Movements and growth rates of tagged bronze whaler sharks (Carcharhinus brachyurus) in southern Africa

<strong>Context: </strong>Shark species that are targeted by recreational anglers and commercial fisheries are vulnerable to over exploitation when fishing effort is not informed or regulated by data on the relative distribution and growth of different age/size classes. <strong>Aims: </strong>We investigate the spatiotemporal distribution, movement patterns and growth rates of <em>Carcharhinus brachyurus</em> in southern Africa. <strong>Methods: </strong>We analysed a 36-year cooperative shore-angling tag-recapture dataset. <strong>Key results:</strong> Distribution was centred in Namibia and the South Coast of South Africa during the austral summer. Large-scale regional movement of individual sharks (<em>n</em> = 21) supports the lack of population structure in southern African. The South Coast of South Africa represented a potentially important nursery region where 96% of all juveniles were tagged. Sub-adults and adults were more widely distributed and recorded significantly greater time at liberty than juveniles, but the distance moved for adults was significantly lower, indicating higher site fidelity. Growth model predictions showed annual growth rates of <em>C. brachyurus</em> were among the slowest when compared to other carcharhinids. <strong>Conclusions and implications:</strong> These slow life-history traits, affinity to coastal regions and cross-border movements leave the southern African <em>C. brachyurus </em>population vulnerable to overexploitation in the absence of regionally aligned research and management.

**背景**：受休闲垂钓者与商业渔业捕捞的鲨鱼物种，若未基于不同年龄/体型组的相对分布与生长数据来指导捕捞作业或实施管控，则极易面临过度捕捞风险。**研究目标**：本研究旨在探究非洲南部海域尖吻鲨（Carcharhinus brachyurus）的时空分布、移动模式与生长速率。**研究方法**：本研究分析了一套历时36年的合作式岸钓标记重捕数据集。**主要研究结果**：该物种在南半球夏季的分布核心区域为纳米比亚与南非南海岸。样本量n=21的个体所展现出的大规模区域移动，佐证了非洲南部海域该种群不存在显著的种群结构分化。南非南海岸是一处潜在的重要育幼区，该研究中96%的幼鲨均在此处被标记。亚成体与成体的分布范围更广，放流后至重捕的存活时长显著长于幼鲨，但成体的移动距离显著更短，表明成体具有更高的栖地保真度。生长模型预测结果显示，相较于其他真鲨科物种，尖吻鲨的年生长速率处于较慢的行列。**结论与启示**：这类缓慢的生活史特征、对近岸海域的栖息偏好以及跨境移动特性，使得非洲南部海域的尖吻鲨种群在缺乏区域协同研究与管理措施的情况下，极易面临过度捕捞风险。