 40D exhibited the lowest selectivity in both seasons. No differences were detected between the 40S and 50D codends during summer. The 40S was more appropriate in autumn, allowing more individuals below the LFM to escape. However, even in this case a large proportion of juveniles remained in the codend. Fisher selection behaviour revealed a low discard probability but a high presence of juveniles in the landings. These findings demonstrated that further improvement of the codend selectivity is needed to reduce the capture of L. vulgaris at sizes before its unique spawning. Nevertheless, this will result in substantial economic losses for fishers. Therefore, alternative management measures should be investigated to ensure the sustainable exploitation of the species in the Mediterranean.