Effect of harvesting quota during summer fishing moratorium on a traditional Paphia undulata production area in Beibu Gulf, China: An Ecopath modeling perspective.

Understanding the changes in trophic structure and system characteristics of marine ecosystems in response to targeted fishing during a summer fishing moratorium is critical for the conservation and sustainable utilization of marine resources. In this study, an Ecopath with Ecosim (EwE) model was constructed based on fishery and environmental survey data collected during the 2023 summer fishing moratorium after a first-time application of a harvesting quota-based fishing campaign for Paphia undulata in Beibu Gulf, China. The results showed that trophic levels ranged from 1.00 to 3.68, with P. undulata occupying a low trophic level of 2.46. Total primary production/total respiration (TPP/TR) was 2.15, the connectance index (CI) was 0.37, and the system omnivory index (SOI) was 0.17. These parameters suggest that this ecosystem is in an early stage of development, with a relatively simple food web structure. The current biomass of P. undulata was 43.43 t km-2, while the estimated ecological carrying capacity was 83.78 t km-2. TPP/TR, CI, and SOI showed only minor changes after targeted fishing, indicating the robust recruiting potential of the P. undulata community. Notably, the measured current biomass was approximately half of the carrying capacity, corresponding to the theoretical maximum sustainable yield. These findings provide a scientific reference for adjusting harvesting quotas and implementing ecosystem-based fisheries management strategies. To support sustainable fisheries, targeted marine management measures should be explored, including detailed resource assessments, functional zoning, and gear modification trials.