Opportunistic Visitors: Long-Term Behavioural Response of Bull Sharks to Food Provisioning in Fiji

Shark-based tourism that uses bait to reliably attract certain species to specific sites so that divers can view them is a growing industry globally, but remains a controversial issue. We evaluate multi-year (2004–2011) underwater visual (n = 48 individuals) and acoustic tracking data (n = 82 transmitters; array of up to 16 receivers) of bull sharks Carcharhinus leucas from a long-term shark feeding site at the Shark Reef Marine Reserve and reefs along the Beqa Channel on the southern coast of Viti Levu, Fiji. Individual C. leucas showed varying degrees of site fidelity. Determined from acoustic tagging, the majority of C. leucas had site fidelity indexes >0.5 for the marine reserve (including the feeding site) and neighbouring reefs. However, during the time of the day (09:00–12:00) when feeding takes place, sharks mainly had site fidelity indexes C. leucas is that, if present in the area, they are attracted to the feeding site regardless of whether feeding or non-feeding days, but they remain for longer periods of time (consecutive hours) on feeding days. The overall diel patterns in movement are for C. leucas to use the area around the feeding site in the morning before spreading out over Shark Reef throughout the day and dispersing over the entire array at night. Both focal observation and acoustic monitoring show that C. leucas intermittently leave the area for a few consecutive days throughout the year, and for longer time periods (weeks to months) at the end of the calendar year before returning to the feeding site.以投饵手段将特定鲨鱼物种稳定吸引至指定区域供潜水游客观赏的鲨鱼观赏旅游业，在全球范围内规模持续扩张，但同时也是一项颇具争议的议题。本研究针对2004至2011年的多组监测数据展开评估，数据采集自斐济维提岛南部海岸鲨鱼礁海洋保护区及贝卡海峡沿线珊瑚礁的长期鲨鱼投喂站点，研究对象为牛鲨（Carcharhinus leucas），包含48份水下目视调查样本以及搭载最多16台接收器的监测阵列所记录的82个声学发射器追踪数据。不同个体的牛鲨展现出程度各异的位点保真度（site fidelity）。通过声学标记分析可知，多数牛鲨在该海洋保护区（含投喂站点）及邻近珊瑚礁区域的位点保真指数均大于0.5。不过在每日投喂时段（09:00-12:00），牛鲨的位点保真特征表现为：若该区域内存在牛鲨，无论当日是否开展投喂活动，它们都会被投喂站点吸引，但在投喂日会停留更长时长（连续数小时）。牛鲨的整体昼夜移动模式为：清晨时段聚集于投喂站点周边区域，日间逐渐扩散至整个鲨鱼礁范围，夜间则分散至整个监测阵列覆盖区域。聚焦观测与声学监测结果均显示，牛鲨会在全年中间歇性离开该区域，连续数日外出，并在每年年末会离开更长时间（数周至数月），之后再返回投喂站点。