Acoustic telemetry reveals cryptic residency of whale sharks

Although whale sharks (Rhincodon typus) have been documented to move thousands of kilometres, they are most frequently observed at a few predictable seasonal aggregation sites. The absence of sharks at the surface during visual surveys has led to the assumption that sharks disperse to places unknown during the long ‘off-seasons’ at most of these locations. Here we compare 2 years of R. typus visual sighting records from Mafia Island in Tanzania to concurrent acoustic telemetry of tagged individuals. Sightings revealed a clear seasonal pattern with a peak between October and February and no sharks observed at other times. By contrast, acoustic telemetry demonstrated year-round residency of R. typus. The sharks use a different habitat in the off-season, swimming deeper and further away from shore, presumably in response to prey distributions. This behavioural change reduces the sharks' visibility, giving the false impression that they have left the area. We demonstrate, for the first time...

尽管已有文献记录显示鲸鲨（Rhincodon typus）可移动数千公里，但它们最常被观测到的地点仅为少数几处具有季节性聚集特征的可预测位点。目视调查期间海面未观测到鲸鲨的现象，使得研究者们推测，在多数聚集点的漫长“非旺季”中，鲸鲨会扩散至未知区域。本研究将坦桑尼亚马菲亚岛（Mafia Island）两年间的鲸鲨目视观测记录，与同期标记个体的声学遥测数据进行对比分析。目视观测结果呈现出清晰的季节规律：鲸鲨观测峰值出现在10月至次年2月，其余时段均未观测到个体。与之形成鲜明对比的是，声学遥测数据表明鲸鲨全年都栖息于该区域。在非旺季，鲸鲨会切换栖息生境：它们下潜至更深水域、离岸更远的区域，这一行为推测是为了适配猎物的分布变化。这种行为改变降低了鲸鲨的可见性，从而营造出它们已离开该区域的假象。本研究首次证实……