Data from: Discovery of a multi-species shark aggregation and parturition area in the Ba Estuary, Fiji Islands

Population declines in shark species have been reported on local and global scales, with overfishing, habitat destruction and climate change posing severe threats. The lack of species-specific baseline data on ecology and distribution of many sharks, however, makes conservation measures challenging. Here we present a fisheries-independent shark survey from the Fiji Islands, where scientific knowledge on locally occurring elasmobranchs is largely still lacking despite the location’s role as a shark hotspot in the Pacific. Juvenile shark abundance in the fishing grounds of the Ba Estuary (north-western Viti Levu) was assessed with a gillnet- and longline-based survey from December 2015 to April 2016. A total of 103 juvenile sharks identified as blacktip Carcharhinus limbatus (n = 57), scalloped hammerhead Sphyrna lewini (n = 35), and great hammerhead Sphyrna mokarran (n = 11) sharks were captured, tagged, and released. The condition of umbilical scars (68 % open or semi-healed), mean sizes of individuals (± SD) (C. limbatus: 66.5 ± 3.8 cm, S. lewini: 51.8 ± 4.8 cm, S. mokarran 77.4 ± 2.8 cm), and the presence of these species over recent years (based on fishermen interviews), suggest that the Ba Estuary area is a critical habitat for multiple species that are classified as “Near Threatened” or “Endangered”. Specifically, the area likely acts as a parturition ground over the studied period, and potentially as a subsequent nursery area. We identified subareas of high abundance and found that temperature, salinity and depth acted as small-scale environmental drivers of shark abundance. The data suggests a tendency for species-specific spatial use, both horizontally (i.e. between sampling areas) and vertically (i.e. across the water column). These results enhance the understanding of shark ecology in Fiji and provide a scientific basis for the implementation of local conservation strategies that contribute to the protection of these threatened species.现有研究已在区域及全球尺度上记录到鲨鱼种群衰退现象，过度捕捞、栖息地破坏与气候变化正对其构成严重威胁。然而，多数鲨鱼物种的生态学特征与分布格局均缺乏物种特异性的基础数据，这使得针对性保护措施的制定面临诸多挑战。本研究基于斐济群岛开展了一项独立于渔业的鲨鱼调查——尽管该区域是太平洋的鲨鱼热点区域，但目前对当地分布的板鳃类动物（elasmobranchs）的科学认知仍十分匮乏。2015年12月至2016年4月期间，研究团队借助刺网（gillnet）与延绳钓（longline）相结合的调查方式，对维提岛西北部巴湾渔场的幼鲨丰度进行了评估。共计捕获、标记并放流幼鲨103尾，经鉴定分别为乌翅真鲨（Carcharhinus limbatus，n=57）、路氏双髻鲨（Sphyrna lewini，n=35）与无沟双髻鲨（Sphyrna mokarran，n=11）。脐疤状态（68%为开放性或半愈合状态）、个体平均体长（均值±标准差：乌翅真鲨66.5±3.8cm、路氏双髻鲨51.8±4.8cm、无沟双髻鲨77.4±2.8cm），结合近年渔民访谈记录证实的物种出现情况，均表明巴湾海域是多个被列为‘近危（Near Threatened）’或‘濒危（Endangered）’物种的关键栖息地。具体而言，在本研究的调查周期内，该区域极有可能是这些物种的产仔场，同时也可能作为后续的育幼场。研究团队还识别出幼鲨丰度较高的子区域，并发现水温、盐度与水深是调控小尺度范围内鲨鱼丰度变化的关键环境驱动因子。数据还显示，不同鲨鱼物种存在物种特异性的空间利用偏好，具体体现在水平方向（即不同采样区域之间）与垂直方向（即不同水层之间）。本研究结果深化了学界对斐济海域鲨鱼生态学的认知，同时为制定当地针对性保护策略提供了科学依据，助力这些受威胁鲨鱼物种的保护工作。