Integrating biological traits of Ensis minor into regional management plans: a case for adaptive fisheries policies

The razor clam ( Ensis minor ) is an infaunal filter-feeding bivalve of considerable economic importance in the Mediterranean, historically playing a key role in the livelihood of Italian coastal communities in the northern Adriatic and central Tyrrhenian Seas. This study aimed to investigate the fundamental biological traits of E. minor across areas where data were either outdated or previously unavailable, to inform appropriate conservation and management strategies. To assess age, samples were collected from November 2017 to November 2020 on board hydraulic dredges during annual scientific surveys in the Monfalcone, Chioggia, and Venice districts (Adriatic Sea) and the Naples, Gaeta, and Rome districts (Tyrrhenian Sea). An aging technique based on shell longitudinal sectioning (i.e. acetate peel replicas) was applied to evaluate potential differences in growth patterns over time and space. Additional samples were collected at the landing site in the Naples district between January 2018 and November 2019 to determine size at sexual maturity via microscopic examination of the gonads, and to investigate the reproductive cycle through histological analyses. Age estimates were obtained for 366 individuals and revealed no significant differences among the study areas; thus, length-at-age data were described using a single von Bertalanffy growth model (L∞ = 139.7 mm, k = 0.275, t0 = -0.75 years), with the commercial size of 80 mm TL attained at 2.3 years. The microscopic analysis of 809 individuals (32 – 108 mm TL) indicated that sexual maturity is reached at approximately 41 mm TL. Histological analyses of 335 adult individuals revealed that during the colder months, the resumption of the gametogenic cycle and the reproductive season occurs, coinciding with accelerated shell growth. These results suggest that current fishing practices primarily target individuals that have reproduced at least twice during their lifetime, consistent with the minimum reproductive size policy. Fishing closures from late autumn to early spring are recommended to protect the species during its reproductive season and to allow juveniles to settle, ensuring stock replenishment. In the long term, adaptive management measures should be implemented at the district level, guided by the species’ biological responses to environmental changes and supported by ongoing monitoring.