Fishing Activity Affected Odontocete Cetacean Distribution in a Marine Protected Area in the East China Sea

Effective marine conservation and spatial management require a thorough understanding of the distribution patterns of odontocete cetaceans. However, knowledge of their spatiotemporal distribution within China's Jiushan Archipelago National Nature Reserve remains limited. To address this gap, passive acoustic monitoring was conducted monthly in the reserve from October 2023 to December 2025, with the study area expanded to include adjacent waters beginning in August 2024. A total of 400 acoustic tracks, 116 feeding-related detections, and 238 acoustic encounters were recorded. Cetaceans were detected within the reserve during every calendar month, whereas outside the reserve, detections occurred only in February and from April through September. The mean cetacean track detection rate was higher within the reserve (0.21 ± 0.03 detections/km; mean ± SE) than in adjacent non-reserve waters (0.06 ± 0.02 detections/km). Monthly cetacean detections increased from January, peaked in July, declined through November, and rose again thereafter. High-use cetacean distribution and feeding areas were concentrated along the eastern island chain within the reserve, in waters with depths of 10-11 m, and at a distance of 300-400 m from the nearest islands. Cetacean detection rates and acoustic encounter durations were significantly elevated during the fishing-ban period relative to fishing-allowed period. Fishing vessels significantly reduced both cetacean acoustic detections and feeding activity, whereas gillnets selectively suppressed cetacean feeding behavior without affecting overall cetacean detection rates. These findings establish a robust scientific foundation for enhancing cetacean conservation and optimizing fisheries management within the reserve and in comparable coastal ecosystems.